418
FXUS63 KLOT 012008
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
308 PM CDT TUE APR 1 2025
KEY MESSAGES
- SHOWERS/T-STORMS EXPECTED TO DEVELOP LATE THIS EVENING AND
CONTINUE AT TIMES INTO WEDNESDAY MORNING WITH THREAT FOR
LOCALLY HEAVY RAINFALL AND PERHAPS SOME ISOLATED OCCURRENCES
OF MARGINALLY SEVERE HAIL.
- CONDITIONAL THREAT OF SEVERE THUNDERSTORMS WEDNESDAY AFTERNOON
INTO EARLY EVENING.
- STRONG SYNOPTIC SOUTHERLY WINDS EXPECTED WEDNESDAY AFTERNOON,
GUSTS TO 45+ MPH POSSIBLE AREA WIDE, HIGHEST THREAT SOUTH OF
I-80.
DISCUSSION
ISSUED AT 308 PM CDT TUE APR 1 2025
THROUGH WEDNESDAY NIGHT:
STRONG CYCLOGENESIS IS UNDERWAY OVER THE CENTRAL HIGH PLAINS
WITH A 988MB LOW NEAR THE KANSAS/COLORADO BORDER EARLY THIS
AFTERNOON. A STRONG (130KT 250MB) PACIFIC JET IS ROUNDING THE
BASE OF THE LONGWAVE TROUGH OVER THE WESTERN HALF OF THE COUNTRY
AND WILL BE SPINNING UP A VIGOROUS MID-LATITUDE CYCLONE FROM
THE CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY BY
WEDNESDAY AFTERNOON.
TONIGHT INTO EARLY WEDNESDAY MORNING:
STRENGTHENING WARM FRONT WILL BEGIN LIFTING NORTH ACROSS THE
MISSISSIPPI VALLEY TONIGHT AS VERY STRONG 60-70KT SOUTHERLY LOW
LEVEL JET DEVELOPS IN RESPONSE TO STRONG HEIGHT FALLS. THIS
POWERHOUSE LOW LEVEL JET WILL RAPIDLY TRANSPORT MOISTURE
NORTHWARD AND UPWARD STEEPLY SLOPED ISENTROPIC SURFACES
(290-300K). THIS EXTREMELY STRONG ISENTROPIC ASCENT SHOULD
RESULT IN INCREASING COVERAGE OF SHOWERS AND THUNDERSTORMS
ACROSS NORTHERN IL AND POSSIBLY NW INDIANA LATE THIS EVENING
INTO THE OVERNIGHT HOURS. THE HIGHEST CHANCES OF RAIN LOOK TO BE
NORTH OF I-80 WITH LESSER CHANCES WITH SOUTHWARD EXTENT. HARD
TO PINPOINT A SOUTHERN TERMINUS OF THE RAIN CHANCES, SO WHILE
POPS ARE LOWER ACROSS THE SOUTHERN CWA, THERE REMAINS A CHANCE
OF SHOWERS/STORMS.
THE RAPID NORTHWARD TRANSPORT OF THIS HIGHER THETA-E AIR MASS
BENEATH MODERATELY STEEP LAPSE RATES SHOULD RESULT IN MUCAPE
VALUES OF 500 TO LOCALLY OVER 1000 J/KG LATE TONIGHT INTO EARLY
WEDNESDAY MORNING. FORECAST SOUNDINGS SUGGEST EFFECTIVE SHEAR
IN THE 30-40KT RANGE COINCIDING WITH THIS MODERATE INSTABILITY,
SO IT'S POSSIBLE THERE COULD BE SOME OCCASIONALLY MORE INTENSE
CELLS/TRANSIENT SUPERCELLS POSING A THREAT OF ISOLATED
INSTANCES OF HAIL 1"+ IN DIAMETER. WHILE STORM MOTION SHOULD BE
VERY FAST, THERE IS A POTENTIAL FOR SOME TRAINING OF CONVECTION
WHICH COULD RESULT IN SOME LOCALIZED 1-2" TOTALS IN JUST AN
HOUR OR SO. MOST OF OUR CWA COULD HANDLE THAT TYPE OF RAINFALL
WITH JUST MINOR/NUISANCE TYPE FLOODING, BUT SHOULD THAT
MAGNITUDE OF RAIN OCCUR IN A MORE URBANIZED/POOR DRAINAGE AREA,
THEN THERE WOULD BE A THREAT OF SOME LOW END AND LOCALIZED FLASH
FLOODING.
