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  • Tim McGill

90s Keep Coming

Air Quality Alert

The Illinois Environmental Protection Agency has declared an air pollution action day for the greater Chicago Metropolitan Area is in effect until midnight. An air pollution action day is declared when weather conditions are such that widespread ozone and or particulate levels are expected to be at or above the unhealthy for sensitive groups category of the air quality index. Active children and adults especially people with pulmonary or respiratory disease such as asthma should limit prolonged outdoor activity.

We are ahead of schedule on 90° days in Chicago. Sunday was the 13th day this year with a high of 90° or hotter. We will add three more 90° days this week to bring the total to 16 by the end of Wednesday. On average we see 11 by the end of July and around 17 for an entire year.

The HRRR Model has our highs climbing into the lower 90s again today.

The air temperature should just about match the heat index values today since our dew points will be relatively low. Tuesday's heat index values will be a bit higher than the air temperatures that are forecast because of the higher dew point expected. It should feel like the middle 90s tomorrow.

There will be some relief from today's heat along the lakefront and through most of the city thanks to a wind off the lake. Stronger southwest breezes tomorrow will probably prevent a lake breeze from developing.

Dew points climb from the relatively comfortable 50s today to the 60s early Tuesday morning.

There is a small chance for some scattered showers and thunderstorms Tuesday afternoon/evening mainly north of the city.

Heat index levels will peak on Wednesday when our dew points climb back into the sultry 70s. Dew points are the preferred measurement of moisture for meteorologists. Those tropical level dew points combined with lower 90s should make it feel like close to 100° by the middle of the week.

The smoke from western wildfires won't be as thick in the Midwest skies today as it has been but it will be present. The HRRR Model vertically integrated smoke forecast has the thickest wildfire smoke north and west of Illinois. Still, we can expect to see hazy sunshine on this Monday.

The National Blend Of Models keeps the 90s coming through Wednesday to stretch the streak to 5 straight 90° days. That would be the longest streak of 90s so far this year. We drop back to about average by Thursday. Average highs are around 84°. By early next week we could see highs slide back into the 70s.

August might start off a bit cooler than average before shifting back above. For the first time in several days some blues are showing up in the Midwest in the first long term temperature forecast. The 6-10 day forecast has outlooked Chicago for below average temperatures overall from July 31st through August 4th. It's is the lightest blue possible over Chicago so it represents the lowest portion of the probability range. The longer range 8-14 day forecast favors us for above average temperatures overall from August 2nd through August 8th. Average highs are in the lower to middle 80s for the end of July and start to August.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecasts keeps us around average for the week ending on August 13th with areas just west and south of us expected to be cooler than average. The following week we are forecast to move back above average. The forecast for the week ending on August 20th favors us for above average temperatures overall.

Saturday's Storms Review

Saturday's high heat and humidity fueled some gusty thunderstorms that did some damage in the Chicago area. The storms had an ominous appearance as the approached.

There were several severe weather reports on Saturday. Damaging winds were the biggest contributor to those reports but locally heavy rain caused issues too.

Best Chance Of Rain Wednesday Night

We are now down 1.41" of rain below average for July at O'Hare and more than six inches since the start of 2021. More rain is needed for our drought stricken areas and some could come late Wednesday into early Thursday.

There was some slightly better news on the drought in our northern suburbs last week. Here is a recap from Friday's post of our drought conditions based on the latest analysis from the US Drought Monitor:

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 has the best chance of rain late Wednesday into early Thursday. Beyond that, most of the next ten days is dry.

The GFS model total rainfall forecast through Thursday evening targets the areas that need the most rain with the highest numbers. The range of rainfall is as little as a quarter of an inch well south and west of the city to nearly two inches in portions of Lake and McHenry county where the stubborn drought persists.

Some of the storms coming during the middle of this week may be severe. The Storm Prediction Center has placed most of us in a marginal risk category for severe storms late Wednesday into Thursday with areas well northwest of the city in a slight risk. The greatest risk from these storms would be damaging winds and hail and but an isolated tornado can't be completely ruled out.

A marginal risk category is level 1 out of 5 possible risk levels. Slight risk means "an area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity."

A slight risk category is 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."

The longer range precipitation probability forecasts for the Chicago area starts out near normal and then shifts part of the area to above normal rainfall. Once again near normal would actually be an improvement since we are running a little over an inch and a quarter of rain below average for July. The latest 6-10 day forecast has the Chicago area favored for about average precipitation overall from July 31st through August 4th. The longer range 8-14 day forecast also has us favored for about average precipitation overall from August 2nd through August 8th.

Here is my 7 day forecast:

Today: Hazy sunshine, hot High: 93

Tuesday: Mostly sunny, hot & more humid Low: 73 High: 93

Wednesday: Partly/mostly sunny, sct. t-storms overnight Low: 72 High: 91

Thursday: Sct. showers/t-storms mainly early, partly/mostly cloudy Low: 73 High: 84

Friday: Partly to sunny, cooler Low: 65 High: 79

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

Sunday: Sct. shower/t-storm early?, partly to mostly sunny Low: 65 High: 80


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