DRENCHING RAINS THREATEN FLOODING FAVORING AN AREA ROUGHTLY FROM THE I-88 CORRIDOR SOUTH SATURDAY AFERNOON INTO SAT NIGHT—A SECOND ROUND OF SHOWERS AND T-STORMS THREATENS SUNDAY NIGHT INTO MONDAY

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 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, USTABLE AIR with an upper air system threatens to hold cloud cover and sporadic shower and possible t-storm clusters into Monday.

MEANTIME ON FRIDAY:

It was nother 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 7day period ending midnight Sat night) will post a modest 1-deg 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.

LONGER RANGER:

WE APPEAR TO BE ENTERING A PERIOD with the regular arrival of ACTIVE PRECIP 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.

HERE’S MY LATEST FRIDAY CHICAGO METRO FORECAST (8/4/2023):

TONIGHT: Partly cloudy, warm and hazy. Moderate humidities with a little patchy ground fog cooler surrounding areas. Low 69—but low and mid 60s cooler inland locations.

SATURDAY: Clouding over, warm with more humid air moving in. Prospects for showers and possible t-storms, initially scattered and impacting 20 to 30% of the area, develop during the morning, especially southern sections of the Chicago metro area. Shower and t-storm coverage and prospects increase as the day proceeds and continues Saturday night.  Downpours possible in the heavier storms and the area at greatest risk for some possibly significant rainfall runs either side of the I-88 corridor and south.  High 84—but 70s beaches. Low SaturDay night 71.

SUNDAY: Lingering showers thin out—peek of sun may appear, humid. Clouds begin building again in the afternoon with some scattered afternoon and evening showers and t-storms growing more widespread Sunday night.  30 to 60% areal coverage of storms  by later Sunday may increase to 80% of the area Monday night. High Sunday 85—-but 70s lakeshore. Low Sunday night 69.

TUESDAY: Partly sunny and warm. Moderate humidities. High 84.

WEDNESDAY: Sun through building clouds, warm. Scattered afternoon and/or evening t-storms possible.  High 85.

THURSDAY: Showers and thunderstorms likely. Humid. High 82.

FRIDAY: A sun/cloud mix, warm and humid. Chance of scattered t-storms. High 83.