DRENCHING RAINS THREATEN FLOODING IN PARTS OF THE AREA–THE AREA FROM THE I-88 CORRIDOR SOUTH APPEARS AT HIGHEST RISK SATURDAY AFTERNOON AND NIGHT; A SECOND ROUND OF SHOWERS AND T-STORMS THREATENS SUNDAY NIGHT INTO MONDAY

by: Tom Skilling, Bill Snyder, Diana Brandonisio

Posted: Aug 4, 2023 / 11:01 PM CDT

Updated: Aug 5, 2023 / 02:31 AM CDT

6-10 DAY PRECIPITATION OUTLOOK
On Friday it was another beautiful summer day with 94% of the day’s possible sunshine as well as moderate air quality and humidities. The high reached 86 at O’Hare and 85 at Midway. Dew points were in the low and mid 60s—except closer to 70 in surrounding agricultural areas where crops were transpiring added moisture into the atmosphere. The haze is a combination of some moisture in the air—but also a some wildfire smoke sweeping into the area from the Western U.S. and Canada where fires are burning.

Every day this week has featured highs in the mid 80s with the exception of Tuesday with its high of 90. The week (the 7-day period ending midnight Sat night) will post a modest 1-degree surplus.

Easterly winds as high as 20 mph produced 2 to 4 ft. waves on Lake Michigan and prompted a BEACH HAZARDS STATEMENT which continues into Saturday morning.

6-10 DAY TEMPERATURE OUTLOOK
The moisture content of the atmosphere is to SOAR this weekend. Focusing rain & t-storm development Saturday will be a vigorous upper wave which is to lift and cool the air leading to potential downpours, popping over 20 to 30% of the area Saturday morning and up to 60 to 80% of the area Saturday afternoon into Saturday night.

Much of northern and central Illinois is outlooked for potential heavy or excessive rains—in other words, rains which could be heavy enough to produce areas of flooding. We’ve been seeing clusters of t-storms flare from time to time in recent days to Chicago’s south and southwest. Evidence mounts the weekend big rain producing t-storms will shift north into at least a portion of the Greater Chicago metro area.

Modeling suggest general rainfalls of 0.60″ to as much as 2.25″ is to fall in coming days. BUT WITH T-STORMS INVOLVED—it’s not out of the realm of possibility a corridor of heavy rains may lay out in portions of the Chicago metro area.

RAINFALL thins out Sunday but cooling aloft begins in the afternoon with the area still in a humid, moisture rich air mass. The destabilizing effect of the upper level cooling is to boost production of what could be a second round of showers and possible t-storms later Sunday, but more likely Sunday night.

The presence of COOL, UNSTABLE AIR with an upper air system threatens to hold cloud cover and sporadic shower and possible t-storm clusters into Monday.

WE APPEAR TO BE ENTERING A PERIOD with the regular arrival of ACTIVE PRECIPITATION PRODUCING SYSTEMS. After a pause Tuesday—a second system could be in later Wednesday and Thursday—and YET ANOTHER by early the following week. There are even hints scattered showers and t-storms can’t be ruled out parts of next weekend. SO THE WET PATTERN which dominated July locally appears prepared to carry over into August.

8-14 DAY PRECIPITATION OUTLOOK
WE APPEAR TO BE ENTERING A PERIOD with the regular arrival of ACTIVE PRECIPITATIONS PRODUCING SYSTEMS. After a pause Tuesday—a second system could be in later Wednesday and Thursday—and YET ANOTHER by early the following week. There are even hints scattered showers and t-storms can’t be ruled out parts of next weekend. SO THE WET PATTERN which dominated July locally appears prepared to carry over into August.

24-HR EXCESSIVE RAINFALL POSSIBLE
This is the area in which EXCESSIVE RAINFALL is possible in 24 hour period through 7am CDT Sunday morning per the National Weather Service’s Weather Prediction Center.

STORM PREDICTION CENTER
Day 3 Categorical Outlook (Friday – Sunday)

WEATHER PREDICTION CENTER
Day 3 Excessive Rainfall Outlook (Friday – Sunday)

US DROUGHT MONITOR FOR CORN AREAS
Reflects Aug. 1, 2023 [USDA]

US DROUGHT MONITOR FOR SOYBEAN AREAS
Reflects Aug. 1, 2023 [USDA]

MODERATE AIR QUALITY
Air quality in Chicago late Friday

4TH WARMEST YEAR TO DATE
Chicago temps are the 4th warmest of the past 153 years. Shown here are how much each month’s average temps (including the opening 4 days of August) has varied from normal temps.