November 2009 Archives

Nighttime cooling has produced areas of low cloudiness and fog from moisture lingering in the wake of the past week's damp weather system. When temperatures lower at night, air masses grow saturated with moisture at the point readings match the dew point. It's the instant relative humidities reach 100 percent.

Despite areas of clouds, Chicago remains a safe distance from the country's major precipitation-producing weather systems over the pre-Thanksgiving weekend -- one on the Gulf Coast with big rains and another sweeping into the Rockies. It's a situation which should allow the weekend here to remain mild, further extending one of the longest spells of above-normal November temperatures on the books. Highs are to reach the 50s Saturday through Monday -- readings 10 to 15 degrees above normal and more typical of late October than November. The number of consecutive above-normal days reaches 19 Sunday, the 2nd longest such period at Midway Airport since weather records began in 1928. Only 1999 managed more -- 25 of them.

Though winds are light Saturday -- often an impediment to breaking clouds up this time of year -- computer models indicate the layer of moisture supporting Saturday morning's clouds is quite shallow. This should permit daytime heating to mix the air, dissipating the cloudiness and allowing generous sunshine to emerge. Hazy sunshine is likely to return both Sunday and Monday.

As additional evidence of how mild it's been of late, the coldest temperature recorded this fall has been 28 degrees, and the coolest daytime high this month has been 47. A vast majority of years have produced temperatures colder than each of these readings by now: 128 of the past 137 years have recorded a colder autumn low temperature by now, and only one year (1933) has seen its lowest November daytime maximum higher than this year's 47.

Changing pattern to send temps tumbling by Thanksgiving;
potential cold December open ahead
Many indicators continue to suggest large pattern changes loom over the next two weeks -- changes likely to send temperatures broadly lower over the United States. The colder air appears likely to hit in two waves -- and there may be temporary warming between them.

Cold weather surges into the Midwest on gusty winds Tuesday afternoon and Wednesday amid chilly showers.  Readings may be chilly enough to allow at least some mixed snowflakes to the reach the ground with the spells of cold rain. The chilly air is likely to hold Thanksgiving temperatures near 40 degrees. Even colder air may hit next weekend and carry into December.

Dear Tom,
On the evening of Aug. 10 I was checking the weather for many cities coast to coast and they were all 79 degrees. Is that rare and is it more likely to occur in summer?
Norman Alexandroff
Dear Norman,
Having a large expanse of uniform temperatures across the nation is quite unusual and would be far more likely to occur in summer than any other time of the year. Temperature contrasts are almost always greater in the winter with arctic air and snow cover much more frequent across the northern states. Summer's sluggish weather patterns are more conducive to smaller temperature ranges -- especially at night when sunshine is not a factor. Conditions that would bring similar temperatures on a regional basis are far more common and can occur throughout the year given the right conditions.

Jennifer Barwock of Posen, Ill., captured this image of a double rainbow Thursday afternoon (Nov. 19) in Oak Forest. Thanks Jennifer for sharing this great picture with us!



Photo courtesy of Jennifer Barwock, Posen, Ill.

John Hazzard has always done a wonderful job keeping the WGN Weather Center informed about soil and farming conditions for Illinois farmers. He tells us today that weather conditions are back to being favorable again for harvesting corn in our area now that the recent storm system has departed. Hazzard also sent us the photos below, which were taken 2 miles east of Wilmington, Ill., of Dave and John Meyer harvesting corn on a beautiful Friday afternoon. As John told us:

"The corn had to be dumped from the combine into an auger wagon, then taken to the semi truck sitting out on the road because of the wet field conditions. The corn moisture is between 20-30 wetter than the last five-year average due to the weather conditions over the past 6 months. Soybean harvest is 95 percent done, but the corn is very slow to come out -- only 30 percent of corn acreage has been harvested in this area. This time last year everyone was done with both crops; what a difference a year makes..."

Fortunately, the good news according to Hazzard is that the yields in both soybeans and corn are either average or above average. Thanks John for the timely update as well as the photos!





Photos courtesy of John Hazzard

Friday marks the 17th consecutive day of milder than normal temperatures in Chicago--one of the five longest such spells on record in the month of November at Midway Airport. Weather observations there date back to 1928. With above normal readings expected to continue into early next week, the mild spell is on track to become this area's 2nd longest of any November. That so many above normal days have occurred is likely to surprise many Chicagoans. A heavy, week-long overcast peppered with bursts of light rain and, until Thursday, wind chill-generating gusts, have contributed to a much cooler "feel" to the air than readings alone might indicate. The month's 47.5-degree average temperature at O'Hare is the 20th warmest of the past 139 years, placing the month among the Chicago area's 14 percent of mildest Novembers. Estimates based on temperatures suggest furnace usage should be down 25 percent over typical levels up to this point in the month and 18 percent below the same period a year ago.


A stubborn low pressure responsible for five consecutive days of cloudy skies has lifted out of the area--but, moisture lingers in its wake. And, while clouds may break for passing sun in coming days, spells of overcast skies aren't likely to exit the area completely--fitting in a month which is historically the second cloudiest of the year (December is the cloudiest).


Daytime temperatures are predicted to rise several degrees in each of the next three days. But, indications of change in the weeks ahead abound. Two key cold weather indexes, which look at cold air availability in the arctic as well as the predicted buckling of the jet stream over the North Atlantic---a development which frequently ends up sending cold air spilling southward over the eastern U.S., including the Midwest---have turned negative. It's an indication of colder weather on the way. The chill appears likely to hit in bursts---the first to produce a rain-generating disturbance here late Monday into Tuesday. That push of cold air is to last through through Thanksgiving (next Thursday) and may deliver this area's coldest readings of the season to date. There are growing indications flurries or snow showers could sweep at least parts of the metro area Wednesday and Thursday. Still colder air appears a threat as December hits 12 days from now. That chilly spell could allow some sticking snow at some point in December's opening 5-days, according to several preliminary computer forecast scenarios.
 
West Coast hit by driving rains, huge mountain snows, 100 mph wind gusts
 
The storm pounding the West Coast Thursday has prompted warnings for all manner of extreme weather---from heavy rain and flooding, to mountain snows measured in feet, and high winds responsible for huge waves lashing the coastline. Gusts hit 103 mph at Rogue Valley International Airport near in southern Oregon near Medford Thursday.
 

Dear Tom,
I was married on Dec. 8, 1945 and it was a very warm day. A week later when my friend got married on Dec. 15 it was below zero. Can you provide the details?
Delores Faltynek Antioch
 
Dear Delores,
We asked climatologist Frank Wachowski to check the weather archives and he found your recollections to be right on---illustrating how quickly Chicago weather can change this time of the year. You wedding day was indeed very mild with a balmy high of 53 degrees. Your friend was not as fortunate as winter hit with a vengeance in the following week. A cold front dropped temperatures into the 20s and a major snowstorm followed on Dec.13 and 14 bringing about 4 inches of snow. Your friend's Dec. 15 wedding took place on a very wintry day with a high of just 11, a low of 2 below zero and 4 inches of snow on the ground.

 

Clouds cover area skies a 5th consecutive day Thursday and periods of rain are to continue. Wednesday's 0.17 inches at O'Hare made it the wettest day since late October. The day's 47-degree peak reading was the third consecutive day in which temperatures failed to escape the 40s. With a fourth day of 40s predicted Thursday, the metro area is in the midst of its longest cool spell since a set of seven consecutive 40s Oct. 10-16. 

To say it's been dreary is a bit of an understatement. Chicagoans have seen only 1 percent of the area's possible sun since Sunday---and November, typically the second-cloudiest month of the year here, is showing every sign of living up to its cloudy reputation over the coming week. The sluggish storm which has spun in place all week shrouding the area under a veil of clouds, is finally to lift out of the Midwest Friday. But computer models hold a fair amount of moisture in the lowest 5,000 feet of the atmosphere in the wake of the departing storm. This is more than adequate to produce clouds and could make sunshine a comparatively rare commodity.  What's more, suggestions that a wet new storm is to come together across the Midwest Monday is hardly a boon to those in search of sun. Though the details of its development aren't yet carved in stone, a number of forecast scenarios predict  strengthening over eastern Iowa and Missouri Monday, leading to the onset of chilly rains in Chicago Monday night and Tuesday.

Temperatures over much of the coming two weeks remain above seasonal norms, but display a downward glide. One lobe of chilly air is likely to be drawn into the Midwest on the blustery backside of next week's storm, producing a cool Wednesday and Thanksgiving Day. It's possible mid-week cooling will be sufficient to introduce snow or rain showers. But even colder air may loom beyond that. Though temperatures are likely to moderate after Thanksgiving (next Thursday,) preliminary indications suggest December---which is just 13 days away--may open on a wintry note as even colder air descends into the Chicago area. 
 
