443
FXUS63 KLOT 272346
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
646 PM CDT THU MAR 27 2025
KEY MESSAGES
- SCATTERED SHOWERS AND STORMS ARE EXPECTED TO DEVELOP ACROSS
THE REGION OVERNIGHT. A FEW STORMS WILL PRODUCE PEA TO NICKEL
SIZE HAIL.
- FRIDAY WILL BE WARM AND BREEZY WITH HIGHS IN THE 70S AND
SOUTHWESTERLY WINDS GUSTING 30 TO 40 MPH.
- RAIN AND/OR THUNDERSTORMS POSSIBLE AT TIMES OVER THE WEEKEND
WITH A SUBSTANTIAL TEMPERATURE GRADIENT STALLED ACROSS
NORTHERN ILLINOIS. SOME THUNDERSTORMS SUNDAY AFTERNOON COULD
BE SEVERE AND PRODUCE DAMAGING WINDS, ESPECIALLY TOWARD
CENTRAL ILLINOIS AND INDIANA.
DISCUSSION
ISSUED AT 208 PM CDT THU MAR 27 2025
THROUGH FRIDAY NIGHT:
RAP-MESOANALYSIS DATA AUGMENTED BY OBSERVATIONS DEPICT A BROAD
REGION OF LOW SURFACE PRESSURE ALONG THE LEE SIDE OF THE ROCKY
MOUNTAINS WELL TO THE WEST OF A SURFACE HIGH PRESSURE SYSTEM
CENTERED OVER THE CAROLINAS. A BROAD WARM FRONTAL ZONE EXTENDS
EASTWARD FROM THE REGION OF LOW PRESSURE FROM THE DAKOTAS
THROUGH THE MIDDLE MISSISSIPPI RIVER VALLEY. SHOWERS AND A FEW
THUNDERSTORMS CONTINUE TO FESTER ALONG THE TERMINUS OF A REMNANT
LOW-LEVEL JET AND WITHIN A REGION OF PERSISTENT MID-LEVEL
FRONTOGENESIS ACTING UPON THE BROAD WARM FRONTAL ZONE, MAINLY
FROM NORTHWESTERN MO INTO CENTRAL IL. OUR AREA HENCE REMAINS
CLOUDED OVER, LEADING TO MUTED TEMPERATURES AND LIGHT WINDS.
TONIGHT, THE BROAD REGION OF LOW PRESSURE WELL TO OUR WEST WILL
CONSOLIDATE AND SHIFT EASTWARD INTO THE NORTHERN PLAINS. AS THIS
OCCURS, LOW- TO MID-LEVEL SOUTHWESTERLY FLOW WILL INCREASE ACROSS
THE MID-MISSISSIPPI RIVER VALLEY, FACILITATING THE NORTHEASTWARD
ADVECTION OF A RESERVOIR OF STEEP MID-LEVEL LAPSE RATES (AN
ELEVATED MIXED LAYER, OR EML) NORTHEASTWARD INTO THE GREAT
LAKES. AS THE WARM FRONTAL ZONE SHARPENS AND LOW-LEVEL JET
REINTENSIFIES OVERNIGHT IN OUR GENERAL REGION, ISENTROPIC
SURFACES WILL BECOME INCREASINGLY SLOPED ALLOWING FOR EFFICIENT
UPGLIDE. WHILE CONFIDENCE IN SHOWERS AND STORMS DEVELOPING IS
HENCE HIGH (>90% CHANCE IN OUR GENERAL REGION), EXACTLY WHERE
CARRIES LOWER CONFIDENCE (40-60% AT ANY GIVEN POINT) OWING TO
DIFFERENCES AMONGST MODEL SUITES AND THE RATE AT WHICH THE BASE
OF THE EML MOISTENS. GLOBAL GUIDANCE SUCH AS THE EPS/GEFS FAVORS
THE AXIS OF SHOWERS AND STORMS EXTENDING FROM SOUTHEASTERN IOWA
TO CENTRAL INDIANA, WHILE HIGH-RES GUIDANCE SUMMARIZED BY THE
HREF FAVORS THE AXIS FURTHER TO THE NORTH FROM EASTERN IOWA TO
LAKE MICHIGAN. THIS IS A FAIRLY TYPICAL SOURCE OF FORECAST
UNCERTAINTY WITH CONVECTION ALONG A NORTHEASTWARD-ADVANCING EML
PLUME AND INTENSIFYING LOW-LEVEL JET, AND CAN BE PRONE TO
SIZABLE FORECAST ERRORS IN OBSERVED LOCATIONS OF STORMS.
