The Gulf of Mexico is "open for business" as a strong low-level jet stream drags moisture from 80° waters quickly northward Monday. As a result, an expanding area of significant rainfall spreads northward from the Texas coast, reaching Chicago by noon. Rain will continue into the night, but the responsible upper-level jet will move eastward along with the rain on Tuesday. By then, the still-expanding rain shield will cross the Appalachians into the Atlantic seaboard for Election Day, including thunderstorms and heavy rain in the central Gulf states.
Thereafter, massive high pressure will take up lodging in the Great Basin, spawning occasional breakaway high pressure cells which will drift east across the Midwest and cause extended dry weather for the rest of the week, with a gradual cooling trend to follow.
--Dennis Haller, WGN-TV
October 2004 Archives
Saturday’s strong WSW winds in the wake of an intense autumn storm caused minor but widespread tree limb and power line damage to the area. The highest gust in Chicagoland was reported at Valparaiso, Ind.: 58 m.p.h. at 11:18 a.m. , with peak gusts of 52 m.p.h. at Waukegan and 49 m.p.h. at Midway and 47 m.p.h. at O’Hare in the late morning hours. As this system pulls farther northeast from Chicago, moderate morning winds will continue to diminish throughout the day Sunday. Quick on its heels, a less violent low pressure system tracks south of Chicago. This system takes full advantage of available Gulf moisture and spreads rain as far north as Chicago on Monday, and up along the spine of the Appalachians on Tuesday. Thereafter, high pressure and dry weather settle in for the rest of the week with temperatures on the cool side of normal.
-Meteorologist Dennis Haller
After 30 years of forecast experience at the Milwaukee and Chicago National Weather Service forecast offices, meteorologist Richard Koeneman has been a member of the WGN-TV/Tribune weather page team since its inception in 1997 and has been a frequent contributor ever since. In 2000 he moved to beautiful North Carolina where he lives on the mountains of Appalachia, but he remains an active contributor via email, telephone, faxes and regular visits to Chicago. He's currently writing a book on Chicago's climatology.
GALES OF NOVEMBER COME EARLY
Today's storm is so typical of this time of year as we transition from the sunny mild days of early autumn to the dark, chilly gloom of November.
Today is a "backwards" day in Arlington Heights. Temps fell from a balmy 69º around midnight this morning to the low 50s late this afternoon. Tonight we turn the clocks backwards setting the stage for Halloween's early 4:46 p.m. CST sunset.
Strong gale force winds gusting to more than 40 m.p.h. blasted the area all day, removing most lingering leaves from the trees and raising whitecaps on Lake Arlington.
Steve Kahn
Temperatures soared Friday to within 2° of Chicago’s all-time Oct. 29 high reaching 76°—a reading warmer than Los Angeles (68°), Phoenix (69°) and Las Vegas (62°). The warmth followed a record mild Chicago morning temp of 61°. The degree of warmth was so abnormal over the central U.S. that temp records perished Friday from Texas north to Illinois. The surge of tropical air delivered Chicago its highest October dewpoint reading (68°) in more than half a century. In a violent interaction between the high humidity and powerful overhead jet stream winds, t-storms erupted in a series of squall lines prompting tornado watches which covered sections of eight states. By 9 p.m. Friday, severe t-storms in Chicago’s western suburbs downed trees and powerlines as they raced through DeKalb County at speeds up to 65 m.p.h. They produced cloud-to-ground lightning at a rate of 100 strokes every 5 minutes.
New records Friday included 85° in Peoria and 83° at Springfield.
Temperatures soar Friday to levels 20° above normal. For the only the 17th time on an Oct. 29, the city stands to record a high in the 70s. This afternoon’s predicted 76° is within striking distance of the day’s record of 78° recorded most recently five years ago—but in 1901 as well.
Powerful southerly winds blowing over a broad swath of the nation’s mid-section deliver higher humidities. Friday’s relatively humid mid/upper 60° dewpoints are rare in late October. Since 1990, only two other days have hosted readings as high here so late in the season. Similarly humid air on this date 8 years ago fueled an outbreak fast moving severe t-storms responsible for some 50 to 80 m.p.h. gusts, which downed trees and powerlines while damaging several area buildings. Northwest suburban McHenry clocked 80 m.p.h. winds and O’Hare was whipped by a 60 m.p.h. gusts.
