268
FXUS63 KLOT 132332
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
632 PM CDT THU AUG 13 2026
KEY MESSAGES
- A STORMY PATTERN IS EXPECTED TO REMAIN IN PLACE THROUGH THE
WEEKEND.
DISCUSSION
ISSUED AT 230 PM CDT THU AUG 13 2026
AT THE TIME THIS DISCUSSION WAS PUBLISHED, AN MCV WAS TRACKING
EAST OVER US-24. MEANWHILE NORTH OF THE MCV, WIDESPREAD RAIN IS
FALLING WITH ISOLATED TO WIDELY SCATTERED LIGHTNING. THIS SYSTEM
WILL CONTINUE TO TRACK EAST THROUGH THE AFTERNOON.
THERE COULD BE A BREAK IN THE LATE AFTERNOON FOR AREAS SOUTH OF
INTERSTATE 80, AS CONTINUED RAIN IS EXPECTED NORTH ALONG A
PROJECTED LOW LEVEL VORTICITY AXIS AND 500 MB JET AXIS ALONG THE
ILLINOIS/WISCONSIN STATE LINE. WITH THE CURRENT MCV MOVING
THROUGH THE AREA, IT IS DIFFICULT TO PINPOINT THE EXACT LOCATION
OF THE STATIONARY FRONT THAT WAS PREVIOUSLY ANALYZED JUST SOUTH
OF THE FORECAST AREA. THAT BECOMES IMPORTANT BECAUSE THE RIGHT
ENTRANCE REGION OF THE PREVIOUSLY MENTIONED 500 MB JET (AND
THEREFORE AREA OF FOCUSED UPPER LEVEL DIVERGENCE) WILL BE
SITUATED JUST NORTH OF THE STATIONARY FRONT. HIGH-RES CAMS ARE
PROJECTING WEAK PERTURBATIONS WITHIN THE 500 MB FLOW THIS
EVENING AND THROUGH THE OVERNIGHT. WITH PRECIPITABLE WATER
AMOUNTS BETWEEN 1.5 TO 2 INCHES, THIS SET-UP IS INCREASING
CONCERNS FOR FLOODING THREAT IN THE AREA. THE ONE FLY IN THE
OINTMENT FOR THIS SET-UP IS THE ABSENCE OF A STRONG LOW LEVEL
JET. HAD THERE BEEN A STRONGER LOW LEVEL JET PROJECTED, PERHAPS
THERE WOULD NEED TO BE CONSIDERATION TO EXPAND THE PREVIOUSLY
ISSUED FLOOD WATCH NORTHWARD. SHOWERS ARE EXPECTED TO DEVELOP
OVER NORTHERN ILLINOIS WITH THE RISK OF TRAINING STORMS OVER THE
SAME AREA. IT IS NO SURPRISE THAT ENSEMBLES ARE SHOWING A BROAD
SWATH OF 1 TO 2 INCHES OF RAIN THAT COULD FALL OVERNIGHT, WITH
AN AXIS OF LOCALLY HIGHER AMOUNTS OVER THE SOUTHWEST PORTIONS OF
THE FORECAST AREA.
THERE IS LOWER CONFIDENCE IN THE EXACT TIMING OF WHEN THE RAIN
ENDS ON FRIDAY MORNING. AS THE UPPER LEVEL JET WEAKENS AND MOVES
EAST, RAIN SHOULD SLOWLY TAPER OFF BY MID-MORNING WITH THE
POTENTIAL FOR A DRIER PERIOD EXPECTED IN THE AFTERNOON. HOWEVER,
AS THE BROAD UPPER LEVEL RIDGE OVER THE SOUTHEASTERN PORTION OF
THE CONUS REMAINS IN PLACE, ANOTHER SHORT WAVE WILL RIDE OVER
THE TOP OF THE RIDGE TOMORROW AFTERNOON AND EVENING PROVIDING
ENOUGH FORCING FOR THE NEXT SYSTEM TO DEVELOP IN IOWA AND MOVE
EAST. RAIN COULD BEGIN IN THE EARLY EVENING, BUT THE BETTER
CHANCES FOR THE HEAVIER DOWNPOURS ARE EXPECTED CLOSER TO
MIDNIGHT WHEN THE CORE OF THE WAVE MOVES OVER. GIVEN WHAT THE
FORECAST IS FOR RAINFALL OVERNIGHT TONIGHT ON ALREADY SATURATED
SOILS, THERE IS GROWING CONCERNS FOR FLOODING THREATS
TOMORROW NIGHT INTO SATURDAY MORNING AND COLLABORATED WITH THE
WEATHER PREDICTION CENTER TO INCREASE THE RISK TO A LEVEL 3 OUT
OF 4 FOR EXCESSIVE RAINFALL. THE POTENTIAL FOR WATER LOADED
DOWNBURSTS KEEPS MUCH OF THE FORECAST AREA IN A MARGINAL (LEVEL
1 OUT 5) RISK FOR SEVERE STORMS TOMORROW NIGHT, BUT WEAKER SHEAR
PROFILES KEEP THE CONFIDENCE IN SEVERE DEVELOPMENT LOW.