LATE WEDNESDAY MORNING INTO EARLY WEDNESDAY EVENING:
MORNING SHOWERS AND THUNDERSTORMS ARE LIKELY TO SLOW THE
NORTHWARD ADVANCE OF THE WARM FRONT DURING THE MORNING AND
PERHAPS EARLY AFTERNOON HOURS, LIKELY AIDED BY THE CHILLY
EASTERLY FLOW OFF THE LAKE. IN FACT, TEMPS NEAR THE LAKE IN THE
IMMEDIATE CHICAGO METRO AREA COULD BE IN THE UPPER 30S OR LOWER
40S WEDNESDAY MORNING INTO THE EARLY AFTERNOON. EVENTUALLY, THE
POWERFUL SYNOPTIC LOW SHOULD OVERWHELM ANY LINGERING MESOSCALE
EFFECTS AND ALLOW THE WARM FRONT TO RAPIDLY LIFT NORTHWARD
ACROSS OUR CWA WEDNESDAY AFTERNOON. TEMPERATURES WILL QUICKLY
CLIMB WELL INTO THE 60S TO LOWER 70S IN THE WAKE OF THE WARM
FRONTAL PASSAGE WITH DEWPOINTS INTO THE LOWER 60S, SO A VERY
DRAMATIC AIR MASS CHANGE WILL TAKE PLACE WEDNESDAY AFTERNOON,
PARTICULARLY NEAR THE LAKE.
TYPICALLY, NOCTURNAL ELEVATED CONVECTION LASTING WELL INTO THE
MORNING WOULD PROVE TO BE PRETTY DETRIMENTAL TO AFTERNOON
CONVECTIVE POTENTIAL. HOWEVER, IN THIS CASE WITH SUCH A POWERFUL
CYCLONE TO OUR NORTH, THERE IS CONCERN THAT THERE COULD BE
RAPID RECOVERY OF THE AIR MASS DURING THE AFTERNOON. MOST
GUIDANCE DEPICTS AND AXIS OF 750-1500 J/KG OF MLCAPE DEVELOPING
AHEAD OF THE FRONT THAT WILL BE ADVANCING ACROSS OUR AREA DURING
THE LATE AFTERNOON/EARLY EVENING.
THE FORECAST SHEAR PROFILES ARE VERY CONCERNING WED AFTERNOON
AND EVENING WITH 40-50KT OF SOUTH-SOUTHWESTERLY FLOW AT 925 MB
VEERING TO SOUTHWESTERLY AT OVER 100KT AT 500MB. THIS RESULTS IN
VERY LONG AND EXCEPTIONALLY FAVORABLE HODOGRAPHS FOR
SUPERCELLS. VERY LARGE, CYCLONICALLY CURVED HODOGRAPHS IN THE
0-1KM LAYER WITH MOSTLY STREAMWISE VORTICITY ALSO WOULD FAVOR
THE POTENTIAL FOR TORNADOES, ESPECIALLY GIVEN THE LOW LCLS.
WHILE THE SHEAR PROFILES ARE EXTREME, THERE REMAINS CONSIDERABLE
UNCERTAINTY. FIRST, DOES THE FORECAST MAGNITUDE OF INSTABILITY
ACTUALLY MATERIALIZE AS MODELED TOMORROW AFTERNOON. SECOND,
CONVERGENCE LOOKS RATHER WEAK ALONG THE FRONT AND IT IS UNCLEAR
IF IT WILL BE ENOUGH FOR CONVECTIVE INITIATION, ASSUMING
SUFFICIENT INSTABILITY. FINALLY, GUIDANCE GENERALLY HAS OUR CWA
IN THE CONVERGENT, RIGHT EXIT REGION OF THE STRONG UPPER LEVEL
JET.
ULTIMATELY, THERE ARE MANY POTENTIAL SCENARIOS WHERE WE END UP
WITH ONLY WEAK, NON-SEVERE CONVECTION IN THE LATE
AFTERNOON/EARLY EVENING OR NO CONVECTION AT ALL. UNFORTUNATELY,
GIVEN SUFFICIENT INSTABILITY AND INTENSE CONVECTION DEVELOPS,
THE POTENTIAL WOULD EXIST FOR FAST MOVING TORNADIC SUPERCELLS,
WITH THE POTENTIAL FOR STRONG TORNADOES.