"These digital images of Wednesday evening's (Oct. 27) extraordinary total lunar eclipse come to us from Mary Anne Best, who photographed the astronomical event from her deck in Remington, Indiana. Fears that clouds might obscure the eclipse proved unfounded, thanks to an injection of relatively "dry" air into the area by the easterly winds in progress at the time. It was the first total lunar eclipse visible from North America since November 8, 2003. The entire eclipse ran from 7:05 pm through 1:03 am CDT---though the period of totality was just 1 hour and 22 minutes in length and occurred between 9:23 pm and 10:45 pm. Another total lunar exlipse won't occur for another 2.5 years--on March 3, 2007. However, that one will favor Europe, Africa and the Middle East and may only be partially visible in the eastern Americas, says Sky and Telescope Magazine.
Our photographer, Mary Anne Best, is one of our WGN weather observers and was kind to share these images with us. Many thanks Mary Anne for passing them along!"
-Tom Skilling
Rain has never fallen any heavier in San Diego than on Wednesday. The 2.67” deluge surpassed any Oct. 27 total since 1850. The only heavier 24-hour rain there occurred 67 years ago on Feb. 6, 1937, when 2.71” fell. Remarkably, Wednesday’s downpours bring that city’s October, 2004 total to 4.49”—an amount which dwarfs the 0.44” considered normal for the month.
The huge autumn storm behind southern California’s record rain is roaring across the Rockies, burying mountainous areas beneath 1-3 feet of snow for the second time this season. The system is headed for the Midwest, where strong southerly winds Friday are to initiate vigorous warming—but may provoke a significant severe weather outbreak into Friday night. The predicted 74° Chicago high may be among the city’s final 70s of the year. Records indicate only one additional 70° occurs on average—and only about half the time.
-Tom Skilling
The damp, drizzly weather predicted Wednesday is what’s left of a disturbance responsible for downpours in parts of the state Tuesday. As much as 1.46” fell at Moline and 1.28” at Quincy. The heaviest of that rain has passed largely south of Chicago. By the deep layer of moist air in its wake is likely to make it difficult for cloudiness to clear in any important way through Thursday morning.
A storm walloping the West with flooding rains in Los Angeles and coastal California while burying that region’s mountains under as much as 2-3 feet of wet, early season snow whipped by 30-50 mph winds, lifts into the Plains Thursday. Strong, well organized southerly winds beneath its eastern flank promise a return of 70s here Friday—a respectable warm-up at a time of the year known to feature flurries.
-Tom Skilling
Gusty winds off Lake Michigan will slash Chicago temperatures noticeably Tuesday. Afternoon readings, which soared Monday to levels more typical of mid-September, will top out closer to seasonal norms Tuesday. That’s should come as no surprise to area residents. Only five of the 134 years for which Oct. 25 official observations are available have produced readings as warm as Monday’s 75°—17 degrees above normal. Air that warm so late in the season can be expected to occur on a given day in late October only once every 22 years. But, news on the warm-weather front isn’t all bad. A fresh batch of south winds will send temps soaring back to the 70s late week.
Record heat baked Texas again Monday even as an arctic chill strengthened its grip in Canada. Galveston recorded 86° and Corpus Christi hit 91°—both new records. Temperatures Monday ranged 122 degrees from -26° near the North Pole to 96° at Laredo, Texas.
A series of Pacific storms will continue to bring repeated bouts of wind, rain and snow to the West. Last week, the season’s first major storm brought portions of that area record amounts of rain and snow, and a new round of winter storm watches and warnings are being posted in anticipation of the next storm, which should impact the area tonight and Tuesday.
The effect of this weather pattern on Chicago will be to keep temperatures well above normal this week, but increase prospects for precipitation as the systems advance into the Midwest. After a spectacular Sunday with crystal-clear skies and highs in the upper 60s, Chicagoans can look forward to similar temperatures for the rest of the week, but southerly winds will bring moisture into the region, setting the stage for showers and thunderstorms by midweek. Temperatures will briefly plunge Saturday, but a quick rebound is slated for Sunday’s Halloween festivities with readings headed back toward 60º.
