409
FXUS63 KLOT 271720
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1220 PM CDT THU MAR 27 2025
KEY MESSAGES
- RAIN IS POSSIBLE AT TIMES LATE TONIGHT THROUGH FRIDAY MORNING.
- ISOLATED TO SCATTERED THUNDERSTORMS, SOME WITH SMALL HAIL, ARE
POSSIBLE LATE THURSDAY NIGHT INTO EARLY FRIDAY.
- STRONG WINDS AND WARM WEATHER ARE EXPECTED FRIDAY AFTERNOON.
- RAIN AND/OR THUNDERSTORMS POSSIBLE AT TIMES OVER THE WEEKEND
WITH A SUBSTANTIAL TEMPERATURE GRADIENT STALLED ACROSS
NORTHERN ILLINOIS.
DISCUSSION
ISSUED AT 355 AM CDT THU MAR 27 2025
THROUGH FRIDAY NIGHT:
THE MAIN FORECAST CONCERN AND FOCUS IS ON CONVECTIVE TRENDS LATER
TONIGHT INTO FRIDAY MORNING. THIS WILL BE FOLLOWED BY A WINDY AND
UNSEASONABLY WARM FRIDAY AFTERNOON AND EVENING.
FOR TODAY, EXPECT OCCASIONAL LIGHT SHOWERS AND SPRINKLES, WITH AN
OVERALL FOCUS ON AREAS NEAR AND SOUTH OF A VYS TO RZL LINE
(POPS PEAKING AT 40-50%) FOR THE HIGHEST COVERAGE AND BEST CHANCE
OF A COUPLE HUNDREDTHS OF AN INCH OF RAIN. THIS WILL BE DUE TO A
COUPLE IMPULSES INTERACTING WITH A FAIRLY SHARP BAROCLINIC ZONE
DRAPED FROM NORTHWEST SOUTHEAST ACROSS THE REGION. DECENT MID-
LEVEL F-GEN AND ASSOCIATED LIFT WILL CONTEND WITH DRY SUB-CLOUD
LAYER AIR, ESPECIALLY WITH NORTHEASTWARD EXTENT. EXTENSIVE CLOUD
COVER WILL KEEP TEMPS LOWER THAN THEY OTHERWISE MAY HAVE BEEN WITH
MORE SUNSHINE, TOPPING OUT IN THE LOWER TO MID 50S. SOUTHERLY
WINDS WILL BACK TO SOUTHEAST/EAST-SOUTHEAST LATER THIS AFTERNOON,
RESULTING IN MODEST COOLING ALONG THE IL SHORE PRIOR TO SUNSET.
A WARM FRONT WILL LIFT NORTH ON THURSDAY NIGHT INTO FRIDAY,
BRINGING OUR BEST RAIN (AND SOME THUNDER) CHANCES OF THE WORK
WEEK THUS FAR. STEEPENING MID-LEVEL LAPSE RATES AND ROBUST WARM
AND MOIST ADVECTION AND RESULTING ISENTROPIC ASCENT NEAR AND NORTH
OF THE LIFTING FRONTAL ZONE SHOULD SET THE STAGE FOR ELEVATED
CONVECTION AFFECTING A GOOD CHUNK OF THE AREA, PARTICULARLY
OVERNIGHT.
THE ECMWF/EPS YET AGAIN (A CONSISTENT THEME) SHOWED A SHARPER
CUTOFF TO THE FOOTPRINT ON THE NORTHEAST SIDE OF THE ELEVATED
CONVECTION, SO LIMITED POPS TO HIGH CHANCE (~50%) ALONG THE IL/WI
STATE LINE. CONFIDENCE IS HIGHEST IN SHOWERS AND SCATTERED
THUNDERSTORMS (70%+ POPS) NEAR AND SOUTH OF A FORRESTON (NW OGLE
COUNTY) TO JOLIET TO KOUTS IN LINE. HAIL MAY BE POSSIBLE WITH ANY
DEEPER CORES GIVEN THE STEEP MID-LEVEL LAPSE RATES IN PLACE,
THOUGH MODEST EFFECTIVE SHEAR (UNIDIRECTIONAL AND ONLY MODESTLY
INCREASING FLOW IN THE POTENTIALLY UNCAPPED MUCAPE LAYER) SHOULD
TEND TO KEEP THE THREAT FOR ANY MARGINALLY SEVERE HAIL OFF TO OUR
SOUTHWEST, WITH THE BEST (STILL LOW) CHANCE IN THE CWA SOUTH OF A
DIXON TO WATSEKA LINE.
