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  • Tim McGill

Steamy Thru Sunday But Cooler Pattern Coming

Mostly Rain Free Weekend

O'Hare squeezed out a 90° high on Thursday. That was the 20th time this year it hit 90° or more. We average 17 90° days a year. We have possibly three more coming between today through Sunday. That would mean six straight days with highs of at least 90°. That would be the longest streak of 90s this year.

The good news yesterday was that the heat index values were not as extreme as the past few days. They reached into the lower to middle 90s but did not hit 100°. That brief "break" is over as heat index values will soar back to more sweltering levels today and this weekend.

The HRRR Model has our highs today at least 10° above average as they top out in the lower 90s.

The HRRR Model has the heat index (or apparent temperature) between 95° to near 100° in our hottest spots today.

Similar steamy heat index values expected on Satu5day. They should peak between 90° to 100°.

The heat index or apparent temperature values at O'Hare will stay at dangerous levels through Sunday as a result of a combination of highs near 90° or above and dew points in the lower 70s.

Southwest winds will be a bit breezy today and tomorrow. That breeze might help with the heat just a bit.

Relatively low chances of scattered showers and thunderstorms this afternoon and again Saturday afternoon. Most of the weekend should be dry.

Our dew points stay at tropical levels through most of Sunday before falling Sunday night into Monday. They may fall into the 50s by the middle of next 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. So three more days with dew points in the "uncomfortable" to "sweltering" range before more comfortable levels arrive early next week. By Monday our dew points fall back into the "pleasant" to "a little sticky" category and could approach "delightful" levels by Wednesday.

The National Blend Of Models has highs hitting 90° or hotter through Sunday. We fall back to about average early next week. The following weekend could be nearly 15° cooler than this weekend.

The longer range temperature probability forecasts for the first time in several days don't both favor us for warmer than average weather. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from September 1st through September 5th. The longer range 8-14 day forecast drops us back to about average temperatures overall from September 3rd through September 9th. Average highs for this period are in the lower 80s to upper 70s.

No signs of slowing down this late summer heat in the even longer range week 3-4 forecast. We are favored for above average temperatures overall well into September.

Stubborn Drought Continues

The latest analysis from the US Drought Monitor is in and it doesn't show any improvement for our northern suburbs mired in a moderate to severe drought. Keep in mind that it doesn't include the rain that fell Wednesday and Thursday this week. That may show up in next week's analysis.

Some of the most parched portions of our area got soaked earlier this week A portion of northern McHenry county picked up between 150% to 400% of average rainfall in a 7-day period that ended on August 26th.

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 doesn't show much rain for the weekend until late Sunday night. It hints at an unsettled start to next week with some periods of scattered showers and thunderstorms Monday through Wednesday.

The threat of severe storms stays north and northwest of Chicago today. The Storm Prediction Center has again placed portions of the upper Midwest in either a marginal risk (level one out of 5) area or slight risk (level two out of 5) for severe weather.

Here are the corresponding descriptions for each of the risk categories:

The total precipitation forecast through Tuesday morning from the GFS model is showing a range of rainfall from as little as a quarter of an inch to nearly an inch of rain. Like the past few days, there could be locally heavier amounts because of the abundant moisture in the air available to fuel storms.

The longer range rainfall forecasts give us hope for above average rainfall to start of September.. The latest 6-10 day forecast has the Chicago area favored for above average precipitation from September 1st through September 5th. The longer range 8-14 day forecast also favors us for above average precipitation from September 3rd through September 9th.

Here is my 7 day forecast:

Today: Partly to mostly sunny, pm sct. shower/t-storm possible High: 92

Saturday: Mostly sunny, isolated. shwr/t-storm possible Low: 73 High: 93

Sunday: Partly to mostly sunny, sct. shwrs/t-storms late Low: 73 High: 92

Monday: Partly/mostly sunny, sct. shwr/t-storm possible Low: 69 High: 84 (cooler lakeside)

Tuesday: Partly to mostly sunny, sct. shower possible Low: 67 High: 82 (cooler lakeside)

Wednesday: Partly to mostly sunny Low: 65 High: 80 (cooler lakeside)

Thursday: Mostly sunny Low: 63 High: 81 (cooler lakeside)


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