With the week ahead upper jet stream flow pattern expected to be southwesterly, the primary track of weather systems will be north of Chicago. Temperatures are expected to average some 8° above normal; and with showers forecast on five days out of the next seven, significant rainfall appears in store. Six of this month’s first nine days warmed up to 70° or higher. Since that time readings have struggled to reach the 60° mark, that is until yesterday’s high of 76°. Weather historian Frank Wachowski says the average number of 70° days in October is eight; so with as many as two more possible this week, Chicagoans have a good chance of experiencing at least the “normal” number of 70° days this October.
Yesterday’s 1.17” at O’Hare airport makes the official monthly total rainfall 2.17”. With computer models indicating an inch or more possible by week’s end, this month’s “normal” precip total of 2.71” could easily be exceeded.
A balmy Saturday afternoon in Arlington Heights with a smell of "spring" in the air. Waves of showers and thunderstorms Friday night and Saturday morning brought 1.25" of rain. Sun in and out of clouds this afternoon with a gusty south winds to about 30 m.p.h.and temperatures in the lower 70s. Sure doesn't seem like late October.
Steve Kahn
Thundery downpours, which began overnight, are likely to deposit a total of 1-2” of rain here before day’s end. That’s more than all of the rain which has fallen in the past 55 days and marks the beginning of a decidedly wetter pattern. A cold front responsible for the rain may not pass until 3 or 4 p.m. Saturday. As morning downpours yield to sun, temps are likely to surge into the 70s—the warmest here in two weeks. That heating threatens to fuel afternoon t-storms. With powerful jet stream winds overhead and a more rapid than usual temp decline with altitude, the elements supporting severe weather appear to be in place. Weather watches may become necessary.
This morning’s t-storms are part of a cluster which produced hail 1.75” in diameter Friday afternoon at Volga, in NE Iowa. Thundery rains by nightfall had accumulated to nearly 1” at Dubuque and Doppler rainfall estimates ranged as high as 3” in sections of eastern Iowa and western Illinois.
The date for our annual Fermilab/WGN Tornado and Severe Weather
Seminar has been set. The 2005 seminar(s) will take place at 1PM and,
as always, be repeated at 7PM, Saturday, April 9. You're invited to
attend either. We'll be sharing information on our speakers and the
topics we'll be tackling in April in coming months on this blog and
are looking forward to seeing many of you there. As always, there will
be no charge for admission and seating is always on a first come/first
served basis, so we suggest getting there early.
The Spring, 2005 program will be the 24th we've put on since Brian
Smith, at the time a researcher and student of the legendary tornado
Dr. Ted Fujita at the University of Chicago, subsequently a severe
weather forecaster for years at NOAA's National Severe Storms Forecast
Center and now (and for many years now) the Warning Coordination
Meteorologist at the National Weather Service Forecast Office in Omaha
and I put the first program together back at Geneva High School out in
the Fox Valley in the early 1980s. We were offered the chance to move
the program to the beautiful Ramsey Auditorium at the Fermilab
National Acceleratory Laboratory in Batavia a year later and have been
there ever since. Working there with Bill Flaherty and Fred Ullrich
and their phenomenal staff at Fermilab all these years has been an
incredible honor and pleasure and we're looking forward to the April
9, 2005 program.
Over the years, we've welcomed many of the best and brightest in
the field of severe weather research and prediction, whose insights
into this fascinating branch of meteorological study, have been shared
by tens of thousands from all over the Midwest who have traveled in to
attend the annual seminars. Always a genuine thrill is working with
Dr. Joe Schaefer, Director of the Storm Prediction Center in Norman,
Oklahoma, who has joined us for years now, as well as working with my
colleagues from the National Weather Service Chicago Forecast Office,
including Jim Stefkovitch, our NWS-Chicago Meteorologist in Charge
(MIC) who first spoke at our Fermilab program three years ago and
later accepted the MIC post here and the incredibly hard working Jim
Allsopp, Warning Coordination Meteorologist, who's not missed one of
our Fermilab programs that I can remember and presents a tornado
spotting segment each year which is always illuminating and
informative.
