761
FXUS63 KLOT 220506
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1106 PM CST TUE JAN 21 2025
KEY MESSAGES
- WIND CHILLS OF -15F TO -20F WILL PERSIST THROUGH THIS EVENING.
THE COLD WEATHER ADVISORY REMAINS IN EFFECT UNTIL MIDNIGHT.
- ACCUMULATING SNOW (LOCALLY UP TO 1") IS EXPECTED WEDNESDAY
THROUGH EARLY THURSDAY MORNING LEADING TO SLIPPERY TRAVEL.
- LAKE EFFECT SNOW MAY LINGER ACROSS NORTHEAST PORTER COUNTY
DURING THE DAY ON THURSDAY.
UPDATE
ISSUED AT 904 PM CST TUE JAN 21 2025
THIS EVENING, A MERIDIONALLY-ORIENTED WARM FRONT EXTENDS DOWN
THE SPINE OF THE PLAINS WITH A BROAD REGION OF EFFICIENT LOW
LEVEL WARM ADVECTION OUT AHEAD OF IT OVERSPREADING WESTERN
PORTIONS OF THE MIDWEST. THIS WARM ADVECTION IS DRIVEN BY A
SOUTHWESTERLY LOW LEVEL JET AHEAD OF THE FRONT THAT WILL BE
INTENSIFYING THROUGH THE NIGHT BEFORE MOVING OVER OUR CWA. THIS
SYSTEM WILL BRING LIGHT TO MODERATE SNOW TO PARTS OF THE AREA
TOMORROW, BEGINNING IN THE MORNING WITH THIS WARM ADVECTION
REGIME. IT'S A CONSISTENT AND AGREED-UPON SIGNAL THAT THE SNOW
PROBS DURING THE MORNING AND AFTERNOON TOMORROW WILL BE FOCUSED
TOWARD THE NOSE OF THE 925MB JET, WHICH TRANSLATES TO AREAS
MAINLY NORTH OF THE I-88 CORRIDOR AND UP INTO SOUTHERN WI AS LOW
LEVEL MOISTURE MAY REMAIN SCARCE FARTHER SOUTH. THIS IS THE
PATTERN WE'RE SEEING UPSTREAM AS THE ONLY SNOW CURRENTLY BEING
REPORTED ALONG THIS JET IS FOUND WAY UP IN MN. THE RAP AND NAM
HAVE BEEN WANTING TO BRING SOME SNOW NEAR AND NORTH OF I-80 AND
ACROSS MUCH OF THE CHICAGO METRO DURING THE DAY TOMORROW, BUT
THEY ARE NOTABLY MORE SATURATED THAN OTHER CAMPS. IF SNOW DOES
FALL ON AREAS SOUTH OF I-88 DURING THE DAYTIME, THE BEST CHANCES
APPEAR TO BE THE DURING THE MORNING BEFORE SOME ADDITIONAL DRY
AIR LOOKS TO WEDGE INTO THE AREA FOR THE AFTERNOON.
SNOW COVERAGE SHOULD BEGIN TO EXPAND SOUTHWARD LATE IN THE DAY
WITH THE APPROACH OF THE UPPER WAVE, ALTHOUGH MOST GUIDANCE
KEEPS SNOW OUT OF THE CHICAGO METRO UNTIL AFTER DARK. SNOW
CHANCES WILL BE PUSHED OFF TO THE EAST BY THE COLD FRONT EARLY
THURSDAY MORNING. THERE REMAINS A BIT OF DISCREPANCY REGARDING
COVERAGE AND INTENSITY OWING TO DIFFERENCES IN MOISTURE AND
FORCING. BUT THE GOING FORECAST FOR A FEW TENTHS TO AROUND A
HALF AN INCH ACROSS MUCH OF OUR CWA STILL LOOKS GOOD WITH
LOCALLY HIGHER AMOUNTS TO AROUND AN INCH NORTH OF I-88.
