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  • Tim McGill

Get Set To Sweat This Weekend

It's The Heat & The Humidity

Looks like July will end on a hot note. So far 16 of the first 22 days of this month have been below average. The month is now running just under 3° below average. We will erase most if not all of that deficit over the next six days. This will be the hottest weekend of the year so far and probably the hottest since last July. Brace for not just more heat but high levels of humidity too.

The HRRR Model has our highs climbing to near 90° today but that is only half of the weather story.

The high humidity will make it feel hotter. The heat index values or apparent temperature will be well into the 90s. It will feel like close to 100° in some spots both Saturday and Sunday. The apparent temperature forecast graphic almost looks like it is on fire.

Southwest winds will deliver the high levels of heat and humidity for the next several days. Winds tomorrow will gust to around 20 mph. There may be a spotty shower or thunderstorm today but the best chance of rain will be later Saturday into Saturday night. Even then only about 30% of the area will see some rain.

Dew points will be at some of the highest levels we have seen this summer. Dew points are the preferred measurement of moisture for meteorologists. The dew point will hover near or just above 70° the next few days. The humidity will jump from uncomfortable to oppressive.

More hazy sunshine today with wildfire smoke still in our skies. The HRRR Model vertically integrated smoke forecast still has wildfire smoke drifting from the west coast and Canada into the Midwest and beyond. The haze from this smoke will actually keep us from getting as hot as we could. It will probably hold our highs down a couple of degrees as long as the haze is here in the Chicago area.

The National Blend Of Models has a forecast of five straight days with highs of 90° or hotter. That would be the longest streak of 90s so far this year. A week from today we drop back below average. Average highs are around 85°.

Our warmer than average pattern might stick around right into the first week of August. The long range temperature probability forecasts favor most of the country for an above average period overall from the end of July into the first five days of August. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from July 28th through August 1st. The longer range 8-14 day forecast also favors us for above average temperatures overall from July 30th through August 5th. Average highs are in the lower to middle 80s for the end of July and start to August..

Drought Diminishes Slightly

Some signs of improvement for the drought in northern Illinois. The latest the US Drought Monitor analysis reduces the intensity and reach of the drought. We are down 1.14" of rain below average for July at O'Hare and more than six inches since the start of 2021.

The area of Illinois in a moderate drought (level 1 out of 4) has dropped slightly from 7.32% last week to 7.17% this week. The area of the state in a severe drought (level 2 out of 4) has increased slightly from 2.40% a week ago to 2.31% this week. There is not longer any portion of Illinois experiencing an exceptional drought (level 3 out of 4). Last week just under 1% of the state fell into that category.

Rainfall over a two week period that ended on July 21st shows large portions of our area received very little rainfall during those 14 days. Hardest hit was already parched portions of Lake and McHenry counties where just 10% to 25% of average rainfall fell.

The latest GFS model suggests a few scattered showers or thunderstorms today and then late Saturday into early Sunday morning. Most of next week is projected to be dry.

The GFS model total rainfall forecast through the weekend has a range of rainfall from around just under a half inch for most of us to nearly an inch in northern Indiana. This model has been overdoing the rainfall as of late so these numbers might be high overall but there will be some locally heavy rainfall with individual thunderstorms. The atmosphere is ripe with moisture.

Some of the storms late Saturday into Saturday could be severe. The Storm Prediction Center has placed us in a marginal to slight risk for severe weather for that period. The greatest risk from these storms would be damaging winds.

Most of the area will be in the slight risk category or level 2 out of 5 possible risk levels. Slight risk means "an area of organized severe storms, which is not widespread in coverage with varying levels of intensity."

A marginal risk is level 1 out of 5. It is the low end of the risk categories but means "an area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity".

The longer range precipitation probability forecasts are encouraging for the Chicago area and parched portions of the Rockies. The latest model run has us moving from near normal precipitation to above average precipitation as we end July and begin August. The latest 6-10 day forecast has the Chicago area favored for about average precipitation overall from July 28th through August 1st. The longer range 8-14 day forecast also has us favored for above average precipitation overall from July 30th through August 5th. A big portion of the Rockies is finally favored for above average precipitation in both forecasts.

The Midwest region overall had some discouraging drought news from the latest analysis. The area of our region in both a severe and extreme drought increased. The area in a moderate drought did decrease slightly.

The western US got worse news. Every category of drought saw at least a small increase. Over 65% of the region is in an extreme drought with just over 28% in an exceptional drought.

Here is my 7 day forecast:

Today: Hazy sun & cloud mix, spotty shower or t-storm possible High: 89

Saturday: Partly to mostly cloudy, sct. showers/t-storms (some strong) Low: 73 High: 91

Sunday: Partly to mostly sunny, hot & humid Low: 72 High: 93 (cooler lakeside)

Monday: Partly to mostly sunny Low: 72 High: 92 (cooler lakeside)

Tuesday: Partly to mostly sunny Low: 73 High: 92

Wednesday: Partly to mostly sunny, sct. t-storm possible Low: 72 High: 91 (cooler lakeside)

Thursday: Partly to mostly sunny, sct. t-storm possible Low: 71 High: 85

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