Historic odds of a trace or more of snow falling in November's 12 remaining days: 88 percent
 
The possibility of snow grows this time of year. Snowfall records in Chicago extend back 125 years to 1884.  At a least a trace of snow has fallen in 88 percent of those years between now and the start of December. Measurable snow (0.1 inches or more) has fallen in the same period in 60 percent of years and an inch of snow has fallen by December first 38 percent of the time.
 

Dear Tom,
I am putting in a bid for sidewalk snow removal in the Lincoln-Belmont-Ashland shopping area. Can you provide the average frequency of the number of snows per season of various amounts?
Bill Haderlein, Chicagoland Deck Cleaning & Sealing

Dear Bill,
Indeed we can. The following statistics are derived from 80 years (1929-2008) of Midway Airport snowfall data, courtesy of Chicago weather historian Frank Wachowski.

On average, Chicago receives at least one-half inch of snow 17 times per snow season. Snow storms in the range of 1-3 inches occur about 7 times; 4-6 inches, twice; 7-10 inches, once; more than 10 inches, about once every other year.

A note of caution: The number of storms that might occur in any given snow season varies greatly from year to year. The extreme winter of 1978-79 put down 10 snows in excess of 4 inches and a season total of 89.7 inches.

Joan Knight sent us this a gorgeous sunset picture taken in Lombard this past Friday the Nov. 13th. Wow, what a great shot!

Thanks Joan!


Photo courtesy of Joan Knight, Lombard, Illinois

Check this out! David Leonard sends us these shots of a rain gauge produced by his 2nd grade son Kyle as part of his science curriculum. Kyle's teacher is Mrs. Durkin of Willow Creek School in Woodridge, Illinois and provided him the instructions on how to make the
instrument. Leonard writes:

" It was pretty cool to see how a seven year old went about the process of creating this rain gauge. The pop bottle cut off at the top and inverted to serve as a rain collector, water was filled to a certain level to compensate for the different shape at the bottom and the placement of the ruler at the water level. His measurement of the rain received last night was approx. 0.5 cm."

Very cool indeed--and congratulations Kyle on a job well done!

Tom Skilling





Photos courtesy of David Leonard, Woodridge, Illinois

Chicago's weather has turned wet for the first time in over two weeks bringing to an end the driest November open in a decade. Just 0.01 inches had fallen in the city up to the time rains arrived Tuesday afternoon. Rainfall is predicted to continue in waves through Thursday totaling 0.40 to 1 inches making it the area's heaviest spell of precipitation in the 18 days since 0.81 inches fell October 30.


Northeast winds, so successful in halting the northward spread of rain Monday, proved no match for the deep-layered surge of moist air which pushed rain into the metro area by Tuesday afternoon. The most impressive area totals ranged from 0.91 inches at Rensselaer and 0.71 inches at Hebron, both in northwest Indiana---to 0.61 in De Kalb County's Sandwich. Chicago rains, while enough to wet the pavement, weren't nearly as impressive---totaling just 0.08 inches at Midway and 0.05 at O'Hare---but more was expected to fall overnight.

The stalled low pressure system responsible for the wet weather is a "cut-off low." The term originates from the fact the strongest upper levels winds, which might otherwise push such a disturbance along, become situated well to the north. Systems spin in place when this happens, unable to move very quickly.  The varied barometric pressures on the storm's north side were behind Tuesday's howling northeast wind gusts which approached 40 mph here and limited wind chills to the low and mid 30s. 

Areas downstate bore the brunt of storm's rainfall for a second consecutive day. Totals there were impressive. Westville in east-central Illinois' Vermillion County just east of Champaign recorded 3.23 inches of rain while Lincoln was soaked by 3.14 and Danville was hit by 2.45.  To put those amounts in perspective, the entire month of November in Chicago typically sees 3.01 inches.
 

Alaska in the Deep Freeze; Interior temps drop under -40 degrees
 
Cold air has reached brutal proportions in the northernmost reaches of North America.  Temperatures in Alaska dropped to -45 degrees at Tanana--in the state's Interior not far from Fairbanks Tuesday, to -44 degrees at Bettles. Open water in southern Alaska appeared to "steam" as the bitterly cold air turned water vapor immediately to ice crystals, much as happens when brutally cold air makes contact with the "warmer" water of Lake Michigan here in winter. Days continue to shorten in across the northern hemisphere assuring cold air production is just beginning in the arctic. The sun sets in Barrow, Alaska Thursday for 64 days---not to rise again until late January.

Even where the sun is still visible during the day well to Chicago's north, it sits low in the sky. At its highest point Tuesday, the disc of the sun was just 6.1 degrees above the horizon in Fairbanks compared to 29 degrees above the horizon at its peak here in Chicago. (Note: Were the sun 90 degrees above the horizon, it would be directly overhead while a sun angle of 0 degrees means the sun's disc sits below the horizon.)


 
 



 

Dear Tom,
What are the extremes for Chicago's average annual temperatures? Any sign the average is rising due to global warming?
Robert Roschke,  Chicago

Dear Robert,

In 138 years of official data, Chicago's average annual temperatures have ranged from 45.3 degrees (1875) to 54.5 degrees (1921). The trend of temperatures has been upward, but it's difficult to draw conclusions because the observation site has been relocated several times and each move disrupted the climatological continuity of the temperature record.

However, 80 years of data (1929-2008) from a single location -- Midway Airport -- indicate a warming trend, probably due more to a strengthening urban heat island effect than to global warming. Annual temperatures rose from 50.6 degrees during the first half of the period (1929-1968) to 51.2 degrees during the second half (1969-2008).

 

Sections of downstate Illinois, including the St. Louis area,  were drenched by 1 to 2-inch rains Monday at the same time a foot of heavy, wet early season snow snapped power lines near the Nebraska/northeast Kansas border just northwest St. Joseph, Missouri.  Morrowville, Kansas was hit by 12 inches of snow while rainfall in the storm's mild eastern sector reached 2.01 inches at downstate Fairview Heights, Illinois and 1.62 at St. Louis. The storm responsible is behind the powerful east to northeast winds which continue to rake the Chicago area Tuesday morning and produced 30+ mph gusts here Monday. With origins in Canada, the dry low level flow proved a formidable barrier to the northward spread of the storm's rain.  While northwest Indiana's Hebron recorded 0.22 inches of rain and 0.10 fell at Valparaiso---both in Indiana-- just 0.01 inches fell at Midway with a trace at O'Hare.

The wet storm, spinning in place over Missouri late Monday, is mired in an atmospheric blocking pattern which has the system, for all intents and purposes, spinning in place. Since any forward motion isn't expected to resume until late this week, it's likely the storm's impact on Chicago's weather has days to run. Computer models suggest the dry air riding Monday's northeast winds into the area is to moisten slowly allowing  rain prospects to rise. Once the atmosphere becomes saturated later Tuesday and Tuesday night, the rainfall which results could linger through Thursday.

While the air is to take on an increasingly damp, raw feel, temperatures are actually running above November averages. Winds and clouds are interfering with normal nocturnal (nighttime) cooling, a development which contributes to daily temperature surpluses. Tuesday marks the 14th consecutive of above normal November temperatures---and each day over the coming 7 days appears likely to finish ABOVE normal as well.
 
Changes loom Thanksgiving week; signs of colder temps and more storminess
 
Important atmospheric changes appear to loom next week. A dome of milder than normal air is predicted to take shape over eastern Canada and the Davis Strait between Labrador and Greenland. Such a development often signals a surge of cool air into eastern North America as the continent's jet streams begin buckling.  Ridging in the jet over the western Atlantic is offset by troughing in the eastern U.S. which produces northwest steering winds above the Midwest--a flow able to tap cold air at higher latitudes and tug it south. Two storm systems may be by-products of this pattern evolution and an analysis of temperatures suggests readings by the end of next week and the following weekend may dip 15 to 20-degrees below the levels predicted later this week.

Such a pattern change isn't out of line with typical late November developments.  125 years of snow records here reveals the week leading up to Thanksgiving has produced at least a trace of snow 74 percent of the time while measurable snow (0.1 inches or more) has fallen in 42 percent of all years since 1885.


 

Dear Tom,
With winter approaching, how soon can we expect temperatures to drop below
zero? 
Myra Weisbach

Dear Myra,
Chicago¹s earliest encounter with subzero weather took place nearly 60 years ago on the frigid Thanksgiving morning Nov. 23, 1950 when the mercury plunged to 1 below. The next day was even colder, with a low of minus 2 degrees. Subzero cold that early in the season is unusual, with the bulk of the city¹s negative temperatures occurring from mid December through mid February. The frigid season in Chicago peaks during February¹s opening days, a time of year that coincides with the winter¹s most persistent snow cover. Early March usually marks the end of below zero weather, though the 1 below zero reading on March 22, 1888 is the latest on record. Last winter Chicago logged 10 below zero days--the coldest was a minus 18 on Jan. 16.