We'll tell you about our April, 2005 speakers in subsequents
blogs here.
-Tom Skilling
An optical phenomenon known as "sun dogs" or "mock suns"--and more technically referred to as "parhelia" by optical meteorologists--was visible toward sunset Thursday evening (Oct. 21). Many thanks to the National Weather Service's Al Pietrycha, who digitally photographed the event and relayed the shot to us. It's Al's photo you're viewing here.
The response by area residents to sun dogs has always interested me. They can't be said to be rare. By the same token, they don't occur everyday either. That's why the number of phone calls which, over the years, have come into our office here at WGN about them, has always surprised me. Sun dogs, which appear as bright, prism-colored arrays either side of the sun's disc, are actually a form of halo and are the product of the refraction (or bending) of sunlight as it passes through high altitude (cirrus) clouds composed of ice crystals. It's been estimated sun dogs are visible up to two dozen times a year across most sections of the U.S. and Canada.
- Tom Skilling
Rainfalls have topped one foot in recent days while the snowfalls threaten to top out at 7 and 8 feet in the hardest hit locations out West. The first major storm of the Fall, 2004 season is responsible.
Precipitation records have perished in recent days in parts of the region. Santa Ana, Calif., north of San Diego, recorded 3.15” Wednesday, breaking its all-time October rainfall record. The 9.78” west of Las Vegas at Mt. Charleston becomes Nevada’s heaviest single-day total ever, eclipsing the previous record of 7.13” near Lake Tahoe more than 40 years ago in 1963. Weather warnings continued late Thursday over sections of 8 states.
Chicagoans enjoyed the first sun in four days Thursday. The 58° high was the 10th of October’s first 21 days not to reach 60°. Only three other years since 1959 have produced more sub-60° October highs by the 21st at O’Hare.
This weekend's Midwest storm is very similar to a major storm that struck the Midwest almost 3 years ago to the date on October 24, 2001. The storm produced a major severe weather outbreak in the southeastern Midwest and a major snowstorm in northwestern sections.
This weekend's storm is likely to produce severe weather across the central and southern Midwest, but not the snow to the north.
You can check out the details of the 2001 storm on this summary prepared by the Midwest Climate Center in Champaign.
Steve Kahn and Paul Dailey
The mammoth storm which has churned across the Rockies since Wednesday ranks among the strongest of the past six years. Rainfall near Los Angeles reached 14.63” late Wednesday at Opids Camp and 7.28” at Three Peaks outside San Francisco. The 9.18” at Mt. Charleston west of Las Vegas fell on soil so dry, predicted flash flooding never materialized. Meantime, snowfalls of 3 feet near Lake Tahoe threatened to reach as much as 4-7 feet in the Wasatch Mountains east of Salt Lake City.
It was a third straight day under the clouds in Chicago Wednesday. In contrast to September’s record of 90%, October has hosted only 54% of possible sun. Only three other Octobers since 1990 have logged as little or even less sunshine.
Wednesday’s 53° high was the 7th straight day below 56°. Only twice before, in 1875 and 1909, have so many daytime high tempers in the mid-50s or lower occurred in mid October.
A suite of 2-week computer forecasts continues to suggest a turnaround in Chicago’s abnormally dry fall weather. Total rainfall here in the coming 14 days may approach 3”. However, to date, rain numbers (1.46”) here remain incredibly low despite the heavy overcast of recent days. There hasn’t been less rain in the Sept. 1-Oct. 20 period since 1979. And, only seven other years since 1871 have been drier this time of the year.
By contrast, powerful t-storms blasted the South again Tuesday. Softball sized hail fell near Opelinka, Ala. Three twisters—far fewer than Monday’s 28—touched down in sections of Mississippi, Alabama and Tennessee. Out West, mud and rock slides cascaded onto California highways. Parts of the Los Angeles area may see 3-6” of rain while as much as 4 feet of snow is to fall at higher elevations near Lake Tahoe and 1-3” in Utah’s Wasatch Range.
