533
FXUS63 KLOT 010529
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1229 AM CDT TUE APR 1 2025
KEY MESSAGES
- SEVERAL WAVES OF SHOWERS AND STORMS ARE EXPECTED TUESDAY NIGHT
INTO WEDNESDAY. A FEW STORMS MAY BE SEVERE.
- PERIODIC RAIN CHANCES WILL RETURN LATE WEEK INTO THE WEEKEND.
DISCUSSION
ISSUED AT 330 PM CDT MON MAR 31 2025
THROUGH TUESDAY:
QUIET BUT COOL WEATHER IS EXPECTED TONIGHT, AS THE SOUTHERN
PERIPHERY OF A SURFACE HIGH PRESSURE RIDGE MOVES EAST ACROSS THE
AREA. SKIES WILL BECOME PARTLY CLOUDY THIS EVENING WITH SURFACE
WINDS TURNING NORTHEAST AND EVENTUALLY EASTERLY OVERNIGHT.
OVERNIGHT LOWS WILL DIP INTO THE UPPER 20S IN OUTLYING AREAS AND
THE LOWER 30S ALONG THE LAKE AND IN THE CITY.
MID-LEVEL RIDGING DEVELOPS ACROSS THE REGION TUESDAY,
DOWNSTREAM OF AN UPPER LEVEL TROUGH ACROSS THE WESTERN CONUS.
EAST-SOUTHEASTERLY SURFACE WINDS WILL STRENGTHEN IN RESPONSE TO
FALLING SURFACE PRESSURES ACROSS THE PLAINS, WHILE SOUTHERLY
WARM ADVECTION FLOW STRENGTHENS TO 30-40 KTS ABOVE THE BOUNDARY
LAYER. ASSOCIATED ISENTROPIC ASCENT/MOISTENING IS EXPECTED TO
RESULT IN THE DEVELOPMENT OF ELEVATED SHOWERS ACROSS THE FAR
WEST/NORTH PARTS OF THE CWA LATE IN THE AFTERNOON, WHICH LOOKS
TO BE BE A MIX OF RAIN/SNOW THANKS TO THE COOL THERMODYNAMIC
COLUMN AND COOL BOUNDARY LAYER TEMPS/WET BULBS, ESPECIALLY
ACROSS THE NORTHERN PARTS OF THE CHICAGO METRO AREA WHERE THE
LAKE INFLUENCE KEEPING TEMPERATURES IN THE UPPER 30S. PRECIP
SHOULD INITIALLY BE LIGHT, AND NO ACCUMULATION IS EXPECTED WITH
THE MIX QUICKLY TRANSITIONING TO ALL RAIN TUESDAY EVENING AS
STRONG WARM ADVECTION OVERWHELMS THE COLUMN.
RATZER
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT:
YET ANOTHER DEEP MID-LATITUDE CYCLONE WILL AFFECT THE REGION IN
THIS PERIOD, WITH MULTIPLE POTENTIAL HAZARDS. MOST OF THE
THUNDERSTORM CONCERNS WILL BE FOCUSED AFTER MIDNIGHT TUESDAY
NIGHT AND THROUGH WEDNESDAY. INITIAL WARM ADVECTION/ISENTROPIC
ASCENT DRIVEN PRECIP DURING TUESDAY EVENING WILL LIKELY BE
LIGHTER INTENSITY AND DEVOID OF LIGHTNING WITH LITTLE TO NO
ELEVATED INSTABILITY. HIGHEST (CHANCE/30-50% POPS) IN OUR LATEST
FORECAST ARE GENERALLY OVER THE NORTHWEST HALF TO THIRD OF THE
AREA, WHERE THE DRY ANTECEDENT LOW-LEVELS WILL MORE READILY
SATURATE SUFFICIENTLY. AS NOTED IN THE SECTION ABOVE, THERE'S A
SMALL WINDOW INTO THE EARLY EVENING NEAR THE WISCONSIN BORDER
WHERE WET SNOWFLAKES MAY MIX IN, THOUGH NO ACCUMULATIONS AND
IMPACTS ARE EXPECTED.
HIGH 980S MB SURFACE LOW PRESSURE WILL TRACK NORTHEAST ACROSS
THE MID-MO VALLEY LATE TUESDAY NIGHT INTO EARLY WEDNESDAY. IN
ADVANCE OF THE CYCLONE, INTENSE WARM AND MOIST ADVECTION FROM A
50-70 KT LOW-LEVEL JET WILL QUICKLY STEEPEN MID-LEVEL LAPSE
RATES AND SET THE STAGE FOR A LIKELIHOOD OF FAIRLY EXTENSIVE
ELEVATED CONVECTION (SHOWERS AND AT LEAST SCATTERED EMBEDDED
THUNDERSTORMS) OVERNIGHT AND PARTICULARLY DURING THE PRE-DAWN
HOURS. THIS WILL OCCUR NORTH OF A NORTHWARD LIFTING WARM FRONT
EXTENDING NORTHEAST FROM THE SURFACE LOW. WITH THIS LATEST
ISSUANCE, CATEGORICAL POPS IN THE PRE-DAWN HOURS ARE FEATURED
NEAR AND NORTHWEST OF I-55.