Thanks to Daniel Giampaolo for sending this photo of Friday's sunset to us from Bensenville!  Beautiful shot, Daniel!
 
Tom Skilling
 

Darryl Angelico of Northbrook sends us this shot of a squirrel having fun with this pumpkin---perhaps doing a little carving while enjoy his/her version of pumpkin pie!

Terrific photo, Darryl!  THANKS for sharing it with us!
 
Tom Skilling

 
Photo courtesy of Darryl Angelico, Northbrook, IL
 

Judy Thorpe shares photos of the incredibly beautiful sunset which took place October 30 of this year. The colors of these mammatus clouds is nothing short of breathtaking. Judy tells us:

" The organization of the clouds reminded me of standing waves from college physics. What causes such a pattern in clouds to develop, and the intense color?"

It's an interesting observation, Judy--and a great question. Mammatus clouds are most often found on the underside of a thunderstorm anvil. They signal the presence of turbulent winds at and near cloud level. THANKS for sharing these with us!

Tom Skilling

Today is the average date of the first measurable snow in Chicago.  So today is a good day to kickoff Winter Weather Preparedness Week.  The National Weather Service will be offering tips and advice that will help you prepare for and get through another typically tough Chicagoland winter.  Today's focus is on how to prepare your family with a family protection plan that includes a list of items to keep handy just in case.  This brochure also includes items to keep in your car as part of "Winter Storm Survival Kit".

 

Speaking of winter and snow, here is a link that will tell you everything you need to know about snow but were afraid to ask.

 

Very dry, cool northeasterly flow held off the incoming rain Sunday for a good portion of the metro area. A solid area of rain continually pushed northeast and tried unsuccessfully much of the afternoon to cross U.S. Interstate 80 into the western and closer-in southern suburbs, evaporating as it fell into the much drier air.

By Sunday evening rainfall amounts south of I-80 were on the order of a tenth to a quarter inch, while north of the I-80 corridor just a trace was reported. Overnight the air to the north was expected to gradually become saturated, allowing rain to reach the ground over much of the metro area by Monday morning.
 
Clouds and rain expected the first half of Chicago's workweek
As low pressure strengthens and moves slowly northeast out of Missouri into Illinois, clouds and extended periods of rain are likely in Chicago through Wednesday. Best estimates are that heaviest rainfall, perhaps as much as a half to three-quarters of an inch, will likely occur later Tuesday into early Wednesday. A break in the clouds is forecast later in the workweek with a warm-up over the weekend.

Dear Tom,
If I throw a bucket of water from a hot air balloon at say 15,000 feet, will this water appear as rain drops or as big globs when it approaches ground level?
Don Sadecki, Westchester
Dear Don,
You'll get raindrops at the ground. Larger drops fall faster than smaller ones, but drop size has an upper limit. It's a matter of drop stability.
German physicist Dr. Philipp Lenard made the first accurate measurements of raindrop sizes, shapes and fall speeds around 1900. He found that raindrops can attain sizes no greater than one-fifth inch in diameter; they become unstable and shatter at larger diameters, and the largest drops fall at about 20 mph.
As a large raindrop falls faster and faster, the friction of its passage through the air causes it to flatten, then to bulge upward in the middle rather like an inverted paper bag, and finally to shatter into smaller drops that fall more slowly.

Most locations received little more than a few sprinkles or brief showers late Saturday afternoon and overnight as a cold front moved through, but Chicago's long dry period that extends back to the last day in October is about to end. Low pressure is expected to develop over Missouri Monday and ever so slowly work it's way north and east through Illinois, finally weakening as it reaches Wisconsin and Michigan later in the week. Rain is forecast to move into the Chicago area possibly as early as later this afternoon and then continue overnight into Monday. The slow-moving low pressure portends an extended period of cloudiness and off-and-on showers through Thursday.

Above normal temperatures to continue

The clouds and rain ahead should cut back considerably on the range of daily temperatures with readings holding for the most part in the 40s through mid-week.  So even though it will feel cool and damp to Chicagoans, daily average temperatures will be in the middle 40s, some 5 degrees above normal for mid-November. Beginning on November 4th, average daily temperatures at the O'Hare official observing site have been above normal. A warm-up is forecast the latter half of this week and seasonably mild readings could extend well into Thanksgiving week.

Dear Tom,
What is Chicago's longest string of daily lows at 10 degrees below zero or lower? What about zero or lower? And what is our longest string of highs 90 degrees or higher? What about 100 or higher?
Lou Liebovich, Hoffman Estates

Dear Lou,
Computer scans of three data sets -- Chicago's official temperatures (1871-2009) and data from Midway Airport (1928-2009) and O'Hare International Airport (1959-2009) --provide the answers. Chicago's longest string of days with low temperatures of 10 degrees below zero or lower is 7 days (Jan. 14 to 20, 1994); zero or lower: 10 days (Jan. 4 to 13, 1912, and Jan. 2 to 11, 1979); highs at or above 90 degrees: 12 days (July 6 to 17, 1936). That 90-degree string also included the city's longest string at or above 100 degrees: a sweltering 8 days (July 7 to 14, 1936. 

Rain's been a scarce commodity in November but is threatening a windy comeback. Only 0.01 inch has fallen over the past two weeks, quite a change from an October in which 23 of the month's 31 days hosted at least a trace of rain. It's been the driest open to a November in a decade.

The rain's return is likely to begin quite modestly late Saturday night as post-frontal sprinkles build to a few light showers behind a wind-shifting cold front -- pause Sunday morning, then increase in number and coverage Sunday afternoon and night. Computer model handling of the wet system's movement into next week has been stunningly inconsistent in recent days -- potentially impacted by the massive Mid-Atlantic storm responsible for three days of driving rains and punishing winds in the region.  Gusts Friday peaked at 60 mph at Cape May and 58 mph at Atlantic City -- both on New Jersey's coast. Gusts hit 56 mph at Ocean City, Md., and roared across Brooklyn, N.Y., at 47 mph. Air ascends into the atmosphere on a massive scale in storms as powerful as this one, forcing upper steering winds to flow around it. Such a split in the winds at jet-stream level can have continental weather implications, slowing the eastward progression of weather features. There is little doubt the storm has played a key role in slowing mild air's arrival here in recent days -- and, now that it's here, is likely to slow its retreat until Sunday's predawn hours.

Most aggressive among a suite of computer projections sweeping rain into Chicago, then holding rainfall in place for up to 5 days (through Thursday), has been the global forecast model run by the European Medium Range Forecast Center. The model generates precipitation totals approaching 2 inches and suggests the storm responsible is to lift from New Mexico and the Texas Panhandle into southwest Missouri by late Sunday, and then into downstate Illinois Monday.  There, the system stalls as the upper air low producing it separates from powerful jet stream winds which might otherwise push it along.

Wet weather would be bad news for area farmers, who in recent weeks have finally been able to make progress harvesting crops. Veteran Will County farmer John Hazzard reported late Friday that most soybeans have been harvested -- but only 10 percent of the corn crop has been taken out in the hope further drying may occur. Corn moisture is well above normal, and harvested corn must be dried at the elevators to which farmers take their crop -- a slow process because elevators are able to process only so much corn on a given day. Hazzard reports yields have been good but estimates the corn harvest may take many weeks to complete.
 
Weather history indicates a majority of years see at least some measurable snow between now and Thanksgiving
Frigid arctic air gripping northwestern sections of North America and responsible for subzero temperatures in northern Canada and sections of Alaska in recent weeks, has shown little inclination to pour south in any great quantity. But longer-range projections are hinting that may change -- and it could happen toward the end of the coming two weeks during Thanksgiving week. A ridge forecast to build over Greenland at that time favors model projections of jet stream buckling over North America which would bring colder air crashing into a large swath of the Lower 48.  Weather records show cold air before November's close isn't unusual and that 62 percent of all years since snow records began in 1884 have recorded measurable snow between now and Thanksgiving.

Dear Tom,
My 5-year-old asks when the dinosaurs disappeared and if weather was the cause.
Jennifer Krause
Dear Jennifer,
Five major "life extinctions" have occurred on Earth, one of which ended the reign of the dinosaurs about 65 million years ago (though recent evidence suggests some dinosaurs survived and today's birds are descended from them).
A widely accepted theory to explain the dinosaur extinction draws together information from a variety of independent investigations. An asteroid estimated to be 6-10 miles in diameter crashed into Mexico's Yucatan Peninsula. The impact threw a massive amount of debris into the atmosphere, and heat generated as it rained down planetwide caused much of Earth's vegetation to burn. Volcanic eruptions elsewhere contributed additional atmospheric dust, and temporary global cooling hastened the dinosaur extinction.

