547
FXUS63 KLOT 010827
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
327 AM CDT TUE APR 1 2025
KEY MESSAGES
- WAVES OF SHOWERS AND STORMS ARE EXPECTED LATE TONIGHT INTO
WEDNESDAY MORNING. A FEW STORMS MAY BE CAPABLE OF LARGE HAIL
AND GUSTY WINDS.
- ADDITIONAL WAVES OF STORMS ARE EXPECTED LATE WEDNESDAY MORNING
THROUGH EARLY EVENING, SOME OF WHICH COULD BE SEVERE WITH ALL
HAZARDS POSSIBLE.
- PERIODIC RAIN CHANCES WILL RETURN LATE WEEK INTO THE WEEKEND.
DISCUSSION
ISSUED AT 328 AM CDT TUE APR 1 2025
THROUGH WEDNESDAY NIGHT:
THE FORECAST FOCUS IN THE SHORT TERM REMAINS THE POTENTIAL FOR
MULTIPLE WAVES OF THUNDERSTORMS BEGINNING LATE TONIGHT AND
CONTINUING THROUGH THE DAY ON WEDNESDAY, SOME OF WHICH COULD BE
SEVERE.
HIGH PRESSURE IS CURRENTLY CENTERED ACROSS THE WESTERN GREAT
LAKES EARLY THIS MORNING LEADING TO PREDOMINANTLY QUIESCENT
WEATHER IN THE NEAR TERM. A PATCH OF LAKE EFFECT CLOUDS HAVE
KEPT SKIES MOSTLY CLOUDY NEAR THE LAKE FOR MUCH OF THE NIGHT.
WHERE SKIES REMAIN CLEAR FURTHER INLAND, EXPECT TEMPERATURES TO
DROP INTO THE UPPER 20S BY DAYBREAK, WITH LOWER 30S EXPECTED
NEAR THE LAKE AND IN THE CHICAGO METRO.
LEE CYCLOGENESIS IS ANTICIPATED IN THE WY/NE/CO/KS VICINITY
THIS MORNING. THE RESULTANT LOW PRESSURE SYSTEM WILL SERVE AS
THE MAIN DRIVER OF OUR WEATHER OVER THE NEXT 36 HOURS AS IT
DEEPENS AND MOVES NORTHEAST ACROSS THE CENTRAL PLAINS INTO THE
UPPER MIDWEST TONIGHT INTO WEDNESDAY. WARM ADVECTIVE RAIN AND
SNOW SHOWERS HAVE ALREADY DEVELOPED ACROSS NEBRASKA AND SOUTH
DAKOTA EARLY THIS MORNING INDICATING THIS PROCESS IS ALREADY
UNDERWAY. THIS BAND OF PRECIPITATION WILL SHIFT EAST TOWARD THE
AREA THROUGH THE DAY WELL AHEAD OF THE SURFACE LOW. THERE
REMAINS A CHANCE THAT THE SOUTHERN PERIPHERY OF THE BAND MAY
GRAZE FAR NORTHERN ILLINOIS LATE THIS AFTERNOON INTO EARLY
EVENING IN THE FORM OF RAIN AND SNOW, THOUGH THE BETTER
SATURATION REMAINS MOSTLY NORTH OF THE AREA INTO WISCONSIN.
EITHER WAY, NO IMPACTS ARE EXPECTED OTHER THAN PERHAPS SOME
BRIEF REDUCTIONS IN VISIBILITY WHERE SNOW MANAGES TO BECOME THE
PREDOMINANT PRECIPITATION TYPE FOR A SHORT 1-2 HOUR WINDOW.
IN RESPONSE TO THE DEEPENING LOW PRESSURE SYSTEM APPROACHING
THE REGION, SURFACE WINDS ARE EXPECTED TO STEADILY INCREASE LATE
THIS AFTERNOON THROUGH THE EVENING, WITH NON-THUNDERSTORM WIND
GUSTS TO 35-40 MPH EXPECTED AT TIMES OVERNIGHT THROUGH THE DAY
ON WEDNESDAY. WIND ADVISORY LEVEL GUSTS CAN'T BE RULED OUT BUT
CONFIDENCE IS NOT HIGH ENOUGH TO ISSUE WIND HEADLINES ON THIS
SHIFT.