REGARDLESS OF WHERE STORMS DO DEVELOP, MODEST CONVECTIVE-LAYER
SHEAR OF 20-25KT AND RELATIVELY LOW FREEZING LEVELS NEAR 10KFT
WILL SUPPORT PERIODIC INSTANCES OF PEA TO NICKEL SIZE HAIL, IN
ADDITION TO HEALTHY DOWNPOURS AND FREQUENT LIGHTNING STRIKES.
(NOTE THAT HREF 48-HOUR PMM QPF SUPPORTS A FEW SWATHS OF >1"
RAIN SOMEWHERE IN OUR GENERAL REGION OVERNIGHT).
SHOWERS AND STORMS MAY LINGER BEYOND DAYBREAK ACROSS
NORTHEASTERN OR EASTERN ILLINOIS TOMORROW MORNING UNTIL THE
CONTINUED EASTWARD- ADVANCEMENT OF THE SURFACE LOW TO OUR
NORTHWEST PULLS THE WARM FRONT INTO WISCONSIN. DECREASING
CLOUDINESS WILL ALLOW FOR MIXING HEIGHTS TO QUICKLY BUILD UPWARD
INTO THE REMNANT LOW-LEVEL JET, THOUGH A STRENGTHENING LOW-
LEVEL INVERSION MAY TEND TO LIMIT THE EFFICIENCY WITH WHICH
WINDS CAN MIX TO THE GROUND (E.G. WAA-DRIVEN WINDS). WITH THAT
SAID, FORECAST MIXING PROFILES AMONG HRRR/RAP/NAM3 DATA SUPPORT
FREQUENT GUSTS OF 30 TO 40 MPH. TEMPERATURES WILL ALSO ROCKET
UPWARD TOMORROW, WITH 850MB TEMPERATURES NORTH OF +10C AND AT
LEAST PARTIAL SUNSHINE SUPPORTING HIGHS WELL INTO THE 70S. IN
ALL, TOMORROW WILL LOOK AND FEEL QUITE A BIT DIFFERENT COMPARED
TO TODAY.
WINDS WILL REMAIN BREEZY AFTER SUNSET TOMORROW NIGHT AS
TEMPERATURES ONLY GRADUALLY FALL (OFFSETTING IMMEDIATE
DECOUPLING). OVERNIGHT LOWS WILL FALL TOWARD THE UPPER 50S.
BORCHARDT
ISSUED AT 327 PM CDT THU MAR 27 2025
SATURDAY THROUGH THURSDAY:
A SURFACE LOW WILL QUICKLY TRACK EASTWARD ACROSS CENTRAL
WISCONSIN FRIDAY NIGHT. AN ASSOCIATED COLD FRONT IS EXPECTED TO
SHIFT SOUTHWARD TOWARD NORTHERN ILLINOIS LATE FRIDAY NIGHT AND
SATURDAY, WITH CONTINUED NOTABLE MODEL SPREAD IN THE SOUTHWARD
EXTENT OF THE FRONT. THE GEFS AND RELATED DETERMINISTIC GFS HAVE
TRENDED MUCH FARTHER NORTH AND MORE INLINE WITH THE EPS/CMCE,
WHICH DOES INCREASE CONFIDENCE THAT THE FRONT WILL NOT SURGE
THROUGH THE ENTIRE AREA DURING THE DAY SATURDAY. BUT BOTH
CLIMATOLOGY AND PATTERN RECOGNITION WOULD SUGGEST GUIDANCE MAY
BE A BIT FARTHER NORTH THAN WHAT ULTIMATELY CONSPIRES. THE
LATEST OFFICIAL FORECAST SHOWS THE FRONT PUSHING OVER FAR
NORTHEAST ILLINOIS DURING THE MORNING, SHIFTING SOUTHWARD TO
NEAR THE I-80 CORRIDOR IN THE AFTERNOON, THEN STALLING DURING
THE NIGHT. MAX TEMPS IN THE MID 70S ARE LIKELY SOUTH OF I-80 ON
SATURDAY WHILE TEMPS IN THE 50S AND 60S FALL THROUGH THE
AFTERNOON. BEHIND THE FRONT, DRIZZLE OR FOG IS POSSIBLE.
MEANWHILE, A CONVECTIVELY-ENHANCED WAVE OVER EASTERN TEXAS WILL
SHIFT ACROSS INDIANA AND RESULT IN A POCKET OF SHOWERS AND
PERHAPS A FEW STORMS EAST OF I-57 SATURDAY AFTERNOON INTO THE
EVENING.