Jay Kleeman sends us these beautiful photos of sunset Friday night as seen from Mount Prospect. Thank you Jay for sharing these pictures with us!





Photos courtesy of Jay Kleeman

The remnants of Hurricane Ida morphed into a nasty Nor'easter and continues to lash the east coast with heavy rain and strong winds.  Winds have gusted to over 100 mph and nearly 10" of rain has soaked portions of North Carolina and Virginia.

Here are some of today's impressive numbers from our WeatherBug network:

Wind Gusts (since midnight)

41 mph  Kill Devil Hills, NC

61 mph  Arlington, VA

54 mph Ocean City, MD

Rainfall (from midnight to 5:30 AM today)

1.54"  Ocean City, MD

  .94"  Chesapeake, VA

  .63   Norfolk, VA

While we don't experience Nor'easters here, we do sometimes get powerfull storms that deepen over the Great Lakes to produce "hurricane-like" conditions.  We just passed the 34th anniversary of one of the more notorious such storms to hit the Great Lakes.  The November 10th, 1975 storm sunk the S S Edmund Fitzgerald and killed 29 people.  The storm churned up waves greater than 30 feet and 50 knot winds. It was the inspiration for the Gordon Lightfoot song, "Wreck of the Edmund Fitzgerald". 

It was like a scene out of the Perfect Storm on the East Coast Thursday. Torrential rains---in spots more than 9 inches of it---fell horizontally as easterly winds roared ashore up and down the Mid-Atlantic Seaboard from New England to North Carolina at speeds found only in the region's most potent storms.  NOAA offshore buoys bobbed about in mountainous three-story waves as shoreline cameras captured scenes of oceanic chaos as swarms of frothy waves lapped ominously at sand dunes and buildings normally out of the water's reach---but in harm's way Thursday as relentless east winds pushed a dome of Atlantic water over the shoreline at levels not seen in 13 years. The stormy environment, a by product of Hurricane Ida's remnants interacting with a sprawling Canadian high pressure, appears to have contributed to the disappearance of three commercial fishermen off Cape May, New Jersey. A 19 hour air and sea search for them was called off at 5 p.m. Virginia Governor Timothy Keane declared a state of emergency and urged people in the hardest hit areas of his state to stay home as power lines fell and standing water closed roads. Among the areas in Virginia hard hit by flooding was the Norfolk area.

Wind speeds were stunning. A Weather Bug sensor clocked a gust of 106 mph around 11 a.m. Thursday morning on the beach at Ocean City, Maryland while another nearby captured a 91 mph gust. Winds reached 68 mph at Fenwick Island, Delaware, 67 mph at Virginia Beach and 65 mph at Norfolk---both in Virginia---and 56 mph farther north at Atlantic City. 

Rainfall surged past 9 inches at some locations. Swansboro, North Carolina was socked with 9.26 inches of rain while 9.12 soaked Jones Creek, Virginia.
 
 
Paltry November rains here lowest in a decade, 5th lowest on record
 
The East Coast storm appears to be contributing to a slowdown in U.S. weather movement---a development which could extend the 60s predicted Friday into Saturday.  And while a chilly, wet storm is predicted by models to lift into the Midwest Monday, Chicago's paltry 0.01 inches tally this month is the lowest in a November in a decade and the 5th lowest of any November over the past 139 years.

 

Dear Tom,
On Nov. 11, 1911 Springfield. Missouri experienced a huge temperature drop attributed to a "Great Blue Norther." Can you elaborate?
Les Herbst Lake Villa

Dear Les,
A "Blue Norther" is a fast-moving cold front accompanied by a strong north or northwest winds, a dark blue-black sky and a large, rapid temperature drop. Such was the case on Nov. 11, 1911 in Springfield, Missouri when the cold front passed. Earlier in the day, with clear skies and brisk south winds, the temperature soared to a record high of 80 degrees. Around 3:30 p.m. dark
ominous clouds rapidly approached followed by an abrupt wind shift to the northwest. Sustained winds of 54 mph and gusts to 74 mph damaged numerous trees and houses. Temperatures plunged, falling to 13 degrees by midnight, setting a record low for the day. Nearly a century later the record low still stands, but the 80 degree high was equaled in 1989.

John H. Kloch shares his beautiful photo of Thursday morning's sunrise taken on Cary Bluff just east of Lindsey, Wisconsin--which is south of Marshfield.  What a terrific shot!  THANKS John!

Tom Skilling


Photo courtesy of John H. Kloch, Cary Bluff, Wisconsin

 

Sheldon Faworski sent us this picture of Thursday evening's gorgeous sunset in Elizabeth, Illinois. Sheldon tells us he shot this at 4:50 p.m.

Thanks Sheldon!


Photo courtesy of Sheldon Faworski, Elizabeth, Illinois.

Temperatures appear likely to surge within striking distance of 60-degrees Thursday and into the mid to upper 60s Friday afternoon. Cloudiness plays a key role in the extent of daytime heating which takes place this time of year. November's lower sun angle means any interference by clouds can limit warming. The expectation that cloud cover here over the next two days will be of the high, thin variety underpins our prediction of 60-degree readings. High clouds tend to interfere less with sunlight than denser low clouds. The predicted parade of 60s may even extend into a third day Saturday before a wind-shifting cool front passes, swinging winds around to the northeast off Lake Michigan. That plus a thick, occasionally showery overcast is likely to allow a flood of cooler air into the area which, along with predicted rain Sunday, should lead to a much cooler back half of the weekend.

Highs in the 60s become less frequent from this point forward each year. An average of four 60s have occurred beyond Nov. 12 in the past 138 years. By contrast, freezing temperatures grow more numerous. Weather records reveal only 7 percent of the Chicago's 32-degree or lower temperatures have typically occurred by now.

A howling northeaster (or nor'easter) pumped 50+ mph wind gusts into sections of the Eastern Seaboard Wednesday. Gust hit 57 mph at Ocean City, Maryland. The storm--which combined the remnants of Hurricane Ida with widely varied pressures beneath the southern flank of a sprawling high draped from the Midwest to New England, produced the roaring winds which set in motion seething, white-capped surf conditions from the Carolinas north to the Delmarva Peninsula. The system's driving rains drenched a multi-state region and totaled nearly 10 inches (9.83) at Opelika, Alabama.

Far to the northwest a powerful storm in the Bering Sea sent 70 mph hour gusts across western Alaska.  Forecasters warned 65 to 90 mph gusts could sweep the Turnagain Arm southeast of Anchorage in the south-central section of the state. As much as 10 to 20 inches of snow was predicted in the Susitna Valley south of the Alaska Range.
 
75 percent of the past 138 years have produced a colder temp by now
 
Chicago's coolest temperature to date has been 29-degrees recorded on Oct. 11. Three quarters of all years since 1871 have produced a colder reading by Nov. 12.

Dear Tom,
With the holidays approaching I remember a big Thanksgiving Eve snowstorm that probably was in the middle 70s. What year was that?
Ray Consentino, Homer Glen

Dear Ray,
The storm you remember took place on Nov. 26-27, 1975. The snow began Wednesday afternoon and fell with increasing intensity throughout the evening rush hour. The heavy snowfall clogged highways and canceled flights paralyzing holiday travel. Snowfall that Wednesday totaled 7.5 inches, and when the snow finally ended on Thanksgiving morning the city's official site at Midway Airport had logged 8.6 inches of snow. On Thanksgiving morning the snow was eight inches deep, tying 1895 for the city's deepest Thanksgiving snow cover. Just five years ago, another traffic-snarling Thanksgiving Eve snowstorm dropped 4.3 inches on Nov. 24, 2004.

Check out these pictures!

Bridget Soraghan from Schererville sent us this great sundown picture. She says:

"as the sun was going down it turned pink outside, and I thought I would capture this amazing sunset!'

Amazing indeed! Thanks for the great shot!

Friday is to be the mildest of the coming 7 days though highs Wednesday and Thursday are to exceed the normal maximum of 49-degrees. Wednesday's initially chilly readings---the product of cooling beneath clear skies and light winds overnight---should give way to mid 50s fairly expeditiously beneath the sunniest skies here in three days.

November's temperature turnaround has caught Chicagoan's attention. Readings are averaging 4.5-degrees above the month's long term average, and, in an uncommon development, continue warmer than October. Generous sunshine again Thursday may well foster near 60-degree highs.