NOT MUCH HAS CHANGED IN OUR THINKING REGARDING THE THUNDERSTORM
POTENTIAL TUESDAY NIGHT THROUGH THE DAY ON WEDNESDAY WITH
MULTIPLE WAVES OF SHOWERS AND STORMS ANTICIPATED, BEGINNING LATE
TONIGHT (MAINLY AFTER MIDNIGHT). SIMILAR TO THE SYSTEM FROM
THIS PAST SUNDAY, EACH MODEL AND THEIR RESPECTIVE RUNS SHOW AND
WILL LIKELY CONTINUE TO SHOW DIFFERENT TIMING, PLACEMENT, AND
COVERAGE FOR THE VARIOUS ROUNDS OF STORMS WHICH ADDS TO THE
FORECAST UNCERTAINTY.
WITH THAT SAID, ELEVATED SHOWERS AND THUNDERSTORMS ARE EXPECTED
TO DEVELOP LATE TONIGHT (MAINLY AFTER MIDNIGHT) AND CONTINUE
THROUGH MUCH OF THE OVERNIGHT HOURS. EFFECTIVE BULK SHEAR AROUND
30-40KT (IN THE MUCAPE LAYER) COMBINED WITH STEEPENING MID-
LEVEL LAPSE RATES WOULD BE SUPPORTIVE OF MARGINALLY SEVERE HAIL
WITH THE STRONGEST STORMS, PARTICULARLY AFTER ~3 AM CDT. WILL
ALSO HAVE TO KEEP AN EYE ON ANY POTENTIAL MESOSCALE GRAVITY WAVE
DEVELOPMENT WHICH COULD LEAD TO LOCALLY STRONG WIND GUSTS
REACHING THE SURFACE. ADDITIONAL ROUNDS OF THUNDERSTORMS ARE
LIKELY TO CONTINUE INTO THE DAYTIME HOURS WEDNESDAY MORNING.
THERE REMAIN CONCERNS THAT THE MULTIPLE ROUNDS OF MORNING
CONVECTION COULD SHIFT THE MOST FAVORABLE CONDITIONS FOR SURFACE
BASED CONVECTION AND ACCORDINGLY SEVERE (AND POTENTIALLY
SIGNIFICANT SEVERE) WEATHER FURTHER SOUTH AND EAST BY THE
AFTERNOON. WITH THAT SAID, THE STRENGTH OF THE LOW-LEVEL MASS
RESPONSE REMAINS CONCERNING (55+ KT AT 925MB AND 70+ KT AT
850MB!) WHICH COULD ALLOW FOR RAPID RECOVERY IN SPITE OF THE
MULTIPLE ROUNDS OF MORNING CONVECTION AMIDST MOSTLY CLOUDY
SKIES. FOR THIS REASON WE PLAN TO CONTINUE MESSAGING THE
POTENTIAL FOR SEVERE WEATHER AREAWIDE ON WEDNESDAY AND IS IN
LINE WITH SPC'S LATEST DAY 2 OUTLOOK MAINTAINING A LEVEL 3 OUT
OF 5 FOR SEVERE WEATHER.
LASTLY, GIVEN THE EXPECTED MULTIPLE ROUNDS OF CONVECTION,
LOCALIZED FLOODING WILL BE POSSIBLE IN LOW-LYING, URBAN, AND
POOR DRAINAGE AREAS.
PETR
THURSDAY THROUGH MONDAY:
PRIMARY FORECAST FOCUS AND CHALLENGE WILL BE PERIODS OF RAIN,
MAINLY IN THE FRIDAY/SATURDAY TIMEFRAME.
THERE IS SOME AGREEMENT THAT THURSDAY/THURSDAY NIGHT WILL BE DRY
FOR THE BULK OF THE AREA. A WEAK WAVE MAY BRING SOME SHOWERS TO
THE SOUTHERN CWA LATER THURSDAY AFTERNOON INTO THURSDAY EVENING.
BLENDED LOW CHANCE POPS FOR THIS POTENTIAL SEEM FINE FROM THIS
DISTANCE. FRIDAY MORNING INTO AT LEAST EARLY FRIDAY AFTERNOON IS
ALSO LOOKING POTENTIALLY DRY AND THEN THE BEST TIME PERIOD FOR
RAIN APPEARS TO BE FROM FRIDAY EVENING THROUGH SATURDAY EVENING.
