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.
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.
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.
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.
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.
One of the wettest and cloudiest Octobers ever in Chicago is in the record books. The 7.69-inch rainfall measured at Midway Airport was the fourth wettest since observations began there in 1928. O'Hare International Airport is Chicago's official observation site, and its total of 6.04 inches was the ninth greatest in the 139 years of city records dating back to 1871. Rainfall frequency was also extraordinary, with measurable rain (0.01 inches or more) occurring on 19 of the 31 days, which tied October's all-time record set in 1883. Illinois State Climatologist Jim Angel noted that even greater rainfall downstate raised the state average to 8.35 inches---the second wettest since cumulative state records were begun in 1895 (9.23 inches in 1941 is the wettest on record.)
Chicago's October's sunshine was only 33 percent of possible sun (58 percent is normal)--the second-cloudiest on record dating back to 1893. It actually tied two other years (1917 and 1984.) Only the 31 percent in October 1925 had less sunshine. Chicago's October temperatures also averaged about 5 degrees below normal.
Early November outlook
Chicago temperatures are expected to average slightly below normal through Wednesday, but there are indications of a warming trend. The Climate Prediction Center's 6 to 10-day and 8 to 14-day outlooks call for area temperatures to average slightly above normal, and precipitation to be well below normal (good news for area farmers!).
It's an October responsible for unusual weather which we'll not soon forget once it closes at midnight Saturday. Rain has fallen more frequently than in any October since 1925 -- on 22 days since the first of the month, 19 of them measurably.
Midway Airport's eye-catching 7.69" October total -- which includes Thursday night and Friday's 2.26" downpours -- finishes nearly three times "normal." The month's gray skies have permitted only 33% of October's possible sunshine -- a far cry from the 58% which is normal -- and the least October sun here over the past quarter century. It's among the three lowest October sun tallies since 1893. And if the wet, gray weather hasn't been enough, October's 48.9-degree average temperature comes in at 5 degrees below the long-term average, making it the 19th coolest in 139 years. It's estimated home heating may have been up as much as 21 percent over a year ago.
The wind-driven deluge Thursday and Friday -- the 2nd to drench the area in a week -- produced eye-catching totals. Early measurements from Weather Bug rain gauges ranged as high as high as 3.65" at Hebron and 3.54" at Darien. Chesterton picked up 2.74" and Kankakee County's Bonfield was swamped by 2.55" while National Weather Service CO-OP observers reported 3.10" at Portage, Ind.; 2.50" at Woodridge; 2.39" at Romeoville; and 2.26" at Oak Brook and Peotone.
State Climatologist Dr. Jim Angel of the Midwestern Regional Climate Center reports statewide rainfall in October will finish 2nd wettest since 1895. It's the wettest to occur in Illinois since 1941.
Friday's 67 degrees not enough; October the first in 92 years not to generate a 70-degree high
While temperatures and surging humidities (dew points, a measure of atmospheric moisture, surged into the mid 60s) produced a springlike feel to the air Friday and highs of 67 degrees at O'Hare and 68 degrees at Midway, the month closes at midnight as the first October in 92 years which has failed to produce a single 70-degree high. That's happened in only two Octobers over the 139-year Chicago weather record. Temperatures did reach 70 Friday at Gary!
For the second time in a week, the area is being walloped by significant rains. The October rain tally had reached 4.63" at O'Hare and 5.46" at Midway even before the current system's precipitation began Thursday, assuring the month a spot among the Top 10 wettest Octobers on the books here. The frequency with which rain has fallen the past 30 days has been stunning. The last time an October produced 22 days with a trace or more of rain occurred 84 years ago in 1925.
The waves of rainfall predicted to sweep the Chicago area Friday are a continuation of overnight downpours, some from 41,000-foot thunderstorms. They fall on saturated soils unable to absorb them. With no option but to run-off, the 1" to local 2.5" totals predicted by Friday evening will stream into area rivers threatening flooding. The Fox River near Montgomery was within 0.2 feet of flood stage even before the latest deluges arrived.