ADDITIONALLY, WE'RE STILL EXPECTING A GOOD PUSH OF WIND TONIGHT
THROUGH EARLY TOMORROW AFTERNOON WITH THAT LOW LEVEL JET MOVING
OVER. GUSTS IN THE 30 TO 35 MPH RANGE ARE EXPECTED INTO EARLY
AFTERNOON WITH SOME UP TO NEAR 40 MPH POSSIBLE. A FEW SITES OUT
IN EASTERN IA ARE ALREADY GUSTING TO 25 TO 30 MPH ON THE LEADING
EDGE OF THE JET. WINDS WILL GRADUALLY SUBSIDE DURING THE
AFTERNOON AND EVENING. ONLY MINOR TWEAKS WERE MADE TO THE GOING
FORECAST AND UPDATED PRODUCTS HAVE BEEN SENT.
DOOM
DISCUSSION
ISSUED AT 304 PM CST TUE JAN 21 2025
THROUGH WEDNESDAY NIGHT:
AN ARCTIC HIGH CONTINUES TO SLIDE ACROSS THE MIDWEST AND GREAT
LAKES THIS AFTERNOON WHICH HAS RESULTED IN BITTERLY COLD
TEMPERATURES DESPITE THE NEARLY UNABATED SUNSHINE. HIGHS TODAY
HAVE LEVELED OFF AROUND 0 DEGREES AND LOOK TO REMAIN NEARLY
STATIONARY THROUGH SUNSET. WITH WINDS EXPECTED TO REMAIN BREEZY
THROUGH THIS EVENING, WIND CHILLS IN THE -15F TO -20F RANGE ARE
EXPECTED TO PREVAIL THROUGH MIDNIGHT. THEREFORE, THE COLD
WEATHER ADVISORY WAS EXTENDED UNTIL MIDNIGHT TO HIGHLIGHT THIS
THREAT.
AFTER MIDNIGHT, TEMPERATURES ARE EXPECTED TO GRADUALLY WARM AS
STRONG SOUTH-SOUTHWEST WINDS DEVELOP AND ADVECT IN "WARMER" AIR.
HOWEVER, TEMPERATURES ARE STILL EXPECTED TO BE IN THE SINGLE
DIGITS THROUGH THE NIGHT WITH WIND CHILLS HOVERING IN THE -10F
TO -15F RANGE. SINCE THESE WIND CHILL MAGNITUDES ARE ABOVE THE -20F
THRESHOLD USED FOR ADVISORIES, THE EXPECTATION IS FOR NO
ADDITIONAL COLD WEATHER HEADLINES TO BE ISSUED ONCE THE
AFOREMENTIONED ONE EXPIRES. THOUGH WIND GUSTS WILL BE INCREASING
INTO THE 20-25 MPH RANGE OVERNIGHT WHICH WILL KEEP A NOTABLE
CHILL IN THE AIR TO START OUR WEDNESDAY.
THE BROAD SHORTWAVE TROUGH CURRENTLY IN ALBERTA WILL BE
PIVOTING INTO THE NORTHERN PLAINS AND EVENTUALLY THE GREAT LAKES
THROUGH THE DAY ON WEDNESDAY. AS THIS OCCURS, THE SURFACE LOW
AHEAD OF THE SYSTEM WILL BE PIVOTING INTO THE NORTHERN GREAT
LAKES WHICH WILL FORCE A COLD FRONT TO ADVANCE ACROSS THE UPPER
MIDWEST WEDNESDAY MORNING. SNOW IS EXPECTED TO DEVELOP BENEATH
THIS WAVE AND ALONG THE COLD FRONT AND BEGIN TO MOVE INTO FAR
NORTHERN IL TOWARDS THE MID-MORNING AND EARLY AFTERNOON HOURS.
HOWEVER, THE FRONT IS FORECAST TO GET HUNG UP NEAR THE IL-WI
LINE WHICH SHOULD KEEP THE BULK OF THE SNOW ALONG THE STATE LINE
AND POINTS NORTH THROUGH MUCH OF THE DAY. THOUGH, THE FRONT IS
EXPECTED TO PIVOT SOUTHWARD THROUGH THE REST OF THE AREA LATE
WEDNESDAY AFTERNOON AND EVENING AS THE SHORTWAVE DIVES INTO THE
OHIO RIVER VALLEY. SINCE THE FRONT SHOULD BE FAIRLY PROGRESSIVE
AS IT MOVES ACROSS NORTHERN IL AND NORTHWEST IN, THE DURATION OF
SNOW AT ANY ONE LOCATION SHOULD BE ONLY 3-4 HOURS AT MOST AND
THUS KEEP ACCUMULATIONS AROUND HALF AN INCH. HOWEVER, LOCALLY
HIGHER TOTALS UP TO AN INCH ARE POSSIBLE ESPECIALLY NEAR THE IL-
WI LINE WHERE LONGEVITY IS FORECAST TO BE MAXIMIZED.
