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  • Tim McGill

When Will Real Fall Weather Settle In?

Above Average Outlook Well Into October


Four of the past five days have seen highs in the 80s. Some spots were near 90° Wednesday. Joliet and Morris had a high of 87°. Today and tomorrow will hit 80° or more too. September is now running just under 4° above average. The average temperature for the month is now at 70.3° making this the 5th warmest September on record so far.


Including today, 21 out of 30 days since the start of meteorological fall on September 1st have been above average. Models are keeping Chicago relatively mild well into the middle of the month. There may be a day or two that drops back below average but the overall outlook is for an unseasonably warm pattern to persist.


The GFS Model has our highs once again climbing into the lower 80s today. A light breeze off of Lake Michigan will hold temperatures along the lakefront in the middle 70s. Average highs for today's date are around 70°.


More 80s expected on Friday. The GFS Model has highs tomorrow topping out in the lower to middle 80s. More sunshine will bump up our highs by a degree or two. Less lake cooling as the winds shift a bit more southerly. Highs along the lakefront will be in the upper 70s to lower 80s.


Fast forwarding to a week from this Saturday with the temperature anomaly forecast for the country shows all of the Midwest and most of the nation well above average. Northern Illinois is forecast to be between 10° to nearly 20° above average. The average high for a week from Saturday is 66°.


We are in the middle of back to back to back 80s. Yesterday's high hit 82° at O'Hare. Today's high will be in the lower 80s and tomorrows should be in the middle 80s. Notice the wind shift early Friday. A more southerly breeze will limit the amount of lake cooling.


Dry today and most of Friday with only a slight chance of rain starting tomorrow night.



Another day with moderate levels of wildfire smoke aloft here. The HRRR Model vertically integrated smoke forecast wafts some smoke into our skies. This could mean a more "milky" look to the sun and help to give our sunset an orange-reddish hue.






Mild Into The Middle Of October

The National Blend Of Models has our highs staying at least a bit above average for the next ten days in a row. After back to back 80s today and tomorrow our highs slip back into the 70s for the weekend and bottom out near 70° Monday and Tuesday. 68° is the average high for early next week.



The longer range temperature outlooks continue to show a strong warm signal for the middle of October in Chicago. The 6-10 day outlook has us favored for above average temperatures overall from October 5th through October 9th. The longer range 8-14 day forecast also favors us for above average temperatures overall. It has our area within the highest probability contour on the map. It covers the period from October 7th through October 13th. Average highs for this period are in the middle to upper 60s.





The even longer term 30 day temperature anomaly forecast still has a strong warm signal for the Midwest and most of the country for the period covering the last couple of days of September through nearly the end of October. We are outlooked to be between 4° to 8° above average overall for the period from September 27th through October 28th. 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.








Wet At Times This Weekend


Rain has returned to the forecast for this weekend. Look for occasional showers and maybe a few rumbles of thunder. It will not be a washout with several dry hours both Saturday and Sunday.


Our lawns could use it. O'Hare is now down 1.86" of rain below average for September. The drought has deepened this week. I'll have a new analysis tomorrow.


I reviewed the latest US Drought Monitor analysis last 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 30 days of rainfall (ending on September 28th) reveals just how dry it has been. Most of our northern Illinois has seen between 10% to 50% of average rainfall during this period.


The GFS model's meteogram for O'Hare shows periods of scattered showers with the possibility of a few thunderstorms mainly later Saturday and during the day Sunday.



The GFS model's total precipitation forecast through Monday morning suggests we could squeeze out around a half inch to nearly an inch of rain in total


The longer range rainfall forecasts has a dry signal for us during the middle of next month. The latest 6-10 day forecast has the Chicago area favored for about below rainfall from September October 5th through October 9th. The longer range 8-14 day forecast also has us outlooked for below average precipitation from October 7th through October 13th.







Here is my 7 day forecast:


Today: Partly to mostly sunny, warm High: 82 (75 lakeside)


Friday: Mostly sunny, unseasonably warm Low: 60 High: 84 (79 lakeside)


Saturday: Partly to mostly cloudy, sct. showers possible early & late Low: 63 High: 77


Sunday: Mostly cloudy, scattered showers (isolated t-storm possible) Low: 64 High: 74


Monday: Scattered showers early, partly to mostly cloudy Low: 59 High: 70


Tuesday: Partly to mostly sunny Low: 58 High: 70


Wednesday: Partly to mostly sunny Low: 59 High: 72


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