The weather of autumn 2004 turned wild Monday south of Chicago in the central Mississippi Valley. While residents here shivered through a third day of unusually chilly temperatures, making mid-October the 8th coolest since 1871, swarms of twisters were swooping from powerful t-storms in Arkansas and southern Missouri east to the Tennessee Valley. By late Monday—with three tornado watches still in effect—the tally of twisters had grown to 27 and was still on the rise. Record heat racing north from Texas provided fuel for these storms, which exploded to life beneath diverging branches of the jet stream. While Chicago topped out at 53° Monday, record heat baked the southern Plains. Dallas recorded 93° while Corpus Christi peaked at 96°. High humidities there (the dewpoint was 77°) generated a heat index of 107°.
October 2004, with less than 2 weeks to go, now ranks among the coolest 14% on record here with 67% of its days posting deficits.
The gradual transition into the latter part of fall continues. Clouds and showers will extend far to the north of a low pressure system as it moves through southern Illinois during the next 24 hours. As that system moves east, a break in clouds will occur later Tuesday into Wednesday. However, clouds and warming will spread back over northern Illinois Thursday in advance of a low pressure system that will follow a track through Wisconsin. Warming southerly winds will draw milder and moisture-laden air into the southern Great Lakes with thunderstorms and heavy rains in excess of an inch likely Friday.
Back in 1930, this was the coldest Oct. 18-24 in Chicago records. That extremely cold air mass and associated west-to-northwest winds created a massive early season lake-effect snowstorm off the east end of lakes Ontario and Erie, burying Gouverneur, N.Y., and areas just south of Buffalo under four feet of snow.
Wind gusts in excess of 40 m.p.h. howled over northeast Illinois and the Great Lakes during the past 24 hours. Cold northwest winds brought the season’s first snow cover to portions of Upper Michigan and freezing temperatures to Chicago’s suburbs this morning. The week ahead actually starts out and ends up cool, but the intermediate days will be warm enough to boost the overall weekly average to about 53°. Temperature-wise this Oct. 17-23 would thus be somewhat “typical”—placing it almost midway between the extremes—the record high 69.2° average in 1920 and the 36.6° averaged back in 1930. A primarily southwest jet stream flow aloft will hold cold air well to the west and north, but at least three low pressure systems are expected to track through the area this week. Frequent rainy periods with heavy downpours possible Thursday could push this week’s total rainfall well in excess of an inch and a half.
Powerful winds combine with the chilliest temps since last April to bring a wintry feel to the air Saturday. Windchills across the Chicago area are to hold in the 20s through the day. Not since last April 12 have daytime readings here been any colder than the 45° predicted Saturday afternoon. Such a reading is closer to a normal afternoon high a month from now in November. In only five years of the 133 on record has Oct. 16 produced a daytime reading which failed to rise out of the 40s. They include: 1871, 1872, 1875, 1943 and 1976.
The intensifying autumn storm responsible for Chicago’s blustery weather was behind the area’s low barometric pressure reading Friday (29.37”)—the lowest pressure here since May 31. Saturday’s powerful winds buffeted the Plains and western Midwest yesterday. Buffalo, S.D. reported a gust of 57 m.p.h. Friday and nearby locations reported sustained winds in excess of 30 m.p.h. for 30 consecutive hours.
Welcome to the WGN Weather Center Blog! This is the newest addition to a host of products which originate from this facility and we're really excited by it. We've been looking forward to introducing this to you for some time.
The weather programs you see on WGN-TV, CLTV and our Chicago Tribune weather page all originate in this facility. It was just a year ago we moved into our new digs here, installed a new, state of the art computer graphics system and welcomed our CLTV colleagues to the office. Now, all of the Tribune's Chicago weather operations are under one roof and the talented group of people, each with a passion toward tracking our always changing Chicago and Midwest weather, are together in one location. It's been a thrill to bring this group together and to now be in a position to communicate with you online through this blog.
Having all of our weather assets in one location where we can collaborate has afforded us the unique opportunity to produce some truly proprietary local meteorological work and we want this blog to be one means we can share it with you as well as some of the behind the scenes effort and thinking which is involved in our daily forecast work here. Through it, you'll have the opportunity to share observations about the weather issues you've found interesting with those of us you see on camera and with the veteran behind the scene meteorologists, including Steve Kahn, Richard Koeneman, Paul Dailey and Dennis Haller ---each with 40 and more years of service at the National Weather Service and regular contributors to our Chicago Tribune weather page and with others who link to this site.
