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  • Tim McGill

Not Done With The 90s

Steamy & Stormy Pattern Returns

The Blue Angels benefitted from dry weather this weekend as they performed at the 2021 Air Show. It may have been dry in terms of rainfall for their performances but there was a big difference in the moisture in the air Sunday compared to Saturday. Saturday was steamy with highs near 90° but a cold front late in the day set us up for a cooler and more pleasant Sunday. It was a brief break from high heat and humidity because we are already muggy on this Monday.

Today's high at O'Hare will be near 90°. If we hit that mark, it will be the 18th time this year O'Hare has reached 90°. We average 17 90° days for an entire year. We average another two more 90° days from this point in the year forward. We have at least two days this week that should see highs near or above 90° with at least one more chance at 90° this weekend.

The HRRR Model has our highs near 90° or just above today. Rising humidity will make it feel hotter.

The combination of heat and humidity will make it feel like the lower to middle 90s.

It will be even more uncomfortable on Tuesday. Heat index values will climb to near 100° for most of us.

At least we will be spared the thicker wildfire smoke from our skies 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 heat index or apparent temperature values will be high all week. They jump today as dew points soar to over 70° late this afternoon.

Southwest breezes will be light today and strengthen a bit tomorrow. They will transport the steamy air from the south to the Midwest all week long.

There may be a scattered shower or thunderstorm early Monday mainly to the west of the city but most of the day should be rain free with only a slight chance of a shower or thunderstorm. The threat of rain goes up early tomorrow morning and stays relatively higher during the day on Tuesday. The exact timing of occasional periods of scattered showers and thunderstorms is tough to call with the kind of steamy and stormy pattern expected this week.

Today's dew points soar to over 70° late this afternoon and then stay stuck near or just above 70° all this week and through most of the upcoming weekend. We finally see dew points drop significantly by Monday 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. We will be in the "uncomfortable" to "sweltering" range of dew points for the next several days By early next week we will see dew points drop back into the "delightful" or "pleasant" category.

We have more 90° days on the way this week with an additional day possible Saturday. The National Blend Of Models has highs near 90° or above today through Wednesday along with Friday and Saturday. We finally cool back to about average Monday and even fall below that the following Tuesday and Wednesday.

The long range temperature probability forecasts keep Chicago and most of the Midwest above average from the end of this month into the start of September. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from August 28th through September 1st. The longer range 8-14 day forecast also favors us for above average temperatures overall from August 30th through September 5th. Average highs for this period are in the lower 80s to upper 70s.

Hit Or Miss Rainfall This Week

Saturday's .60" of rain that fell at O'Hare was the first measurable rainfall there in ten days. 1.93" of rain has fallen there so far this month which is down 1.13" from average. O'Hare is now .26" below average since June 1st. The rainfall deficit is much higher in our northern suburbs that continue to experience drought conditions.

Here is a recap from Friday's post that includes the latest analysis from the US Drought Monitor:

Most of northern Illinois didn't see any measurable rain during the seven day period from August 13th through the 19th. Zero to 5% of average rainfall fell during the period.

So it is no surprise we got mostly discouraging news from the latest US Drought Monitor analysis. The only good news is the portion of Illinois in a severe drought (level 2 out of 4 levels) dropped from 1.19% last week to .79% this week. The bad news is 7.33% of the state is now in a moderate drought (level 1 out of 4 levels) up from 6.05% last week. Northern Illinois is the only part of the state reporting drought conditions. More bad news. The portion of the state considered "abnormally dry" has increased to 15.42% from 15.20% last week.

The latest GFS model suggests scattered showers and thunderstorms Tuesday into Wednesday morning with another active period late Thursday into early Saturday morning. The pattern then becomes drier for the end of the weekend and most of next week. The latest meteogram is just showing a few showers or thunderstorms possible late next Monday.

The total precipitation forecast through Sunday afternoon from the GFS model is offering at least some hope for help with the drought. It targets our northern suburbs with as much as an inch and a half to two inches of rain and then tapers off amounts to three quarters of an inch south of the city.

The longer range rainfall forecasts are a bit more promising today for a more active pattern to finish out August and start off September. The latest 6-10 day forecast has the Chicago area favored for above average precipitation from August 28th through September 1st. The longer range 8-14 day forecast also favors us for above average precipitation also from August 30th through September 5th.

The Midwest region's drought news is all bad with the latest analysis. There was at least a small increase in every level of drought for the region.

The west region some minor good news with this latest analysis. The areas in a moderate, severe and extreme drought all saw at least a small decrease. Unfortunately the area in the most dire drought category saw an increase. 25.71% of the region is in an exceptional drought. That is up from 25.35% last week. More than 95% of the west is in some level of drought.

Here is my 7 day forecast:

Today: Partly to mostly sunny, hot & humid, isolated shower/t-storm possible High: 90

Tuesday: Partly to mostly sunny, sct. shwrs/t-storms Low: 72 High: 91

Wednesday: Partly/mostly sunny, sct. shwrs/t-storms Low: 74 High: 92

Thursday: Partly/mostly sunny, sct. shwr/t-storm possible Low: 74 High: 86 (cooler lakeside)

Friday: Partly to mostly sunny, sct. shwrs/t-storms Low: 73 High: 89

Saturday: Mostly sunny, sct. shwr/t-storm possible Low: 73 High: 90

Sunday: Partly to mostly sunny, sct. shwrs/t-storms late Low: 73 High: 88


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