803
FXUS63 KLOT 181944
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
244 PM CDT MON MAY 18 2026
KEY MESSAGES
- ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS ON TUESDAY, SOME
OF WHICH COULD BE STRONG TO SEVERE MAINLY DURING THE AFTERNOON
HOURS.
- SUMMER-LIKE WARMTH AND BREEZY WINDS WILL PREVAIL THROUGH
TUESDAY, THEN COOLER TEMPERATURES AND DRY CONDITIONS WILL
RETURN FOR THE MIDDLE OF THE WEEK.
- MILDER WEATHER RETURNS HEADING INTO THE WEEKEND, THOUGH WITH
AT LEAST INTERMITTENT SHOWER/THUNDERSTORM POTENTIAL.
DISCUSSION
ISSUED AT 244 PM CDT MON MAY 18 2026
THROUGH TONIGHT...
CONVECTION AND ASSOCIATED MCV RESPONSIBLE FOR THIS MORNING'S
SEVERE WEATHER HAS MOVED INTO LOWER MICHIGAN. AIR MASS IN THE WAKE
OF THIS WAVE IS SUBSTANTIALLY MORE STABLE AND COMBINED WITH MODEST
HEIGHT RISES IN ITS WAKE SHOULD PREVENT ANY RENEWED CONVECTIVE
DEVELOPMENT THIS AFTERNOON OR EVENING.
SEVERE CONVECTION CURRENTLY DEVELOPING OVER THE CENTRAL PLAINS
IS LIKELY TO CONGEAL INTO A LARGE QLCS THAT WILL MOVE TOWARD THE
MID-MISSISSIPPI VALLEY TONIGHT. MOST INTENSE CONVECTION IS LIKELY
TO FOCUS FARTHER SOUTHWEST ACROSS MISSOURI, LIKELY INTERCEPTING
THE LOW LEVEL JET AND ORPHANING THE CONVECTION FARTHER NORTH
ACROSS IOWA. THIS SHOULD RESULT IN CONVECTION OVER IOWA
DIMINISHING AS IT MOVES EASTWARD INTO NORTHERN IL WITH SOME
GUIDANCE SUGGESTING VERY LITTLE SHOWER ACTIVITY WOULD ACTUALLY
MAKE IT INTO OUR CWA. HAVE REFLECTED THIS TREND IN POP GRIDS, BUT
OPTED TO MAINTAIN AT LEAST CHANCE POPS GIVEN THE INHERENT
UNCERTAINTIES IN FORECASTING CONVECTIVE EVOLUTION.
PRESSURE FIELD IS RECOVERING IN THE WAKE OF THE MORNING CONVECTION
WHICH HAS ALLOWED WINDS TO PICK AND BECOME RATHER GUSTY FROM THE
SOUTHWEST. GUSTINESS OF THE WINDS WILL GENERALLY TEND TO ABATE BY
SUNSET, EXCEPT PERHAPS REMAINING SOMEWHAT GUSTY TONIGHT IN THE
URBAN HEAT ISLAND OF CHICAGO.
-IZZI
TUESDAY...
CONVECTIVELY INDUCED VORTICITY MAXIMUM WILL SLIDE THROUGH NORTHEAST
ILLINOIS INTO EARLY TUESDAY, WELL OUTPACING THE COLD FRONT, AND
THEREFORE WE MAY HAVE SOME SHOWERS HANGING ON INTO THE AREA, BUT
CONFIDENCE IS MEDIUM-HIGH THAT THUNDERSTORM COVERAGE WILL BE ON THE
LOWER SIDE. ANY LINGERING MCS COLD POOL FOOTPRINT AND RESIDUAL
CLOUDINESS WILL LIKELY DELAY DESTABILIZATION INTO MIDDAY TUESDAY,
THOUGH ADDITIONAL STORM DEVELOPMENT APPEARS SOMEWHAT PROBABLE ACROSS
THE SOUTHEAST HALF OF THE FORECAST AREA TUESDAY AFTERNOON/EVENING AS
THE COLD FRONT FINALLY PUSHES THROUGH THE FORECAST AREA.
SOUTHWESTERLY FLOW AHEAD OF THE FRONT WILL MAINTAIN MID TO POSSIBLY
UPPER 60S DEWPOINTS AND SUPPORT MLCAPE APPROACHING 1500 J/KG.
