290
FXUS63 KLOT 201118
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
518 AM CST MON JAN 20 2025
KEY MESSAGES
- DANGEROUSLY COLD WIND CHILLS THIS MORNING AND THEN -20 TO
-29F WIND CHILLS EXPECTED MONDAY NIGHT THROUGH TUESDAY MORNING.
- INTERMITTENT FLURRIES ARE POSSIBLE AREAWIDE MONDAY
AFTERNOON/EVENING, WITH A SLIGHT CHANCE FOR SNOW SHOWERS
CREATING SLIPPERY TRAVEL FOR AREAS SOUTH OF I-80.
- 30 PERCENT CHANCE FOR ACCUMULATING SNOW AND SOME TRAVEL
IMPACTS WEDNESDAY TO THURSDAY.
DISCUSSION
ISSUED AT 221 AM CST MON JAN 20 2025
THROUGH TUESDAY:
BRUTALLY COLD WIND CHILLS ARE EXPECTED THIS MORNING. MANY
OBSERVATIONS AT THE TIME THIS DISCUSSION WAS POSTED ARE
RECORDING WIND CHILLS BETWEEN -14F TO -24F, AND THE COLDEST ARE
STILL EXPECTED IN A COUPLE MORE HOURS. SKIES ARE MOSTLY CLEAR,
EXCEPT FOR THE NORTHERN FRINGE OF LAKE AND PORTER COUNTIES IN
INDIANA. THE MAIN LAKE EFFECT SNOW MACHINE IS OFF TO THE
NORTHEAST IN MICHIGAN, BUT MICHIGAN CITY AND LA PORTE HAVE
CONSISTENTLY HAD SNOW OBSERVATIONS THIS MORNING. DESPITE WINDS
BECOMING MORE WESTERLY AND DECREASING FETCH ON THE LAKE, FELT IT
PRUDENT TO KEEP THE SLIGHT CHANCE (15 TO 25 PERCENT) FOR LAKE
EFFECT SHOWERS IN THE NORTHERNMOST PART OF OUR NORTHWESTERN
INDIANA AREA THROUGH THIS MORNING. LITTLE TO NO ACCUMULATIONS
ARE EXPECTED.
A STRONG LOBE OF VORTICITY AND BETTER HEIGHT FALLS AHEAD OF AN
UPPER LEVEL TROUGH IS PROJECTED MOVE SOUTHEASTWARD FROM THE
DAKOTAS THROUGH THE DAY. WITH TEMPERATURES AS COLD AS THEY ARE,
IT WOULD NOT TAKE MUCH TO SQUEEZE OUT SOME FLURRIES ACROSS THE
ENTIRE FORECAST AREA THIS AFTERNOON/EVENING. BUT MODEL SOUNDINGS
ARE DEPICTING STEEPER LOW LEVEL LAPSE RATES BEHIND THE COLD
FRONT AS IT SWINGS THROUGH. WHILE THERE IS LOWER CONFIDENCE IN
EXACT LOCATION AND TIMING OF SNOW SHOWERS, IT LOOKS LIKE A MORE
FAVORABLE SET-UP FOR SNOW SHOWERS THAT HAVE THE POTENTIAL FOR
LIGHT ACCUMULATIONS TO CREATE SOME SLIPPERY TRAVEL. FOR NOW,
A SLIGHT CHANCE (15 TO 25 PERCENT) FOR SNOW SHOWERS WAS ADDED
TO THE FORECAST FOR AREAS SOUTH OF I-80, THOUGH TIMING AND
PLACEMENT MAY BE REFINED THROUGH THE DAY.