FOCUS THEN TURNS TO THE POTENTIAL FOR SEVERE WEATHER OVER AT
LEAST PART OF THE FORECAST AREA ON SUNDAY. VEERING LOW-LEVEL
FLOW WITH ONLY SPOTTY UPSTREAM PRECIP SATURDAY NIGHT SHOULD
ALLOW THE FRONT TO RETREAT NORTHWARD AS A WARM FRONT. A LARGER
SURFACE LOW WILL THEN TRAVERSE ALONG OR NEAR THE WARM FRONT
SOMEWHERE ACROSS NORTHERN ILLINOIS ON SUNDAY. LIKE ON SATURDAY,
THE GEFS HAS TRENDED MUCH FARTHER NORTH WITH THE WARM FRONT,
WITH MUCH OF THE GUIDANCE NOW PUTTING AT LEAST THE SOUTHERN HALF
OF THE CWA IN THE WARM SECTOR. IMPRESSIVE MID TO UPPER-LEVEL
DYNAMICS, SPECIFICALLY WITH AN INCOMING 70 KNOT MID-LEVEL JET
STREAK, OVER MODEST LOW-LEVEL MOISTURE ADVECTION WILL SUPPORT A
SEVERE STORM RISK SOUTH OF I-80, AND POTENTIALLY FARTHER NORTH
AND WEST DEPENDING ON IF/WHERE THE WARM FRONT STALLS DUE TO THE
INFLUENCE OF LAKE MICHIGAN. SHEAR VECTORS AND SOMEWHAT
UNIDIRECTIONAL LOW-LEVEL FLOW FAVOR LINEAR/BOWING CONVECTIVE
SEGMENTS WITH WIND DAMAGE AS THE PRIMARY THREAT (LARGE HAIL WITH
ANY MORE DISCRETE CELLS). BUT AGAIN CLIMATOLOGICALLY SPEAKING,
BOTH THE STORM MODE (BROKEN/BOWING SEGMENTS) IN THIS AREA AND
THE POTENTIAL FOR A STALLED WARM FRONT DOES SUPPORT A LOW END
TORNADO RISK (PARTICULARLY QLCS). STILL A FEW DAYS OUT TO REFINE
THESE DETAILS, WITH FRONTAL LOCATION BEING A SIGNIFICANT FACTOR
WITH HOW THE FORECAST EVOLVES THIS WEEKEND.
AS THE MAIN TROUGH AXIS CROSSES THE FORECAST AREA SUNDAY NIGHT,
A RESIDUAL BAND OF RAIN SHOULD MIX WITH OR EVEN TRANSITION TO
SNOW. THERE IS A LOW (10%) CHANCE OF SOME MINOR SLUSHY
ACCUMULATIONS LATE SUNDAY NIGHT INTO MONDAY MORNING, BUT OVERALL
EXPECTATIONS ARE FOR LITTLE IMPACT AT THIS TIME. DRIER AND
COLDER CONDITIONS WILL FOLLOW THROUGH TUESDAY WITH HIGHS
GENERALLY IN THE 40S. LONG-TERM ENSEMBLE GUIDANCE CONTINUES TO
HIGHLIGHT ANOTHER STRONG MID-LATITUDE CYCLONE ACROSS THE CENTRAL
CONUS WEDNESDAY INTO THURSDAY MORNING. FORECAST UNCERTAINTY IS
QUITE HIGH LOCALLY AS THE ASSOCIATED WARM FRONT IS FAVORED TO
SETTLE ACROSS THE WESTERN GREAT LAKES REGION. ANY PUSH INTO THE
WARM SECTOR OF THIS SYSTEM WILL BRING AN INCREASE IN SEVERE
STORM POTENTIAL.
KLUBER
AVIATION /00Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 646 PM CDT THU MAR 27 2025
FORECAST CONCERNS FOR THE TERMINALS...
- RAIN SHOWERS WITH EMBEDDED THUNDERSTORMS EXPECTED LATE TONIGHT
INTO FRIDAY MORNING. A FEW STORMS COULD BE STRONG WITH
INSTANCES OF HAIL.
- MVFR CEILINGS TO DEVELOP WITH THE RAIN AND PERSIST THROUGH
FRIDAY MORNING WITH IFR CONDITIONS POSSIBLE WITH
THUNDERSTORMS.
- GUSTY SOUTHWEST WINDS FRIDAY AFTERNOON WITH GUSTS IN EXCESS
OF 35 KTS POSSIBLE.
