187
FXUS63 KLOT 131930
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
230 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 /18Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 1248 PM CDT THU AUG 13 2026
AN AXIS OF STRATIFORM RAIN WILL CONTINUE SLIDING ACROSS THE
AIRSPACE THIS AFTERNOON WITH DROPS IN VISIBILITY TO 1-3 MILES
AND OCCASIONAL LIGHTNING STRIKES. WINDS WILL REMAIN FAIRLY LIGHT
(5KT OR LESS) AND GENERALLY OUT OF THE EAST-NORTHEASTERLY
DIRECTION. CIGS WILL REMAIN LARGELY MVFR UNTIL THE BACK EDGE OF
THE STRATIFORM SLIDES OVERHEAD.
IN THE WAKE OF THE STRATIFORM PRECIPITATION, RENEWED
THUNDERSTORM DEVELOPMENT IS ANTICIPATED ALONG A STALLED FRONTAL
BOUNDARY DRAPED ACROSS THE LOWER GREAT LAKES. THE OVERALL REGIME
WILL BE FAVORABLE FOR A PROLONGED PERIOD OF TRAINING STORMS,
POTENTIALLY LASTING MORE THAN 6 HOURS AT ANY GIVEN LOCATION.
HOWEVER, THERE IS AN UNUSUAL AMOUNT OF UNCERTAINTY ON WHERE THE
FOCUSED CORRIDOR OF THUNDERSTORMS WILL BE. AM EYEING ECHOES
DEVELOPING ACROSS CENTRAL IOWA AS A POTENTIAL CLUE FOR AN
EASTWARD EXTENSION. FOR NOW, WILL MAINTAIN THE INHERITED PROB30
GROUPS IN FAVOR FOR ADJUSTMENTS IN LATER TAF PACKAGES. WINDS
SHOULD REMAIN EAST-NORTHEASTERLY OVERNIGHT.
COVERAGE OF SHOWERS AND STORMS SHOULD WANE AFTER DAYBREAK GIVING
WAY TO ISOLATED SHOWERS. NORTHEASTERLY WINDS AND MVFR CIGS MAY
CONTINUE THROUGH THE REMAINDER OF THE TAF PERIOD.
BORCHARDT
LOT WATCHES/WARNINGS/ADVISORIES
IL...FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH FRIDAY MORNING
FOR ILZ008-ILZ010-ILZ011-ILZ019-ILZ020-ILZ021-ILZ023-
ILZ032-ILZ033-ILZ039-ILZ106-ILZ107-ILZ108.
IN...FLOOD WATCH FROM 7 PM CDT /8 PM EDT/ THIS EVENING THROUGH
FRIDAY MORNING FOR INZ010-INZ011-INZ019.
LM...NONE.
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