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  • Tim McGill

Warm September Headed For The Record Books

Back To Back To Back 80s?


Tuesday's high was 15° cooler than Monday's but still above average. Monday's high hit 87° and yesterday saw a high of 73° at O'Hare. 20 out of 29 days since the start of meteorological fall on September 1st have been above average. September is running nearly 4° above average and now ranks as the 5th warmest on record for Chicago.


We have more 80s coming before this week ends. The GFS Model has our highs climbing into the lower 80s today. The model keeps it cooler lakeside with a breeze off of Lake Michigan. Highs along the lakefront will reach into the lower 70s.


We'll make it back to back 80s on Thursday. The GFS Model has Thursday similar to today with lower 80s for most of us but middle 70s along the lakefront.


Can we make it three days in a row with 80s? It will come close to 80° on Friday. The temperature anomaly forecast has highs in northern Illinois around 5° to 10° above the average of 70° for late September.


So back to back 80s seem certain for today and tomorrow. The light breezes off the lake will keep it cooler lakeside. Virtually no chance of rain through Thursday.


Look for a possible reddish hue to the sunset tonight because of moderate levels of wildfire smoke once again wafting into ours skies. The HRRR Model vertically integrated smoke forecast brings some smoke aloft here this afternoon. The thickest concentrations will be over the norther Rockies and the southwest.





Warm End To September

The National Blend Of Models keeps us warm through the end of September and into the start of October with 80° highs today through Friday. Average highs are around 70° this time of the year. A pattern change could bring in more cloud cover along with occasional showers for the start of next week. Highs slide back into the 60s Monday through Wednesday.


All of the Midwest and most of the country is outlooked for an overall warm start to October. The 6-10 day outlook has Chicago favored for above average temperatures overall from October 4th through October 8th. The longer range 8-14 day forecast also favors us for above average temperatures overall. It covers the period from October 6th through October 12th. Average highs for this period are in the upper 60s to near 70°.




The even longer term 30 day temperature anomaly forecast has a strong warm signal for the Midwest and most of the country for the period covering the last week of September through just over the first three weeks of October. We are outlooked to be between 4° to 8° above average overall for the period from September 24th through October 24th. 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.









Start Of October May See Some Rain


The first weekend of October my be wet at times. Not a washout but occasional showers and even a few rumbles of thunder are possible especially late Saturday into Sunday. We need the rain. O'Hare is now down 1.77" below average for September rainfall. In the meantime, the drought has deepened the past few days. I'll have the latest analysis at the end of this week.


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 two weeks of rainfall (ending on September 28th) reveals just how dry the past couple of weeks have been. Most of our northwest suburbs along with a portion of Chicago and just south of the city has only seen just 25% to 50% of average rainfall.


The GFS model's meteogram for O'Hare shows a more active pattern could be coming in terms of rainfall starting late Saturday into Sunday. Another round of at least scattered showers are forecast for late Monday through Tuesday and lingering into early Wednesday.



The GFS model's total precipitation forecast through this weekend is calling for most of us to see between a half inch to three quarters of an inch of rain in total. The model has been overdoing it lately with it's precipitation amounts so take this with a grain of salt.



The longer range rainfall forecasts start us off near normal and trend towards a dry pattern. The latest 6-10 day forecast has the Chicago area favored for about average rainfall from September October 4th through October 8th. The longer range 8-14 day forecast has us outlooked for below average precipitation from October 6th through October 12th.





Here is my 7 day forecast:


Today: Sunny skies early then partly cloudy, warm High: 82 (72 lakeside)


Thursday: Partly to mostly sunny Low: 60 High: 82 (75 lakeside)


Friday: Partly to mostly sunny, spotty shower possible late Low: 61 High: 79


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


Sunday: Mostly cloudy, scattered showers Low: 63 High: 74


Monday: Mostly cloudy, scattered showers Low: 59 High: 69


Tuesday: Mostly cloudy, scattered showers Low: 56 High: 68


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