Changes have been made to the coming weekend's forecast including lowering predicted high temperatures and introducing the chance of some rain---though a majority of hours this weekend are still expected to remain dry. Details of the system which may produce at least some of the weekend rain Sunday still vary among models. This suggests a forecast situation still subject to change. But, the unifying conclusion of all models is that cooler air is to settle in, dampening hopes this weekend will be anything near as warm as last with its 70-degree highs. Several computer projections indicate frontal waves capable of instigating showers Sunday---while two others are the most aggressive in developing rainfall here. These forecasts suggest a windy storm will develop over eastern New Mexico and the Texas Panhandle Saturday evening then advance to Missouri by Monday morning and to central Illinois and Indiana by Monday evening. Such a scenario would lead to a classic autumn storm, with a thick, temperature-restricting overcast, strong east/northeast winds and impressive rainfall. But this solution is hardly unanimous and will have to be monitored in the days ahead.


Ida swamps Southeast with local 7-inch totals, 50+ mph gusts
  
Rainfall across sections of the Southeast with Hurricane Ida's remnants Tuesday  reached 6.74 inches Gonalez, Florida and 6.61 at Foley, Alabama while winds gusts hit  54 mph at Mobile, Alabama and 52 mph at Pensacola, Florida. Heavy rains extended north into the Carolinas and powerful winds in coming days resulting from the widely varied pressures between Ida's remnants and a sprawling high pressure to the north are expected to produce easterly gales near Washington, D.C. south to the Carolinas. Waves are likely to top 20 feet there.
 

Dear Tom,
My family visited Glacier National Park in July and a park ranger said the glaciers were in retreat. Could you provide more information?
The Stein family, Chicago

Dear Stein family,

U.S. Geological Survey researchers are carefully monitoring the disappearance of glaciers and snowfields in Glacier National Park and they indicate that it is occurring quickly.

One report, prepared in 2008, says, "Glaciers don't respond to anything else except climate change, unlike, for example, forests that can adapt. ... In 1850 there were an estimated 150 alpine glaciers of 25 acres or larger (in the park). Now there are only 25 glaciers left. By 2030, computer models suggest that all the remaining glaciers and snowfields will be gone."

Park snowfall has increased 10 percent in the past 50 years, researchers say, but higher temperatures and melting have overwhelmed the heavier snows.

Tim Anderson of Clifton, Illinois snapped this photo in his backyard on Sunday (10/9/2009) and e-mails asking, "What causes this weird arrangement?" Weird indeed.  What a fascinating shot. 

It appears the fuzzy clouds in the midst of the three openings in the altocumulus clouds which cover most of the sky mark areas in which air is ascending. Offsetting subsidence appears to be occurring around each of the fuzzy-looking altostratus clouds in the midst of each of the three openings in the clouds as evidenced by the clear patches around the periphery of each of these altostratus. Clouds evaporate in areas of sinking air; conversely, regions of rising air are areas in which the ascending air is cooling and clouds develop when the cooling takes the air to saturation.  Great shot, Tim!  THANKS for sharing it with us!
 
Tom Skilling

Dan Giampaolo of Bensenville sends us these shots of Sunday's clouds with what Dan describes as "tails".  These tails are actually "virga"---streamers descending from the base of the clouds produced as precipitation falls from them. This precipitation evaporates as it falls into the drier air below. Great photos, Dan---THANKS for sharing them with us!
 
Tom Skilling

 



Photos courtesy of Dan Giampaolo, Bensenville, Illinois
 

Rhonda HartlineI sent us this picture of early Monday morning's sunrise in Portage, Indiana. She tells us:

I saw a beautiful sunrise early this morning (about 6:20 am.) and couldn't help but take a photo.  I teach in Portage but live in Valparaiso and I took this from my driveway. I hope you enjoy it.

We certainly do enjoy it Rhonda! Thanks for the great shot!!

Rick Stegall sent us this picture of a flyby done during the Veterans Day parade in Utica, Illinois this past Sunday.

Thanks for the great shot Rick!
 

In most years, ever-shorter days and lowering sun angles assure November ends up cooler than October. But not this year. The weather of Autumn 2009 continues its unusual ways. Buoyed by this past weekend's back to back 70s---71-degrees Saturday and 70-degrees Sunday---November's opening 9 days have averaged 0.5-degrees milder than October's full-month average of 48.8-degrees. That's only happened in 12 of the 139 years on record since 1871. One has to go back 22 years to find the last time a November opened warmer than October. 

Putting two consecutive 70-degree temperatures together this late in the season is unusual enough. Not since 1999---and before that 1971---has that happened in Chicago over the past half century.

A sprawling high pressure, draped from the Plains to the Northeast U.S. and Canadian Maritimes, is behind Tuesday's cool, occasionally gusty northeast winds here in Chicago. But it is also acting to block the northward spread of moisture accompanying Tropical Storm Ida.

Though not directly responsible for the deadly downpours which set in motion the devastating mudslides responsible for 130 deaths across El Salvador in recent days, there's little doubt Ida played a role in enticing prolific rains with a tropical Pacific system into the Central American country. Ida, with a circulation disrupted by the mountains of Nicaragua and Honduras late last week, returned to hurricane status quickly once the system moved over the bathtub-warm waters of the Caribbean and southern Gulf over the weekend. The system's northward drift over cooler northern Gulf waters sapped some of Ida's wind energy Monday---though the powerful low pressure's rain-generating capability is to remain formidable in coming days. A slowdown in its forward movement is an ominous development for the Southeast---including the southern Appalachian region---where repeat downpours make local 6 to 8-inch rains all but a certainty.

The variation in pressure between Ida and a huge Canadian high to the north produced gusty winds across much of Florida and northeast Gulf Coast Monday. Peak gusts reached 52 mph at the Tyndall Air Force base control tower,  49 mph at Sand Key, 44 mph at Pensacola, 42 mph at Hollywood--all in Florida. Rainfall by late evening had surged to 3.45 inches at Pensacola, 2.79 at Pascagoula, Mississippi and 2.77 at Saraland, Alabama---just the beginning of the wet weather expected to linger in the region as Ida's remnants slow.     

Dear Tom
Someone told me that Lakes Michigan and Huron are really one lake. Is This true?
Ken Cleys Woodridge

Dear Ken,
Though they have long been, and will always be considered to be two different lakes, geologically and hydrologically, Lake Michigan and Lake Huron are actually one lake joined at the Straits of Mackinac. They lie at the same surface elevation of 577 feet, both lakes' level rise and fall together and flow of water between the lakes can reverse through the Mackinac Straits. 

Great Lakes' water levels reported by the Great Lakes Environmental Research Lab and the U.S. Army Corps of Engineers provide only one reading for the Michigan-Huron duo. Because of their large size, early explorers gave the lakes different names. Combined, lakes Michigan and
Huron would cover more than 45,000 square miles, larger than Lake Superior's nearly 32,000 square miles.

Jeffrey Bergandine sends us this photo of clouds in the shape of---as he describes it (and I like this)---flat turtle shells and tells us his 10 year old son William and he wonders what kind of clouds these are?  These are referred to as altocumulus stratiformis undulates according to the World Meteorological Organization's International Cloud Atlas.  Any time the prefix "alto" appears in a cloud designation, it means these are mid-level clouds---or clouds with bases between 6,000---but less than 18,000 feet above the terrain.  Great shot, William and Jeffrey!  THANKS for sharing it--and thanks for sharing the fact your enjoy our Chicago Tribune weather page!
 
Tom Skilling



 
Photo courtesy of Jeffrey and his son William Bergandine,
 
 
 

Bruce Vinkler and Julie Gidwitz send us these photos of an unsual cloud formation they observed while driving late Sunday morning on I-80/94 while driving through northwest Indiana. They tell us:
 
"We observed an interesting cloud formation. There was a high thin veil of clouds that the sun was able to shine through, with some intermittent virga (very small areas by comparison). One area of the thin cloud veil was "pierced" in an almost perfect circle with some other thin clouds within the circle.  At the center of the circle was an area of cloud that appeared to be some more virga.  This formation persisted for quite some time, and a few other areas of "circles" started to form, although not as large as the one shown. What caused this?"
 
It is clear we're looking at quite a swath of altocumulus (mid-level clouds) and it is also clear, as you've accurately described, that virga (a streamer of evaporating precipitation) is occurring from the cloud in the midst of the opening. What appears to be going on is there is localized area of lift (upward vertical motion)  in the vicinity of the precipitating cloud and that that cloud-clearing subsidence occurring on a localized basis as air sinks at the periphery of this region of "lift".

THANKS for sharing this with us Bruce and Julie!  VERY interesting indeed!
 
Tom Skilling
 



Photos courtesy of Bruce Vinkler and Julie Gidwitz
 
 

Thanks to Dana from Naperville for this beautiful shot from the Healing Field of Honor in Naperville!  It's beautiful!
 