MONDAY AFTERNOON WILL SEE TEMPERATURES "WARM" INTO THE SINGLE
DIGITS TO THE NORTH AND TEENS IN THE SOUTHERN FORECAST AREA WITH
WIND CHILLS "UP TO" -15F TO -5F. STRONG COLD AIR ADVECTION
BEHIND THE FRONT WILL DROP TEMPERATURES BELOW ZERO AGAIN TONIGHT
AND INTO TUESDAY MORNING. WIND CHILLS ARE EXPECTED TO DROP TO -20F
TO CLOSE TO -30F FOR AREAS NEAR THE WISCONSIN STATELINE. FOR
THIS REASON, THE COLD WEATHER ADVISORY WAS EXPANDED TO INCLUDE
OUR COUNTIES TO THE SOUTH AS CONFIDENCE HAS INCREASED IN WIND
CHILLS BEING OBSERVED. IT SHOULD BE NOTED THAT -30 (AND COLDER)
IS OUR CRITERIA FOR EXTREME COLD WARNINGS. WHILE OUR NORTHERN
COUNTIES WILL APPROACH THAT MARK, WINDS ARE EXPECTED TO DIMINISH
SLIGHTLY OVERNIGHT. AND WITHOUT A SNOWPACK, CONFIDENCE WAS NOT
THERE TO JUSTIFY UPGRADING THE ADVISORY TO A WARNING AT THIS
TIME.
DK
TUESDAY NIGHT THROUGH SUNDAY:
WE'LL FINALLY BEGIN TO DISLODGE OUR ARCTIC AIRMASS TUESDAY
NIGHT AS THE SPRAWLING MID 1030S MB HIGH PRESSURE SHIFTS OFF TO
OUR SOUTH AND EAST. WHILE IT'LL STILL BE COLD, IT LOOKS LIKE
TEMPERATURES SHOULD ACTUALLY LEVEL OFF AND EVEN SLOWLY RISE
AFTER MIDNIGHT AS SOUTHERLY BREEZES KICK IN, WITH LOW
TEMPERATURES POTENTIALLY OCCURRING IN THE EVENING. WHILE AIR
TEMPERATURES MAY RISE THROUGH THE NIGHT, INCREASING WINDS
SUGGEST THAT WIND CHILLS WILL PROBABLY REMAIN FAIRLY STEADY,
GENERALLY HOVERING AROUND -15, JUST A SMIDGE WARMER THAN LOCAL
COLD WEATHER ADVISORY CRITERIA. AS A RESULT, HAVE NOT EXTENDED
THE ADVISORIES INTO TUESDAY NIGHT AT THIS TIME, BUT WILL MESSAGE
CONTINUED CHILLY AND BLUSTERY CONDITIONS. DEPENDING ON HOW
STRONG WINDS GET, LOCAL EXTENSIONS TO THE COLD WEATHER
ADVISORIES MAY BE NEEDED, BUT THIS MIGHT BE MORE OF A GAME
TIME/TACTICAL DECISION AS WE GET CLOSER.
AS WE TRANSITION OUT OF THE ARCTIC AIRMASS, THE UPPER PATTERN
GETS PRETTY CONVOLUTED, AS A GIGANTIC REGION OF CYCLONIC FLOW
SETS UP ACROSS THE NORTHERN 2/3RDS OF THE CONUS WITH NUMEROUS
EMBEDDED VORT MAXES/PERTURBATIONS MEANDERING ABOUT WITHIN THE
GYRE. THIS ENERGETIC PATTERN IS DRIVING SOME PRETTY NOTABLE
SPREAD IN THE MEDIUM RANGE GUIDANCE, WHICH LOWERS OVERALL
FORECAST CONFIDENCE TO CLOSE OUT THE WEEK. THAT SAID, THERE'S A
GROWING SIGNAL (MAINLY IN THE ENSEMBLE SUITE) FOR A PERIOD OF
LIGHT SNOW DURING THE WEDNESDAY - WEDNESDAY NIGHT TIMEFRAME AS
AN INITIAL BROAD SURFACE TROUGH AND EMBEDDED SURFACE LOW DRIFTS
ACROSS THE REGION. WHILE FORCING DOESN'T CURRENTLY LOOK
PARTICULARLY ROBUST WITH UVVS GENERALLY PEAKING IN THE -2 TO -4
UBAR/SECOND RANGE, MOST FORECAST PROFILES SATURATE DOWN TO
AROUND 850 MB (OR LOWER) THROUGH WEDNESDAY MORNING AND
AFTERNOON. ADDITIONALLY, DGZ DEPTHS ARE INCREDIBLY DEEP, IN
EXCESS OF 3 KM AT TIMES, ALONG WITH DEEP ISOTHERMAL LAYERS. AS A
RESULT, EVEN JUST MODEST ASCENT MAY BE ENOUGH TO CRANK OUT HUGE
STELLAR DENDRITES ALOFT WHICH COULD MORE READILY BREAK THROUGH
ANY LINGERING NEAR-SURFACE DRY LAYERS. WITH THIS IN MIND,
CONTINUE TO INCREASE POPS A BIT ABOVE BLENDED GUIDANCE AND HAVE
INTRODUCED SOME LIGHT (AN INCH OR LESS) SNOW ACCUMULATIONS INTO
THURSDAY MORNING. WITH GROUND TEMPERATURES STILL LIKELY TO BE
VERY COLD, ANY SNOW WOULD HAVE LITTLE DIFFICULTY STICKING EVEN
TO TREATED SURFACES.
