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  • Tim McGill

Warm & Windy Tuesday With Strong Storms South

80s Streak Continues


Yesterday was the 3rd straight day with a high of 87° or warmer. Monday's high hit 88°. Today will be the 5th straight day with highs in the 80s. Our meteorological fall seems a lot more like summer.


The GFS Model has our highs again climbing into the upper 80s today. Highs should be just over 10° above average. The average high for today's date is 76°.


A cold front will slide south of the area late today. This sets us up for a brief break from this early fall heat tomorrow. Our highs on Wednesday will slide back into the upper 70s. It will be cooler than the past several days but still a few degrees above average.


80s return though Thursday and summery weather sticks around through early next week. This upcoming weekend will be as warm as this past weekend with highs soaring well into the 80s. The temperature anomaly forecast has most of the Midwest about 10° to nearly 20° above average. Our highs will again be in the upper 80s to near 90° on Saturday and Sunday.


Gusty southwest winds will sweep in unseasonably warm and humid air again today. Notice the wind shift later this afternoon. A cold front flips our winds to the northwest and sets us up for cooler night. Some spots well west of the city will actually fall into the upper 50s tonight and highs tomorrow slide back into the 70s.


An isolated shower or thunderstorm can't be ruled out for any of us today but the best chance of rain is late this afternoon into early tonight south and east of the city. There may even be some severe storms in portions of northern Indiana. More on that below.


Thicker concentrations of wildfire smoke aloft wafted back into our skies yesterday. The HRRR Model vertically integrated smoke forecast thins out the smoke later today after the passage of a cold front.


The National Blend Of Models has highs in the 80s for seven of the next eight days. It seems like the summer of 2021 doesn't want to end just yet.



Our extension of summer may stretch through the end of September. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from September 19th through September 23rd. The probability is between 80% to 90% for above average temperatures during the period. The longer range 8-14 day forecast also favors us for above average temperatures overall from September 21st through September 27th. The probability is around 70%. 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.








Little Drought Relief In The Forecast


Northern Illinois' rainfall deficit continues to grow. O'Hare has only seen .01 of rain so far this September. The month is now running 1.42" below average. There has been less than a third of an inch of rain there in the past 19 days. Today is the only decent chance for rain in the next several and the chances aren't that high.


Here is a recap of our drought conditions that I posted on 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 13th) has been particularly dry. Most of the Chicago area has seen between 25% 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.



The latest GFS model shows a possible scattered shower or thunderstorm late today but is basically dry through the weekend. There is at least one other model suggesting some showers or thunderstorms late Friday into Friday night. The pattern overall is quiet for the next several days but may become more active by the middle of next week.


The GFS model total precipitation forecast through this weekend is stingy with rainfall. The best chance of rain is today and most of that will stay well south and east of the city.


The Storm Prediction Center has the city and our southwest suburbs in a marginal risk (level 1 out of 5) area for severe weather today into tonight. There is a slight risk (level 2 out of 5) for severe storms well south of the city and into northern Indiana also. The area most favored for severe storms today is east of I-55. The greatest threat would be damaging winds and hail but a tornado can't be ruled out.


A slight risk is level 2 out of 5 possible risk levels. It means the possibility of "an area of organized severe storms, which is not widespread in coverage with varying levels of intensity".


A marginal risk is level 1 out of 5 possible risk levels. It is the low end of the risk categories but means "an area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity".


The longer range rainfall forecast hints there could be some hope for help with the drought. The latest 6-10 day forecast has the Chicago area favored for above average rainfall from September 19th through September 23rd. The longer range 8-14 day forecast also favors us for above average precipitation from September 21st through September 27th.





Here is my 7 day forecast:


Today: Partly to mostly cloudy, windy, sct. showers/t-storms late mainly south High: 86


Wednesday: Mostly sunny, cooler Low: 60 High: 78


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


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


Saturday: Mostly sunny Low: 66 High: 87


Sunday: Mostly sunny Low: 67 High: 88


Monday: Mostly sunny Low: 86 High: 87


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