OUR OTHER CONCERN IS FOR POCKETS OF HEAVY DOWNPOURS AND HIGHER
RAINFALL RATES OVERNIGHT INTO EARLY FRIDAY. THERE ARE SOME
SIMILARITIES IN A BROAD SENSE SYNOPTICALLY TO MORE CONCERNING
SUMMER-TIME NORTHWEST FLOW FLASH FLOOD SETUPS JUST NORTH OF
ADVANCING WARM FRONTS. HOWEVER, THE PWATS AREN'T EXPECTED TO BE
OFF THE CHARTS FOR LATE MARCH AND MORE WESTERLY FLOW ALOFT SHOULD
LIMIT TRAINING AND BACKBUILDING VS. THE SHARP NW FLOW SETUPS.
THERE SHOULD BE LINGERING SHOWERS AND ISOLATED TO SCATTERED
THUNDERSTORMS PAST DAYBREAK FRIDAY, PARTICULARLY NEAR AND EAST OF
I-55, WHERE WE HELD ONTO LIKELY POPS UNTIL MID MORNING. ONCE
LINGERING CONVECTION CLEARS, CONFIDENCE REMAINS HIGH IN A DRY,
WARM, AND WINDY AFTERNOON. THE TIGHT PRESSURE GRADIENT, MODEST
PRESSURE FALLS, AND STRONG LOW-LEVEL SOUTHWESTERLY WIND FIELD
SUGGESTS WIND GUSTS UP TO AT 35-45 MPH, AND SOME POTENTIAL FOR
ABOVE ADVISORY (45 MPH) CRITERIA GUSTS. 850 MB TEMPS IN THE MID
TEENS CELSIUS (SUMMER-LIKE VALUES) WILL RESULT IN TEMPS SOARING
WELL INTO THE 70S, WITH SOME 80F READINGS A GOOD BET, ESPECIALLY
OVER THE SOUTHWEST CWA.
THE WINDY AND WARM CONDITIONS WILL CONTINUE THROUGH MUCH OF FRIDAY
NIGHT, AS THE UNSEASONABLY MILD AIR MASS STAYS WELL MIXED IN THE
PRESENCE OF STILL STRONG SOUTHWESTERLY LOW-LEVEL FLOW. GUSTS
PUSHING 45 MPH THUS WILL BE POSSIBLE EVEN AFTER SUNSET. TEMPS IN
THE 70S EARLY WILL ONLY SLOWLY FALL THROUGH THE 60S THROUGH THE
NIGHT, WELL ABOVE NORMAL HIGHS FOR THE DATE.
CASTRO
SATURDAY THROUGH WEDNESDAY:
WARM FRONT IS FORECAST TO BE NORTH OF THE AREA SATURDAY
MORNING, WITH THE MAIN FOCUS FOR OVERNIGHT PRECIPITATION TO OUR
NORTH ACROSS IA-WI, ASSOCIATED WITH AN EASTWARD TRACKING SURFACE
WAVE. GUIDANCE IS IN GENERAL AGREEMENT HOWEVER, IN SAGGING THE
FRONT BACK SOUTH AS A LAKE-ENHANCED COLD FRONT DURING THE
AFTERNOON. WHILE SOME DIFFERENCES IN TIMING ARE EVIDENT BETWEEN
THE VARIOUS MODEL ENSEMBLES, THERE IS CONSENSUS INDICATING THIS
"BACK DOOR" COLD FRONT WILL SLIDE DOWN THE LAKE, SHIFT WINDS TO
THE NORTHEAST, AND BRING MUCH COOLER TEMPERATURES (40S ALONG THE
LAKE, 50S INLAND) THROUGH AT LEAST THE I-90 CORRIDOR FROM
NORTHERN IL INTO NORTHWEST IN BY EVENING. SHOWER CHANCES ALSO
INCREASE BY SATURDAY AFTERNOON AS A PAIR OF MID-LEVEL SHORT
WAVES APPROACH THE AREA, ONE FROM THE PLAINS HEADING INTO THE
UPPER MIDWEST, AND ANOTHER FARTHER SOUTH TRACKING INTO THE LOWER
OHIO VALLEY. ENSEMBLES CONTINUE TO SHOW SOME SPREAD WITH THE
AMPLITUDE AND EXACT TRACK WITH THESE DISTURBANCES, THOUGH
GENERALLY FAVOR INCREASE SHOWER POTENTIAL ALONG THE FRONT TO OUR
NORTHWEST (IA/SOUTHWEST WI) AND FARTHER SOUTH INTO PARTS OF
CENTRAL IL/IN. THE WFO LOT CWA APPEARS TO BE IN A PRECIP MINIMUM
BETWEEN THESE TO AREAS OF FOCUS, THOUGH AN OVERALL UPTICK IN
SCATTERED COVERAGE APPEARS LIKELY SATURDAY AFTERNOON.
