WGN Weather Center Blog

Temperatures will rise as a warm front approaches from the west today, a prelude to the first 80° temperatures experienced in the Chicago area since a high of 82° was recorded nearly two weeks ago on Sept. 17. In fact, if forecasts prove correct, 80° highs could be recorded 3 times this week—Monday, Tuesday and Saturday—just one short of the entire month of September’s total (4). Even with a midweek cool-down, highs are forecast to reach only into the 60s Wednesday and Thursday, temperatures are projected to average nearly 11° above normal for the next seven days. Though periodic showers or thunderstorms are in the forecast for the week ahead, it appears that Chicago will be positioned well south of the area of strongest frontal lift and available moisture. Oct.1-7 rainfall could well total less than a quarter inch here with one to two-inch totals possible across central Wisconsin and Lower Michigan.
-Paul Dailey, WGN-TV Meteorologist

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Illinois State Climatologist Jim Angel reports that this September will go down as this state’s 22nd coolest since 1895, with statewide temperatures averaging some 2 degrees below normal. Chicago readings the last six days have been subnormal, and September temperatures will average nearly 1.5 degrees below the most recent 30-year norms. However, the warm front moving east through Illinois today will be followed by slowly strengthening southerly winds that will more than counterbalance the diminishing daylight and lower sun angle, ushering in a significant warm-up that will see highs warm into the 70s Sunday with July-like highs in the mid 80s projected Monday and Tuesday—temperature levels more than 15 degrees above early October normals. Actually, back-to-back 80s are not all that unusual. Chicago weather records at Midway Airport dating back to 1928 reveal 44 of the 78 Octobers (56 percent) have experienced consecutive 80°-plus days.
--By Paul Dailey, WGN Weather Center Meteorologist

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September’s projected average temperature, 63.2º, comes in at 0.6º below the month’s climatological normal of 63.8º, noteworthy in that it ends a string of eight consecutive months during which Chicago’s (monthly) temperatures ran above normal. In addition, based upon preliminary temperature reports for the first 27 days of the month, September temperatures will average below normal across all of Illinois.
But don’t give up on summer just yet. In a weather pattern reversal characteristic of this time of the year, persistent northwesterly upper-level winds that have delivered several cool outbreaks in recent weeks are about to give way to southwesterlies. In response, Chicago’s temperatures will surge 45° from the middle 40s Saturday morning into the middle 80s Monday afternoon. A few showers and thunderstorms will accompany the warm-up, though they will be sporadic.
-Richard Koeneman -WGN-TV Meteorologist

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The terrain of metropolitan Chicago ranges from sand dunes, forests and corn fields to the concrete canyons of the Loop—features that profoundly affect nighttime air temperatures when the sky is clear and winds are calm.
It’s not surprising, therefore, that the area’s overnight minimum temperatures display big variations. Similarly, when the air is calm, temperatures recorded at official “thermometer level,” about four feet above ground, usually run several degrees higher than readings right at the ground. Experience tells us that patchy frost can be expected when temperatures fall into the upper 30s.
The average date of the area’s first autumn frosts varies by nearly a month, from late October in downtown Chicago to early October in the chilliest outlying locations. This season’s first frost is right on schedule, happening early Friday morning in outlying rural locations.
-Richard Koeneman WGN-TV Meteorologist

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Air of Canadian origin blasts across Chicagoland late today, initiating a temperature plunge that will culminate in a 28° drop by Thursday morning.
Air aloft will chill also, with readings a mile above the area hovering just above freezing through the day on Thursday, thereby establishing a vertical temperature differential sufficient to generate lake-effect rain showers. Borne along by brisk winds blowing from the north or northeast, those showers may dampen the area on Thursday. Were this early or mid winter, a similar situation would likely result in a significant lake-effect snow event.
It’s to be a short-lived cool spell. Winds, surface and aloft, turn westerly and then southwesterly by Saturday, and temperatures respond.
Area readings push toward 70º on Sunday, merely a prelude to a more vigorous warm surge on Monday that carries the city’s temperatures well into the 80s.
-Richard Koeneman WGN-TV Meteorologist