Tom Skilling
 

Photo courtesy of Dana from Naperville
 

Carl Rollberg witnessed firsthand some of the effects of Hurricane Ida as it swept by Mexico's Cancun while awaiting a flight back to Chicago on Saturday. It turned out to be a turbulent flight. Carl writes:
 
"In the whole week that we were there, we didn't have one sunrise or sunset.  I got some pretty good pictures anyway.....The 2nd one is a photo from Gate 12- American Airlines while we waited fro our plane Saturday afternoon.  I guess they're the outer bands of Hurricane Ida.  When I got home I checked the storm track and it appears that I'm right.  We had a real bumpy ride home.  Two rows in front of my the panel that has personal light and ventilation became partially unattached.  The passenger under it just calmly pushed it back up."
 
Thanks so much for sharing this with us, Carl and glad you're home safely!
 
Tom Skilling
 




Photos courtesy of Carl Rollberg, Calumet Park, Illinois
 

It was an icy morning is fog-bound Scotland Monday. Our friend and intrepid Scottish weather reporter Mark Vogan sends us these shots from the Glasgow area--they are something!  Mark writes:
 
"We awoke to a low of 27 degrees with freezing fog that lay some 150-250 feet thick over the valley floor. Here at the house, heavy frost coated all outside objects along with low visibility with the fog, only to find crystal clear skies and brilliant sunshine as I drove up through and above the inversion layer. . We sit in between weather systems and today after 27 degrees, we only rose to 45 degrees here at my house and likely only the upper 30s in Glasgow, we being slightly higher in elevation saw more sunshine, where Glasgow was stuck in the shallow inversion of "trapped cold air."
 
Wonderful report and photos, Mark!  THANKS as always for keeping us posted on weather developments in the UK!  Please give your lovely wife Karen our best!!
 
Tom Skilling

Coming off a delightful late fall weekend that brought the city its first back-to-back 70-degree days since Sept. 24-25, prospects for mild weather here loom well into mid-November.  With a prevailing west-to-east jet stream promising to spread mild Pacific air across much of the nation for the next two weeks, arctic air should remain bottled up across this continent's polar regions. Readings here should fluctuate through the 50s and 60s -- well above current normal temperatures around 50.  While this weekend's 70s did not break any records here, new record highs were established Sunday in areas from Michigan to New York, including 72 at Grand Rapids and 71 at Muskegon, both in Michigan.
 
Category 2 Ida heading for Gulf Coast
A lackluster 2009 hurricane season has become active in its final weeks. A hurricane watch has been posted for the Gulf Coast from eastern Louisiana to the Florida Panhandle as Ida, packing top winds of 105 mph, approaches the area by Monday night or early Tuesday.  Ida's death toll is approaching 100 in El Salvador after three days of flooding rains there.

Dear Tom,
From Nov. 12-14, 1964, Chicago firemen battled numerous multi-alarm major fires. What were the weather conditions like?
Doran Swan, Chicago
Dear Doran,
The weather was windy, dry and unseasonably warm -- perfect conditions for fires to spread rapidly and burn out of control. Chicago climatologist Frank Wachowski found high temperatures reached the 60s on Nov. 11-12 and peaked at 71 degrees on the 14th. Afternoon humidities fell to near 30 percent and winds were strong and gusty from the south and west with a maximum gust to 59 mph on Nov. 12. Three of the biggest fires were at the old Goldblatt's warehouse at 4000 S. Kedzie, buildings near 25th and Michigan, and in an abandoned railroad warehouse near 18th and Clark. Wachowski noted that weather reports from Midway Airport reported heavy smoke northeast of the field.

Here is a picture of extremely high ice clouds taken over the North Atlantic at sunrise. Carl Behrent, who took the picture, estimates that he was flying at 35,000 feet, and that the ice clouds (the thin light blue structures) were seen at 55,000 to 60,000 feet. Thanks Carl for sharing this beautiful photo!



Photo courtesy of Carl Behrent

After a cloudy, chilly and rainy October that failed to produce an official 70-degree high in Chicago for the first time since 1917, the city is finally getting some October-like weather in November. Afternoon highs are slated to break the 70-degree barrier again Sunday as southerly winds carry the late-season warmth into the city. The warm weather is expected to linger into Monday, bringing the city four straight days of 60-degree-plus highs, an occurrence logged this late in the season at Midway Airport only 13 times since 1928. In addition to the return of warmth, Chicago is also drying out after an October that produced precipitation on 23 of the month's 31 days. In contrast, November's opening week produced just one day with rain -- a mere 0.01 inch.

Ida regains strength
Hurricane Ida weakened to a tropical depression after a Nicaragua landfall, but is expected to regain hurricane strength Sunday as it pushes north into the Gulf of Mexico. It could bring rain and strong winds to the Gulf Coast by Tuesday.

Dear Tom,
I was just a kid but I think I remember a big snowstorm that occurred just after Halloween. It must have been in the early 1950s. Am I correct?
Brian Schwartz
Dear Brian,
The year was 1951 and the first week of November featured two major snowstorms. Halloween was a chilly affair with highs only reaching the lower 40s. A surge of cold air followed and held the mercury to just 29 degrees on Nov. 2, setting the stage for a fast-moving Alberta Clipper that dumped 4.4 inches of snow on the city during the afternoon of the 3rd. That was just the beginning as a second, more powerful snowstorm hit on Nov. 6-7, bringing another 9.3 inches of snow. That storm was accompanied by howling northeast wind gusts to 65 mph at the lakefront Meigs Field airport. The winds produced high waves that brought major flooding and property damage along the lakefront.

The warmest weekend in six weeks is underway. Chicago area temperatures broke above 60 degrees for the first time in a week Friday, reaching 62 at O'Hare and Midway airports, and 63 at the lakefront. Among the warmest area highs Friday were 65 degrees at Rockford; 64 at Aurora and DuPage Airport; and 63 degrees at La Grange, Wheaton, Lansing and Plainfield.

Weekend readings look even warmer: A pair of 70-degree highs (or readings awfully close) remain a good bet Saturday and Sunday -- temperature levels not seen here since late September.

Powerful south winds reached speeds of 43 mph in gusts at building-top levels on LaSalle Street Friday and 36 mph at Rockford, Lincolnwood, Burlington and north of the Wisconsin state line in Racine -- and have gusted to 30 mph at times overnight, mixing the air and preventing the usual nocturnal temperature drop. So Saturday's highs build from a higher starting temperature.

The air mass which dominates Midwest weather was so warm to the west of the city Friday it produced a second day of record-breaking highs in the Plains including 81 degrees at Valentine, Neb., 80 at Yankton and 77 at Rapid City -- both in South Dakota.  Add to the air mass' inherent warmth the broad subsidence of air which is to occur Saturday beneath the nose of a powerful jet stream -- a process which helps heat the air as the sinking air is compressed in the higher pressures found near Earth's surface -- and there can be little question why weekend temperatures here are headed to levels 20 degrees above normal.

Warm spell to extend to 4 days -- not common this late in the season
With high temperatures exceeding 60 degrees predicted through Monday, this warm spell has only a comparative handful of peers over the term of Chicago weather records. Four days of temperatures 60 degrees or higher have occurred beyond Nov. 6 only once every six years on average. Records at the South Side site record only 13 comparable late-season warm spells in 81 years since 1928.

Dear Tom,
I have seen frost on garage rooftops at sunrise when temperature reports are 38 or 39 degrees. What gives?
Robert Wolfson
Dear Robert,
Frost forms when the shallow layer of air at the ground (or on any other surface such as a rooftop) cools below its saturation temperature (and below freezing) by contact with a cold surface that itself has cooled to a subfreezing temperature. Water vapor in the air condenses directly, in ice-crystal form, onto the cold surface: frost forms.
Under clear, calm nighttime conditions, surfaces like blades of grass (but it works for roofs, too) radiate a great deal of heat and their temperature drops sharply. The cold-air layer can be very shallow, often only a fraction of an inch. Air temperatures in National Weather Service reports are taken by temperature sensors a few feet above the ground and sheltered from radiational cooling.

The Chicago area appears headed for its mildest weekend since September--one which may include high temperatures within striking distance of 70-degrees.  The eastbound mild air behind the predicted weekend warm-up sent temperatures Thursday soaring to near 80-degrees in the western Plains. In Denver, where up to 4 feet of snow fell in the mountains to the west of the Mile High City less than a week ago, the temperatures soared to 77-degrees with 81-degree readings at La Junta and Springfield--both in Colorado. Highs in nearby Nebraska included 81 at Sidney, 80 at Imperial and 78 at Chandron while Elkhart and Dodge City in Kansas topped out at 80.

