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  • Tim McGill

October Rollercoaster Temperature Ride

Highs Headed Upwards


Fall is known for its sometimes wild swings in temperatures and we are in the middle of one right now. Sunday's low of 42° at O'Hare was the coolest since late May but we bounce back today with a high in the lower 70s. So in a span of 30 hours we go from the coldest morning in over four months to an afternoon with temperatures around 10° above average and more typical for late September.


It will be a warm start to the week with another streak of above average days through at least Wednesday. Saturday was the only day so far this month that was below average. That ended a streak of 20 straight warmer than average days that began back in September. So far October is running just over 9° above average.


Average highs for today's date are around 62°. The GFS Model has our highs today topping out near 70° with plenty of sunshine.


Temperatures on Tuesday should be a degree or two warmer. The GFS Model has our highs soaring into the lower 70s tomorrow.



Wednesday should be just as warm. The GFS Model temperature anomaly forecast pushes our temperatures up between 12° to 16° above average. That would mean a high in the lower to middle 70s.



Sunny skies and southwest breezes means highs near 70° today and tomorrow. The winds will be light today but just a bit breezy tomorrow.


Little to no chance of rain through Tuesday.









Big Drop By The Weekend

Three straight days with highs of 70° or more before a dramatic drop by the weekend. The National Blend Of Models has our highs in the lower 70s through Wednesday. It has our highs sliding into the 60s by Thursday and then falling into the 50s for Friday through the following Monday. Lows Saturday and Sunday morning in outlying areas could be cold enough for at least some patchy frost.



Our longer range temperature outlooks has a fairly strong signal for a mild end to the month. The 6-10 day outlook has us favored for above average temperatures overall from October 23rd through October 27th. The longer range 8-14 day forecast favors us for above average temperatures from October 25th through October 31st. Average highs for this period are in the upper 50s to near 60°.





Looking even longer range, the outlook is for milder than average temperatures well into November. The longer term 35 day temperature anomaly forecast still has most of the middle part of the country warmer than average overall for the next five weeks. We are outlooked to be between 1° to 4° above average overall for the period from October 16th through November 21st. 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.









Back To A Dry Pattern


14 of the first 18 days of October received at least a trace of rainfall. The total rainfall so far this month at O'Hare is now just under two inches or .24" above average. Models are suggesting a return to a more dry pattern for the next several days. More on that below.


Even with the surplus of October rain we are still down 1.72" of rain below average since the start of September.


The most recent US Drought Monitor analysis was released last Thursday. It reflects the benefit of our recent rainfall. Here is a recap of that report:


The ongoing drought in northern Illinois was dealt a blow over the past week or so. Some serious rain put a significant dent in the drought. I have more details on the status of the drought further down in my post. The drought started back in the middle of April and arguably had two peaks. One was in the middle of June when nearly 3% of the state was in at least an extreme drought (level 3 out of 4). The second peak occurred just last week when the worst level of drought actually decreased but nearly 16% of the state was in at least a moderate drought, the highest point so far this year.




The areas in at least a moderate drought (level 1 our of 4) dropped nearly 28% while the area in an at least a severe drought (level 2 out of 4) decreased a whopping 86% from last week's analysis. We no longer have any part of the state in an extreme or exceptional drought (levels 3 and 4 out of 4).


The side by side comparison of this week's Illinois drought map next to last week's helps to visualize the improvement we have seen in just seven days time.



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.


The drought news for the entire Midwest was good too. The areas in every level of drought decreased since the last update.



The wet first half of October has helped put that dent in the drought reflected in the latest analysis. Most of northern Illinois has received between 150% to 300% of average rainfall so far this month.


The GFS model's meteogram for O'Hare keeps us dry through most of Wednesday then brings in some scattered showers and maybe a rumble of thunder late that day into early Thursday morning. A few spotty light showers possible late Thursday too but rainfall amounts are projected to be paltry this week.



The GFS model's total precipitation forecast through the weekend squeezes out only a few one hundredths to a tenth of an inch of rain in total.


The longer range precipitation outlooks is more promising for some precipitation. The latest 6-10 day forecast has the Chicago area favored for above average rainfall from October 23rd through October 27th. The longer range 8-14 day forecast has us outlooked for above average precipitation from October 25th through October 31st too.






Here is my 7 day forecast:


Today: Sunny, mild & pleasant High: 71


Tuesday: Mostly sunny Low: 53 High: 72


Wednesday: Partly to mostly sunny, shower possible late Low: 54 High: 73


Thursday: Partly to mostly cloudy, sct. showers possible Low: 53 High: 60


Friday: Partly to mostly sunny Low: 42 High: 56


Saturday: Partly to mostly sunny Low: 38 High: 54


Sunday: Partly to mostly cloudy, shower possible late Low: 40 High: 57




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