763
FXUS63 KLOT 280601
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
101 AM CDT FRI MAR 28 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.
UPDATE
ISSUED AT 945 PM CDT THU MAR 27 2025
OVERALL, THE FORECAST APPEARS TO BE IN GOOD SHAPE. WARM
ADVECTION IS INTENSIFYING THIS EVENING AS STRENGTHENING
SOUTHWESTERLY WINDS IN THE 925-700 MB LAYER ARE BEGINNING TO CUT
ACROSS TIGHTLY PACKED ISENTROPES PER RECENT MODEL ANALYSES.
RECENT NIGHTTIME MICROPHYSICS RGB IMAGERY REVEALS THAT STRATUS
IS EXPANDING SOUTH AND WESTWARD INTO SOUTHEAST IOWA AND CENTRAL
ILLINOIS. A FEW PRECIPITATION CORES HAVE ALSO RECENTLY STARTED
SPROUTING FROM DEEPER CLOUD COVER OFF TO OUR SOUTH AND WEST.
MODEL GUIDANCE IS ONLY VARYING-DEGREES OF MARGINALLY HELPFUL
THIS EVENING. THESE TYPES OF REGIMES ARE USUALLY EXCEEDINGLY
DIFFICULT FOR GUIDANCE TO HANDLE, AS INTENSE ISENTROPIC UPGLIDE
INTERACTS WITH RELATIVELY THIN POCKETS OF MOISTURE WITH
BUILDING CONDITIONAL INSTABILITY. A SMALL MISDIAGNOSIS HERE AND
THERE OF THE RH FIELDS IS ALL THAT SEPARATES A MODEL FROM
SUCCESSFULLY PRODUCING (ELEVATED) CONVECTION OR NOTHING. IN
THIS CASE, A QUICK GLANCE AT NEAR-TERM RAP PROFILES (FOR
EXAMPLE) REVEAL IT'S ALREADY DOING A POOR JOB HANDLING THE
EXPANSIVE SATURATED LAYER AROUND 4-6 KFT PER SURFACE
OBSERVATIONS FROM EAST CENTRAL IOWA INTO WEST CENTRAL ILLINOIS.
BASED ON THE SPROUTING ISOLATED CONVECTION FROM NEAR CEDAR
RAPIDS TO LINCOLN, IL, GENERAL EXPECTATION IS FOR SCATTERED
SHOWERS AND STORMS TO DEVELOP TO OUR SOUTHWEST, AND GRADUALLY
EXPAND NORTH AND EAST OVERNIGHT. WITH THE BULK OF THE
WAA/UPGLIDE NOT SLATED TO ARRIVE UNTIL AFTER 2 AM, IT LOOKS LIKE
THE HIGHEST PRECIPITATION COVERAGE MAY HOLD OFF UNTIL THE LATE
OVERNIGHT AND INTO THE VERY EARLY MORNING HOURS TOMORROW.
HAVE GENTLY BOOSTED POPS TOWARDS 70%, FAVORING THE NORTHERN
TERMINUS OF THE INCOMING ELEVATED INSTABILITY RESERVOIR WHERE
THE BEST OVERLAP OF MOISTURE, INSTABILITY, AND ASCENT FROM A
SUBTLE PERTURBATION DRIFTING OUT OF SOUTH DAKOTA LOOK TO
OVERLAP (I.E. ACROSS ROUGHLY THE NORTHEAST 2/3RDS OF OUR
FORECAST AREA)
GIVEN THE ELEVATED NATURE OF CONVECTION TONIGHT, EFFECTIVE DEEP
LAYER SHEAR VALUES AREN'T EXPECTED TO BE EXCEPTIONALLY LARGE
GIVEN EFFECTIVE INFLOW BASES NEAR 1 KM. ADDITIONALLY, DEEP LAYER
SHEAR IS FORECAST TO WEAKEN A BIT AS INSTABILITY BUILDS. STILL,
THE SHEAR/INSTABILITY SPACE LOOKS SUFFICIENT TO SUPPORT A FEW
STRONGER CORES WITH A THREAT FOR A FEW DIME TO PERHAPS A QUARTER-
SIZED HAILSTONE LATE TONIGHT/EARLY FRIDAY MORNING.
FINALLY, WHILE THIS SETUP CONCEPTUALLY MATCHES A FEW THINGS WE
LOOK FOR AHEAD OF HEAVY RAIN EVENTS, THE LACK OF DEEPER
TROPOSPHERIC MOISTURE (PWATS PEAKING NEAR AN INCH) AND,
IMPORTANTLY, BACKED/WESTERLY WINDS ABOVE 500 MB, IT SEEMS LIKE
DEEPER CORES SHOULD HAVE A PROPENSITY TO PROPAGATE EASTWARD
ENOUGH TO LIMIT RESIDENCE TIME OF HEAVIER RAINFALL OVER ANY ONE
LOCATION. SO, WHILE LOCALLY HEAVY RAINFALL IS CERTAINLY
POSSIBLE, NOT CURRENTLY TOO CONCERNED WITH THE FLASH FLOOD
THREAT.