THE BEST LOW-LEVEL MOISTURE AND INSTABILITY AXIS IS DEPICTED
ALONG/WEST OF THE MISSISSIPPI RIVER SATURDAY AFTERNOON, AHEAD OF
AN AREA OF SURFACE LOW PRESSURE ASSOCIATED WITH THE NORTHERN,
MORE AMPLIFIED SHORT WAVE. THIS IS WHERE THE GREATEST THUNDER
POTENTIAL LOOKS TO BE SATURDAY AFTERNOON/EVENING, THOUGH SOME OF
THIS MAY SPREAD INTO WESTERN PARTS OF IL/LOT CWA IN A
DIMINISHING TREND. CURRENT FORECAST SOUNDINGS ARE NOT VERY
IMPRESSIVE ACROSS OUR WESTERN CWA AT THIS TIME HOWEVER. ENSEMBLE
GUIDANCE CONTINUES TO SHOW CONSIDERABLE SPREAD WITH THE
STRENGTH AND TRACK OF THE AFOREMENTIONED SURFACE LOW AND THE
EASTWARD TIMING OF THE TRAILING COLD FRONT SATURDAY NIGHT INTO
SUNDAY. EPS/CMCE ARE DEEPER AND FARTHER NORTHWEST WITH THE LOW
AND SLOWER WITH THE FRONT, WHILE THE GEFS (AND SREF THROUGH 12Z
SUNDAY) ARE WEAKER AND FARTHER SOUTHEAST INTO IL. OVERALL,
SUNDAY DOES LOOK TO BE RATHER SHOWERY AND PERHAPS THUNDERY
DEPENDING ON WHICH OF THESE SOLUTIONS END UP VERIFYING. HIGHEST
THUNDER POTENTIAL WOULD GENERALLY BE ACROSS OUR SOUTHEASTERN CWA
WITH THE SLOWEST FRONTAL MOVEMENT, OR EVEN EAST/SOUTHEAST OF
THE AREA IN THE CASE OF THE FASTER TIMING. IN EITHER EVENT, THE
STRONGEST INSTABILITY IS PROGGED SOUTH/SOUTHEAST OF THE FORECAST
AREA. SHOWERS PERSIST BEHIND SUNDAY NIGHT INTO EARLY MONDAY
BEHIND THE FRONT AS THE MAIN UPPER LEVEL TROUGH WORKS ACROSS THE
AREA. COLDER AIR WRAPPING IN BEHIND THE DEPARTING LOW, COOLING
THE COLUMN AND ALLOWING A MIX OR CHANGE TO WET SNOW LATER SUNDAY
NIGHT INTO MONDAY MORNING. DEEPER EPS EVEN SUGGESTS A LINGERING
DEFORMATION BAND MAY MAINTAIN THE THREAT OF PRECIPITATION INTO
MONDAY AFTERNOON.
DRY BUT MUCH COOLER CONDITIONS ARE INDICATED LATE MONDAY INTO
TUESDAY, AS HIGH PRESSURE SPREADS BRIEFLY ACROSS THE REGION.
DESPITE THE CONSIDERABLE MODEL SPREAD SEEN WITH THE WEEKEND
SYSTEM, GLOBAL ENSEMBLES CURRENTLY SHOW VERY GOOD AGREEMENT IN
RETURNING TO A WESTERN CONUS UPPER TROUGH/DOWNSTREAM CENTRAL
CONUS UPPER RIDGE BY MID-WEEK, THOUGH THE PATTERN IS PROGRESSIVE
AND BRINGS RAIN AND POSSIBLY THUNDERSTORM CHANCES BACK INTO THE
AREA IN THE LATE TUESDAY INTO WEDNESDAY PERIOD ALONG WITH
WARMER TEMPERATURES.
RATZER
AVIATION /18Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 1220 PM CDT THU MAR 27 2025
KEY MESSAGES FOR THE 18Z TAFS:
- VFR CLOUD COVER THIS AFTERNOON WITH A FEW ISOLATED LIGHT
SHOWERS AND SPRINKLES.
