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  • Tim McGill

Squeezing Out More Summer

Summer Weather Slipping Into Fall

Chicago's falls are getting warmer as summer-like weather spills into autumn more and more. The average fall temperature has risen just over 1° here in the past 50 years. That is big from a climatological standpoint.

Climate Central analyzed 246 cities across the country to see the change in the average fall temperature since 1970. Close to 95% of the cities studied have warmed during this period. More than half have warmed by more than 2°.

Nearly 70% of the cities studied recorded at least seven additional days above their normal fall average since 1970. Nine cities saw an incredible increase of an extra month and Reno, Nevada topped the list with an additional 43 days. We have seen an increase of nearly 7 more warm fall days in Chicago.

Our record warm summer stole the headlines last week. Here is a recap from my post about the torrid months of June through August, 2021:

2021's summer was a sizzler for our country. Meteorological summer (June-August) this year had an average temperature of 74.0° for the lower 48 states. That is 2.6° above average and essentially ties with the Dust Bowl year of 1936 as the warmest summer on record.

We know our falls are warming but so what? Here is how Climate Central summarized the issues with a warming autumn season:

We will squeeze out more summer-like weather from meteorological fall this weekend.

Today and tomorrow will feel just like July. HRRR Model has our highs today topping out near 90°. The average high for today's date is 78°. Combining the temperatures with our expected rise in humidity means it will feel like at least the lower 90s.

Sunday should be similar to today as they top out in the upper 80s to near 90°. If my forecast verifies and if it were still summer, this weekend would be tie as the 6th warmest of the season.

This unseasonable warmth sticks around through Tuesday. The temperature anomaly forecast has most of the country above average that day with the Midwest between 5° to 15° above. Highs on Tuesday here are expected to be in the upper 80s.

Gusty southwest winds will deliver the hot and humid air that will make for some steamy September weather this weekend. Notice the wind shift Sunday afternoon to the northeast. That front could drop temperatures late that day especially along the lakefront.

Their is a slight chance for a shower or thunderstorm tonight but a better chance Sunday night.

Thicker wildfire some aloft will waft into our skies this afternoon. The HRRR Model vertically integrated smoke forecast has some of the highest concentrations over the Midwest and south through the southern plains. This smoke may end up keeping us a degree or two cooler than what we ordinarily be without it.

The National Blend Of Models has our highs hitting 80° or warmer for the next straight four days. That would stretch the streak to five days in total if we include yesterday's high of 80° at O'Hare. We slide briefly into the 70s on Wednesday and then climb back to 80° or above for possibly another streak of five straight days.

The strong warm signal in the longer range temperature probability forecasts. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from September 16th through September 20th. The longer range 8-14 day forecast also favors us for above average temperatures overall from September 18th through September 24th. Average highs for this period are in the middle to upper 70s.

The Climate Forecast System or coupled forecast system (both names abbreviated CFS) is a medium to long range numerical weather prediction and a climate model run by the National Centers for Environmental Prediction (NCEP). The signal for the next 30 days isn't strong but it is indicating it will be warmer than average overall from now through the beginning of October.

Another Dry Pattern Developing

There is only one day in the next ten with a significant chance of rain here. O'Hare has seen just under a third of an inch of rain in the past 16 days. So far September is down just over an inch of rain below average.

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

The latest US Drought Monitor analysis is in and it is good news overall for Illinois.

The past two weeks of rainfall (ending on September 10th) have been particularly dry. Most of the Chicago area has seen between 10% to 75% of average rainfall during the period. It was especially dry in southern Cook County, southwestern McHenry County and northern Indiana.

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 latest GFS model continues to keep us dry mainly dry for the next ten to eleven days. It shows just one day next week with a significant chance of rain so far.

The forecast for rainfall through next Wednesday afternoon from the GFS model still shows reason for some hope for help with the drought in our northern suburbs. The model is squeezing out around an inch to an inch and a half of rain north of the city. The amounts taper off to around a quarter of an inch south of Chicago.

More rainfall than average could be falling here during the middle and latter part of September. The latest 6-10 day forecast has the Chicago area favored for above average rainfall from September 16th through September 20th. The longer range 8-14 day forecast also favors us for above average precipitation from September 18th through September 24th.

Here is my 7 day forecast:

Today: Mostly sunny, breezy, warmer & more humid High: 89

Sunday: Partly to mostly sunny, breezy Low: 72 High: 88 (cooler lakeside)

Monday: AM sct. shower/t-storm?, partly to mostly cloudy Low: 67 High: 83 (cooler lakeside)

Tuesday: Partly to mostly sunny, sct. showers/t-storms possible late Low: 69 High: 87

Wednesday: Partly to mostly cloudy, sct. showers/t-storms possible Low: 65 High: 78

Thursday: Partly to mostly sunny Low: 64 High: 83

Friday: Partly to mostly sunny Low: 65 High: 84


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