CARLAW
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 /06Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 100 AM CDT FRI MAR 28 2025
- ISOLATED TO WIDELY SCATTERED SHRA EXPECTED OVERNIGHT INTO THE
MORNING WITH MVFR CIGS POSSIBLE AT TIMES.
- CONFIDENCE IN A PERIOD OF TSRA IS HIGHEST BETWEEN ~9-13Z.
SMALL HAIL WILL BE POSSIBLE WITH THE STRONGEST STORMS WITH
ASSOCIATED MVFR CIGS/VSBYS.
- STRONG SW WINDS DEVELOP THIS AFTERNOON WITH GUSTS TO ~35 KTS.
- PERIOD OF LLWS POSSIBLE TONIGHT, PARTICULARLY IF SURFACE GUSTS
EASE MORE THAN EXPECTED.
SPOTTY LIGHT ALREADY SHOWERS ARE ALREADY UNDERWAY ACROSS THE
AREA EARLY THIS MORNING WITH SOME EMBEDDED THUNDERSTORMS WELL
SOUTHWEST OF THE TERMINALS. THESE SHOULD BE FAIRLY HIT AND MISS
FOR AT LEAST A COUPLE MORE HOURS. GUIDANCE CONTINUES TO SUGGEST
A MORE CONSOLIDATED AXIS OF SHOWERS WILL DEVELOP AND LIFT ACROSS
THE TERMINALS AS WE GET CLOSER TO DAYBREAK. OPTED TO SHIFT THE
TEMPO FOR TSRA AN HOUR LATER AT ALL SITES (9-11Z RFD, 10-13Z FOR
DPA/ORD/MDW/GYY) BASED ON LATEST RADAR AND MODEL TRENDS. THE
STRONGEST STORMS WILL BE CAPABLE OF PRODUCING SMALL HAIL.
CONFIDENCE IN CIG TRENDS IS ON THE LOWER SIDE OVERNIGHT. SO FAR
MVFR STRATUS HAS BEEN RATHER SPARSE, OTHER THAN A NARROW AXIS
FROM NEAR MDW TO GYY. DUE TO THIS, HAVE TRENDED LESS PESSIMISTIC
WITH THIS UPDATE FOR MOST SITES, RELEGATING THE PERIOD OF MVFR
CIGS/VSBYS TO THE TIMING OF GREATEST SHOWER/STORM COVERAGE.
WIDELY SCATTERED SHOWERS MAY LINGER FURTHER THE MORNING HOURS
AS A TRAILING SHORTWAVE CURRENTLY OVER NORTHWEST IOWA PUSHES
ACROSS NORTHERN ILLINOIS. ACCORDINGLY, OPTED TO HANG ONTO -SHRA
THROUGH 15Z AND VCSH THROUGH MIDDAY.
WINDS ARE EXPECTED TO STEADILY INCREASE INTO THE AFTERNOON WITH
A PERIOD OF STRONG SOUTHWESTERLY WIND GUSTS UP TO AROUND 35 KT
EXPECTED. PREVAILING GUSTS SHOULD BEGIN TO EASE WITH SUNSET,
THOUGH A STRONG LOW-LEVEL JET WILL MOVE OVERHEAD WHICH COULD
ALLOW FOR AT LEAST SPORADIC STRONG GUSTS TO PERSIST THROUGH THE
EVENING HOURS. DUE TO THE POTENTIAL FOR CONTINUED STRONG SURFACE
GUSTS, OPTED TO HOLD OFF ON A FORMAL LLWS MENTION, THOUGH IT IS
POSSIBLE THIS MAY NEED TO BE ADDED WITH LATER UPDATES.
PETR
MARINE
ISSUED AT 1030 PM CDT THU MAR 27 2025
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 ON FRIDAY. BEHIND
THE FRONT, SOUTHWESTERLY WINDS WILL INCREASE QUICKLY IN
MAGNITUDE ON FRIDAY AFTERNOON. GALE FORCE GUSTS IN EXCESS OF 35
KTS ARE EXPECTED, AND WILL THEN LAST INTO THE EVENING HOURS,
ALTHOUGH GALES MAY BECOME MORE INTERMITTENT WITH TIME,
PARTICULARLY ACROSS THE INDIANA NEARSHORE ZONES. A FEW GALES
ABOVE 40 KTS APPEAR POSSIBLE DURING THE AFTERNOON, PARTICULARLY
ACROSS THE ILLINOIS NEARSHORE. SINCE WATER TEMPERATURES REMAIN
COLD (LEADING TO STABILITY OVER THE LAKE), THE THREAT FOR GALE
FORCE WINDS WILL BE WITHIN THE FIRST FEW MILES OF THE LAKESHORE.
THE GALE WATCH HAS BEEN UPGRADED TO A GALE WARNING FOR THE
NEARSHORE WATERS.
NWS CHICAGO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...GALE WARNING FROM 1 PM THIS AFTERNOON TO 3 AM CDT SATURDAY FOR
THE IL AND IN NEARSHORE WATERS.
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