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  • Tim McGill

Cooler Air Arrives Right On Cue

More Sun Today With Brisk Breeze


Meteorological fall starts today and it will actually feel like fall for the next several days. There could be four straight days with highs only in the 70s. The last time we did that was back in early July. Lows for many of us will fall into the 50s Thursday morning.


Average highs for September 1st are around 80°. The GFS Model has our highs only in the middle to upper 70s today. It will be even cooler along the lakefront with a brisk breeze off of Lake Michigan.


It will perhaps feel most like fall this week on Thursday morning. That's when temperatures could fall into the lower to middle 50s outside of the Chicago metropolitan area.



Highs both today and tomorrow will be about 4° to 5° below average. Dew points remain at very pleasant levels in the middle to upper 50s.


The main weather issue is the stronger northeast winds that will mean a moderate to high swim risk along the southern shores of Lake Michigan. More on that below.


There is little to no chance of rain the next couple of days.



What a difference this week is compared to last! A week ago we were sweltering with a dangerous combination of high hat and humidity. Our dew points will be between "delightful" and "pleasant" through the end of the week. Relative humidity is one way to express the amount of water vapor in the air but dew points are the preferred measurement of moisture in the air for meteorologists like me.



The moderate to high swim risk continues through Thursday morning. A beach hazards statement will be in effect along the southern shores of Lake Michigan until 7 am tomorrow. Gusty northeast winds will whip up large waves and generate dangerous rip currents.



The southern shores of Lake Michigan, Lake Erie and Lake Ontario all have a high swim risk today.



The biggest waves here could build to 6 feet. The National Weather Service warns that waves that size are typically the most dangerous since they can catch swimmers off guard.


The National Blend Of Models has our highs stuck in the 70s for the next five days in a row. The last time we had that many successive days with highs in the 70s or cooler was at the end of May and beginning of June. We should warm up to right around average for Sunday and Labor Day.



For the second day in a row there are back to back cooler than average long range temperature probability forecasts. The 6-10 day forecast has outlooked Chicago for below average temperatures overall from September 6th through September 10th. The longer range 8-14 day forecast keeps the cooler pattern coming and also favors us for below average temperatures overall from September 8th through September 14th. Average highs for this period are in the upper 70s.



The Climate Forecast System or coupled forecast system (both names abbreviated CFS) is a medium to long range numerical weather prediction and a climate model run by the National Centers for Environmental Prediction (NCEP). It keeps us cooler than average overall through the entire month of September.







Best Chance Of Rain Friday Night


A cold front should cross through Friday night and it may squeeze out a few showers. We need more than just a few showers though to put a dent in the drought that continues in our northern and northwest suburbs.


In the past couple of weeks there has been little rainfall where it is most needed. Portions of McHenry county (in blue and purple) picked up some heavy rainfall from thunderstorms last week but most of that county is still very dry. Parts of Lake County, McHenry County and DeKalb County have only seen 10% to 25% of average rainfall for the two week period ending on August 31st.


The latest analysis from the US Drought Monitor did not show any significant improvement for our northern suburbs mired in a moderate to severe drought.


Here is a recap from Friday's post:


The latest US Drought Monitor analysis is discouraging. The portion of Illinois in a severe drought (level 2 out of 4 levels) dropped remains unchanged from last week at .79%. The area in a moderate drought (level 1 out of 4 levels) has increased to 7.93% compared to 7.33% last week. There is also a growing area considered "abnormally dry". That has increased to 21.63% from 15.42 % last week.



The Midwest region's drought news is mixed. The area in a moderate and extreme drought has expanded a bit while the area in a severe drought diminished a bit. The area in an exceptional drought remains unchanged from a week ago.


The latest GFS model shows the possibility of a few showers late Saturday night into early Sunday but a better chance of rain late Monday into Tuesday. The model has been very fluid with the forecast for rain this weekend so stay tuned. I think most of Labor Day weekend will actually be dry with the best chance of rain overnight Friday.



The total precipitation forecast through Sunday evening from the GFS model is now calling for less rain than previous model runs. The range of rainfall expected has now fallen barely any rain at all to about a third of an inch.



The longer range rainfall forecasts have us near or just below normal for precipitation through the middle of the month. The latest 6-10 day forecast has the Chicago area favored for around average precipitation from September 6th through September 10th with areas west of the city favored to be below average. The longer range 8-14 day forecast favors us for about average precipitation from September 8th through September 14th.




Here is my 7 day forecast:


Today: Becoming sunny, breezy & cooler High: 78 (74 lakeside)


Thursday: AM spotty sprinkles?, partly to mostly sunny Low: 59 High: 79 (cooler lakeside)


Friday: Partly to mostly sunny Low: 60 High: 78


Saturday: Partly to mostly sunny, shower possible late Low: 63 High: 79


Sunday: Partly to mostly sunny Low: 60 High: 81


Monday: Partly to mostly sunny, shower possible late Low: 61 High: 82


Tuesday: Partly to mostly sunny, spotty shower possible Low: 62 High: 80


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