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  • Tim McGill

Heat & Humidity Headed Higher

A Terrific Tuesday


If you enjoyed Monday, you will probably like today too. A few more clouds, a bit more humidity and a degree or two higher today but little change overall.


The HRRR Model has our highs today in the lower to middle 80s for most areas. A breeze off the lake will hold highs in the upper 70s along the lakefront. Average highs for today's date are around 83°.



Wildfire smoke concentrations aloft will again be thin compared to what we saw last week. The HRRR Model vertically integrated smoke forecast has low levels of smoke from western wildfires wafting into our skies today. Thicker smoke just to our west may eventually arrive later this week.



Our heat index or apparent temperature values will slowly but surely climb this week but not to the levels we saw last week when they peaked at close to 110°. The worst heat index levels this week will hit on Thursday and Friday when the reach into the lower 90s.


A breeze off the lake continues through tomorrow and beyond, possibly all the way through Friday. Look for highs along the lakefront in the upper 70s today and tomorrow.


There is a slight chance for an isolated shower or thunderstorm firing up this afternoon and a better chance Wednesday afternoon for a scattered shower or thunderstorm. Most of us should be rain free though today and tomorrow.


The dew points which were so comfortable over the weekend and on Monday will be building along with the heat. They climb to near 70° by Tuesday and stay relatively high through Saturday. A cold front should cross through here Saturday and flush out some of the humidity for Sunday.


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. Our dew points were at "delightful" levels (50s) over the weekend but reach "uncomfortable" levels Tuesday and approach "sweltering" levels by the end of the week.



Our highs peak at near 90° Thursday and Friday. The National Blend Of Models cools us down a couple of degrees for the weekend but we remain at or above average well into next week.



A fairly strong signal for a warmer than average end to August. The 6-10 day forecast has outlooked Chicago for above average temperatures from August 22nd through August 26th. The longer range 8-14 day forecast also favors us for above average temperatures overall from August 24th through August 30th. Average highs are in the lower 80s for this part of August.



The even longer range Subseasonal Experiment (SubX) temperature anomaly forecasts suggest a warmer than average end to August and start to September. The forecast for the week ending on September 3rd has us outlooked for above average temperatures. The forecast for the week ending on September 10th also favors us for above average temperatures overall. It takes a close inspection of both graphics to see the pixel representing the Chicago area is yellow. That corresponds to a temperature anomaly of .15° to .45° Celsius above average.




Mostly Hit Or Miss Rainfall


1.33" of rain so far this month at O'Hare which is down .91" from average. O'Hare is now .04" below average since June 1st. North of O'Hare is where we find the most parched portions of Illinois across Lake and McHenry county. Only hit or miss showers and thunderstorms expected today through Friday with a slightly better chance for some rain on Saturday.

Here is a recap of my Friday update on drought conditions based on numbers from last week's US Drought Monitor analysis:


It's another case of mostly good news from the latest US Drought Monitor analysis. The best news is that portions of Illinois in a severe drought dropped almost in half. 1.19% of the state is now in a severe drought (level 2 out of 4 levels) down from 2.19% last week. The bad news is 6.05% of the state is now in a moderate drought (level 1 out of 4 levels) up slightly from 6.00% last week. Northern Illinois is the only part of the state reporting drought conditions. There is more bad news. The portion of the state considered "abnormally dry" has increased to 15.20% from 10.99% last week.


The latest GFS model suggests a spotty shower or thunderstorm tomorrow and still points to Saturday as the better chance for rain.



The GFS model total rainfall forecast through our upcoming weekend doesn't show much help for folks in a drought. Just a tenth of an inch of rain or a bit more for our northern suburbs is expected with up to nearly a half inch in northern Indiana.



The signal has grown stronger from models for a wetter than average end to August. The latest 6-10 day forecast has the Chicago area favored for above average precipitation from August 22nd through August 26th. The longer range 8-14 day forecast also favors us for above average precipitation from August 24th through August 30th with Chicago in the bullseye of highest probability on the map.



Most of the Midwest is also favored for above average rainfall in the long range forecasts too. The Midwest region's drought news is mixed with the latest analysis. The good news is the area in both the moderate and severe drought levels dropped slightly. The bad news is the area in an extreme drought increased slightly and for the first time a portion of the region slipped into an exceptional drought, the highest level.

The west region saw a a slight decrease in their extreme and exceptional drought area, the two highest categories of drought. The area in the two lowest levels of drought, moderate and severe, increased slightly. More than 95% of the west is in some level of drought and just over a quarter of it is in the worst level of drought, the exceptional category.




Here is my 7 day forecast:


Today: Partly to mostly sunny High: 84 (78 along lakefront)


Wednesday: Partly/mostly cloudy, sct. t-storm possible Low: 69 High: 85 (80 lakeside)


Thursday: Partly to mostly sunny, sct. t-storm possible Low: 70 High: 88 (82 lakeside)


Friday: Partly to mostly sunny, sct. t-storm possible Low: 72 High: 88 (82 lakeside)


Saturday: Partly to mostly cloudy, sct. showers/t-storms Low: 71 High: 85


Sunday: Mostly sunny Low: 71 High: 85 (cooler lakeside)


Monday: Mostly sunny Low: 67 High: 84 (cooler lakeside)



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