THE EARLIER SPRINKLES HAVE LARGELY COME TO AN END ACROSS THE
AREA THIS EVENING, BUT AN ADDITIONAL PERIOD OF SHOWERS AND
THUNDERSTORMS IS EXPECTED LATE TONIGHT INTO FRIDAY MORNING. IN
THE MEANTIME EXPECT OVERCAST VFR SKIES AND LIGHT SOUTHEAST WINDS
AROUND 5-10 KTS.
THE NEXT ROUND OF SHOWERS WILL BEGIN TO MOVE INTO NORTHERN IL
AND NORTHWEST IN AROUND 05-06Z AHEAD OF A WARM FRONT WITH A MORE
ROBUST LINE OF SHOWERS AND EMBEDDED THUNDERSTORMS ARRIVING
AROUND 08-09Z. WHILE THE THUNDERSTORMS SHOULD ONLY LAST A FEW
HOURS AT ANY ONE LOCATION, THE SHOWERS ARE EXPECTED TO PERSIST
THROUGH FRIDAY MORNING BEFORE CONDITIONS IMPROVE FOR THE
AFTERNOON. ADDITIONALLY, THERE IS THE POTENTIAL FOR A FEW STORMS
TO BECOME STRONG TO POSSIBLY SEVERE WITH A THREAT FOR HAIL UP
TO AN INCH IN DIAMETER ESPECIALLY FOR AREAS SOUTH OF VYS TO RZL
LINE.
CEILINGS WILL ALSO BE LOWERING TO MVFR WITH THE SHOWERS TONIGHT
AND PERSISTING THROUGH EARLY AFTERNOON BEFORE SKIES SCATTER BACK
TO VFR FOR THE REMAINDER OF THE PERIOD. POCKETS OF IFR CEILINGS,
AND VISIBILITIES, ARE LIKELY WITH ANY EMBEDDED THUNDERSTORMS BUT
SHOULD IMPROVE BACK TO MVFR BY DAYBREAK FRIDAY MORNING. FINALLY,
WINDS WILL INCREASE FRIDAY MORNING AS DIRECTIONS SHIFT FROM
SOUTHEASTERLY TO SOUTHWESTERLY BY MID-MORNING. GUSTS DURING THE
AFTERNOON ARE EXPECTED TO PEAK AROUND 35 KTS, BUT HIGHER GUSTS
NEAR 40 KTS ARE POSSIBLE. WHILE THE GUSTS ARE FORECAST TO
SUBSIDE FRIDAY EVENING, LOCALIZED 20-30 KT GUSTS MAY LINGER
THROUGH FRIDAY NIGHT. FURTHERMORE, THERE IS ALSO THE POTENTIAL
FOR SOME LOW-LEVEL WIND SHEAR TO MATERIALIZE FRIDAY NIGHT IF
GUSTS SUBSIDE. SINCE THE LLWS THREAT IS LOWER CONFIDENCE HAVE
DECIDED TO FOREGO A FORMAL MENTION AT THIS TIME.
YACK
MARINE
ISSUED AT 208 PM CDT THU MAR 27 2025
THURSDAY NIGHT INTO FRIDAY, A SEASONABLY STRONG LOW PRESSURE
SYSTEM WILL MOVE FROM THE NORTHERN PLAINS TOWARD THE GREAT LAKES
CAUSING A SURFACE WARM FRONT TO LIFT NORTHWARD THROUGH THE
REGION. BEHIND THE FRONT, SOUTHWESTERLY WINDS WILL INCREASE IN
MAGNITUDE WITH GALE FORCE GUSTS IN EXCESS OF 35 KT POSSIBLE,
STARTING FRIDAY AFTERNOON AND LASTING THROUGH EARLY SATURDAY
MORNING. SINCE WATER TEMPERATURES REMAIN COLD (LEADING TO
STABILITY OVER THE LAKE), THE THREAT FOR GALE FORCE WINDS WILL
BE WITHIN THE FIRST 2 TO 3 MILES OF THE LAKESHORE. A GALE WATCH
REMAINS IN EFFECT FOR THE ILLINOIS AND A PORTION OF THE
NORTHWESTERN INDIANA NEARSHORE FRIDAY AFTERNOON THROUGH EARLY
SATURDAY MORNING.
NWS CHICAGO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...GALE WATCH FROM FRIDAY AFTERNOON THROUGH LATE FRIDAY NIGHT FOR
THE IL AND IN NEARSHORE WATERS.
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