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  • Tim McGill

Raw, Windy Wednesday But Weekend Looks Wonderful

Gusty Northerly Winds Bring Cool Change

Autumnal equinox arrives today at 2:20 pm and it will be accompanied by gusty northerly winds and temperatures at least 10° below average. In other words, it will really feel like fall.

Meteorological fall arrived on September 1st and the first three weeks of the season has felt more like summer. So far September is running just over 4° above average. Today and tomorrow will bring our temperatures more in line for the season. Wednesday and Thursday will collectively be the coolest couple of days since late May.

The HRRR Model has our highs today struggling to reach the 60s in some spots. Most of us should top out in the lower 60s but where heavier rain falls (especially in northern Indiana) the highs there may fail to get out of the 50s.

Tonight and tomorrow night could be the coolest nights we have seen in nearly four months. The GFS Model has our lows Thursday night falling into the 40s in our outlying areas. Lows will drop into the 50s in and around the city.

Our highs both today and tomorrow will be at least 10° below average. Winds today will gust to near 35 mph inland and up to 45 mph along the Illinois shoreline of Lake Michigan. Winds tomorrow subside a bit but stay strong with gusts near or just above 30 mph.

The greatest chance of rain is through midday today and then from around daybreak Thursday through the afternoon. Probabilities are highest the closer to the lakefront you are and then gradually diminish the further west you go from Lake Michigan.

The winds and waves they generate today have prompted an array of advisories and warnings along Lake Michigan's shoreline. A beach hazards statement has been issued for Lake County and portions of Cook County in Illinois as well as Lake and Porter Counties in Indiana. A lakeshore flood advisory is in effect for Cook County's shoreline until 10 AM Thursday for waves building to 12-16 feet. This will mean beach erosion and at least some minor lakeshore flooding. A lakeshore flood warning is in effect until 7 PM Thursday for Lake and Porter Counties in Indiana where waves could build to 14-18 feet.


Advisories & Warnings

The high lake levels from a "storm surge rise" of about one to two feet in southern Lake Michigan will exacerbate the flooding situation. That combined with what the National Weather Service categorizes as "large and battering waves" means very dangerous conditions along the lakefront through most of Thursday.

The northerly wind today through tomorrow will be traveling nearly the entire length of the lake. The waves may build to a peak late today and tonight.

Stay away from the lakefront through Thursday. There is a high swim risk along most of Lake Michigan's shoreline as well as portions of the shorelines for some of the other Great Lakes.

A Few Warmer Day Coming

Our cool couple of days will be followed by warmer temps this weekend and most of next week.

The National Blend Of Models has highs in the 60s today and tomorrow but Friday's highs soar back well into the 70s. We could even tag 80° here Monday.

We won't be the only warm spot early next week. The temperature anomaly forecast for Monday has most of the country well above average. The Midwest will be 5° to 10° above average while parts of the Rockies will be more than 20° above.

The longer range forecast has a fairly strong signal for a warmer than average end to September and start to October. The 6-10 day outlook has Chicago favored for above average temperatures overall from September 27th through October 1st. The longer range 8-14 day forecast also favors us for above average temperatures overall. It covers the period from September 29th through October 5th. Average highs for this period are in the upper 60s to lower 70s.

The even longer term 30 day forecast still has most of the country (and nearly all of the Midwest) favored for above average temperatures through just beyond 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.

Squeezing Out Some September Rain

O'Hare has seen some September rain the past two days but is still well below average for the month. So far September is down 1.56" of rain from where it should be at this point of the month. More rain today and tomorrow will be welcomed in the most parched portions of northern Illinois.

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.

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% over average rainfall.

The GFS model's meteogram for O'Hare has some showers and maybe even a few rumbles of thunder at times today especially near the lakefront. Lighter amounts of rain possible at times tomorrow and then a few showers are possible Friday night into Saturday morning. Most of the weekend though should be dry.

The GFS model total precipitation through this weekend favors areas closer to Lake Michigan for the most rainfall. Most of this rain would come today and tomorrow. Very little rain is expected well west of the city.

More discouraging drought news in the long range rainfall forecasts. The latest 6-10 day forecast has the Chicago area favored for below average rainfall from September 27th through October 1st. The longer range 8-14 day forecast has us outlooked for below average precipitation too from September 29th through October 5th. In both cases we are firmly in the bullseye of highest probabilities of being dry compared to average.

Here is my 7 day forecast:

Today: Showers mainly early, mostly cloudy, windy & cool High: 65

Thursday: Mostly cloudy, sct. showers (especially near the lake), windy Low: 50 High: 64

Friday: Mostly sunny Low: 51 High: 77

Saturday: Partly to mostly sunny Low: 53 High: 72

Sunday: Mostly sunny Low: 53 High: 76 (cooler lakeside)

Monday: Mostly sunny Low: 57 High: 80 (cooler lakeside)

Tuesday: Mostly sunny Low: 59 High: 76 (cooler lakeside)


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