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  • Tim McGill

Warm Weekend But Fall To Arrive Soon

So Far September More Like July

It was a fantastic Friday (if you like your falls on the warm side). It will be a sensational Saturday and Sunday will be steamy. I love alliterations in my forecasts :)

Friday's high of 88° at O'Hare was 13° above average. It was also the 8th day out of the last 9 with a high of 80° or warmer. It will be cooler today thanks to a cold front that came through last night. While it will be cooler, it should still be at least a bit above the average high of 75°.

Our meteorological fall so far is running about 3° above average.

The GFS Model has our highs reaching into the upper 70s to near 80° today. A wind off the lake will keep it cooler at the beaches and along the lakefront with lower 70s there.

The GFS Model brings the heat back for Sunday. Highs tomorrow will again be about 10° to 15° above average. We should soar to near 90° with the help of plenty of September sunshine. Once again it will be cooler lakeside with a light lake breeze holding highs there in the lower 80s.

I'm fast forwarding to Wednesday's highs forecast for those of you who favor more typical fall temperatures. Highs Wednesday could slide into the 60s for the coolest day we have seen in nearly four months.

The coolest period this week should be Thursday morning. It's another case of weather whiplash. We'll go from 10° to 15° above average on Sunday to 10° to 15° below average by early Thursday. Lows could dip down into the middle to upper 40s.

The one thing Saturday and Sunday will have in common is plenty of sunshine. After today's highs in the middle to upper 70s we warm up into the middle to upper 80s for a steamy Sunday. Dew points today are pleasant but the climb from the 50s to the 60s by early Sunday which will have a more muggy feel.

Winds shift from the northeast today to the southeast tomorrow. It's this shift that brings in the warmer and more humid air for the end of the weekend.

There is little to no chance of rain both Saturday and Sunday.

Gusty northeast winds today will whip up big waves and generate dangerous rip currents. A beach hazards statement is in effect until 7 pm this evening for Lake & Cook counties in Illinois and Lake & Porter counties in Indiana.

Waves will be between 3 to 6 feet today before subsiding overnight as winds diminish.

The National Blend Of Models shows the dramatic drop in temperatures coming by the middle of next week. We go from a peak of near 90° on Sunday to just 67° for the high on Wednesday. Highs then settle into the 70s for Friday through the following weekend.

More good news for fall weather fans. For the first time in a looooong time both of the long rang temperature outlooks are calling for us to be cooler than average overall as September ends and October starts. The 6-10 day forecast has outlooked Chicago for below normal temperatures overall from September 23rd through September 27th. The longer range 8-14 day forecast also favors us for below average temperatures overall. It covers the period from September 25th through October 1st. Average highs for this period are in the lower to middle 70s.

The even longer term 30 day forecast contradicts these cooler forecasts. It favors us for warmer than average temperatures overall from now through the middle of next month. 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. The GEFS has the Midwest and most of the country outlooked for above average temperatures overall all the way into the middle of October.

Some Rare September Showers Yesterday

Some welcome showers and thunderstorms accompanied the passage of a cold front yesterday evening but much more rain is needed to put a dent in the ongoing drought for our northern suburbs.

Here is a recap of my post from Friday with the latest US Drought Monitor report:

The latest US Drought Monitor analysis is in and it is mostly good news for the Midwest but there is some bad news locally.

The US Drought Monitor analysis shows a slight increase in the area under a moderate drought ( 1 one out of 4 levels). The area grew to 10.11% from 9.81% last week. The area in a severe drought (level 2 out of 4 levels) did not change and remains at .79%. The area considered "abnormally dry" (the precursor to a moderate drought) nearly doubled and now stands at 32.94%.

For the Midwest the news was better. The areas in a moderate, severe and extreme drought all dropped slightly. The area in an exceptional drought (level 4 out of 4 levels) is unchanged at .99%. The most parched portion of the Midwest is northern Minnesota.

The past two weeks of rainfall (ending on September 16th) shows why the drought has deepened. Most of the Chicago area has seen between just 10% to 50% of average rainfall during the period. Some suburbs west and south of the city and a portion of the city itself has only seen just 10% to 25% of average rainfall. South of the city and northern Indiana has seen just 5% to 10% of average.

O'Hare had only received .01" of rain for the month of September up until yesterday. The latest GFS model's meteogram gives us hope for at least some rain here Monday and Tuesday.

The GFS model total precipitation forecast through Tuesday squeezes out heavier amounts of rain north and west of Chicago with lighter amounts from city southward. The model suggests as much as just over an inch of rain could fall. The good news is the areas favored for more rainfall are the areas that need it the most.

Despite that bit of good news, the longer range rainfall outlooks are still not encouraging. The latest 6-10 day forecast has the Chicago area favored for below average rainfall from September 23rd through September 27th. The longer range 8-14 day forecast has us outlooked for below average precipitation too (with higher probabilities) from September 25th through October 1st.

Here is my 7 day forecast:

Today: Partly cloudy early then becoming sunny, cooler High: 79 (74 lakeside)

Sunday: Mostly sunny, warmer & more humid Low: 65 High: 88 (83 lakeside)

Monday: Partly to mostly cloudy, scattered shower/t-storm possible Low: 68 High: 81

Tuesday: Partly to mostly cloudy, scattered showers & thunderstorms Low: 66 High: 77

Wednesday: Partly to mostly sunny, scattered showers Low: 50 High: 68

Thursday: Mostly sunny Low: 51 High: 71

Friday: Mostly sunny Low: 52 High: 75


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