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The atmosphere becomes more energetic and the weather becomes more vigorous in the autumn, and Chicago is about to experience some examples of that in upcoming days.
The autumn season, standing as it does between summer and winter, can on occasion deliver a little of the weather characteristic of both those seasons. The weather plate in upcoming days will offer Chicagoans varied servings of sunshine and summery warmth, blustery winds, autumnal chill, clouds and showers, a 33° temperature drop and a 45° temperature rise.
However, past autumns have delivered far larger fluctuations. Chicago’s temperatures plunged 57º from 84º on Oct. 31, 1950, to 27º four days later. In 1992, the city’s temperatures surged 55º from an early-morning low of 21º on Oct. 19 to 76º by the 23rd.
-Richard Koeneman, WGN-TV Meteorologist

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The anniversaries of Chicago’s extreme weather events usually receive prominent publicity: Jan. 20, 1985 (-27º, the city’s lowest temperature); July 23, 1934 (109º, the city’s highest, though unofficial, temperature; Jan. 26-27, 1967 (23.0”, the city’s biggest snowstorm).
But today’s date, Sept. 25, has seemingly slipped through the cracks of the public consciousness even though it’s a significant date in Chicago’s weather history: Chicago officially logged its earliest-ever snow on this date in 1928 and also in 1942.
Although both snows were trace events (that is, they resulted in no accumulation), they created quite a public stir at the time. Sept. 25 in 1928 was a raw day, with high/low temperatures of 50°/39º; it was even worse in 1942: 46°/30º and 0.18” of rain in addition to the trace of snow.
This autumn may bring another early-snow event: Showers possibly accompanied by a few wet flakes might occur Friday.
--By Richard Koeneman, WGN Weather Center Meteorologist

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Powered by torrential rains accompanying violent thunderstorms Friday evening and additional heavy showers on Saturday, rain totals accumulated since the first of September are climbing into record territory. At Chicago’s official weather observation site (O’Hare), month-to-date rainfall now stands at 5.76 inches, an amount that is 176 percent of the normal full-month total of 3.27 inches, and sufficient to make this the 14th wettest September since 1871, even if not another drop of rain falls through the remainder of the month.
Substantial as it is, this month’s rain total is not likely to challenge Chicago’s all-time September rainfall record: 14.17” logged in 1961. The remnants of Hurricane Carla delivered 5.21 inches of wind-driven rain Sep. 12-14, adding that total to other heavy rains in that record-wet month.
A cooperative weather observer in St. Charles logged 4.04” in t-storms Friday evening into Saturday afternoon.
-Richard Koeneman, WGN-TV Meteorologist

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With a 140 m.p.h. jet stream directly overhead, a strong influx of warm, moist air from the Gulf of Mexico, and a warm front just to the west and south of Chicago, all the ingredients were set for a severe storm outbreak late Friday afternoon. Heavy downpours hit in eastern Kane, northern DuPage, and northern Cook counties. St. Charles and Mount Prospect reported over 3 inches of rain in an hour and a half. Those areas and many others reported flooded streets and paralyzed traffic. O’Hare’s 1.73 inch total far exceeded the previous record (1.09 inches in 1965) for Sept. 22. Aided by instability created by the diverging jet stream flow aloft on top of the converging winds at the warm frontal boundary below, towering storms built to 58,000 feet tall. Downdrafts resulted in widespread hail and wind damage (70 m.p.h. reported at Hanover Park and 60 m.p.h. near West Chicago). Funnel cloud reports and Doppler radar signatures prompted at least seven tornado warnings.
--By Paul Dailey, WGN Weather Center Meteorologist

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Another powerful weather system, the latest and strongest in a series of August/September storms to sweep into the Midwest, is descending on Chicago today. Invigorated by an especially energetic jet stream that is blasting across the Midwest and huge temperature variations between the cold western and warm eastern halves of the storm system, the atmosphere is poised to bring potentially violent thunderstorms and locally heavy rainfall to Chicago and much of the Midwest.
Thunderstorms are “weather factories” capable of producing five dangerous phenomena: damaging winds, large hail, intense lightning, flood-producing rains and isolated tornadoes. The National Weather Service’s Storm Prediction Center advises that the greatest potential for severe conditions across northeast Illinois will extend from this afternoon into the overnight hours.
-Richard Koeneman-WGN-TV Meteorologist