REGARDLESS, THE COLD SURFACE TEMPERATURES WILL ALLOW FOR SOME
SNOW COVERED ROADS AND SLIPPERY TRAVEL SO BE SURE TO USE CAUTION
IF TRAVELING TOMORROW.
SNOW IS EXPECTED TO GRADUALLY TAPER AFTER MIDNIGHT WEDNESDAY
NIGHT, THOUGH SOME LINGERING LIGHT SNOW AND FLURRIES MAY PERSIST
INTO THURSDAY MORNING FOR AREAS EAST OF I-57. OTHERWISE, EXPECT
TEMPERATURES TO WARM INTO THE 20S WEDNESDAY AFTERNOON BEFORE
COOLING INTO THE TEENS WEDNESDAY NIGHT. WINDS WILL ALSO BE GUSTY
ON WEDNESDAY AS THE SYSTEM MOVES THROUGH WITH GUSTS IN THE
25-30 MPH RANGE LIKELY AND LOCALLY HIGHER GUSTS POSSIBLE. THOUGH
WINDS WILL SUBSIDE WEDNESDAY EVENING AS THE SYSTEM BEGINS TO
EXIT TO OUR EAST.
YACK
THURSDAY THROUGH TUESDAY:
SNOW WILL BE WINDING DOWN TOWARD DAYBREAK ON THURSDAY THOUGH A
FEW FLURRIES MAY LINGER NEAR/SOUTHEAST OF I-55 THROUGH MID
MORNING. CONDITIONS BECOME FAVORABLE FOR LAKE EFFECT SNOW
ORIENTED INTO NORTHEAST PORTER COUNTY DURING THE DAY ON THURSDAY
(NORTHWESTERLY FETCH, INCREASING INVERSION HEIGHTS, STEEP LAPSE
RATES AND SATURATION THROUGH THE DGZ) WHICH COULD RESULT IN
ADDITIONAL ACCUMULATIONS (LOCALLY UP TO 0.5-1") AND CONTINUED
SLICK TRAVEL. CLOUD DEPTHS BEGIN TO THIN TOWARD THURSDAY EVENING
WITH THE MAIN AREA OF SNOW SHIFTING FURTHER EAST.
WINDS WILL BE BREEZY OUT OF THE NORTHWEST IN THE WAKE OF A COLD
FRONTAL PASSAGE THURSDAY MORNING WHICH COMBINED WITH
TEMPERATURES ONLY WARMING INTO THE UPPER TEENS TO LOWER 20S WILL
RESULT IN WIND CHILLS IN THE SINGLE DIGITS PERSISTING DURING
THE DAY. LOW TEMPERATURES THURSDAY NIGHT DROP INTO THE SINGLE
DIGITS ONCE AGAIN AREAWIDE WITH WIND CHILLS IN THE 0 TO -10
DEGREE RANGE. MORE OF THE SAME IS EXPECTED ON FRIDAY WITH HIGHS
IN THE LOWER 20S. A RETURN TO SOUTHWESTERLY FLOW FRIDAY NIGHT
SHOULD ALLOW TEMPERATURES TO SLOWLY RISE THROUGH THE NIGHT WITH
TEMPERATURES ON SATURDAY CURRENTLY FORECAST TO BRIEFLY WARM
ABOVE FREEZING (33-36F) IN THE AFTERNOON.
