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  • Tim McGill

Humidity Floodgate About To Open

About Average For August Today


Wednesday's high of 85° was just a smidge above average and the warmest high we have seen in six days. We continue to transition today from the cooler and more comfortable weather we started the week off with to the blazing heat and humidity that arrives early next week.

The GFS model has our highs today right around average (84°) again today. Temperatures are only part of our weather story though.



The sudden surge in humidity will make it feel much hotter by early next week. We could have some of the most uncomfortable weather we have see so far this year. The combination of heat and humidity on Tuesday will make it feel like 98° to 103°. The heat index or apparent temperature values will be very high on Monday too but Tuesday is when we peak.


Our temperatures might cool off a degree or two on Friday compared to today but an increase in humidity will offset that. Dew points climb from the 50s this afternoon to the 60s tonight and they are head to near 70° by late Friday night. So even though we will be a couple degrees cooler Friday it will feel just as warm with the added moisture in the air.


Gusty southwest winds on Friday will serve to transport this juicy air from the Gulf of Mexico.


This increase in humidity will fuel some thunderstorms on Friday. They will be scattered but a few could be strong.


Our dew points will continue to climb and by late this weekend they will be in the 70s and stay there into at least Tuesday.


Dew points are the preferred measurement of moisture in the air for meteorologists like me. Relative humidity is dependent on the time of day. When dew points get to the levels we expect by early next week (lower to middle 70s) it gets very uncomfortable.



The National Blend Of Models has highs hovering near 90° this weekend and into Monday and into the lower 90s by Tuesday. We cool slightly by the end of next week as we fall back to just above average.


The haziness we saw on Wednesday will continue today as wildfire smoke wafts into our skies once again. The HRRR Model vertically integrated smoke forecast shows wildfire smoke thickest right at its source out west and thinning slightly as it moves towards the Midwest. Check out this excellent blog post about the impacts this smoke has on our weather. It can keep us a few degrees cooler during the day and also inhibit the growth of puffy cumulus clouds so common on warm summer days.



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



The signal has been fairly strong for the warmer than average pattern that really kicks in this weekend to linger well into August. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from August 10th through August 14th. The longer range 8-14 day forecast continues to favor us for above average temperatures overall from August 12th through August 18th. We are included in some of the highest probabilities. Average highs are in the lower to middle 80s for the start to August.



The even longer range Subseasonal Experiment (SubX) temperature anomaly forecasts keeps us warmer than average through nearly the end of August. The forecast for the week ending on August 20th has us outlooked for above average temperatures. The forecast for the week ending on August 27th favors us for above average temperatures overall too.




Some Scattered Storms To Bring Relief


Yesterday was the 6th straight day without any measurable rainfall. July ended up 1.81" of rain below average and we are now down nearly seven inches below average since the start of spring. August is running about a half inch below average.


Here is a recap of the latest drought analysis that I posted last Friday (I will update this with the new analysis tomorrow):


The latest analysis from the US Drought Monitor shows absolutely no change in drought conditions for northern Illinois from the previous analysis a week ago. The area of Illinois in a moderate drought (level 1 out of 4) remains unchanged at 7.17%. The area of the state in a severe drought (level 2 out of 4) remains unchanged at 2.31%.

The end of July and start to August have been particularly dry. The 7-day period ending on Wednesday morning shows a large portion of our area is parched. Just 10% to 25% of average rainfall has been reported for much of the Chicagoland area during this period.


The latest GFS model has some scattered thunderstorms possible Friday into early Saturday and another round later Sunday into Monday.


It's still disappointing to add up all the rainfall represented by those chances. I ran the GFS model total rainfall forecast through Monday morning and the range of rainfall is from as little as a tenth of an inch to as much as nearly a half inch. The northern suburbs that need the rain the most are unfortunately not targeted for the higher end of the range.


Still a small glimmer of hope in one of the longer range rainfall forecasts. The latest 6-10 day forecast has the Chicago area favored for above average precipitation overall from August 10th through August 14th. The longer range 8-14 day forecast unfortunately shifts us back to an either near normal rainfall forecast for the city to even below average for areas west of Chicago from August 12th through August 19th.




Here is my 7 day forecast:


Today: Partly to mostly sunny, warm, a bit breezy High: 85


Friday: Partly to mostly cloudy, scattered t-storms, breezy Low: 67 High: 83


Saturday: Partly to mostly sunny, sct. shower/t-storm possible Low: 69 High: 87


Sunday: Partly to mostly sunny, sct. shower/t-storm possible Low: 69 High: 89


Monday: Partly to mostly sunny, sct. shower/t-storm possible Low: 72 High: 90


Tuesday: Partly to mostly sunny, sct. shower/t-storm possible Low: 73 High: 91


Wednesday: Partly to mostly sunny, sct. shower/t-storm possible Low: 74 High: 87


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