741
FXUS63 KLOT 311123
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
623 AM CDT MON MAR 31 2025
KEY MESSAGES
- POSSIBLE SEVERE THUNDERSTORMS LATE TUESDAY NIGHT AND ON
WEDNESDAY ALONG WITH HEAVY RAIN AND POSSIBLE LOCALIZED
FLOODING.
DISCUSSION
ISSUED AT 235 AM CDT MON MAR 31 2025
THROUGH TUESDAY:
TEMPERATURES CONTINUE TO DROP EARLY THIS MORNING AS THE LOW
PRESSURE SYSTEM RESPONSIBLE FOR YESTERDAY'S SEVERE THUNDERSTORMS
CONTINUES TO PUSH OFF TO THE NORTHEAST. ANY LINGERING LIGHT
RAIN AND SNOW ACROSS FAR NORTHEAST IL/NORTHWEST IN SHOULD COME
TO AN END TOWARD DAYBREAK WITH NO SNOW ACCUMULATION EXPECTED.
TEMPERATURES TOWARD THE WI/IL STATELINE WILL DROP TO NEAR OR
JUST BELOW FREEZING EARLY THIS MORNING. WHILE CONTINUED STEADY
NORTHWESTERLY BREEZES SHOULD HELP DRY THINGS OFF, A FEW SLICKS
SPOTS CAN'T BE RULED ON ELEVATED SURFACES.
AFTER A CHILLY START TO THE MORNING, CONTINUED NORTHERLY COLD
ADVECTION SHOULD HOLD HIGH TEMPERATURES MAINLY IN THE 40S THIS
AFTERNOON FOR MOST AREAS. WITH THE EXCEPTION BEING DOWNSTREAM OF
THE LAKE IN NORTHWEST INDIANA WHERE HIGHS MAY STRUGGLE TO WARM
ABOVE THE UPPER 30S. LOWER 50S WILL BE POSSIBLE TOWARD
WESTERN/CENTRAL ILLINOIS WHERE DEEPER MIXING AND EARLIER
CLEARING OF CLOUDS IS EXPECTED.
A SURFACE RIDGE AXIS WILL MOVE OVERHEAD TONIGHT ALLOWING WINDS
TO FLOP EASTERLY IN THE EVENING (LIKELY EARLIER NEAR THE LAKE
BEHIND A LAKE BREEZE) ALONG WITH LEADING TO ANOTHER COLD NIGHT
WITH LOW TEMPERATURES IN THE UPPER 20S TO LOWER 30S. CONTINUED
EAST TO SOUTHEASTERLY FLOW DURING THE DAY ON TUESDAY WILL LEAD
TO CONTINUED COOLER CONDITIONS ACROSS NORTHEAST ILLINOIS
DOWNSTREAM OF LAKE MICHIGAN, WHERE HIGHS MAY ONLY TOP OUT IN THE
LOWER 40S. MID 40S TO LOWER 50S ARE FORECAST GENERALLY SOUTH OF
I-90.
TUESDAY NIGHT THROUGH SUNDAY:
PRIMARY FORECAST CONCERN IS FOR THE POTENTIAL FOR SEVERE STORMS
LATE TUESDAY NIGHT AND WEDNESDAY.
A NARROW AXIS OF PRECIPITATION IS EXPECTED TO DEVELOP EARLY
TUESDAY EVENING ACROSS FAR NORTHERN IL AND INTO SOUTHERN WI.
THERMALLY, IT WILL STILL BE COLD ENOUGH THAT THIS PRECIP MAY BE
IN THE FORM OF A RAIN/SNOW MIX, AT LEAST BRIEFLY, BEFORE
CHANGING TO RAIN AND/OR LIFTING NORTH OF THE STATE LINE. HAVE
MAINTAINED A RAIN/SNOW MIX FOR THIS SHORT PERIOD OF TIME. BASED
ON CURRENT TRENDS, NOT EXPECTING ANY ACCUMULATION.