- A PERIOD OF MORE SUBSTANTIAL SHOWERS AND THUNDERSTORMS
OVERNIGHT, WITH IFR CIGS AND VSBYS.
- LOW CLOUDS CLEAR BY MID FRIDAY MORNING, THEN SOUTHWEST WINDS
BECOME INCREASINGLY GUSTY (UP TO AROUND 35 KT) THROUGH THE
AFTERNOON.
AN AREA OF VFR CLOUD COVER BASED IN THE 6-8,000 FT RANGE
CONTINUE TO STREAM ACROSS THE AREA EARLY THIS AFTERNOON. THERE
ARE ALSO SOME ISOLATED SHOWERS, THOUGH MOST OF THESE ARE
EXPECTED TO REMAIN SOUTHWEST OF THE MAIN CHICAGO TERMINALS.
OTHERWISE, EXPECT LIGHT (10 KT OR LESS) SOUTH TO SOUTHWEST
WINDS TO BACK MORE SOUTHEASTERLY INTO THIS EVENING AS A WARM
FRONT BEGINS TO APPROACH THE AREA FROM THE SOUTH.
THE WARM FRONT WILL LIFT NORTHWARD ACROSS THE TERMINAL AIRSPACE
AROUND DAYBREAK FRIDAY MORNING. AS IT BEGINS TO MOVE INTO THE
AREA AFTER MIDNIGHT, A PERIOD OF SHOWERS AND THUNDERSTORMS ARE
LIKELY (60%+ CHANCE) TO DEVELOP AND MOVE ACROSS THE TERMINALS.
CURRENT BEST TIMING FOR THESE STORMS LOOK TO BE IN THE 08-12Z
TIMEFRAME. THE ONLY CHANGE FOR THE NEW SET OF TAFS WAS TO
CONVERT THE PROB30 TO A TEMPO GROUP FOR THESE STORMS.
OTHERWISE, SHOULD SEE SOME LOWER CIGS AND VSBYS WITH THESE
SHOWERS AND STORMS, WITH IFR CONDITIONS FAVORED.
ONCE THE WARM FRONT LIFTS NORTH OF THE AREA AFTER DAYBREAK
FRIDAY, EXPECT THE LOW CLOUDS TO SCATTER OUT FOR THE DAY, WITH
VFR CONDITIONS RETURNING. THE ONLY OTHER NOTE FOR FRIDAY WILL BE
THE INCREASING SOUTHWESTERLY WINDS THROUGH THE DAY. EXPECT WINDS
TO GUST UP AROUND (OR EVEN A BIT ABOVE) 35 KT, ESPECIALLY DURING
THE MID AND LATE AFTERNOON HOURS.
KJB
MARINE
ISSUED AT 544 AM CDT THU MAR 27 2025
STRONG SOUTHWEST WINDS ARE EXPECTED ON FRIDAY AFTERNOON THROUGH
MUCH OF FRIDAY NIGHT. A WARM FRONT WILL LIFT NORTH TONIGHT INTO
FRIDAY MORNING, WITH THE FRONT EXPECTED TO REACH CENTRAL LAKE
MICHIGAN BY MIDDAY. IN THE WAKE OF THE FRONT, A TIGHT PRESSURE
GRADIENT BETWEEN LOW PRESSURE FROM THE PLAIN TO THE UPPER MS
VALLEY WILL RESULT IN RAPIDLY INCREASING SOUTHWEST WINDS FROM THE
LATE MORNING INTO THE EARLY AFTERNOON.
WITH FORECAST SOUNDINGS NEAR THE LAKE SUPPORTING 35+ KT GALE
FORCE SPEEDS/GUSTS INTO THE NEARSHORE, CONFIDENCE WAS HIGH ENOUGH
TO ISSUE A GALE WATCH. THE WATCH IS IN EFFECT FROM 1 PM FRIDAY TO
3 AM CDT SATURDAY FOR THE ENTIRE IL AND FAR NW IN NEARSHORE. AN
UNSEASONABLY WARM AIR MASS ON LAND WILL LIKELY KEEP THE STRONGEST
WINDS CONFINED TO WITHIN THE FIRST 2-3 MILES OF THE NEARSHORE
WATERS DUE TO INCREASINGLY STABLE CONDITIONS FARTHER OFFSHORE.
CASTRO
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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