The warming there was produced by air sinking from the mountains into the Plains where it was compressed and warmed as it descended into the higher pressures found at lower elevations. The process is commonly referred to as the Chinook effect.

As that mild air of Pacific origin continues eastward, it won't be quite as warm by the time it arrives in Chicago. But, it is likely to introduce a 15-degrees temperature increase by Saturday afternoon over the levels observed Thursday. Accompanying that warming will be an influx of Gulf moisture in the lowest several thousand feet of the atmosphere--enough to contribute to the "warmer" feel of the air, but, based on present indications from computer models, not deep enough to produce layer of the atmosphere to produce the kind of cloud cover which would block the sun and thwart warming. Arrival of more significant moisture supporting more extensive cloud cover appears the only means of sidetracking what seems on track to become one of the nicest weekends of the fall season--and that's not expected to happen at the moment.

Low clouds forming over western Illinois late Thursday evening were predicted to expand into the Chicago area Friday morning. But, powerful winds Friday are expected to mix down to the surface in the late morning and afternoon allowing clouds to break, some sun to emerge and temperatures to head toward 60-degrees. Gusts in excess of 30 mph appear a good bet once this happens---and, with gusty winds expected to continue Friday night and Saturday, overnight readings should be significantly milder than those of recent nights.

A fascinating weather scenario may unfold in the Caribbean and Gulf of Mexico in coming days and into next week. Minimal Hurricane Ida--with 75 m.p.h. top winds--went ashore in Nicaragua Thursday. The storm, downgraded to a tropical depression late Thursday, threatened torrential rains totaling 15 to 20 inches at higher elevations. But, computer models suggest the storm's northbound remnants are likely to sweep out over the bathtub warm waters of the Caribbean, allowing the system, in the absence of strong winds aloft to regenerate.  The re-energized system is then likely to spread north into the Gulf of Mexico where it may threaten sections of the coast--- potentially including Florida with downpours and wind mid and late week.
    
Thursday's 100 percent cloud -free skies the sunniest in nearly 2 months
 
Thursday gorgeous, completely cloud-free skies produced Chicago's first 100 percent sunny day in the nearly two months since September 2 and 11.
 

Dear Tom,
What is the meaning of "northwest winds"? Wind coming from the northwest or blowing toward the northwest?

Ralph Bellendir

Dear Ralph,

By international convention, wind direction always refers to the direction from which the air is moving. The proper interpretation of, say, a northwest wind of 10 mph is that the wind is blowing from the northwest to the southeast at a speed of 10 mph.

While we're on the subject, here's an unusual bit of weather trivia: You'll never hear a reported wind speed of 11 mph. Never. Here's why: Wind speeds are always measured in knots (nautical miles per hour). That's the way it's done, worldwide, and then in the United States that value is converted to statute miles per hour. One knot is 1.1508 statute mph. A value of 9 knots converts to 10 mph and 10 knots becomes 12 mph after rounding to a whole number.

 

Thanks to Kelly Anbach of Bensenville for these spectacular fall color shots taken in Hinsdale. They're beautiful! THANKS for sharing them with us, Kelly!
 
Tom Skilling
 





Photos courtesy: Kelly Anbach of Bensenville, Illinois
 

This remarkable picture comes to us from John and Andrea Skillman of Gurnee.  It was taken while vacationing in Alaska on the east side of Resurrection Bay in Seward. The Skillman's first spotted this cloud while eating dinner and aptly describe it as a mushroom cloud. It's more technically referred to as an orographic cloud---one which is induced as terrain forces air to rise---a process which leads to cooling and condensation of airborne moisture produces clouds such as this.  They report it dissipated a short time later as the sun set.  John and Andrea add that Alaska is a great place for seeing weather----which is absolutely true!  THANKS SO MUCH to the Skillmans for such a fascinating photo!
 
Tom Skilling

Allison Phelps, public relations coordinator for The Morton Arboretum in Lisle, give us an update on the fall color display at the arboretum and sent us these great pictures. Allison tells us:

Just to let you know, fall isn't quite over here at The Morton Arboretum. There are still colors to see. Thanks to our expansive collection of exotic trees, visitors can stop in and see the red and yellow leaves of the Persian Ironwood tree or the Paper-Bark Maple with it's bright red leaves accented by the cinnamon-red exfoliating bark!

Thanks again Allison!

-Tom Skilling

Hard to believe that just a week ago Denver was covered in more than a foot of snow.  Today they will see sunshine and a high near 80.  Snow is also melting on top of Mount Kilimanjaro but at a slower pace.  It could be all gone in as little as 22 years though according to a new study.

As the ice melts, more of the darker colored surface is exposed which absorbs more sun and leads to further melting.  The people near Mount Kilimanjaro depend on that meltwater for drinking water.  Check out this article for more information.

My daughter wants to climb Mount Kilimanjaro with me.  She was party inspired by a year of study there and a new book, "Don't Let Her Go".  We have a little more than 20 years to make the climb if we want to see the snow on top.

Speaking of snow...   We are less than two weeks away from the average date of our first measurable snow, November 16th.  No snow in the forecast through the weekend though as we warm into the 60s on both Saturday and Sunday.

Shorter days and weaker, low angle sunlight make it harder to warm this time of year--but that doesn't keep mild temperatures from happening. The atmosphere just has to work harder to produce such "warmth"--by, for instance, generating stronger winds which blow from warmer regions into the Midwest before the incoming air can cool---or by minimizing cloud formation capable of blocking sunlight. It also doesn't hurt to sit beneath the nose of a pocket of powerful jet stream winds, where air sinks, compresses and warms on a broad scale---a setup predicted to fall into place this weekend. That warmth can occur this time of year was evident a year ago. The area was in the midst of a three day 70-degree spree.  Last year's 71 degree high on this date was 18-degrees warmer than the 53 predicted Thursday.

Barring more extensive cloud development Saturday than is currently predicted, readings then could reach 70-degrees for the first time since Sept. 27. Late season 70-degree temperatures aren't common, but they have occurred beyond Nov. 5 an average of one year in three since records began at Midway Airport 80 years ago.

The coming warm-up---likely to produce the first set of back-to- back weekend 60s here since late September---may well be part of a three day spell of 60-degree-plus highs extending from Saturday through Monday. Three consecutive 60s have occurred here this late in the season in 44 percent of years on record.

Frigid arctic air remains trapped in northern North America where temperatures in recent days have dropped as low as 20-degrees below zero. In stark contrast, the tropics remain active. Tropical Storm Ida---with 65 mph winds and gusts of hurricane strength--formed Wednesday off the coast of Nicaragua. The system will lose strength as it punches into Central America on a northward trek.  But, it's possible we've not heard the last of the system. It could emerge into the southern Gulf of Mexico off the Yucatan Peninsula in the next week where reorganization would occur.


Humidity surge this weekend will add to mild "feel"---over-development of clouds would thwart warming
 
Dew points, which reflect atmospheric moisture and have resided in the 30s in recent days, are to take off this weekend as Gulf moisture mixes with mild but comparatively dry Pacific air moving in from the west. They are to reach the 50s which will lead to a noticeably more "humid" feel to the air Saturday and Sunday just as temperatures surge. This should lead a mild feel to the air not experienced here since September.


 

Dear Tom,
We are approaching the 34th anniversary of the sinking of the Edmund Fitzgerald. How rare is it to have a storm of that magnitude on the Great Lakes?
Mike Long
 
Dear Mike,
The legendary storm of Nov. 9-10, 1975 had a central pressure of 28.95 inches when it crossed Lake Superior, equivalent to a Category 1 hurricane. At its peak, it had sustained winds of nearly 80 mph with gusts above 90 and produced giant waves 25-30 feet high.

Though stronger storms have battered the Great Lakes, this storm was certainly on the high end of severity scale. The term "Gales of November", popularized by mariners long before it was made famous by Gordon Lightfoot, refers to the peak of the Great Lakes' storm season, when late-fall storms fueled by clashing warm and cold air masses gain extra energy from the residual summer heat stored in the waters of the Great Lakes.

November is Chicago's fastest cooling month, a point driven home by Wednesday morning's chilly temperatures. Cloud cover and showers overnight prevented a repeat of the mid 20s recorded across a number of far western suburbs Tuesday morning. But, 30s were widespread and clouds and lingering sprinkles and light showers Wednesday will prevent daytime readings from rising out of  the 40s ---the chilliest high temps here of the coming 7 days.  Normal November highs tumble from 55-degrees on the first to 40-degrees on the 30th.

However, the month's tendency to cool hardly means all mild weather is behind us.  A year ago, the Chicago area logged three consecutive 70-degree days (73, 71 and 71  on Nov. 3, 4 and 5.) And weather records reveal an average of one in three years has produced at least one additional 70-degree beyond this date and 93 percent of all years have added additional 60s. The 139-year average is four 60+degree highs past Nov. 4.
 