ATTENTION WILL THEN QUICKLY TURN TO EXPECTED DEVELOPING
CONVECTION OVER IA TUESDAY EVENING THAT WILL LIKELY SPREAD INTO
NORTHERN IL AFTER MIDNIGHT WITH ADDITIONAL THUNDERSTORMS MOVING
ACROSS THE AREA THROUGH THE PREDAWN HOURS. NEW SPC DAY2 IS VERY
SIMILAR TO THE PREVIOUS DAY3 WITH A SLIGHT RISK (2 OF 5) ACROSS
THE WESTERN CWA. MAIN SEVERE THREAT IS EXPECTED TO BE HAIL, BUT
IF STORMS END UP WITH ANY ORGANIZATION, THEN SOME WIND POTENTIAL
WOULD BE POSSIBLE. AS THE LOW LEVEL JET INCREASES, THERE COULD
BE A FEW WAVES OF THUNDERSTORMS AND WITH PRECIPITABLE WATER
VALUES APPROACHING 1 TO 1.25 INCHES BY 12Z WEDNESDAY, HEAVY RAIN
AND LOCALIZED FLOODING WILL ALSO BE POSSIBLE.
HOW THIS ACTIVITY EVOLVES EARLY WEDNESDAY MORNING WILL THEN
AFFECT THE EVOLUTION FOR POTENTIAL SEVERE THUNDERSTORMS ON
WEDNESDAY. MORE WIDESPREAD CONVECTION THAT TAKES LONGER TO END
WEDNESDAY MORNING COULD PUSH THE EFFECTIVE FRONT EAST ENOUGH
THAT NEW THUNDERSTORM DEVELOPMENT WEDNESDAY AFTERNOON MAY ONLY
BE ACROSS THE SOUTHEAST CWA AND MOST MODEL TRENDS WOULD SUPPORT
THIS SOLUTION AT THIS TIME. SHOULD OVERNIGHT CONVECTION NOT BE
AS WIDESPREAD AND/OR END EARLIER, THIS MAY ALLOW NEW STORMS TO
DEVELOP FURTHER WEST, PERHAPS RIGHT OVER THE CWA BEFORE THEY
RACE OFF TO THE EAST.
STILL QUITE A BIT OF UNCERTAINTY FOR THE END OF THE WEEK INTO
THE WEEKEND. THE MODELS AND THEIR ENSEMBLES ARE STILL SHOWING
QUITE A BIT OF SPREAD IN POSSIBILITIES. THE ECMWF SEEMS TO BE
TRENDING WETTER WHILE THE GFS SEEMS TO BE TRENDING DRIER. NO
CHANGES TO THE BLENDED GUIDANCE, WHICH TRENDED CONSIDERABLY
WETTER THIS RUN WITH CHANCE POPS FRIDAY NIGHT THROUGH SATURDAY
NIGHT. MODELS HAVE ALSO BEEN SHOWING A COLDER PATTERN SHIFT FOR
EARLY NEXT WEEK AND LARGELY STILL SHOW THAT, THOUGH LARGE TIMING
DIFFERENCES BASED ON HOW THE LATE WEEK/WEEKEND RAIN PANS OUT.
CMS
AVIATION /12Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 623 AM CDT MON MAR 31 2025
FORECAST CONCERNS INCLUDE...
MVFR CIGS THROUGH EARLY THIS AFTERNOON.
LAKE BREEZE/WIND SHIFT TO NORTHEAST LATE THIS AFTERNOON.
MVFR CIGS WILL SLOWLY SCATTER OUT FROM NORTHWEST TO SOUTHEAST
STARTING LATE THIS MORNING THROUGH MID AFTERNOON. THERE MAY BE A
FEW FLURRIES OR SPRINKLES FOR THE NEXT HOUR OR TWO, BUT WILL NOT
HAVE ANY MENTION WITH THIS FORECAST.
NORTH/NORTHWEST WINDS WILL REMAIN IN THE 10-15KT RANGE INTO
THIS AFTERNOON WITH A FEW GUSTS POSSIBLE TO 20KT THIS MORNING.
WINDS WILL SHIFT TO THE NORTHEAST LATE THIS AFTERNOON FOR THE
CHICAGO TERMINALS AS A LAKE BREEZE MOVES INLAND. WINDS WILL TURN
LIGHT EASTERLY ACROSS THE ENTIRE AREA THIS EVENING AND THEN
SOUTHEASTERLY TUESDAY MORNING. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM CDT TUESDAY FOR THE IL AND IN
NEARSHORE WATERS.
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