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  • Tim McGill

Most Uncomfortable Day Of The Year?

Perfect Storm Of Heat & Humidity



Monday was muggy but today will be sweltering. A heat advisory is in effect from noon to 7 pm. The combination of heat and humidity will make it feel like 100° to 108°. Today will be the 16th time this year we hit a high of 90° or hotter. On average we see 11 90° days by now and 17 for an entire year on average. The hottest day of the year so far in 2021 occurred on July 26th when the high hit 94°. Humidity levels are higher today though so even if we fall short of that high temperature it will still feel hotter than it did back in late July.

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


It's when this tropical level of humidity is factored in that you get the complete picture of how uncomfortable it will be today. The heat index or apparent temperature values will be between 100° to 108°.



More wilting weather expected on Wednesday. The heat index or apparent temperature values will be between 95° to 101° tomorrow afternoon.


Highs will reach above 90° both today and tomorrow as dew points remain in the middle 70s.


Gusty southwest winds at times will continue through tomorrow and deliver air rich in moisture from the Gulf Coast. The highest threat of rain is from 6 pm this evening into early Wednesday morning. More on the severe threat below.


Tropical level dew points stick around through Thursday but relief arrives just in time for the weekend. Dew points should fall into the 50s on Friday. More comfortable humidity levels will continue through the weekend into early 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. "Sweltering" dew points through Thursday then "delightful" dew points settle in on Friday and hang around into early next week.



Highs hover in the lower 90s through Thursday before falling on Friday into the lower 80s. The National Blend Of Models has highs in the lower to middle 80s or around average from Friday through Thursday next week.


Hazy sunshine will be mixed with some puffy cumulus clouds today. The haze will be from wildfire smoke wafting in from out west. The HRRR Model vertically integrated smoke forecast suggests wildfire smoke from western fires and Canada will make its way to the Midwest again and continue to drift all the way to the east coast too.


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



While we settle back to about average temperatures this weekend there are indications that just beyond that we could see another warmer than average pattern settle in. The 6-10 day forecast has outlooked Chicago for above average temperatures from August 15th through August 19th. The longer range 8-14 day forecast favors us for above average temperatures overall from August 17th through August 23rd. 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 Rain Tonight


Much needed rain fell in some of the most parched portions of Illinois yesterday. Lake and McHenry counties picked up around one to as much as four inches of rain. August is now running .39" below average officially at O'Hare. Another round of rain is expected tonight into early tomorrow.


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 downplays tonight's rainfall but does suggest a few periods of scattered showers and thunderstorms Wednesday through Friday. We dry out for the weekend before more rounds of rain are possible next week.


Some of the storms tonight might be strong to severe. More strong to severe storms are possible on Wednesday as well.


The Storm Prediction Center has us in the enhanced risk category (level 3 our of 5 risk categories) for severe storms today into tonight. The timing of these storms appears to be between 6pm through midnight. Strong straight line damaging winds are the biggest threat although a few tornadoes can't be entirely ruled out.


An enhanced risk means an area of greater (relative to Slight risk) severe storm coverage with varying levels of intensity. Numerous severe storms are possible.


Today marks 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 slight risk category for Wednesday. I will update this in tomorrow's blog post.


Today's enhanced risk means "more persistent and/or widespread" storms with a few becoming intense.



The GFS model total rainfall forecast through this weekend squeezes out a range of rainfall from a few tenths of an inch north of the city to around an inch well south of Chicago. Like yesterday, locally heavier rainfall amounts are possible. There is abundant moisture in the air so some individual storms could dump in excess of an inch of rain easily in spots.



Our northern suburbs picked up some much needed rainfall on Monday and more could be on the way for late today and tonight but the pattern dries up this weekend and beyond. The latest 6-10 day forecast has the Chicago area favored for below average precipitation from August 14th through August 18th. The longer range 8-14 day forecast also favors us for below average precipitation from August 16th through August 22nd. That takes us all the way through a week from Sunday.





Here is my 7 day forecast:


Today: Partly/mostly sunny, sct. t-storms late (some strong) High: 93


Wednesday: Partly to mostly cloudy, sct. showers & t-storms Low: 74 High: 90


Thursday: Partly/mostly sunny, sct. showers/t-storms Low: 73 High: 92 (cooler lakeside)


Friday: Mostly sunny, cooler & less humid Low: 68 High: 83 (cooler lakeside)


Saturday: Mostly sunny Low: 64 High: 83 (cooler lakeside)


Sunday: Mostly sunny Low: 65 High: 84 (cooler lakeside)


Monday: Mostly sunny Low: 73 High: 84 (cooler lakeside)


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