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  • Tim McGill

Here We Go Again?

Steamy & Stormy


Tuesday was the hottest day of the year if you consider both the heat and humidity. O'Hare had a peak heat index of 104° but some spots southwest of the city felt as hot as 110° to 114°. That intense heat and humidity created the energy to fuel yesterday's powerful thunderstorms. Every county in northern Illinois and Indiana had a severe thunderstorm warning at some point last night. Nearly 200 thousand people lost power as winds gusting over 60 mph brought trees down across power lines.



Yesterday was the second straight day with numerous reports of severe weather. The National Weather Service is completing their surveys from the tornadoes that touched down on Monday. A total of seven confirmed tornadoes were reported. Three of those tornadoes had EF-1 strength with winds between 86 to 110 mph.



Today will be another day that starts of steamy and eventually becomes stormy. More on our severe weather threat below.


Hang in there! The weekend still looks great. It will be worth the wait. I promise. Two more days of stifling heat and humidity and then cooler more comfortable weather settles in just in time for Friday and this weekend.

Another heat advisory is in effect from noon to 7 pm today. The combination of heat and humidity will make it feel like 100° to 105°.


Today will be the 17th time this year we hit a high of 90° or hotter. We average that many 90° days in an entire year. From this point forward we would normally tag on another four 90° days.

The HRRR Model has our highs today in the lower to middle 90s. Average highs for today's date are around 83°.



It will feel hotter here than New Orleans today. The heat index or apparent temperature values will be between 95° to 105°. So today is the second straight day with a heat advisory from noon to 7 pm.



Still steamy tomorrow but the heat index values won't be quite as high. Thursday's heat index should top out between 95° to 100°.


Gusty southwest winds both today and tomorrow will continue to deliver moisture rich air from the Gulf of Mexico.


The highest threat of rain over the next two days is late today into tonight and then late Thursday into Thursday night.



The dew points should drop dramatically on Friday as they fall from the 70s into the 50s. They should stay at relatively comfortable levels through the weekend. More moderate humidity levels return for the middle of next week.



Relative humidity is one way to express the amount of water vapor in the air but dew points are the preferred measurement of moisture in the air for meteorologists like me. Dew points on Tuesday were off our chart as they topped out above 80° in some spots. At least "sweltering" dew points expected through Thursday then "delightful" dew points expected for Friday and "pleasant" dew points for the weekend.



Today and tomorrow should hit highs of 90° or hotter. The National Blend Of Models has highs around average as we top out in the lower 80s Friday through Monday. We warm back above average for the middle and end of next week.


Another day with hazy sunshine mixed with clouds. The HRRR Model vertically integrated smoke forecast suggests wildfire smoke from western fires being carried by the jet stream and wafting into our skies today.



Here are some articles related to wildfire smoke that you may be interested in:



We will be seasonably warm this weekend but the period covering next week and the following weekend should be above average overall. The 6-10 day forecast has outlooked Chicago for above average temperatures from August 16th through August 20th. The longer range 8-14 day forecast favors us for above average temperatures overall from August 18th through August 24th. Average highs are in the lower 80s for this part of August.



The even longer range Subseasonal Experiment (SubX) temperature anomaly forecasts start us out near normal and then flip us back to above average. The forecast for the week ending on August 27th has us outlooked for about average temperatures. The forecast for the week ending on September 3rd favors us for above average temperatures overall.





Another Round Of Strong Storms


All of northern Illinois received rainfall yesterday. O'Hare officially saw .38 and is now just .14" below average. I will post the latest drought analysis numbers from the US Drought Monitor on Friday. After several rounds of rain this week I expect we will see a real dent in the drought.


Here is a recap from my post on Friday with the updated drought statistics for our northern suburbs:


Mostly good news from the latest US Drought Monitor analysis. The good news is that portions of Illinois in a moderate and severe drought have dropped slightly. 6% of the state is now in a moderate drought (level 1 out of 4 levels) down from 7.17% last week. 2.1% of the state is now in a severe drought (level 2 out of 4 levels) down from 2.31% last week. Northern Illinois is the only part of the state reporting drought conditions. The bad news is the portion of the state considered "abnormally dry" has increased to 10.99% from 9.74% last week.


The latest GFS model keeps our pattern active today into tomorrow with thunderstorms expected this evening into tonight and a chance for more scattered storms tomorrow and again early Friday. No rain is expected Friday afternoon through the weekend and next week should be drier than this week.



Some of the storms this evening and tonight may become severe. We even have a chance for a fourth round of severe storms on Thursday.


The Storm Prediction Center has us in the slight risk category (level 2 our of 5 risk categories) for severe storms today into tonight. The timing of today's storms should be similar to yesterday. The highest threat window is between 6 pm and 10 to 11 pm. Strong straight line damaging winds are the biggest threat but once again a few tornadoes can't be entirely ruled out.


An slight risk means "an area of organized severe storms, which is not widespread in coverage with varying levels of intensity." Isolated intense severe storms are possible that should be short-lived and/or not widespread.



Yesterday marked the one-year anniversary of the powerful derecho that swept through several states last year. Check out the National Weather Service's recap of that event here.



The Storm Prediction Center has us in a marginal risk of severe weather on Thursday. I will update this in tomorrow's blog post.



Here is the Storm Prediction Center's definitions of the five risk categories:



The GFS model total rainfall forecast through this Friday brings additional rainfall between a half inch to nearly an inch with the heavier amounts favored south of the city.



The long range rainfall forecast starts out dry then trends to about average. The latest 6-10 day forecast has the Chicago area favored for below average precipitation from August 16th through August 20th. The longer range 8-14 day forecast also favors us for near normal precipitation from August 18th through August 24th.




Here is my 7 day forecast:


Today: Partly/mostly cloudy, sct. t-storms late (some strong), breezy High: 92


Thursday: Partly/mostly sunny, mainly pm sct. showers/t-storms Low: 73 High: 92


Friday: Partly to mostly sunny, cooler & less humid Low: 70 High: 82 (cooler lakeside)


Saturday: Mostly sunny Low: 63 High: 83 (cooler lakeside)


Sunday: Partly to mostly sunny Low: 63 High: 84 (cooler lakeside)


Monday: Partly to mostly sunny Low: 65 High: 84 (cooler lakeside)


Tuesday: Partly to mostly sunny Low: 66 High: 85 (cooler lakeside)


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