With this blog, we've a place now where we can share insights on the weather we're not able to address through our current on-air and print efforts. It affords us a chance to share with you and expand upon elements of our work and the thoughts we have on weather events which, until now, have remained behind the scenes and undisseminated---but also, an importantly, for you to get involved. This is a work in progress and an entity whose shape and form will change and expand as we listen to the topics which interest you and we better understand your interests.
We are approaching the matter of postings which appear here carefully until we get a feel for the level of response our blog engenders and caution that our day to day duties may limit our ability to respond to individual inquiries as frequently or completely as we might like--especially in the early stages of our blog.. But, we encourage weather questions for our Ask Tom segments and columns be addressed to "asktomwhy@tribune.com". This also affords you another means of communicating with us.
We spend a good deal of time in the production of the daily Chicago Tribune weather page. It's been a labor of love here since the project began more than 7 years ago Now, for the first time, we are going to be able to share many of our page's most important and popular features with you online and in real time, archiving them as we go. You'll be able to access and read our coverage of important weather events anytime you wish.
We look forward to having you with us on our new WGN/Tribune weather blog and hope you enjoy it.
- Tom Skilling
What a wonderful new forum for reporting, discussing and learning about Chicago's weather.
Steve Kahn
There was no thunder or lightning. But, rain late Thursday fell with the intensity of a thunderstorm downpour over south suburban sections of the Chicago area. A narrow 10 mile wide corridor from Kankakee County northeast into Indiana’s Lake and far northern Porter Counties was hardest hit. As much as 1.50” of rain fell, much of it in just an hour’s time. The rain, expected to linger at times into Friday could mix with some wet snowflakes in spots late Friday night into Saturday morning. It’s the first stage in the formation of a massive autumn low pressure system expected to dominate the weather here through early Saturday night.
Chicago’s 56° Thusrday high was the city’s coolest since May 15. But, the chill was of record proportions just to the southwest in Missouri. There, 54 and 51° highs recorded at West Plains and Vichy were the coolest ever for October 14.
Dear Tom,
We are planning a Caribbean trip in early December. Are there any areas that lie outside the hurricane zone?
Caroline Keating
Dear Caroline,
With a little luck the entire Caribbean should be hurricane- free by then. The Atlantic Basin hurricane season runs from June 1-November 30, but in most years tropical cyclone activity drops off sharply by mid November. Since 1887 there have only been about 10 tropical cyclones roaming the waters of the Atlantic or Caribbean in December, though two did develop last year when T.S. Odette brought heavy rainfall to Hispaniola around December 7 and T.S. Peter meandered through the open Atlantic for a few days around December 10. The most notable December storm, Hurricane Lili, formed near Bermuda on December 11 and died near the Dominican Republic on Christmas Eve in 1984.
Chicago may post its coolest daytime temperature of the autumn Thursday afternoon. Much will depend on the extent of sunshine. Limited sun would result in a mid 50° peak reading, the city’s lowest of the season. Until now, the 58° highs October 2 and 4 have been the chilliest afternoon readings.
Temps since the start of meteorological autumn on Sept. 1 have averaged 68.9°—ranking in the middle of the 133 other Sept. 1 through October 13 readings on record for the 43 day period since 1871. City temp records reveals 20 other early autumn periods with similarly mild readings and limited precipitation. Novembers which followed produced above normal readings 15 of the 20 years. The ensuing three month “meteorological” winter periods (Dec.-Feb.) also posted surpluses. Many factors affect seasonal weather, so there’s no guarantee that will be the outcome this year—but the implication is interesting.
Dear Tom,
Will any of this year’s hurricanes have their name retired?