AS NOTED ABOVE, MID-LEVEL LAPSE RATES WILL BECOME QUITE STEEP AS
AN EML PLUME IS ADVECTED NORTHEASTWARD. HOWEVER, MOST MODEL
GUIDANCE IS VERY MEAGER WITH INSTABILITY UNTIL CLOSER TO
DAYBREAK, ALONG WITH VARIANCE IN THE MAGNITUDE OF UNCAPPED
MUCAPE THAT CAN BE REALIZED. FURTHERMORE, EFFECTIVE BULK SHEAR
(IN THE MUCAPE LAYER) MAY BE ON THE MARGINAL SIDE AT AROUND 30
KT. THE DAY 2 SPC OUTLOOK HAS GENERALLY AREAS NEAR AND WEST OF
I-39 IN A LEVEL 2 OF 5 (SLIGHT RISK) SEVERE THREAT, AND THIS
OVERALL APPEARS TO BE THE MOST FAVORED REGION FOR MARGINALLY
SEVERE HAIL, AS MUCAPE MAY APPROACH OR EXCEED 1K J/KG PRIOR TO
12Z WEDNESDAY.
WITH THE ABOVE BEING SAID, THESE TYPES OF PATTERNS NEED TO BE
MONITORED CLOSELY FOR GRAVITY WAVE DEVELOPMENT AND PROPAGATION
WITHIN THE STABLE LAYER. SHOULD THIS OCCUR, THEN THERE MAY BE AN
ACCOMPANYING LOCALIZED DAMAGING WIND THREAT FROM ELEVATED
CONVECTION, SUPPORTING THE 5% WIND PROBS IN THE SPC OUTLOOK. THE
FINAL ITEM OF NOTE FOR THE TUESDAY NIGHT INTO EARLY WEDNESDAY
PERIOD IS THE GUSTY EAST-SOUTHEAST SYNOPTIC WINDS, WHICH COULD
GUST UP TO 35-40 MPH AT TIMES, POTENTIALLY STRONGEST ALONG THE
IL LAKESHORE.
WEDNESDAY'S SYNOPTIC PATTERN CONTAINS SOME OF THE HALLMARKS OF
SIGNIFICANT EARLY SEASON SEVERE WEATHER EVENTS, INCLUDING A DEEP
SURFACE LOW TRACKING JUST NORTHWEST OF OUR AREA. HOWEVER, THERE
ARE KEY ITEMS OF UNCERTAINTY THAT WILL ULTIMATELY DICTATE THE
MAGNITUDE OF SEVERE THREAT AND FOCUS AREAS. THE LATEST GUIDANCE
SUGGESTS A LIKELIHOOD OF FAIRLY EXTENSIVE ELEVATED CONVECTION
LINGERING INTO WEDNESDAY MORNING, AND EVEN ANOTHER POTENTIAL
ROUND INITIATED FROM LATE MORNING INTO THE EARLY AFTERNOON NEAR
AND NORTH OF THE WARM FRONTAL ZONE. CONVECTION AND ASSOCIATED
OVERCAST WILL THEN LIKELY DELAY (LIMITED) DESTABILIZATION INTO
A SHORTER WINDOW IN THE LATE AFTERNOON. MOIST PROFILES DUE TO
DEW POINTS PUSHING INTO THE 60S AMIDST TEMPS IN THE UPPER
60S-LOWER 70S, AND MID-LEVEL LAPSE RATES GENERALLY OF 6.5C/KM
OR LESS TEND TO POINT TOWARD A MESSY, "NOW-CAST" TYPE OF SETUP
IN THE FAVORED TIMING WINDOW.
WHILE OUR WHOLE AREA REMAINS IN A LEVEL 3 OF 5 ("ENHANCED"
RISK) SEVERE THREAT IN THE UPDATED SPC DAY 3 OUTLOOK, SUSPECT
WE MAY BE ABLE TO BETTER HONE IN ON THE MOST LIKELY THREAT
LOCATIONS WITHIN OUR CWA AS THE EVENT DRAWS CLOSER. IT'S
POSSIBLE THAT THIS SETS UP SOMEWHERE IN THE EASTERN HALF OR
SOUTHEAST 1/2 TO 2/3 OF THE CWA. OVERALL EVOLUTION AND STORM
MODE QUESTIONS PRECLUDE MUCH IN THE WAY OF SPECIFICS, OTHER THAN
THAT EXTREME LOW-LEVEL (WITH CURVED LOW-LEVEL HODOGRAPHS) AND
DEEP-LAYER WIND SHEAR MAY CERTAINLY CONTRIBUTE TO A HIGHER END
SEVERE THREAT (TORNADOES/DAMAGING WIND) MATERIALIZING SOMEWHERE
IN THE AREA BETWEEN ~4PM-9PM CDT.