All signs point toward such a warm-up this weekend---a mild spell likely to extend into early next week.  Late season warm-ups are extremely sensitive to cloud cover. Too much cloudiness or an outbreak of precipitation can take a serious toll on late year warm spells. So can a wind-shift off Lake Michigan. But, barring more cloudiness than is currently foreseen, the Chicago area could be in for a string of four 60-degree daytime highs from Friday afternoon through Monday.  It would make the upcoming weekend this area's first since late September to host back to back 60s.

Computer models do indicate a weakness in the pressure field Saturday night into Sunday morning which has to be monitored. This may well allow a wind-shifting front to sag southward across the area.  Such a development would permit southeast winds to take hold reaching lakeside counties after a trip over cool lake waters a portion of Sunday, lowering shoreline temperatures. But these same models take the front back north of the area and strengthen south winds Sunday afternoon and evening. Such a scenario would put 60s within reach of most of the Chicago area Sunday. And well organized south winds Monday and indications that most cloudiness is to remain to the west of the area until Monday night and Tuesday appear to favor more 60s Monday. Temperatures at such levels this time of the year are 15 to 20-degrees above normal.

Southwest sizzles in hottest late season air on record
 
Record warmth across the Southwest U.S. Tuesday produced a 96-degree high in Phoenix---the hottest temperature there ever so late in the season--- and a peak reading of 93 in Tucson. 

 

Dear Tom,
I was able to see the stars clearly when I moved to Des Plaines 60 years ago, but now I miss seeing them at night. I understand gradually losing the ozone layer and the use of fossil fuels is to blame. Will I ever see the stars again?
Louise Koehler, Des Plaines

Dear Louise,

Triton College astronomer Dan Joyce shares your frustration and laments that "the grandeur of the nighttime sky" (as he refers to it) that was once a common spectacle has faded.

However, the decay of the atmosphere's ozone layer is not to blame because ozone only blocks the ultraviolet component of sunlight. Nor are fossil fuels at fault: the switch from coal to natural gas for heating has greatly reduced particulate pollution and our air is now clearer than ever.

The problem is light pollution. Metropolitan outdoor nighttime illumination is now so bright that it overwhelms our ability to discern the stars.

 

A snowstorm blasted Colorado and sections of surrounding states last week. Don Kukla sends us this photo taken last Wednesday evening (October 28, 2009) of the situation at Castle Rock, Colorado. He reported 7" had fallen and that evening forecasts suggest up to 18" might ultimately fall.  Don tells us he watches our WGN weather programs each night and that he misses Chicago!  THANKS for sharing the fabulous photo with us Don!  Always great hearing from Chicagoans--no matter where they are!  Glad we can share a little "home" with you here on our Weather Blog!  All the best!
 

Tom Skilling
 

Photo courtesy of Don Kubla, Castle Rock, Colorado
 

Temperatures are noticeably cooler Tuesday--but the abundance of sunshine is likely to take at least a bit of the edge off the new surge of chilly readings for sun-starved Chicagoans who are only three days beyond the 3rd cloudiest, 9th wettest and 11th coolest October in 139 years of official observations here. The irony of the sun's return is that it's happening in November--typically the city's second-cloudiest month, also the month which cools the fastest. The new pattern delivering the sun pulls a reinforcing shot of cool air into the area Wednesday into Thursday--and  has all but shut down the northward spread of Gulf moisture responsible for rainfall here 22 of the past 32 days. Several brief showers--possibly coaxed into mixing with a few ice pellets Wednesday morning as raindrops fall into very dry low-level air producing evaporation and cooling--may occur Wednesday.

But while 3.85 inches of rain has fallen in the past two weeks here, the coming two weeks are likely to produce only 16 percent as much precipitation--an amount closer to 0.63 inches according to an average of the most recent rainfall projections off one of the National Weather Service's key computer forecast models. It's a development which is music to the ears of area farmers who continue in the midst of the slowest, most vexing harvest season in recent memory. The weekly crop progress report released Monday afternoon by USDA indicates that across the 18 states responsible for 94 percent of this country's corn harvest last season, only 25 percent of this year's corn crop has been harvested compared to the five year average of 71 percent by this date.
 
Warmth (like this weekend's) still a good bet--though odds slide in November
 
With strong warming predicted to lock in later this week, the Chicago area appears in line to record its mildest weekend high temperatures in 6 weeks. The warm-up it to include a series of 60s from Friday through next Monday. it's worth noting that a third of years since 1871 have not only managed 60s this late in the season, but have gone on to produce a 70-degree or warmer temperature in the November's opening week. By November's final week, chances for a 70 here slip to near zero.
 

Dear Tom,
Why is it usually more cloudy in the autumn than in the summer?
Roger Hohman

Dear Roger,

The difference in the amount of heat provided by sunlight is the fundamental cause of seasonal variations in cloudiness.

In the warm season, the nearly overhead sun strongly heats the ground and overlying air. Currents of ascending warm air give rise to cumulus clouds that grow vertically into local cloud patches rather than spreading horizontally into widespread overcasts.

The opposite process prevails in the autumn and winter. Sunshine strikes the ground at a small angle and delivers little heat. The atmosphere grows colder, and the coldest layer is at ground level. Colder air under warmer is stable, and condensation and cloudiness tend to be horizontally stratified, resulting in widespread and long-lasting overcasts.

 

Gene Herrick sent us this beautiful shot of Friday's sunset as seen from Chicago Heights.
Thanks for the great picture Gene!



Photo courtesy of Gene Herrick, Chicago Heights
 

The beautiful sunset Friday caught the attention of a number of people across the area.  No wonder!  The hues of orange and red were like nothing short of spectacular.  Thanks to each of you who contributed pictures!! 
 
Tom Skilling
 

 
Photo courtesy of Dan Diampaolo, Bensenville, Il
 

Thanks to Dan Diampaolo for these beautiful fall color photos from Chicago's western suburbs. Dan tool these near Churchville School (which dates back to 1850) in unincorporated Bensenville. THANKS for sharing these with us Dan!
 
Tom Skilling
 



Photos courtesy of Dan Giampaolo, Bensenville, Illinois
 
 

We more than doubled the average amount of rain (2.71") for October.  The 6.04" that fell last month ties October 2001 as the 5th wettest October on record. It was also an unusually cloudy and cool month.  There were only two "sunny days" .  A "sunny day" means a day with 30 percent or less cloud cover from sunrise to sunset.  The average high temperature of 55.2 was 6.9 degrees below average.

November is a time of transition.  Our average high at the beginning of the month is 54 but by the end it drops to just 40.  The National Weather Service models are predicting a warm and dry start to the month.  Their 14 day outlook keeps most of the country drier than average and the midwest through the northwest warmer than average.  Snow isn't too far off though at least climatologically speaking. The average date of our first measurable snow is about two weeks away.  November averages about 1.8" of snow.

Much of the work week looks to be on the cool side with periods of cloudiness as minor weather disturbances move through. The upper-air flow pattern becomes more northwesterly, steering cooler air into the Midwest and holding milder air well to the south of the Ohio River. The jet stream will shift north by Friday with a weaker westerly flow aloft over Illinois, allowing milder air to ride southerly surface winds into northeast Illinois. While showers will be in the forecast off and on this week, expected rainfall should be on the light side. Thus runoff into rivers and streams will be primarily from the saturated soils, allowing for at least a little drying as the week goes on. Temperatures in the 60s and gusty winds over the coming weekend will also help to dry the soils, but again be tempered somewhat by the possibility of scattered showers.

Flood advisories
Flood advisories remain up for many rivers in states bordering on the Mississippi River from Louisiana all the way north to Illinois and Iowa. Most rivers in northeast Illinois and northwest Indiana are running close to bankfull, but the flood threat is farther to the south, the nearest being at LaSalle on the Illinois River.

Dear Tom,
It seems that 2009 has had an abundance of precipitation. Is this going to be a record wet year?
Chris Mall
Dear Chris,
Chicago is definitely having a wet 2009, but so far, this year is taking a back seat to 2008 which reigns as Chicago's all-time wettest year with a 50.86-inch precipitation total. Buoyed by September deluges that brought 13.63 inches of rain, 2008 marked the first time that the city's annual precipitation broke the 50-inch barrier, topping the old record of 49.35 inches established in 1983.  At October's close precipitation at O'Hare Airport had officially reached 38.61 inches -- nearly 8 inches above normal -- but last year at the end of October the precipitation tally here was 43.28 inches -- 4.67 inches greater. Barring an incredibly wet close to 2009, last year's record should not be eclipsed.