WHILE THERE REMAINS VARIABILITY IN THE HANDLING OF THE UPPER
LEVEL PATTERN INTO EARLY NEXT WEEK, THE GENERAL EXPECTATION IS
FOR AN ELONGATED POSITIVELY TILTED UPPER LEVEL TROUGH
(POTENTIALLY CUT-OFF LOW) TO DEVELOP ACROSS THE WESTERN CONUS
WITH QUASI-ZONAL FLOW EXTENDING EAST. THIS PATTERN LARGELY
FAVORS KEEPING MORE MOISTURE LADEN WEATHER DISTURBANCES LARGELY
SOUTH OF THE AREA AND IS SUPPORTED BY THE LATEST ENSEMBLE
GUIDANCE KEEPING PROBS FOR >0.1" OF PRECIPITATION GENERALLY
UNDER 20% THROUGH EARLY NEXT WEEK.
PETR
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1106 PM CST TUE JAN 21 2025
AVIATION FORECAST CONCERNS FOR 06Z TAFS:
- BLUSTERY SOUTH-SOUTHWEST WINDS GUSTING AROUND 25 KTS OVERNIGHT
AND WEDNESDAY.
- TWO POTENTIAL PERIODS OF LIGHT SNOW. FIRST WEDNESDAY
MORNING/MIDDAY MAINLY TOWARD THE IL/WI BORDER, THE SECOND
HIGHER PROBABILITY PERIOD FOR ALL SITES WEDNESDAY
EVENING/OVERNIGHT. MVFR/IFR POSSIBLE.
VFR MID-DECK WILL DEVELOP AND THICKEN ACROSS THE AREA OVERNIGHT,
WITHING A WARM ADVECTION REGIME ASSOCIATED WITH A 50 KT LOW
LEVEL JET AHEAD OF AN APPROACHING MID-LEVEL WAVE AND WARM FRONT.
PATCHY LIGHT SNOW IS EXPECTED TO DEVELOP ON THE NOSE OF THE LOW
LEVEL JET FROM IA INTO WI, AND ACROSS PORTIONS OF FAR
NORTH/NORTHWEST IL WEDNESDAY MORNING. KRFD APPEARS TO HAVE THE
GREATEST POTENTIAL FOR LIGHT SNOW DURING THIS PERIOD, THOUGH
HAVE MAINTAINED A PROB30 MENTION FOR CHICAGO TERMINALS (EXCEPT
KGYY). FORECAST MODELS VARY WITH THE DEGREE OF SATURATION IN
LOWER LEVELS, WITH LESS LIKELIHOOD OF SNOW THE FARTHER SOUTH AND
SOUTHEAST OF THE IL/WI BORDER. PATCHY FLURRIES OR VERY LIGHT
SNOW COULD LINGER AROUND KRFD INTO THE AFTERNOON, THOUGH A LULL
IS GENERALLY EXPECTED UNTIL THE SECOND (MORE LIKELY) PERIOD OF
LIGHT SNOW DEVELOPS LATE IN THE DAY/EVENING INTO THE OVERNIGHT
HOURS WITH THE APPROACH OF THE MAIN MID-LEVEL WAVE AND A SURFACE
COLD FRONT. THIS IS MORE LIKELY TO PRODUCE A PERIOD OF MVFR
CEILINGS AND LOW-MVFR/IFR VSBYS ACROSS MUCH OF THE AREA
BY LATER WEDNESDAY EVENING/EARLY OVERNIGHT. SNOW SHOULD END WITH
THE COLD FRONTAL PASSAGE, PREDAWN THURSDAY MORNING.
SURFACE WINDS HAVE BACKED SOUTHWEST AHEAD OF THE APPROACHING
SYSTEM, AND HAVE BEGUN TO INCREASE LATE THIS EVENING AS THE 50
KT LOW LEVEL JET SPREADS OVERHEAD. SOUTHWEST WINDS WILL LIKELY
CONTINUE TO GUST AROUND 25 KTS (WITH A FEW HIGHER GUSTS
POSSIBLE) THROUGH EARLY/MID AFTERNOON BEFORE EASING. WINDS WILL
SHIFT NORTHWEST BEHIND THE COLD FRONT, PREDAWN THURSDAY MORNING.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...COLD WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR ILZ003-
ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-
ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.
IN...COLD WEATHER ADVISORY UNTIL MIDNIGHT CST /1 AM EST/ TONIGHT
FOR INZ001-INZ002-INZ010-INZ011-INZ019.
LM...SMALL CRAFT ADVISORY UNTIL 6 PM CST WEDNESDAY FOR THE IL AND
IN NEARSHORE WATERS.
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