463
FXUS63 KLOT 180901
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
301 AM CST TUE FEB 18 2025
KEY MESSAGES
- BITTERLY COLD CONDITIONS ARE EXPECTED THROUGH THURSDAY MORNING.
- THERE IS A 30-40% CHANCE FOR LAKE EFFECT SNOW TO ACCUMULATE
IN PORTIONS OF PORTER COUNTY, IN THROUGH THURSDAY.
- THERE IS A LOW (20-30%) CHANCE OF LIGHT ACCUMULATING SNOW AND
SLIPPERY TRAVEL WEDNESDAY EVENING.
- TEMPERATURES ARE EXPECTED TO GRADUALLY WARM BACK TOWARD AND
EVEN ABOVE NORMAL LATE THIS WEEK INTO EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 301 AM CST TUE FEB 18 2025
THROUGH WEDNESDAY NIGHT:
IT IS DOWNRIGHT COLD OUT THERE EARLY THIS MORNING, PARTICULARLY
ACROSS NORTHERN ILLINOIS WHERE WIND CHILLS ARE ALREADY IN THE -20
TO -25 DEGREE RANGE. SKIES HAVE AT LEAST BRIEFLY CLEARED OUT
SOUTH OF I-80 RESULTING IN TEMPERATURES STEADILY DROPPING
AREAWIDE. HOWEVER, ADDITIONAL HIGH CLOUDS ARE MOVING IN BACK
FROM THE WEST ALREADY. OTHERWISE MAY HAVE CONSIDERED A SHORT-
FUSED EXPANSION OF THE ADVISORY INTO INDIANA. FOR NOW, NO
CHANGES ARE PLANNED WITH THE COLD WEATHER ADVISORY WHICH
REMAINS IN EFFECT THROUGH NOON IN ILLINOIS. TEMPERATURES WILL
STRUGGLE TO WARM OUT OF THE SINGLE DIGITS TODAY ACROSS INTERIOR
NORTHERN ILLINOIS WITH LOW TEENS EXPECTED ELSEWHERE.
CLOUD COVER WILL BEGIN TO INCREASE INTO TONIGHT ON THE NORTHERN
EDGE OF A DISTURBANCE EXPECTED TO PASS LARGELY TO THE SOUTH OF
THE AREA. THIS WILL LIKELY LIMIT OUR OVERNIGHT COOLING COMPARED
TO THIS MORNING, WITH LOWS FORECAST IN THE SINGLE DIGITS ABOVE
ZERO FOR MOST AREAS. THE EXCEPTION TO THIS MAY BE RURAL AREAS
OF INTERIOR NORTHERN ILLINOIS MAINLY OUTSIDE OF THE CHICAGO
METRO WHERE TEMPERATURES MAY STILL STRUGGLE TO REACH ZERO AND
WIND CHILLS COULD BE AS LOW AS -20F AT TIMES. HAVE ACCORDINGLY
MATCHED UP WITH NEIGHBORING OFFICES AND HOISTED ANOTHER COLD
WEATHER ADVISORY FOR LEE, OGLE, WINNEBAGO, BOONE, DEKALB, AND
MCHENRY COUNTIES TONIGHT. IT IS POSSIBLE THAT THESE AREAS END
UP JUST SHY OF THE -20F CRITERIA, BUT IT WILL STILL BE BITTERLY
COLD ACROSS THE AREA AGAIN TONIGHT REGARDLESS. TEMPERATURES ON
WEDNESDAY WILL ONLY BE SLIGHTLY WARMER THAN TODAY WITH HIGHS
ONLY A DEGREE OR TWO WARMER IN MOST AREAS.
LIGHT LAKE EFFECT FLURRIES HAVE DIPPED INTO NORTHEAST PORTER
COUNTY EARLY THIS MORNING AS ARCTIC AIR MOVES OVER LAKE MICHIGAN.
EXPECT LIGHT SNOW TO CONTINUE OFF AND ON THROUGH WEDNESDAY AS
WINDS REMAIN GENERALLY NORTHWESTERLY THROUGH THAT TIME. THIS
COULD RESULT IN A DUSTING TO LOCALLY UP TO 1" OF ACCUMULATION
THROUGH WEDNESDAY MORNING IN NORTHEAST PORTER COUNTY.
THE EARLIER MENTIONED DISTURBANCE IS TIED TO A PACIFIC
NORTHWEST ORIGINATING MID-LEVEL SHORTWAVE WHICH HAS TRENDED
FASTER OVER THE PAST DAY OR SO, WITH GUIDANCE NOW HAVING IT MOVE
WELL AHEAD OF A TRAILING UPPER LEVEL WAVE DIVING OUT OF CANADA
LATE WEDNESDAY. THIS HAS SHIFTED LIGHT SNOW CHANCES TO LATER IN
THE DAY, WITH DRY CONDITIONS FORECAST FOR MOST AREAS (OUTSIDE
OF LAKE EFFECT IN NW IN) THROUGH AT LEAST MID AFTERNOON. A SHORT
PERIOD OF LIGHT SNOW SHOWERS REMAINS POSSIBLE WEDNESDAY EVENING
(20-30% CHANCE), MAINLY NEAR/EAST OF I-55 WHERE SATURATION MAY
BECOME SUFFICIENT AMIDST STEEP LOW-LEVEL LAPSE RATES WITHIN THE
DGZ. ANY SNOW THAT DOES FALL WOULD READILY COAT UNTREATED
PAVEMENT GIVEN THE COLD TEMPERATURES.