The powerful autumn storm behind Friday's downpours has established an uninterrupted flow of Gulf moisture riding 60-plus mph south winds into the Midwest just above the surface. It's a set-up which assures a nearly limitless supply of moisture to fuel Friday's waves of gusty showers and thunderstorms. Though rain won't fall continuously, when it does it may well be heavy. With dew points, a measure of atmospheric moisture, predicted to hover around 60 degrees Friday -- much higher than yesterday's upper 40s -- in combination with mild south rather than lake-cooled southeast winds, Friday should feel "warmer."
Chicago's wet storm was responsible for a half dozen twisters which dipped Thursday from Texas, Louisiana and Arkansas skies. Rainfall topped 5" near Shreveport, La., and flood watches extend over a dozen states from the Gulf north to Illinois and Indiana.
Blinding snows dominated the system's backside and halted travel over sections of 4 states from Colorado and Wyoming into western Nebraska and South Dakota. Snowfall reached 1-2 feet in Denver and up to 4 feet nearby in the mountains. An area three miles southeast of Pinecliffe, Colo., was buried by 45.8" of new snow and drifts in Wyoming were up to 6 feet tall.
Warming slated later next week -- but it may not last
Much cooler air hits Friday night into Sunday morning. Gusty west winds will add to the chill of the 50-degree Halloween Day predicted Saturday. Longer range models hint at the potential for significant warming later next week into the following weekend. The predicted "warm-up" has the look of an El Nino inspired temperature increase. But, several key cold weather indexes turn negative toward the end of the coming two weeks -- suggesting any warming may not last.
REMINDER: Daylight Saving Time ends Sunday morning at 2 a.m. Turn clocks back an hour before heading to bed Saturday night. The change means it will feel like we have an extra hour of sleep Sunday. But sunsets will move from 5:46 p.m. Saturday to 4:45 p.m. Sunday as a result of the change.
It often takes the powerful winds of a large autumn storm to sweep warm air into Chicago this time of year. That's precisely what happens Thursday in advance of the wind-driven and potentially thundery waves of rainfall expected to produce fall's 2nd heaviest rainfall here Thursday night and Friday. An average of 30 computer rainfall projections suggests 1.19" may fall before Friday closes -- but predictions range as high as 2.57". It will take only 0.6" of additional rain to push the month into the ranks of Chicago's 10 wettest Octobers on record over the past 139 years. At Wednesday's close, October's official O'Hare total stood at 4.63".
Thursday's strengthening southeast winds are predicted to gust to 30 mph by nightfall and are likely to grow even stronger at times Thursday night and Friday. They represent a key element of the approaching storm. Any thunderstorms which arrive within the storm's expansive rain shield may well be able to harness energy from the 60-plus mph winds predicted just above the surface, transferring some of that wind energy down to the surface as powerful gusts.
Before the downpours get going late Thursday night, Chicagoans are in for something of a meteorological treat. Sunshine, in short supply this month -- it's been the 5th cloudiest October on record and the least sunny in a quarter century -- should be abundant.
The day's southeast winds sweep into North Shore suburbs after a trip over Lake Michigan's cool waters. That's a development expected to restrict highs in Waukegan and Kenosha to near 60 degrees while Chicago's lakeshore reaches the mid 60s and some warmer south and southwest suburbs peak in the low 70s. The city has yet to log a 70-degree temperature this month, making it only the third October to do so since 1871.
Storm buries Colorado under 2-plus feet of snow;
threatening Plains severe weather outbreak
The storm behind Chicago's two day "warm-up" has hammered the Rockies and western Plains with the region's biggest snow this season. Totals late Wednesday had reached 35" at Pinecliffe, 28.6" near Nederland, 28.5" just outside Golden and 14" at Boulder -- all in Colorado. The area just south of Denver was under a new 11" snowpack as night fell Wednesday.
A severe weather outbreak threatens to the east in the storm's front-side warm sector Thursday. Areas from Texas north to Oklahoma, Arkansas and southern Missouri are at risk for damaging thunderstorm winds including possible tornadoes.