BETTER ENSEMBLE SUPPORT FROM BOTH THE GFS/ECMWF DURING THIS
TIME PERIOD, VS. 24 HOURS AGO. THOUGH STILL UNCERTAINTY WITH THE
HOW FAR NORTH THE RAINS MAY REACH. CONCERN WILL BE HEAVY RAIN
AND POSSIBLE FLOODING, IF THE HEAVIER RAINS MATERIALIZE ACROSS
THE SOUTHERN CWA. THUNDER WOULD ALSO BE POSSIBLE ACROSS AT LEAST
THE SOUTHERN CWA. BLENDED POPS HAVE INCREASED INTO
LIKELY/CATEGORICAL AND THIS SEEMS REASONABLE BASED ON CURRENT
TRENDS. AFTER THIS PRECIP SHIFTS OUT OF THE AREA SUNDAY, SOLID
ENSEMBLE SUPPORT FOR A COLDER PATTERN INTO EARLY NEXT WEEK WITH
LOW TEMPS POSSIBLY BACK IN THE 20S MONDAY MORNING AND AGAIN
TUESDAY MORNING. CMS
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 1229 AM CDT TUE APR 1 2025
FORECAST CONCERNS INCLUDE...
MVFR CIGS EARLY THIS MORNING.
STRONG/GUSTY SOUTHEAST WINDS TONIGHT.
SCATTERED THUNDERSTORMS EARLY WEDNESDAY MORNING.
AN AREA OF HIGH MVFR CLOUD COVER HAS MOVED SOUTH OFF LAKE
MICHIGAN ACROSS THE CHICAGO TERMINALS. APPEARS THESE CIGS ARE
SLOWLY LIFTING TO LOW VFR BASED ON TRENDS ACROSS SOUTHEAST WI.
PLAN TO HAVE A FEW HOURS AROUND 3KFT AND MONITOR TRENDS FOR THE
09Z UPDATE.
NORTHEAST WINDS REMAIN AROUND 10KT UNDER THIS CLOUD COVER, LOWER
ELSEWHERE. WINDS WILL BECOME EASTERLY BY DAYBREAK AND REMAIN
EAST/SOUTHEAST INTO THIS AFTERNOON. SPEEDS WILL SLOWLY INCREASE
THIS MORNING WITH GUSTS INTO THE 20KT RANGE POSSIBLE THIS
AFTERNOON. DIRECTIONS ARE EXPECTED TO TURN TO THE SOUTHEAST
TONIGHT WITH SPEEDS INCREASING INTO THE 18-20KT RANGE AND GUSTS
INTO THE 30KT RANGE ESPECIALLY LATE THIS EVENING INTO EARLY
WEDNESDAY MORNING.
A BAND OF RAIN/SNOW MIX IS EXPECTED TO QUICKLY MOVE ACROSS
NORTHEAST IA AND FAR NORTHWEST IL LATE THIS AFTERNOON. THIS MAY
STAY JUST NORTH OF RFD BUT CLOSE ENOUGH TO INCLUDE PROB MENTION
WITH THIS FORECAST. RAIN SHOWERS ARE THEN EXPECTED TO DEVELOP
ACROSS NORTHWEST IL IN THE LATE EVENING AND SPREAD ACROSS THE
ENTIRE AREA AFTER MIDNIGHT. AS INSTABILITY INCREASES, SCATTERED
THUNDERSTORMS ARE EXPECTED TO DEVELOP OVERNIGHT AND CONTINUE
THROUGH SUNRISE WEDNESDAY MORNING. THERE MAY BE SEVERAL HOURS OF
SCATTERED THUNDERSTORMS DURING THIS TIME PERIOD. TEMPO MENTION
SEEMS REASONABLE FOR THIS POTENTIAL WITH THE NEW 30 HOUR ORD/MDW
TAFS. CMS
MARINE
ISSUED AT 328 AM CDT TUE APR 1 2025
- GALE WARNING NOW IN EFFECT FROM 1 AM TO 6 PM CDT WEDNESDAY
A DEEP SURFACE LOW TRACKING TOWARD THE UPPER MISSISSIPPI VALLEY
LATE TUESDAY NIGHT INTO WEDNESDAY MORNING WILL TIGHTEN THE
PRESSURE GRADIENT OVER SOUTHERN LAKE MICHIGAN. THE RESULT WILL
BE STRENGTHENING EAST-SOUTHEAST WINDS. WITH SUFFICIENTLY COOL
AIR TEMPS OVER THE LAKE LATE TUESDAY EVENING INTO WEDNESDAY
MORNING FOR AT LEAST SLIGHTLY UNSTABLE CONDITIONS, CONCERN HAS
INCREASED FOR A PERIOD OF GALES.
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.
PETR/CASTRO
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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