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  • Tim McGill

Fall Is Back On Hold

80s Back In The Forecast



After a cooler couple of days with highs in the 60s we warm back up today. Most of the next seven days should be well above average with even a few 80° or warmer highs sprinkled in. September is now running a bit over 3° above average.


If it seems like we have been stretching our summers out more and more over the years, you are right. Studies indicate that summer is lasting longer lately while all the other seasons are shrinking.


Here is a summery from the Capital Weather Gang blog about how the seasons are changing:


In the Northern Hemisphere mid-latitudes, the length of summer increased from 78 to 95 days — or about 4.2 days per decade from 1952-2011. Winter contracted from 76 to 73 days, or 2.1 days per decade on average. Spring decreased from 124 to 115 days, and autumn shrank from 87 to 82 days; each shrank about one day per decade. All seasons were warmer.



Meteorological fall started on September 1st and the autumnal equinox began Wednesday but you would never know that by looking at the forecast.


Sunshine and a gusty southwest winds will see temperatures surge at least well into the 70s today. The HRRR Model has our highs today warming about 7° above average topping out near 80°.


A weak cold front will push through tonight and knock our highs down a bit for Saturday. The GFS Model suggests we will cool to near 70°. That's just a smidge below the average high of 73° for this time of year. Saturday will be the coolest day we see of the next ten.



Watch for wind gusts over 30 mph today and while not as strong on Saturday, the winds will still be respectable. Winds tomorrow will gust to near 25 mph.


The cold front crossing through tonight gives us our best chance of rain between 7 pm and midnight. This may be the only significant chance of rain we have for the rest of September. More on the dry outlook below.


Stronger winds and low levels of moisture are cause for fire weather concerns today and tomorrow. The gusty winds Saturday combined with very low levels of moisture (dew points only in the 30s) will elevate the fire risk to near critical conditions.






Summery For September

More 80s are on the way. The National Blend Of Models has highs in the 80s for four of the next ten days. Highs will be near 80° on five of those ten days too.



We start next week off particularly warm. The temperature anomaly forecast has temperatures Tuesday around 15° to 25° above average for most of the Midwest and plains. Those regions will see highs that we normally expected in the middle of July.



The signal remains strong for a relatively warm end to September and start to October in the long range outlooks. The 6-10 day outlook has Chicago favored for above average temperatures overall from September 29th through October 3rd. The longer range 8-14 day forecast also favors us for above average temperatures overall. It covers the period from October 1st through October 7th. Average highs for this period are in the upper 60s to lower 70s.





The even longer term 30 day forecast still suggests not only the Midwest but most of the country staying above average overall well into October. 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.


GEFS Temperature Anomaly Forecast From September 21st Through October 21st







Drought Deepens


O'Hare is now down 1.37" 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.


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.




The news was better for the Midwest as a whole. The areas in a moderate, severe and extreme drought all dropped slightly. There is no longer any part of the region in an exceptional (level 4 out 4) drought. The most parched portion of the Midwest is northern Minnesota and northern Illinois.



An analysis of the past two weeks of rainfall (ending on September 21st) shows just how dry it has been during the middle of this month. Most of the northern Illinois seen just 25% to 75% of average rainfall.


The GFS model's meteogram for O'Hare has some showers tonight into early Saturday morning with an embedded thunderstorm possible. Beyond that, there is no rain in the forecast through next weekend.



The GFS model total precipitation all the way through next Friday only produces paltry amounts of precipitation. Most of the area would see lest than a couple tenths of an inch of rain if this forecast verifies.



The long range precipitation outlooks both signal a dry end to September and start to October. The latest 6-10 day forecast has the Chicago area favored for below average rainfall from September 29th through October 3rd. The longer range 8-14 day forecast has us outlooked for below average precipitation too from October 1st through October 7th. In both cases the Chicago area is in the highest probability contour for below average rainfall.






Here is my 7 day forecast:


Today: Sunny start then becoming partly cloudy, breezy High: 78


Saturday: Mostly sunny, breezy Low: 53 High: 71


Sunday: Sunny start then becoming partly cloudy Low: 52 High: 78 (cooler lakeside)


Monday: Mostly sunny Low: 60 High: 81 (cooler lakeside)


Tuesday: Mostly sunny Low: 61 High: 80 (cooler lakeside)


Wednesday: Mostly sunny Low: 63 High: 82 (cooler lakeside)


Thursday: Mostly sunny Low: 59 High: 79 (cooler lakeside)


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