ASIDE FROM THE UNCERTAIN CONVECTIVE TRENDS (MOST OF OUR GRIDDED
FORECAST INDICATES BROAD-BRUSHED 'SCATTERED' THUNDERSTORMS),
STRONG SOUTH-SOUTHWEST SURFACE WINDS CAN BE EXPECTED IN THE
NORTHWARD ADVANCING WARM SECTOR, WITH GUSTS UP TO 35-45 MPH.
WE'LL ALSO HAVE TO KEEP AN EYE ON THE POTENTIAL FOR A POP OF
WINDS IN THE WAKE OF ELEVATED CONVECTION IN THE EARLY AFTERNOON,
GIVEN THE VERY STRONG WINDS ALOFT. THE SYSTEM COLD FRONT WILL
SWEEP ACROSS THE AREA WEDNESDAY EVENING, BRINGING A RELATIVELY
QUICK END TO THE CONVECTIVE AND SEVERE THREATS, WITH EASING
WESTERLY WINDS AND TEMPERATURES FALLING INTO THE 40S BY EARLY
THURSDAY.
CASTRO
THURSDAY THROUGH MONDAY:
DEEP SURFACE LOW PRESSURE IS PROGGED TO BE LIFTING AWAY FROM
THE AREA TO THE NORTHEAST BY THURSDAY MORNING, WITH SEASONABLY
COOLER CONDITIONS EXPECTED IN ITS WAKE. THE LOW-LEVEL FRONTAL
ZONE IS FORECAST TO STALL TO OUR SOUTH FROM THE OHIO VALLEY BACK
INTO TX HOWEVER, WITH A SERIES OF MID-LEVEL SHORT WAVE
DISTURBANCES AND SURFACE WAVES EXPECTED TO RIPPLE NORTHEAST
ALONG IT. SPREAD REMAINS IN THE GLOBAL GUIDANCE AND ENSEMBLES,
THOUGH MODELS GENERALLY MAINTAIN PERIODIC PRECIP CHANCES INTO
CENTRAL IL/IN, WITH SOME SPREAD NOTED AS TO HOW FAR NORTH THIS
WOULD EXTEND INTO THE WFO LOT CWA. NBM BLENDED GUIDANCE
GENERALLY MAINTAINS SOME CHANCES POPS INTO THE SOUTHERN HALF OF
THE CWA LATE THURSDAY INTO FRIDAY, WITH A MORE NOTABLE WAVE
SPREADING RAIN CHANCES FARTHER NORTH ACROSS THE AREA FRIDAY
NIGHT THROUGH SATURDAY. EPS/GEFS/CMCE ALL SPREAD POPS ACROSS THE
AREA TO SOME EXTENT IN THAT TIME FRAME, SO CAN'T ARGUE WITH THE
BLENDED GUIDANCE AT THIS DISTANCE ESPECIALLY GIVEN SOME OF THE
MODEL SPREAD.
DRIER AND COOLER WEATHER IS THEN DEPICTED FROM SUNDAY INTO
EARLY NEXT WEEK, BEHIND THE PASSAGE OF A LONG-WAVE UPPER TROUGH.
AFTER DAYTIME HIGHS IN THE 50S THURSDAY-SUNDAY, A PERIOD OF 40S
APPEARS LIKELY EARLY NEXT WEEK.
RATZER
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 346 PM CDT MON MAR 31 2025
A DEEP SURFACE LOW TRACKING ACROSS THE MO RIVER 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 GALE FORCE SPEEDS/GUSTS. FORECAST CONFIDENCE WAS
HIGH ENOUGH TO HOIST A GALE WATCH FOR THE ILLINOIS NEARSHORE, IN
EFFECT FROM 10 PM TUESDAY TO 10 AM WEDNESDAY. GALES WILL BE
POSSIBLE ALONG THE FAR NORTHWEST IN NEARSHORE AS WELL, THOUGH
CONFIDENCE WASN'T YET HIGH ENOUGH TO INCLUDE IN THE WATCH.
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 AND
EARLY EVENING. WHILE CLOUD COVER AND ONGOING SHOWERS AND
THUNDERSTORMS MAY LIMIT MIXING DEPTHS ON LAND, WE'LL HAVE TO
MONITOR FOR A PERIOD OF GALES INTO THE FIRST COUPLE MILES OF
THE NEARSHORE, WITH 30 KT SPEEDS/GUSTS INDICATED FOR NOW.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...GALE WATCH FROM THIS EVENING THROUGH WEDNESDAY MORNING FOR THE
IL NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 4 AM CDT EARLY THIS MORNING FOR THE
IN NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page