ADDITIONAL VORT LOBES WILL FOLLOW THROUGH THE END OF THE WEEK,
BUT FORECAST CONFIDENCE REALLY BREAKS DOWN THURSDAY AND FRIDAY
OWING TO SIZABLE DIFFERENCES IN THE PLACEMENT OF THESE WAVES AND
ASSOCIATED JET STREAKS DEVELOP ACROSS THE MODEL SUITE. AT THIS
POINT, HAVE LEFT THE FORECAST "DRY" BUT SUFFICE IT TO SAY THAT
ADDITIONAL CHANCES FOR LIGHT SNOW MAY BE REALIZED DURING THIS
TIME FRAME.
MEDIUM-RANGE GUIDANCE IS MIXED ON WHETHER THE PREDOMINANTLY DRY
NORTHWESTERLY MID AND UPPER FLOW PATTERN WILL EASE OR BECOME
WEST-SOUTHWEST FOR A TIME NEXT WEEKEND, WHICH MAY OPEN THE DOOR
FOR A RETURN OF PRECIP CHANCES (SNOW OR RAIN/SNOW/WINTRY MIX)
SATURDAY NIGHT INTO SUNDAY. GIVEN THE SPREAD IN GUIDANCE, SO SAW
NO REASON TO STRAY FROM THE SLIGHT (~20%) CHANCE POPS OFFERED
BY THE NBM, PRIMARILY SOUTHEAST OF I-55 TOWARDS THE END OF THE
WEEKEND.
CARLAW
AVIATION /12Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 518 AM CST MON JAN 20 2025
THE ONLY AVIATION WEATHER CONCERN IS A POTENTIAL FOR FLURRIES
LATE THIS AFTERNOON AND EVENING.
WSW WINDS AROUND 10 KNOTS WILL GRADUALLY INCREASE THIS MORNING,
WITH GUSTS TO AROUND 25 KNOTS EXPECTED THIS AFTERNOON. SHALLOW
STRATOCUMULUS STREETS ARE EVIDENT IN SATELLITE IMAGERY ACROSS
MINNESOTA AHEAD OF A DISTURBANCE ALOFT. THIS CLOUD COVER IS
EXPECTED TO BUILD SOUTH AND EASTWARD INTO THE REGION LATER THIS
AFTERNOON AND EVENING. LATEST INDICATIONS ARE THAT ANY CIGS
SHOULD GENERALLY REMAIN VFR. IT'S PRETTY EASY TO SQUEEZE OUT
FLURRIES/VERY FINE SNOW EVEN FROM SHALLOW CLOUD LAYERS IN ARCTIC
AIRMASSES, SO WITH LOW-LEVEL MOISTURE AND SUBTLE FORCING
EXPECTED TO INCREASE TODAY, CONTINUED A MENTION OF VFR FLURRIES
AT ALL TAF SITES AS A RESULT.
WINDS WILL EASE A BIT THIS EVENING, ALTHOUGH INTERMITTENT GUSTS
TO AROUND 20 KNOTS WILL LIKELY CONTINUE.
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 9 PM THIS EVENING TO NOON CST
TUESDAY 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 NOON CST /1 PM EST/ TODAY FOR
INZ001-INZ002-INZ010-INZ011-INZ019.
COLD WEATHER ADVISORY FROM 9 PM CST /10 PM EST/ THIS EVENING
TO NOON CST /1 PM EST/ TUESDAY FOR INZ001-INZ002-INZ010-
INZ011-INZ019.
LM...SMALL CRAFT ADVISORY UNTIL 3 AM CST TUESDAY FOR THE IL AND IN
NEARSHORE WATERS.
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