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  • Tim McGill

More Stellar September Weather

80s Back In The Forecast

O'Hare's high of 79° Friday was 6° above average. So far 16 out of 24 days in September have been above average. More "summer" in September is coming with some 80s in the 7-day forecast.

Meteorological fall started on September 1st and is now running 3.3° above average. We will be a bit below average today but then add to the surplus with an above average day on Sunday. We could be looking at a stretch of at least nine straight days above average staring tomorrow.

A cold front came through last night so a westerly breeze will cool us off a bit today. O'Hare dipped to 50° this morning for the coolest low since June 1st. Aurora fell to 43°.

The HRRR Model has our highs today topping out near 70°.

Some sunshine and gusty southwest winds will mean a warmer end to the weekend. The GFS Model has highs on Sunday reaching to near 80°.


Winds gusted to near 40 mph on Friday. Our winds will stay fairly strong through the weekend with gusts both today and tomorrow near 30 mph.

Those gusty winds and very dry conditions (dew points in the lower 30s) will combine to create elevated wildfire conditions through the weekend.

Here is a special statement regarding that from the National Weather Service:

Low relative humidities combined with west winds gusting to 25 mph today and southwest winds gusting to 30 mph on Sunday will result in an elevated wildfire danger this weekend. Exercise increased caution if burning or consider postponing outdoor burning this weekend. Be aware of any burning restrictions in your area.

80s Keep On Coming

We are not done with the 80s yet this year. The National Blend Of Models has highs of 80° or more Sunday and Monday. Highs will flirt with 80° a few days next week too.

Monday will be the warmest day of next week. The temperature anomaly forecast has temperatures Monday around 15° to 25° above average for portions of the Midwest and plains. It should feel just like July for a good chuck of the country.

There is a very strong signal for a warmer than average end to September and beginning of October. The 6-10 day outlook has Chicago favored for above average temperatures overall from September 30th through October 4th. The longer range 8-14 day forecast also favors us for above average temperatures overall. For both forecasts we are in the 60-70% probability range. It covers the period from October 2nd through October 8th. Average highs for this period are in the upper 60s to lower 70s.

The even longer term 30 day temperature anomaly forecast also favors us (and most of the country) for a relatively warm end to September and start to October. We are outlooked to be between 3° to 6° above average overall for the period from September 22nd through October 22nd. 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.

Discouraging Drought News & Forecast

O'Hare is now down 1.36" below average for September rainfall. There is very little rain in the forecast over the next several days to erase that deficit. The forecast is discouraging for getting help with the ongoing drought here in northern Illinois.

I reviewed the latest US Drought Monitor analysis on Friday. Here is a recap:

The latest US Drought Monitor analysis has bad news for Illinois. The moderate drought (level 1 out of 4), severe drought (level 2 out of 4) and extreme drought (level 3 out of 4) areas have all increased since last week. Northern Illinois is the only portion of the state in a drought with the worst conditions in Lake County.

Here is a summary of the impacts the ongoing drought is having on northern Illinois from the National Weather Service:

Volunteer observers across far northern Illinois indicate much lower then typical stream flows on area creeks and rivers, particularly along Beaver Creek and the Kishwaukee River.

Reports also indicate that lawns have gone dormant and there has been some stress to the trees. Few impacts to agriculture have been received recently, though the dry conditions and stressed crops have resulted in an early start to the harvest season across northern Illinois. Data available from the Illinois State Water Survey, USGS, and NCEP indicate that soil moisture, groundwater, and surface water levels remain below normal.

An analysis of the past two weeks of rainfall (ending on September 24th) reveals just how dry the past couple of weeks have been. Most of the Chicago area has seen just 10% to 50% of average rainfall.

The GFS model's meteogram for O'Hare doesn't have any rain in the forecast until late next Friday and into Saturday.

Still not much hope for help with the drought from the longer range precipitation outlooks. The latest 6-10 day forecast has the Chicago area favored for below average rainfall from September 30th through October 4th. The longer range 8-14 day forecast has us outlooked for below average precipitation too from October 2nd through October 8th. In both cases the Chicago area is in the highest probability contour for below average rainfall.

Here is my 7 day forecast:

Today: Mostly sunny, breezy & cooler High: 70

Sunday: Sunny start then becoming partly cloudy Low: 53 High: 79 (cooler lakeside)

Monday: Partly to mostly sunny Low: 62 High: 84

Tuesday: Mostly sunny Low: 61 High: 77 (cooler lakeside)

Wednesday: Mostly sunny Low: 57 High: 78 (cooler lakeside)

Thursday: Mostly sunny Low: 58 High: 77 (cooler lakeside)

Friday: Mostly sunny Low: 57 High: 75 (cooler lakeside)


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