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  • Tim McGill

Brief Break From Summer-Like Heat

Warmer Pattern Right Around The Corner


Yesterday was the 5th straight day with a high in the 80s. Our meteorological fall so far is running about 3° above average. It has felt more like the middle of summer recently than the early part of autumn. That all changes today. We get a brief break from the unseasonable warmth and humidity with temperatures closer to average for the middle of September. Today could be the coolest day of the next nine.


The HRRR model has our highs reaching into the upper 70s for most of us today. A breeze off the lake will keep it cooler along the lakefront with a high in the lower 70s there. The average high for today's date is 76°.


Jacket weather tonight. The GFS Model has lows falling into the lower 50s well west of the city. A few upper 40s can't be ruled out. Lows will be in the lower 60s in and around the city.


Highs will climb into the lower 80s Thursday and then the heat gets turned up more for Friday.

Friday's highs will flirt with 90° in a few spots. We will cool to the lower 80s on Saturday but soar Sunday to near 90° again.


The heat keeps coming next week. Monday's highs will also be near 90°. The temperature anomaly forecast has most of the Midwest about 10° to nearly 20° above average.



So cooler today and then a bit warmer tomorrow. We slide back into the 70s for highs today, fall into the 50s for lows tonight and then climb back into the 80s on Thursday.


A wind develops off the lake this afternoon and continues off the lake (although shifting to the southeast instead of the northeast) on Thursday. That means cooler daytime temperatures lakeside.


There is virtually no chance of rain through Thursday.


The drier and cooler air from Canada will scour out most of the wildfire smoke that has so often wafted into our skies this summer and fall. The HRRR Model vertically integrated smoke forecast shunts all the smoke south of the area today.


The National Blend Of Models has highs in the 80s for six of the next ten days. Highs will be in the 80s Thursday through Tuesday before we return to around average temperatures again by the middle of next week.



Our overall warm pattern could keep on coming right through the end of the month. The signal remains strong for a warm finish to September. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from September 20th through September 24th. The probability is between 70% to 80% for above average temperatures during the period. The longer range 8-14 day forecast also favors us for above average temperatures overall from September 22nd through September 28th. The probability is between 50% to 60%. Average highs for this period are in the middle to upper 70s.




The short term, longer term 6-10 day and 8-14 day) and the even longer 30 day forecasts are all in sync suggesting a warmer than average pattern. The Global Ensemble Forecast System (GEFS) is a weather forecast model made up of 21 separate forecasts, or ensemble members The model tries to give an idea of the amount of uncertainty in a forecast by running an ensemble of multiple forecasts which are each tweaked a bit with their initial conditions. The GEFS has the Midwest and most of the country outlooked for above average temperatures overall all the way into the middle of October.






Drought Likely Deepening


The end of summer and start of fall has been particularly dry. O'Hare has only seen .01 of rain so far this September. The month is now running 1.52" below average. There has been less than a third of an inch of rain there in the past 20 days. The next chance of rain is late Friday into early Saturday morning. I will have the latest drought analysis from the US Drought Monitor this Friday.


Here is a recap of our drought conditions that I posted last Friday:


The US Drought Monitor analysis shows a slight decrease in the area under a moderate drought ( 1 one out of 4 levels). The area shrunk from 9.96% to 9.81% compared to a week ago. The areas in a severe drought (level 2 out of 4 levels) did not change and remains at .79%.


Every drought level dropped for the Midwest region. The area under an exceptional drought, the most dire drought category, dropped form 1.15% to .99%.


The past two weeks of rainfall (ending on September 14th) has been lacking. Most of the Chicago area has seen between just 10% to 50% of average rainfall during the period. Some suburbs west and south of the city and a portion of the city itself as only seen just 10% to 25% of average rainfall. Portions of northern Indiana has seen just 5% to 10% of average.


The latest GFS model shows a possible scattered shower or thunderstorm late Friday night into early Saturday. The next chance of rain after that doesn't come until late Wednesday into Thursday next week. Most of the next ten days will be dry.



The GFS model total precipitation forecast through this weekend is not calling for any drought busting rainfall. The range of rainfall expected is from nothing at all to around a half an inch of rain.


The longer range rainfall forecast starts off with a more active pattern but then dries things up a bit. The latest 6-10 day forecast has the Chicago area favored for above average rainfall from September 20th through September 24th. The longer range 8-14 day forecast also favors us for near normal precipitation from September 22nd through September 28th.






Here is my 7 day forecast:


Today: Mostly sunny, mild, a bit breezy High: 78 (cooler lakeside)


Thursday: Mostly sunny Low: 59 High: 82 (cooler lakeside)


Friday: Mostly sunny, shower or t-storm late? Low: 65 High: 86


Saturday: Becoming mostly sunny Low: 67 High: 83 (cooler lakeside)


Sunday: Mostly sunny Low: 67 High: 89


Monday: Mostly sunny Low: 65 High: 88


Tuesday: Mostly sunny Low: 63 High: 87


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