Len Prokop
Dear Len,
The final decision won’t be made until this winter’s meetings of the World Meteorological Organization, but this active season could have a record-tying four names headed for retirement. There are no specific requirements for name retirement; any storm deemed historically noteworthy can qualify. Considering the large loss of life and the catastrophic property damage caused by hurricanes Charley, Frances, Ivan and Jeanne it is quite likely that all four of these names will be retired. Since Atlantic tropical cyclones were first named in 1953, only two seasons have sent four names into retirement. In 1955, the names Connie, Diane, Ione and Janet were retired and in 1995 Luis, Marilyn, Opal and Roxanne were removed from the list.
Since the start of meteorological autumn on Sept. 1, rain’s been in short supply falling measurably on only five days—Wednesday marks the 6th. Moisture associated with the remnants of Tropial Storm Matthew is behind Wednesday’s damp, raw weather here. Totals over the coming 24 hours (through Wednesday night) across the Chicago area should be limited to several tenths of an inch, but as much as 0.73” fell downstate at Carbondale. Powerful southerly winds associated with a mammoth storm off North America’s west coast are sweeping unseasonably mild air up the west end of the continent—a development which buckles the channel of jet stream winds north into a huge “ridge”, allowing northerly steering winds to dive from Canada into the central U.S. Strong chilling winds are to hit Chicago late Wednesday. The strongest cold surge to-date hits late Friday/Saturday.
Dear Tom,
I recently went on a trip out west that included California and the Southwest. I noticed that while it is generally hotter during the day than it is here, it is much cooler at night. Why such a radical shift between the day and nighttime temperatures?
Brian Hacker
Dear Brian,
It’s a characteristic of very dry air. When air is warmed, the temperature of all its component gases must warm as well. However, it takes more heat (provided by sunlight) to warm water vapor than it does the mix of gases that comprise air devoid of water vapor. Result: Daytime temperatures rise more quickly in dry than in moist air. At night, it’s the reverse. Moist air contains more heat energy than dry air at the same temperature, and so it must lose more heat in order to cool. As a consequence, moist air cools more slowly than dry air.
Tropical storm Matthew’s redezvous with Louisiana has swamped northern sections of that state with up 16” of rain over the past four days. While only high clouds have reached Chicago, Matthew’s northbound storm remnants doused sections of Kansas, Missouri and southern Illinois with rains Monday—rain which had moved to within 250 miles of Chicago late Monday evening. Compared to Homer, Louisiana’s 15.71” over the past four days, Monday’s 3.50” near Grovespring, Missouri was comparatively light. But, even Chicago is to get in on some of the storm’s lingering rainfall with sprinkles from a thickening overcast in scattered sections of the metro area toward evening and spells of light rain expected later Tuesday night and early Wednesday. This rain will amount to nothing compared to the 48-hour 6.72” deluge which flooded Chicago a half century ago on Oct. 9-11, 1954.
Fall, 2004 has been mild, running 2.4° ahead of last autumn.
Check out this live web cam of Mount St. Helens.
- Amy Mowery
Humid Gulf air, noticeably absent here in the past month, is fueling the heaviest rains to hit the area since the 1.41” which fell on August 28. It’s been dry since then. Until the arrival of Friday’s rain, meteorological autumn, 2004 —the period since Sept. 1—has ranked 2nd driest of any on record since 1871. Recent dry weather is history for the moment Friday. As much 0.75” is likely to douse parts of the Chicago area. Rains of that magnitude are more common in the opening 10 days of October than one might think. Weather observations here indicate rains of 0.50” or more have fallen in the month’s opening week and a half on average 3 of 5 years.
Temperatures peaked at 75° Thursday—the second consecutive day of mid-70° temp. Back to back mid 70s have occurred in nearly half of October’s opening two weeks here.
Dear Tom,
How does our current dry spell compare to Chicago’s longest period without measurable precipitation?
Marc Schaffer Skokie, Ill.
Dear Marc,
Though the city has recorded its second driest September in history and the dry pattern has continued through most of October’s opening days, this year’s longest period between measurable precipitation events has only reached 15 days- far from the record 30 day dry spell the city endured in 1919. In that year an inch of snow (.10 water equivalent) fell on January 6. During the next 30 days only a few snow flurries occurred, until measurable precipitation (.01" of rain and snow) fell on February 6. Because that dry spell occurred in mid winter, there was no impact on vegetation, and generous precipitation in February and March provided ample moisture for the upcoming growing season.
