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  • Tim McGill

Sizzling Weather For September

80s Streak To Stretch Through Weekend

We started another streak of 80° days with a high of 81° at O'Hare Thursday. The streak could stretch through next Tuesday. Our meteorological fall so far is running about 3° above average.

The GFS Model has our highs reaching into the upper 80s to near 90° today. That is about 10° to 15° above average. Average highs for this date are around 76°. Higher levels of humidity will make it feel more muggy too.

The GFS Model cools us off closer to average on Saturday. The forecast highs for tomorrow are in the lower 80s with a wind off the lake keeping us cooler there. Highs at the beaches will be in the upper 70s.

By Sunday we are sizzling again for the middle of September. Highs should top out near 90° for the second time in three days.

The temperature anomaly forecast map almost makes it look like the middle of the country is on fire Sunday. Temperatures will be well above average for a good portion of the country. The forecast has most of the Midwest about 10° to nearly 20° above average. Parts of the plains will be nearly 30° above average.

Today's highs will be near 90° but we drop about 10° for Saturday. A cold front will come through this evening. It is marked by a wind shift around 6 pm. Winds eventually turn off the lake on Saturday and cool us off a bit.

Dew points will be in the middle 60s today for a more muggy feel but fall into the 50s early Saturday. It will be both cooler and more comfortable in terms of humidity tomorrow.

The best chance of rain is this evening and into early Saturday morning. The highest probability is just 30%.

The National Blend Of Models has highs in the 80s for three of the next four days before cooling back below average by the middle of next week. If that forecast of 69° for the high on Wednesday verifies, it will be the coolest day we've seen in almost four months.

The longer range temperature forecasts are easing off just a bit after several days with strong signals indicating a warmer pattern. The 6-10 day forecast has outlooked Chicago for near normal temperatures overall from September 24th through September 26th. The longer range 8-14 day forecast favors us for above average temperatures overall from September 24th through September 30th. Average highs for this period are in the lower to middle 70s.

The even longer term 30 day forecast keeps the warmer than average pattern continuing into the middle of next month. 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.

Still Looking For Some September Rain

The latest US Drought Monitor analysis is in and it is mostly good news for the Midwest but there is some bad news locally.

The US Drought Monitor analysis shows a slight increase in the area under a moderate drought ( 1 one out of 4 levels). The area grew to 10.11% from 9.81% last week. The area in a severe drought (level 2 out of 4 levels) did not change and remains at .79%. The area considered "abnormally dry" (the precursor to a moderate drought) nearly doubled and now stands at 32.94%.

For the Midwest the news was better. The areas in a moderate, severe and extreme drought all dropped slightly. The area in an exceptional drought (level 4 out of 4 levels) is unchanged at .99%. The most parched portion of the Midwest is northern Minnesota.

The past two weeks of rainfall (ending on September 16th) shows why the drought has deepened. 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 has only seen just 10% to 25% of average rainfall. South of the city and northern Indiana has seen just 5% to 10% of average.

I've been keeping a running tally of the lack of September rain. O'Hare has only seen .01 of rain for the first 16 days of the month. The month is now running 1.72" below average. There has been less than a third of an inch of rain there in the past three weeks. While there may be a few showers and even an isolated thunderstorm this evening and overnight, it isn't exactly a drought busting type of rain. The latest GFS model's meteogram doesn't even show any significant rain. It focuses more on the rain coming late Monday into Tuesday.

The GFS model total precipitation forecast through this weekend suggests most of us will see little to no rain. Well west of the city it squeezes out about a tenth to a third of an inch. That would all come this evening and overnight.

More discouraging drought news. Looking longer range, the precipitation forecasts are signaling a drier than average end to September. The latest 6-10 day forecast has the Chicago area favored for below average rainfall from September 22nd through September 26th. The longer range 8-14 day forecast has us outlooked for below average precipitation too (with higher probabilities) om September 24th through September 30th.

Here is my 7 day forecast:

Today: Mostly sunny, evening shower or t-storm? High: 88

Saturday: Becoming mostly sunny Low: 65 High: 80 (cooler lakeside)

Sunday: Mostly sunny Low: 66 High: 88

Monday: Partly to mostly cloudy, scattered shower/t-storm possible Low: 68 High: 81

Tuesday: Partly to mostly cloudy, scattered showers & thunderstorms Low: 68 High: 82

Wednesday: Partly to mostly sunny, scattered showers Low: 59 High: 72

Thursday: Mostly sunny Low: 54 High: 71


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