STRONGER MID-LEVEL FLOW ON THE SOUTHEASTERN PERIPHERY OF THE MODEL
GUIDANCE WOULD SUPPORT SOME ADDITIONAL VORTICITY MAXIMUM RIDING
ALONG THE FRONT, AND FLOW TO THE SOUTHEAST OF THE MID LEVEL TROUGH
ACROSS THE NORTHERN GREAT LAKES WILL LIKELY SUPPORT ENOUGH STORM
DEVELOPMENT AND SOME ORGANIZATION FOR A HAIL/WIND THREAT DURING
THIS TIME. THIS WOULD BE FAVORED ALONG AND SOUTHEAST OF I-55,
WITH SHORT TERM ENSEMBLE GUIDANCE SUGGESTING THE WINDOW FOR MUCH
OF NE IL AND NW IN BEING FAIRLY LIMITED IN THE MID TO LATE
AFTERNOON. FOR THE CHICAGO METRO AREA THE PICTURE IS ALSO A BIT
MUDDLED FOR PRECIPITATION CHANCES. HIGH RES GUIDANCE IS MOSTLY
DRY FOR THE AREA, WHEREAS GLOBAL GUIDANCE AND NAM/RAP DOES BRING
SOME SHOWER ACTIVITY ACROSS CHICAGOLAND ALONG THE FRONT IN THE
EARLY AFTERNOON.
KMD
WEDNESDAY ONWARD...
FOLLOWING THE COLD FRONT, SURFACE HIGH PRESSURE IS PROGGED TO
BUILD EAST INTO THE WESTERN GREAT LAKES REGION WEDNESDAY AND
THURSDAY. DRY, BUT BREEZY AND COOLER WEATHER IS EXPECTED BOTH
DAYS, WITH TEMPS MAINLY IN THE 60S, BUT ONLY IN THE 50S NEAR
LAKE MICHIGAN WITH NORTHEAST-EAST FLOW OFF THE LAKE. NIGHTTIME
LOWS IN THE 40S ARE EXPECTED. THE HIGH THEN DRIFTS OFF TO THE
EAST THURSDAY NIGHT, WITH THE UPPER LEVEL PATTERN FAVORING A
SERIES OF MID-LEVEL DISTURBANCES TRACKING THROUGH THE AREA
FRIDAY INTO THE WEEKEND. THIS WILL SUPPORT MILDER TEMPERATURES,
BUT ALSO SOME OCCASIONAL SHOWER/THUNDERSTORM CHANCES INTO THE
HOLIDAY WEEKEND.
RATZER
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 109 PM CDT MON MAY 18 2026
WIND FIELD HAS BEEN SUBSTANTIALLY ALTERED BY STORMS THIS
MORNING, BUT WILL REVERT BACK TO A SOUTH-SOUTHWEST DIRECTION
EARLY THIS AFTERNOON. PRESSURE GRADIENT IS BAGGIER IN THE WAKE
OF THE STORMS THAN ORIGINALLY FORECAST, SO GUSTINESS OF THE
WINDS MAY BE SLOWER TO DEVELOP TODAY THAN INDICATED IN THE TAFS.
SHOWERS AND STORMS THAT DEVELOP OVER THE CENTRAL PLAINS TODAY
WILL MOVE EAST AND LIKELY REACH NORTHERN ILLINOIS IN A QUICKLY
DECAYING STATE LATE TONIGHT/EARLY TUESDAY MORNING. CONFIDENCE IS
LOW IN WHETHER THIS ACTIVITY WILL REACH THE TERMINALS, SO OPTED
TO JUST HANG ONTO A PROB30 IN THE TAFS.
FINALLY, CONFIDENCE IN WINDS TUESDAY IS ON THE LOWER END OF THE
SPECTRUM. THERE IS A CHANCE WIND FIELDS COULD BE ALTERED BY
DIMINISHING STORMS, WHICH COULD PLAY HAVOC ON DIRECTIONS AND
SPEEDS. HOWEVER, IF WIND FIELDS AREN'T SIGNIFICANTLY ALTERED,
THEN WINDS WILL LIKELY BE EVEN STRONGER THAN INDICATED IN THE
TAFS.
- IZZI
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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