OUTSIDE OF THE THUNDERSTORM THREAT WEDNESDAY AFTERNOON,
SOUTHERLY WINDS COULD GUST TO, OR EVEN OVER 45 MPH WEDNESDAY
AFTERNOON SOUTH OF THE WARM FRONT. THERE ARE STILL UNCERTAINTIES
AS TO HOW FAR NORTH INTO OUR CWA THAT THE POTENTIAL FOR 45+ MPH
GUSTS WILL EXTEND, BUT SEEMS PLAUSIBLE (LIKELY?) THAT THE
OVERNIGHT SHIFT WILL NEED TO CONSIDER A WIND ADVISORY FOR AT
LEAST OUR SOUTHERN CWA.
- IZZI
THURSDAY THROUGH TUESDAY:
THE SURFACE COLD FRONT THAT SHIFTS ACROSS OUR AREA ON WEDNESDAY
WILL STALL OUT ACROSS THE OHIO VALLEY FOR THE SECOND HALF OF THE
WEEK. THIS FRONT WILL BECOME THE PRIMARILY FOCUS FOR SEVERAL
ADDITIONAL ROUNDS OF HEAVY RAIN PRODUCING SHOWERS AND
THUNDERSTORMS INTO THE WEEKEND AS DEEP GULF MOISTURE CONTINUALLY
FEEDS INTO THIS FRONTAL ZONE. A MAJORITY OF THIS HEAVY RAIN IS
EXPECTED TO FALL SOUTH OF OUR AREA ACROSS SOUTHERN PARTS OF IL
AND IN, ESPECIALLY ON THURSDAY INTO FRIDAY. BOTH DAYS ARE THUS
EXPECTED TO REMAIN LARGELY DRY ACROSS OUR AREA, WITH THE
EXCEPTION OF SOME CHANCES FOR LIGHT RAIN MAINLY SOUTH OF I-80.
LATE FRIDAY THROUGH SATURDAY, SEVERAL LOW AMPLITUDE IMPULSES WILL
EJECT NORTHEASTWARD OUT OF AN UPPER-LEVEL TROUGH/LOW SHIFTING
ACROSS THE DESERT SOUTHWEST. EACH IMPULSE WILL AID IN THE
NORTHWARD PUSH OF MOISTURE OVER THE SURFACE FRONTAL BOUNDARY, THUS
SUPPORTING INCREASING RAIN (AND PERHAPS A FEW EMBEDDED
THUNDERSTORMS) CHANCES ACROSS MUCH OF OUR AREA FRIDAY AFTERNOON
INTO SATURDAY. RAIN CHANCES WILL PEAK IN THE 70 TO 90% RANGE
AREAWIDE FRIDAY NIGHT, THOUGH THE HEAVIEST RAINFALL IS CURRENTLY
FAVORED TO FALL SOUTH OF I-80. A PERIOD OF DRIER WEATHER IS
FAVORED FOR THE END OF THE WEEKEND.
TEMPERATURES THROUGH THE PERIOD WILL REMAIN SEASONAL, WITH
DAYTIME HIGHS GENERALLY IN THE 50S THROUGH SUNDAY. HOWEVER,
ONSHORE NORTHERLY WINDS FRIDAY INTO THE WEEKEND WILL RESULT IN
COOLER CONDITIONS (IN THE 40S) NEAR THE LAKE MICHIGAN SHORE. A
PERIOD OF COOLER (BELOW AVERAGE) WEATHER ALSO LOOKS TO BE ON TAP
FOR THE AREA EARLY NEXT WEEK AS A NORTHERN STREAM TROUGH DIGS IN
OVER THE GREAT LAKES. THIS COULD SUPPORT AT LEAST A DAY OR TWO
WITH HIGHS IN THE 40S AND SUBFREEZING OVERNIGHT LOWS.
KJB
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 1243 PM CDT TUE APR 1 2025
THE MAIN AVIATION WEATHER CONCERNS FOR THE 18Z TAF PERIOD
INCLUDE:
* A SYSTEM OF SHOWERS AND THUNDERSTORMS IMPACTING ALL SITES
TONIGHT THROUGH THE DAY WEDNESDAY WITH ASSOCIATED MVFR/IFR
EXPECTED.
