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  • Tim McGill

Saying So Long To Summer

Meteorological Fall Starts Wednesday

Meteorological summer ends today. Summer will go out with a near normal day in terms of temperature. Meteorological fall begins Wednesday and right on cue it will feel like fall with cooler than average temperatures.

Today's highs should be right around the average of 81°. The HRRR Model has our highs today in the lower 80s for most of us. A wind off the lake will keep it cooler lakeside with upper 70s for highs there.

Wednesday will probably be the coolest day we have seen in just over four weeks. The GFS Model has our highs on Wednesday sliding back into the middle to upper 70s with just lower 70s along the lakefront. The last time we failed to get warmer than the 70s was August 2nd.

The coolest part of this week will be Thursday morning. Lows will dip into the 50s for many of us outside of the city. In and around the city the lows will slide into the lower to middle 60s.

A more reasonable combination of temperatures and dew points means we no longer have to worry about high heat index or apparent temperature values. Dew points will remain in a more pleasant range for the next several days.

A wind off the lake will strengthen late today and stay fairly strong through Wednesday into early Thursday. A lot of air is being forced between cooler Canadian high pressure to our northwest and the remnants of Ida to our southeast and the result is a fairly strong northeast wind that will pose problems for the lakefront. More on that below.

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

Our dew points be between "delightful" and "pleasant". 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.

There will be a moderate to high swim risk developing late today. A beach hazards statement has been issued for southern Lake Michigan's shoreline. It goes into effect at 7 pm tonight and remains in effect until 7 am Thursday. Gusty northeast winds will whip up large waves and generate dangerous rip currents.

Waves could build to as high as 3 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 concentration of wildfire smoke aloft will thin just a bit by later today. The HRRR Model vertically integrated smoke forecast has the thicker smoke (depicted in orange) near the source of the wildfires out west and across the northern Rockies and plains.

The National Blend Of Models has our highs around or just above average today but the next ten days will be cooler. Highs will slip into the upper 70s to near 80°.

For the first time in a long time 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 5th through September 9th. The longer range 8-14 day forecast keeps the cooler pattern coming and also favors us for below average temperatures overall from September 7th through September 13th. Average highs for this period are in the upper 70s.

The longer range temperature probability forecast has a warm pattern returning. The longer range forecast for the middle of the month favors us for above average temperatures overall.

Dry For Now But Showers By The Weekend

Very little to no chance of rain the next three days but some hope for showers Friday night into early Saturday morning.

Lake and McHenry counties are the most in need of rain. A fairly large swath of land near the Wisconsin state line has seen just 10% to 25% of average rainfall over the past two weeks.

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 suggests some showers Friday night and Saturday. The other period that favors rainfall is Tuesday into Tuesday night.

It is difficult to get rain here when moisture from the Gulf of Mexico is effectively cut off from reaching us. The remnants of Hurricane Ida will stay south and east of us the next few days. There could be flooding from Mississippi to Maryland.

The total precipitation forecast through Sunday evening from the GFS model is squeezing out around a half inch to an inch of rain for us. It may be overdoing it just a bit based on the model performance as of late so stay tuned.

The longer range rainfall forecasts moves us from below average precipitation to near normal. The latest 6-10 day forecast has the Chicago area favored for below average precipitation from September 5th through September 9th. The longer range 8-14 day forecast favors us for about average precipitation from September 7th through September 13th. Very few portions of the country in either forecast are favored for above average rainfall.

Here is my 7 day forecast:

Today: Partly to mostly sunny High: 82 (78 lakeside)

Wednesday: Becoming sunny, cooler, a bit breezy Low: 65 High: 78 (cooler lakeside)

Thursday: Mostly sunny Low: 60 High: 79 (cooler lakeside)

Friday: Partly to mostly sunny Low: 61 High: 79

Saturday: Partly to mostly sunny Low: 64 High: 81

Sunday: Partly to mostly sunny Low: 63 High: 79 (cooler lakeside)

Monday: Mostly sunny Low: 62 High: 80 (cooler lakeside)


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