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It will come as no surprise to flood-weary residents of metropolitan Chicago that excessive rainfall has deluged the area since Aug. 1. Midway Airport’s climate statistician Frank Wachowski reports that 11.10 inches of rain has been logged there since that date—a total that is almost exactly twice the amount that history tells us would normally fall during that period. When added to all precipitation accumulated here since January 1, the year-to-date total climbs to an impressive 34.24 inches. That is 90 percent of Midway’s full-year total of 38.25 inches, and it ranks as the sixth greatest since 1928.
Yet another wet autumn storm has Chicago and the Midwest in its sight. After a sunny but chilly start this morning, increasing afternoon cloudiness heralds the approach of the latest weather system. Scattered showers work into the area late tonight, then become heavier and more numerous on Friday.
-Richard Koeneman WGN-TV Meteorologist

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Tuesday’s chilly 55° high, a reading more typical of November than September and the coolest daytime temperature here in 4 months, failed by just 3° to reach the 52° record low maximum for the date set 68 years ago in 1938. Record readings are, by their very nature, rare. So challenging a record—as happened Tuesday—underscores the unusual nature of the chilly air mass still dominant as Wednesday dawns. At 55°, Tuesday was 18° below normal, more than 20° cooler than Sunday’s 82° and nearly 30° below the 84° high on Sept. 19 a year ago.
Early season chilly air has been a rare commodity here in the past decade. Five of the past ten Septembers haven’t even produced a sub-60° daytime high. In the past 66 years, the only two readings on a par with Tuesday’s 55° and which occurred as early or earlier were the 51° high on Sept. 17, 1981 and the 55° high on Sept. 15, 1993.
-Tom Skilling

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Chicagoans find themselves in rare temperature territory Tuesday. The day’s November-level predicted high of 55° represents a 16° decline from Monday’s 71° and is more than 25° cooler than Sunday’s summerlike 82°. But even more impressive is the fact that only 265 of the 4,050 September high temps on the books here since 1871 have failed to warm above 59°. A high in the 50s Tuesday would mark only the 266th time that’s happened ranking it among the coolest 7% of September daytime highs on record in Chicago.
A second consecutive high In the 50s at Midway Airport Wednesday would establish still another cool weather benchmark for so early in the season. Dependent upon extensive cloudiness lingering, such a reading would mark the first time since May that back to back 50s have occurred and only the fourth time since 1928 that two or more highs in the 50s have been logged this early in the season.
-Tom Skilling

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Temperatures flirted with 80º Saturday but soared into the lower and middle 80s on a very summery Sunday. The 85º high at Midway Airport was the warmest there in nearly a month, since an 87º high on Aug. 23. Far southern areas were even warmer with Pontiac reaching 88º and Kankakee hitting 90º. Buoyed by the heating, the humid atmosphere spawned towering thunderstorms during the late afternoon that brought brief but heavy downpours. At Midway rainfall totaled 0.70” with 0.50” of it falling in a 15-minute cloudburst. September rainfall there is now approaching 4” after an August total of 7.12”. However, rainfall here was trivial compared to the 5.50” deluge that brought flooding to Miller in extreme southwest Missouri.
Warm weather will not be a factor here the rest of the week as chilly air will lower Chicago area daytime highs into the 50s Tuesday and Wednesday as fall makes its first real impact statement of the season.
--By Steve Kahn, WGN Weather Center Meteorologist

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Here are some pictures of Saturday night's beautiful sunset taken by some of our viewers. Thanks to everyone who shared their pictures with us. An explanation of what causes crepuscular rays is on the September 17 portion of the blog.

Photo taken by Alan Dawson Saturday night at the Hickory Hollow Campgrounds in Utica.

Photo taken by Jane Wills of Coal City, Ill.

Photo taken by Ann Wolf of Frankfort, Ill., who took this picture coming home from the Notre Dame vs. Michigan game

Photo in the Mokena area taken by Dawn Holstrom

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This weekend’s summerlike highs around 80º will be distant memories by midweek as the season’s first real autumnal chill blasts into Chicago.
The initial phase of the cool-down will begin Sunday night amid a wave of potentially severe thunderstorms, lowering Monday’s highs into the upper 60s. The real core of the cool air will arrive Tuesday on what promises to a be cloudy and blustery day with light showers and the city’s first sub-60º high since mid-May. Though a modest temperature rebound into the 60s is likely by the end of the week, the autumnal feel will continue with clouds and frequent showers that will add to this month’s substantial rainfall totals.
Eastern Pacific Hurricane Lane made a 120 m.p.h. Category 3 landfall Saturday afternoon on Mexico’s Pacific coast north of Mazatlán. Now weakening, Lane’s remnants threaten flooding and mudslides as it moves north into Mexico’s interior.
-Steve Kahn WGN-TV Meteorologist