* GUSTY SE WINDS THIS EVENING INTO WEDNESDAY, GOING SW LATE
WEDNESDAY AFTERNOON
A LARGE SYSTEM OF SHOWERS AND THUNDERSTORMS WILL IMPACT ALL TAF
SITES BEGINNING TONIGHT AND LAST THROUGH THE DAY ON WEDNESDAY.
STORMS COULD BE STRONG TO SEVERE AT TIMES. PRIOR TO THE MAIN
PUSH OF RAIN, A BRIEF POTENTIAL EXISTS FOR A LIGHT, GENERALLY
NON- IMPACTFUL RAIN/SNOW MIX TO MOVE OVER FAR NORTHERN IL LATE
THIS AFTERNOON. CHANCES FOR THIS ARE HIGHEST (STILL MARGINAL) AT
RFD, ALTHOUGH IT'S A POSSIBILITY THAT THE CHICAGOLAND SITES GET
CLIPPED WITH SOME VERY LIGHT PRECIP.
RAIN WILL THEN FILL IN FROM THE WEST THIS EVENING. THUNDERSTORMS
ARE EXPECTED TO MIX IN OVERNIGHT. DURING THE LATTER PART OF
THE NIGHT AND TOWARD DAYBREAK, IT'S POSSIBLE THAT A FEW OF THESE
STORMS PRODUCE SOME HAIL. SHOWERS, HEAVY AT TIMES, AND EMBEDDED
STORMS WILL CONTINUE THROUGH MOST OF WEDNESDAY. ADDITIONAL
STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE DURING THE
LATTER PART OF THE AFTERNOON. CIGS WILL GO MVFR OVERNIGHT WITH
IFR EXPECTED DURING THE BULK OF THE MORNING BEFORE A RETURN TO
MVFR DURING THE AFTERNOON. PERIODS OF MVFR TO IFR VSBYS ARE ALSO
ANTICIPATED, PARTICULARLY UNDERNEATH ANY HEAVIER SHOWERS OR
STORMS.
ADDITIONALLY, WINDS OUT OF THE EAST WILL LARGELY REMAIN IN THE
10 TO 15 KT RANGE THIS AFTERNOON BEFORE BUILDING DURING THE
EVENING. 25 TO 30 KT GUSTS ARE EXPECTED FOR THE BETTER PART OF
TONIGHT AND WEDNESDAY, WITH PERIODS OF EVEN STRONGER GUSTS
LIKELY, ESPECIALLY LATE TONIGHT AND LATE WEDNESDAY AFTERNOON.
DIRECTION WILL VEER FROM E TO SE THIS EVENING, AND THEN ONTO SSW
WEDNESDAY AFTERNOON.
DOOM
MARINE
ISSUED AT 308 PM CDT TUE APR 1 2025
- GALE WARNING REMAINS IN EFFECT FROM 1 AM TO 6 PM CDT WEDNESDAY
A DEEP SURFACE LOW TRACKING TOWARD THE UPPER MISSISSIPPI VALLEY
LATE TONIGHT INTO WEDNESDAY MORNING WILL TIGHTEN THE PRESSURE
GRADIENT OVER SOUTHERN LAKE MICHIGAN. THE RESULT WILL BE
STRENGTHENING EAST-SOUTHEAST WINDS. A PERIOD OF EAST-SOUTHEASTERLY
GALES REMAINS POSSIBLE OVERNIGHT INTO WEDNESDAY MORNING.
THEN, AS THE DEEP SURFACE LOW TRACKS TOWARD NORTHERN LAKE
MICHIGAN LATER WEDNESDAY, ITS WARM FRONT WILL LIFT NORTH AND BRING
A SHIFT TO STRONG SOUTH-SOUTHWEST WINDS WEDNESDAY AFTERNOON.
WHILE CLOUD COVER AND ONGOING SHOWERS AND THUNDERSTORMS MAY LIMIT
MIXING DEPTHS ON LAND, A PERIOD OF GALES INTO THE FIRST COUPLE
MILES OF THE NEARSHORE WILL ALSO BE POSSIBLE WEDNESDAY
AFTERNOON.
NWS CHICAGO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 1 AM CDT
WEDNESDAY FOR THE IL AND IN NEARSHORE WATERS.
GALE WARNING FROM 1 AM TO 6 PM CDT WEDNESDAY FOR THE IL AND IN
NEARSHORE WATERS.
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