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  • Tim McGill

Heat & Humidity Will Slowly But Surely Return

Magnificent Monday Follows Our Wonderful Weekend


This past weekend gets my vote for the best of the year so far. Highs both days hit 80° with very pleasant humidity levels and plenty of sunshine. Today will be more of the same.


The HRRR Model has our highs today in the lower 80s in our warmer spots southwest of the city and middle 70s near the lakefront with a breeze off of Lake Michigan. Average highs for today's date are around 83°.



Our skies were a bit more blue this weekend because wildfire smoke that had been with us much of last week was steered south by the jet stream. The HRRR Model vertically integrated smoke forecast brings low levels of smoke from western wildfires back here aloft later this afternoon but it still won't be as hazy as it was last week.



Our heat index or apparent temperature values will bounce back this week. Dew points climb back into the 60s tonight and continue to rise through Tuesday.


A wind off the lake both today and tomorrow will keep it cooler along the lakefront. Highs today away from the lake will be in the lower 80s and tomorrow they will climb into the middle 80s.


There is a slight chance for an isolated shower or thunderstorm popping up Tuesday afternoon with areas southeast of the city favored for those.



The dew points were very comfortable over the weekend and even fell into the 40s at one point. The inch up slowly today, climbing into the upper 50s and then slide back into the 60s Tuesday. By Wednesday those dew points approach 70° but they hit their highest levels Friday into Saturday. While it will be rather warm and humid by the end of the week with highs in the upper 80s it still won't be as uncomfortable last week when the heat index topped 110° in some spots. The worst heat index values this week should be in the middle to possibly upper 90s.


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. We start the week off with dew points in "delightful" levels (50s) and end the week with dew points in "uncomfortable" levels approaching "sweltering" levels.



Highs will be near or just a bit below average today and then climb well above by the end of the week. The National Blend Of Models then keeps us at least a bit above average all the way through Monday.


The long range temperature probability forecasts continue to suggest a warmer than average pattern through the end of the month but the signal isn't as strong as it was in previous forecasts. The 6-10 day forecast has outlooked Chicago for above average temperatures from August 21st through August 25th. The longer range 8-14 day forecast also favors us for above average temperatures overall from August 23rd through August 29th. The probabilities are relatively high for this warm weather pattern in both of these forecasts. 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.




Best Chance Of Rain On Saturday


2.09" of rain so far this month at O'Hare which is down .76" from average. O'Hare has a surplus of .11" above average since June 1st. The most parched portions of Illinois include most of Lake and McHenry county. The best chance for some much needed rain there this week will come 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 Wednesday or Friday but more significant rain on Saturday.



The GFS model total rainfall forecast through our upcoming weekend doesn't suggest enough rain to put a real dent in the drought. The range of rainfall forecast is from as little as a third of an inch for our norther suburbs (who need the most rain) to over an inch well south of the city.



The long range rainfall forecasts suggest above average rainfall for the end of the month but the signal isn't that strong. The latest 6-10 day forecast has the Chicago area favored for above average precipitation from August 21st through August 25th. The longer range 8-14 day forecast also favors us for above average precipitation from August 23rd through August 29th. Both forecasts are on the lowest end of the probability range.


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: Mostly sunny, pleasant High: 81 (76 along lakefront)


Tuesday: Partly to mostly sunny Low: 63 High: 84 (78 lakeside)


Wednesday: Partly/mostly cloudy, sct. t-storm possible Low: 68 High: 86 (cooler lakeside)


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


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


Saturday: Partly to mostly sunny, sct. showers/t-storms Low: 71 High: 84


Sunday: Partly to mostly sunny Low: 68 High: 85


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