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By this time last year, Chicagoans had enjoyed four times as many September 80s as the three on the books this month. The lack of 80s is unusual; only two Septembers in the past 40 years have logged fewer 80s by this date—1972 (with only one 80°-plus reading) and 1993 (with two).
The month has just passed its midpoint with an average temperature of 66.4°—a reading 7.3 degrees below the comparable period one year ago and chilly enough to rank 40th coolest of the 136 Sept. 1-15 periods on the books since 1871.
The predicted highs Saturday and Sunday mark the city’s warmest temps in eight days. But, the unfolding meteorological scenario in the Plains offers a clue on what’s ahead here. Grand Forks, N.D.’s record-breaking 86° Friday—16 degrees above normal—will be a distant memory there by Monday as highs fail to clear the 40s.
--By Tom Skilling, WGN-TV Chief Meteorologist

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The strength of the newly declared El Niño in the Pacific may play an important role in this winter’s weather here. El Niños occur when easterly trade winds weaken over the Pacific Ocean west of South America and ocean temperatures warm. Global weather shifts are tied to the event over as much as 70% of the planet when El Niños occur.
Moderate and strong El Niños often boost winter temperatures, reducing snowfall here—sometimes dramatically—in 67% of the winters during which have occurred since 1950. But, the impact of weaker El Niños can be quite different. An analysis of those winters indicates 55%—including several in the barbarically cold late 1970s—have produced near or below normal temperatures and more snow. That’s why all eyes in the meteorological community will be on trends in the strength of the new El Niño in coming months.
-Tom Skilling

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With soils across the area completely saturated after well over twice the normal amount rain in the August and September period—10.38” at Midway Airport versus the typical 4.79”—Wednesday’s thundery downpours translated quickly to run-off and serious flooding. Hardest hit was the city’s South Side and south suburban areas.
Midway Airport’s 1.08” brought that site’s September tally to 3.26”—just 0.19” below the normal rainfall which typically falls over the entire month of September. The past four days alone have generated 2.65”. Areas farther south were hit by the heaviest rains of all Wednesday. Morris in Grundy County was swamped by 4.81” while sections of Indiana’s Lake and Newton Counties were hit with over 5” of rain.
Chicago’s cloudy September continues. After another sunless day Wednesday, the month has seen just 45% of its possible sun—the least in 22 years.
-Tom Skilling

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Just a year ago, Chicago’s high temperature surged to 94°, making it the fourth consecutive day with readings in the 90s. By comparison, Wednesday marks the fifth day the city’s been shrouded by clouds. September’s paltry 49% of its possible sunshine is well below the 62% considered normal. The month is on its way to becoming the fifth in a row with sub-normal sunshine.
With all the clouds, it’s little wonder September has averaged a stunning 7.5° cooler than the same period a year ago. Daytime highs the past four days alone have averaged just 68.1°—not only 6° below normal but cool enough to qualify as the chilliest Sept. 9-12 period in 13 years.
Thundery downpours hammered areas north of Chicago. Waukegan was hit by 1.42” while Kenosha was swamped by 2.09” and downtown Milwaukee recorded 2.30”. Over 300 lightning strokes were detected every 15 minutes Tuesday afternoon.
-Tom Skilling

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The Chicago area was drenched for a fifth time in just six weeks Monday. Sunday’s sporadic rainfall turned heavy for hours Monday morning and rly afternoon—rain which was punctuated by lightning and thunder. Before the day had ended, 1.97” had accumulated at O’Hare, that site’s heaviest since 2.05” on July 20. The total was expected to increase overnight as new showers and thunderstorms, which flared near the Mississippi River late Monday then generated 65 m.p.h. gusts and hail south of Peoria near Havana, set their sights on the metro area.
Area rainfall was heaviest outside the city, topping 2” at Oak Brook, Woodridge, Mt. Prospect, Romeville and Clarendon Hills among others.
Midway Airport’s been hit with five 1”+ rains since August 1—nearly three times normal. That’s the greatest number of heavy rains in the period since six occurred in 1977.
-Tom Skilling

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