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  • Tim McGill

Here Comes Fall (Finally!)

Above Average Streak Near Its End

Today will be the 19th straight day with above average temperatures at O'Hare. We started our Thursday off in the lower 70s just after midnight. We should settle into the middle 60s this afternoon. The month is now running just over 11° above average. Cooler air is right around the corner with more typical temperatures for the middle of October arriving for Friday and this weekend.

Average highs for today's date are around 64°. The GFS Model has our temperatures this afternoon in the middle to upper 60s.

We may make it into the lower 60s early Friday but then fall into the 50s later in the day. The GFS Model brings in some more seasonably cool air by later in the afternoon tomorrow with temperatures forecast in the lower to middle 50s.

The GFS Model continues our cool slide through Friday night. It has our lows falling into the lower to middle 40s for most us by daybreak Saturday.

Saturday could be the coolest day we have seen since late August. The GFS Model has highs only the in upper 50s to near 60°.

Our brush with real fall weather won't last too long. The GFS Model temperature anomaly forecast for Monday afternoon has our temperatures bouncing back to between 8° to 12° above average. The average high for Monday is 62°. That would mean highs in the lower 70s.

The transition to real fall has already begun. After what will be our official high near 70° that occurred early this morning, our temperatures settle into the lower to middle 60s today. We fall into the lower to middle 50s tonight. Lower to middle 60s are expected for highs tomorrow before temperatures tumble into the 40s overnight Friday.

Notice the wind shift later tonight. This is when a push of more seasonably cool air finally arrives.

On and off showers will come today and tomorrow with areas south and southeast of the city favored for the most rainfall.

Quick Shot Of Very Cool Air

Friday and Saturday will be the two coolest days we have seen in nearly four months. The National Blend Of Models has our highs slipping into the lower 60s tomorrow and falling to just 59° on Saturday but we warm back up into the 70s by Monday. Another shot of relatively cool air could be coming by the end of next week.

The longer range temperature outlooks continue to show a fairly strong signal for an overall mild pattern to nearly the end of this month. The 6-10 day outlook has us favored for above average temperatures overall from October 19th through October 23rd. The longer range 8-14 day forecast also favors us for above average temperatures overall too. It covers the period from October 21st through October 27th. Average highs for this period are in the upper 50s to lower 60s.

The even longer range temperature anomaly forecast keeps the overall mild pattern going into next month. The longer term 35 day temperature anomaly forecast still has all of the Midwest and most of the country outlooked for above average temperatures overall all the way through the middle of November. We are outlooked to be between 4° to 5° above average overall for the period from October 12th through November 16th. 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.

Some Showers Then Drying Out

O'Hare now has a surplus of .51" of rain above average for the month of October after .35" of rain fell there yesterday. O'Hare is still down 1.45" of rain below average since the start of September.

Recent rain may have helped to put a dent in the ongoing drought across much of northern Illinois. 12 of the first 14 days of October have seen at least a trace of rain. I'll have the updated analysis from the US Drought Monitor tomorrow.

The most recent US Drought Monitor analysis was released last Thursday. Here is a recap:

The areas in a moderate drought (level 1 our of 4) and severe drought (level 2 out of 4) increased slightly from the previous week while the area in an extreme drought (level 3 out of 4) remained unchanged.

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 mostly good. The areas in a moderate, severe and extreme drought all decreased at least slightly. The area considered abnormally dry increased slightly.

The active pattern this month has brought some much needed rain to the most parched portions of northern Illinois. Most of our area has seen between 150% to 300% of average rainfall during the 7-day period ending yesterday.

The GFS model's meteogram for O'Hare keeps the pattern relatively active today and tomorrow with occasional showers. We dry back out again on Saturday and stay dry through the middle of next week.

The GFS model's total precipitation forecast through the weekend suggests more significant rain is on the way with all of it falling today through tomorrow night. The range of rainfall in the forecast is from a bit more than a quarter of inch of rain to just over an inch and a quarter. Our northern and northwest suburbs that need the rain the most are favored to get the lower end of that range with higher amounts favored south and southeast of the city.

The longer range precipitation outlooks suggest a less active pattern overall could be coming for the end of this month. The latest 6-10 day forecast has the Chicago area favored for below normal rainfall from October 19th through October 23rd. The longer range 8-14 day forecast keeps the relatively dry pattern coming too. It has us outlooked for below average precipitation from October 21st through October 27th.

Here is my 7 day forecast:

Today: Mostly cloudy, occasional showers High: 68

Friday: Cloudy, on and off showers Low: 51 High: 64 (falling into the 50s late)

Saturday: Mostly sunny, cooler Low: 45 High: 60

Sunday: Mostly sunny Low: 44 High: 67

Monday: Mostly sunny Low: 48 High: 71

Tuesday: Mostly sunny Low: 52 High: 69

Wednesday: Mostly sunny Low: 53 High: 68


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