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  • Tim McGill

Sunny Today But Strong Storms Possible Tomorrow

A Lovely Labor Day


It might feel less like fall the next couple of days and more like summer but meteorological summer is officially over. The National Weather Service analysis of the season shows it was rather warm and wet compared to average. O'Hare's average temperature of 75.3° ranks as the 8th warmest summer on record. O'Hare also had 36 days when overnight lows did not fall below 70°. That is the fourth highest on record for Chicago. It was warm and it was muggy. The dew point averaged 65.4° this summer. That was the 4th highest on record.


It wasn't only steamy, it was stormy too this summer. The Chicago office of the National Weather Serviced issued 13 tornado warnings in August alone. That was the most in 35 years. There have been 36 tornado warnings issued by the office so far this year and they all occurred in climatological summer. It's the fourth highest total on record by the start of September.


It was not only steamy and stormy this summer, it was soggy too. Just over 13 inches of rain fell from June through August which was 1.13" above average. Not all of the Chicago area saw that much rainfall though. I have more on the ongoing drought further below in this post.



August helped bring the overall temperature for this summer up. 23 out of 31 days last month were above average. The month ended up just over 3° above average and ranks as the 6th warmest August on record.



So far, September is starting off cool. The first four days of the month were below average. The month was running 1.6° below average before things warmed up on Sunday. Sunday's high of 82° was 3° above average. The month is now running 1.1° below average.


The HRRR Model has our highs today in the lower 80s. Middle 70s are expected along the lakefront with a breeze off of Lake Michigan keeping it cooler there.


Tomorrow will be the warmest day of the week and maybe the warmest for at least the next two weeks. Highs tomorrow should reach into the middle to upper 80s.


So after a warm but pleasant day today in terms of humidity, we will be warmer and more humid on Tuesday. Dew points will climb back into the 60s for a more muggy day.


Our winds shift to the south late tonight and then strengthen on Tuesday with gusts to near 40 mph. That will wind pump in more heat and humidity.


A cold front will come through Tuesday evening with showers and thunderstorms ahead of it. The best window for rain is between 1 pm and 7 pm. Some of these storms could be severe. More on that below.


Wildfire smoke aloft was moderately high over the weekend but won't be as high today. The HRRR Model vertically integrated smoke forecast has the thicker smoke (depicted in orange and red) near the source of the wildfires out west and across the northern Rockies and plains. Relatively lighter concentrations of smoke are expected here on Labor Day.


The National Blend Of Models has our highs in the 80s today and tomorrow before sliding back into the 70s for the middle of the week. We bounce back into the 80s for a warm weekend and stay there into the middle of next week. Our average high fell back below 80° for the first time this fall yesterday. The average high for today's date is 79°.


There is a fairly strong signal from the long range models for a warmer than average middle of September. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from September 11th through September 15th. The longer range 8-14 day forecast favors us for above average temperatures overall from September 13th through September 19th. Average highs for this period are in the middle to upper 70s.



The Climate Forecast System or coupled forecast system (both names abbreviated CFS) is a medium to long range numerical weather prediction and a climate model run by the National Centers for Environmental Prediction (NCEP). The signal for the next 30 days isn't strong but it is indicating it will be warmer than average overall from now through the beginning of October.








Looking Longer Term For Help With Drought


More mixed news from the latest analysis from the US Drought Monitor. The past two weeks of rainfall has been either feast or famine in northern Illinois. Much of the Lake and McHenry County saw between 10% to 50% of average rainfall in the past two weeks while the northwest corner of McHenry County picked up nearly 150% to 400% of average rainfall. Rainfall was also well above average from the city southward to Kankakee during the same period.


The US Drought Monitor analysis reports an increase in the area seeing a moderate drought compared to the previous analysis. The area in a moderate (level 1 out of 4 levels) drought in Illinois has jumped to 9.96% from 7.93%. The areas in a severe drought (level 2 out of four levels) did not change and remains at .79%.


The Midwest region's drought news though is much better. Every drought level saw a decrease in coverage area. The biggest drop was seen in the area in a severe drought (level 2 out of 4). It dropped from 18.95% in the previous analysis to 12.68% in the most recent.


The latest GFS model suggests some scattered thunderstorms Tuesday afternoon with another chance early Thursday morning. Both of those chances of rain don't yield much in terms of total rainfall. After that, the next chance of rain doesn't come until the middle of next week.



The range of rainfall for Tuesday is as little as nothing at all to a couple tenths of an inch. The total precipitation forecast through Wednesday morning from the GFS model is not that promising for decent rainfall here.



A few of Tuesday's storms could be severe. The Storm Prediction Center has placed northern Illinois in a marginal risk (level one out of 5) area for severe weather. The greatest threat would be damaging winds. The highest risk for severe weather is over lower Michigan.


A marginal risk is level 1 out of 5 possible risk levels. It is the low end of the risk categories but means "an area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity".



There is some hope for help with the drought in the longer range rainfall forecasts. They are trending towards a more active pattern by the middle of the month. The latest 6-10 day forecast has the Chicago area favored for below average precipitation from September 11th through September 15th but the longer range 8-14 day forecast favors us for above average precipitation from September 13th through September 19th.





Here is my 7 day forecast:


Today: Sunny, warm & pleasant High: 82 (76 lakeside)


Tuesday: Partly to mostly sunny, windy, pm sct. showers/t-storms Low: 62 High: 87


Wednesday: Mostly sunny, breezy & cooler Low: 59 High: 78


Thursday: Mostly sunny Low: 58 High: 77


Friday: Mostly sunny Low: 59 High: 82


Saturday: Mostly sunny Low: 60 High: 83


Sunday: Mostly sunny Low: 63 High: 81


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