PETR
THURSDAY THROUGH MONDAY:
OUR STRETCH OF BITTER MID-FEBRUARY COLD WILL CONTINUE INTO
THURSDAY, WITH MORNING LOWS LIKELY TO END UP IN THE SINGLE
DIGITS, AND QUITE POSSIBLY BELOW ZERO ONCE AGAIN ACROSS PORTIONS
OF NORTHERN AND CENTRAL ILLINOIS. OUR CURRENT NBM-BASED WIND
FORECAST WOULD HAVE THIS TRANSLATE TO WIND CHILLS BETWEEN -10
AND -20F ACROSS MOST OF OUR FORECAST AREA, MAKING WEDNESDAY
NIGHT/THURSDAY MORNING ANOTHER PERIOD WHERE WE'LL AT LEAST BE
BRUSHING UP AGAINST COLD WEATHER ADVISORY CRITERIA ONCE AGAIN.
DAYTIME TEMPERATURES ON THURSDAY THEN LOOK TO REBOUND INTO THE
MID-TEENS TO MID-20S BEFORE LOW TEMPERATURES SIMILAR TO THOSE
OF THURSDAY MORNING ARE OBSERVED AGAIN FRIDAY MORNING. WINDS
SHOULD BE LIGHTER BY FRIDAY MORNING AS THE CENTER OF A STRONG
1040+ MB CANADIAN SURFACE HIGH SETTLES INTO THE MID-MISSISSIPPI
RIVER VALLEY, SO WIND CHILLS WON'T BE AS BAD AS THEY WERE
EARLIER IN THE WEEK, BUT THEY WILL STILL LIKELY END UP BEING
NEAR OR BELOW ZERO ACROSS OUR FORECAST AREA.
BY SATURDAY, THE SURFACE HIGH WILL HAVE DRIFTED OFF TO OUR
SOUTHEAST, RESULTING IN SOUTHWESTERLY SURFACE WINDS BECOMING
ESTABLISHED ACROSS THE REGION OVER THE WEEKEND. THESE
SOUTHWESTERLY WINDS WILL HELP FACILITATE A WARM UP THAT WILL SEE
TEMPERATURES CLIMB CLOSER TO AND EVENTUALLY ABOVE CLIMATOLOGICAL
NORMALS FOR THIS TIME OF YEAR OVER THE WEEKEND AND INTO EARLY
NEXT WEEK. OF COURSE, THROUGHOUT THIS TIME, WE WILL NEED TO
MONITOR THE POTENTIAL FOR ICE JAMS ON AREA RIVERS AND THE
ASSOCIATED THREAT FOR LOCALIZED FLOODING AS RIVER ICE INITIALLY
FREEZES UP, THEN POTENTIALLY STARTS TO BREAK UP WITH THE ARRIVAL
OF THE MILDER TEMPERATURES.
OUTSIDE OF LAKE EFFECT SNOW POTENTIALLY LINGERING INTO THURSDAY
IN PORTER COUNTY, INDIANA, NO PRECIPITATION IS OTHERWISE
EXPECTED THROUGH THE END OF THE WORKWEEK WITH THE STRONG
CANADIAN HIGH EXERTING ITS INFLUENCE ON THE REGION. THERE IS
SOME ENSEMBLE SUPPORT FOR LIGHT SNOW OR FLURRIES OCCURRING ON
SATURDAY AS THE HIGH DEPARTS AND AN UPPER-LEVEL SHORTWAVE TRACKS
THROUGH THE MIDWEST, THOUGH THERE ISN'T A WHOLE LOT OF AGREEMENT
AT THIS TIME ON WHERE EXACTLY PRECIPITATION WOULD OCCUR, OR
WHETHER IT WILL EVEN OCCUR AT ALL. DUE TO THE LARGE ENSEMBLE
SPREAD AND THE GENERALLY LIGHT QPF BEING OUTPUT BY PRECIPITATING
ENSEMBLE MEMBERS, THE LATEST NBM'S POPS CAME IN UNDER 10%
ACROSS OUR FORECAST AREA ON SATURDAY. OPTED TO LEAVE THESE BE
FOR NOW GIVEN THE HIGH DEGREE OF UNCERTAINTY AT THIS TIME, BUT
DEPENDING ON HOW GUIDANCE TRENDS, ADJUSTMENTS TO THESE POPS MAY
NEED TO BE MADE IN FORTHCOMING FORECAST PACKAGES.
BEYOND SATURDAY, ENSEMBLE GUIDANCE DEPICTS A MORE ACTIVE
NORTHWEST FLOW PATTERN SETTING UP ACROSS THE REGION GOING INTO
NEXT WEEK WITH MULTIPLE SUCCESSIVE SHORTWAVES DIVING INTO THE
MIDWEST/GREAT LAKES. AS A RESULT, THERE WILL LIKELY BE AT LEAST
A COUPLE OF OPPORTUNITIES FOR PRECIPITATION TO OCCUR IN THE
GENERAL REGION NEXT WEEK, THOUGH AT THIS TIME, CONFIDENCE IS
STILL LOW REGARDING EXACTLY WHERE AND WHEN THOSE PRECIPITATION
CHANCES MAY MATERIALIZE.
OGOREK
AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 1054 PM CST MON FEB 17 2025
THERE ARE NO SIGNIFICANT AVIATION WEATHER CONCERNS. VFR
CONDITIONS WITH PERIODS OF SCT-BKN CLOUD COVER AT 10,000 TO
25,000 FT WILL CONTINUE THROUGH THE PERIOD, ALONG WITH NW WINDS
AROUND 10 KT.
CARLAW
LOT WATCHES/WARNINGS/ADVISORIES
IL...COLD WEATHER ADVISORY UNTIL NOON CST TODAY FOR ILZ003-ILZ004-
ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-
ILZ105-ILZ106-ILZ107-ILZ108.
COLD WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM CST
WEDNESDAY FOR ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011.
IN...NONE.
LM...NONE.
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