Autumn's first cool push of air

Say goodbye to summer and hello to autumn as this week (our 2nd week into the season) will really have a fall like feel. It was just last week where we were talking about temperatures in the 80s. Now we're talking about waking up to temperatures in the 40s and highs struggling to make it out of the 50s. Our first major push of cold air comes in and comes in with a bang. With a trough locked in place, many cities across the upper Midwest and Northeast will certainly feel the effects.

Chicago forecast for the week

Want to start off by mentioning that today is officially our first day of Autumn. At least another week for us to enjoy tranquil summerlike weather here in Chicago. Sunny, dry, and warm conditions continue to prevail with temperatures in the upper 70s/lowers 80s for the week.

Chicago's Climate

For those of you that may or may not be into weather/climate and just want to check out some climate facts about the city of Chicago in general or maybe for a future visit...here are some facts about Chicago's climate.

Climate for Chicago, Illinois
Home : Climate Graphs: Illinois : Chicago
Average Temperatures for Chicago
Average Temperature for Chicago, Illinois

Month Low High
Jan 14.3°F 29.6°F
Feb 19.2°F 34.7°F
Mar 28.5°F 46.1°F
Apr 37.6°F 58.0°F
May 47.5°F 69.9°F
Jun 57.2°F 79.2°F
Jul 63.2°F 83.5°F
Aug 62.2°F 81.2°F
Sept 53.7°F 73.9°F
Oct 42.1°F 62.1°F
Nov 31.6°F 47.1°F
Dec 20.4°F 34.4°F

Chicago's coldest month is January when the average temperature overnight is 14.3°F. In July, the warmest month, the average day time temperature rises to 83.5°F.
Average Rainfall for Chicago
Average Rainfall for Chicago, Illinois

Month Precipitation
Jan 1.75in.
Feb 1.63in.
Mar 2.65in.
Apr 3.68in.
May 3.38in.
Jun 3.63in.
Jul 3.51in.
Aug 4.62in.
Sept 3.27in.
Oct 2.71in.
Nov 3.01in.
Dec 2.43in.

The driest month in Chicago is February with 1.63 inches of precipitation, and with 4.62 inches August is the wettest month.
Monthly Sunshine Hours
Percentage of Sunshine for Chicago, Illinois

Month Sunshine Hours
Jan 44%
Feb 49%
Mar 51%
Apr 50%
May 58%
Jun 67%
Jul 66%
Aug 62%
Sept 59%
Oct 55%
Nov 38%
Dec 43%

Sunshine hours refers to the amount sunshine there is during the hours of daylight. A higher percentage means there is more sunshine through the day and a lower percentage will indicate that it is probably cloudier. Sunshine hours are important when you are planning your vacation.

August 4th 2008 Tornado and High Wind Event

On the evening of Monday August 4 2008 a total of 5 tornadoes were confirmed by the National Weather Service. Below is a list of the tornadoes, where they hit, and how strong they were on the Enhanced Fujita (EF) scale.

* Griffith, IN, rated EF2
* Bloomingdale, IL, rated EF1
* Bolingbrook, IL, rated EF1
* Orland Park, IL, rated EF0
* Boswell, IN, rated EF0

The stage was set for a severe weather outbreak Monday. With a strong southerly flow out of the south, the mercury climbed into the 90s ranging from 90-95 degrees across Northern Illinois and Northwest Indiana. Combine that with dewpoints in the upper 60s/lower 70s and heat indices were ranging from 100-105. In fact some areas just to the south and west of Chicago were prompted heat advisories till 8pm CDT Monday evening. In addition, the atmosphere was very unstable as was confirmed by several severe weather indexes. With so much potential energy in the atmosphere, all needed was a lifting mechanism.

Around 6pm CDT that evening, thunderstorms started to form in far Northwest Illinois. This cluster of thunderstorms that effected us on Monday is described by many as a Multiple Convective System or MCS. This basically is a continuous line of long lived thunderstorms that can span many miles for several hours. This is characterized by upper level winds that orient themselves in a northwest flow pattern and allow waves of energy (disturbances) to travel the region. Once the storms reached Winnebago and Ogle counties, the line of storms started forming a bow shape (Bow Echo) to it. This signifies that there are strong winds developing from the storms. In addition with these storms was the presence of a low level circulation. These circulations are generally near the leading edge of a line of storms but north of the bow apex. They help to produce brief spin ups or non major tornadoes (anywhere from an EF0 to an EF2). The first image above is a radar image at 745 PM of the Mesoscale Convective System which was in its mature bow echo stage as it moved through Cook, Dupage, and Will counties. The second one is a radar Image at 758 PM displaying the very strong winds associated with the Bow Echo. Cool colors (green) represent inbound winds toward the radar and hot colors (red) represent winds away from the radar. Note the dark blue and purple colors in Kane county. Radar indicated possible winds near 90 MPH across this location at this time.

Now also to mention was the frequency of lightning as we reported over tens of thousand lightning strikes that evening. I have a video showing the spectacular display.

Chicago Flood 2008

On September 13th 2008, 6.64 inches of rain fell in Chicago. This broke the old record for the maximum rainfall in a day of 2.26 inches set back in 1936. This also breaks the amount of rainfall to fall in a 24 hour period in Chicago history dating back from when records started being recorded in 1871. The old record was 6.49 inches set back in August 14 1987. No one will forget anytime soon the three day rain event (from September 13 to September 15 2008) that flooded so many homes, roads, and rivers. By Sunday night, much of Northern Illinois including the Chicago metro area and Northwest Indiana received a total rainfall accumulation between 6 to 10 inches. Heres the doppler radar showing the storm estimates from the weekend flooding.

Not minor, but major flooding took place. Many of the main rivers shattered old records by several inches. Homes were completely destroyed and several roads had to be abandoned. Here is a list from NOAA of rivers that reached record levels.

***River Crests for Select Locations in northeast Illinois and northwest Indiana

The following is a list of preliminary crest data for select river locations. Some rivers have not yet crested. This data may be updated or corrected as new crest information is made available. To get more information on each data point, go to our Advanced Hydrologic Prediction Service (AHPS) webpage.

Last updated 9/16/08


Location

Flood Stage
Crest (ft) Remarks
HART DITCH
Dyer 15 16.76 9/14/2008 New record. Previous record was 15.66 on Aug 24, 2007
Munster 6 12.81 9/14/2008 New record. Previous record was 9.22 on Aug 24, 2007

LITTLE CALUMET RIVER
Munster 12 17.31 9/14/2008 Record crest. Previous record was 15.66 on Nov 28, 1990
South Holland 16.5 20.16

DES PLAINES RIVER
Des Plaines 5 10.00 9/14/2008 Second highest crest on record.
Riverside 7 9.86 9/14/2008 Second highest crest on record.

FOX RIVER
Dayton 12 21.55 9/15/2008

ILLINOIS RIVER
Morris 16 24.84 9/16/2008

Record crest. Previous record was 23.91 on July 14, 1957
LaSalle 20

33.64 9/16/2008


River still rising. Record crest. Previous record was 32.05 on Dec 5, 1982

KANKAKEE RIVER
Shelby 9 13.06 9/16/2008

Record crest. Previous record 12.98 on Mar 24, 1982. River still rising.
Mommence 5 7.00 9/15/2008
Wilmington 6.5 8.68 9/15/2008

VERMILION RIVER
Leonore 16 24.29 9/15/2008 Third highest crest on record.***