MODELS HAVE SHOWN FAIRLY GOOD AGREEMENT THAT YET ANOTHER WAVE IS
EXPECTED TO PASS OVER THE RIDGE ON SATURDAY PROVIDING ANOTHER
THREAT FOR HEAVY RAINFALL AND FLOODING THREAT ACROSS PORTIONS OF
THE FORECAST AREA. GLOBAL MODELS ARE NOT SUGGESTING A BREAK IN
THE RAIN UNTIL A FRONT DROPS DOWN OUT OF WISCONSIN LATE ON
SUNDAY. SURFACE HIGH PRESSURE IS EXPECTED TO GROW ON MONDAY FOR
THE POTENTIAL FOR A DRY DAY IN THE REGION. HOWEVER, GLOBAL
MODELS ARE STILL SUGGESTING ANOTHER SYSTEM POTENTIALLY BRINGING
A A RENEWED THREAT FOR PRECIPITATION MID-WEEK NEXT WEEK.
DK
AVIATION /00Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 632 PM CDT THU AUG 13 2026
AN AREA OF SHOWERS WILL CONTINUE TO SHIFT SOUTH ACROSS THE
TERMINALS EARLY THIS EVENING. LATER THIS EVENING AND OVERNIGHT,
EXPECTATIONS ARE FOR AN ADDITIONAL AREA OF CONVECTION TO DEVELOP
IN THE REGION. SOME UNCERTAINTY STILL EXISTS ON THE NORTHERN
TERMINUS OF THIS CONVECTION, BUT LATEST SATELLITE AND MODEL
TRENDS SUGGEST THE BULK OF THIS ACTIVITY MAY TEND TO FOCUS JUST
SOUTH OF THE TERMINALS, ALTHOUGH IT MAY GET CLOSE, PARTICULARLY
AT MDW AND GYY. GIVEN THIS, HAVE CONTINUED A LONG-DURATION VCSH
AND PROB30 GROUPS FOR TSRA TO ACCOUNT FOR TRAILING STRATIFORM
PRECIPITATION. ACTIVITY MAY PERSIST THROUGH MUCH OF THE NIGHT
AND INTO FRIDAY MORNING BEFORE DIMINISHING.
OUTSIDE OF SHOWERS, A MOIST AIRMASS WILL SUPPORT THE POTENTIAL
FOR BR DEVELOPMENT TONIGHT. MVFR CIGS MAY DEVELOP FRIDAY MORNING
AND AFTERNOON WITH MIXING, BUT CONFIDENCE ON THIS REMAINS TOO
LOW FOR A MENTION IN THE TAFS. EAST TO NORTHEASTERLY WINDS WILL
PREVAIL THROUGH THE FORECAST PERIOD. AN ADDITIONAL ROUND OF
CONVECTION APPEARS POSSIBLE FRIDAY EVENING/OVERNIGHT.
CARLAW
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH THROUGH FRIDAY MORNING FOR ILZ008-ILZ010-ILZ011-
ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ106-
ILZ107-ILZ108.
IN...FLOOD WATCH THROUGH FRIDAY MORNING FOR INZ010-INZ011-INZ019.
LM...NONE.
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