268
FXUS63 KLOT 202101
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
301 PM CST MON JAN 20 2025
KEY MESSAGES
- SCATTERED FLURRIES EXPECTED THIS AFTERNOON AND EVENING. A FEW
SNOW SHOWERS ARE ALSO POSSIBLE FOR AREAS SOUTH OF THE
KANKAKEE RIVER WHERE SOME SNOW ACCUMULATIONS MAY OCCUR.
- ANOTHER BITTERLY COLD NIGHT AHEAD WITH WIND CHILLS IN THE -20F
TO -30F RANGE. COLD WEATHER ADVISORY REMAINS IN EFFECT UNTIL
NOON TUESDAY.
- 30-40 PERCENT CHANCE OF ACCUMULATING SNOW ON WEDNESDAY WHICH
COULD LEAD TO SLIPPERY TRAVEL.
DISCUSSION
ISSUED AT 300 PM CST MON JAN 20 2025
THROUGH TUESDAY NIGHT:
CLOUD COVER HAS BEEN INCREASING ACROSS MUCH OF THE MIDWEST
(INCLUDING NORTHERN IL) THIS AFTERNOON AS AN UPPER-LEVEL
DISTURBANCE PIVOTS THROUGH THE REGION. GIVEN THE COLD AIR MASS
IN PLACE, CLOUD TOP TEMPERATURES ARE SITTING BELOW -20C WHICH
HAS YIELD SOME FLURRIES AND EVEN A FEW BONAFIDE SNOW SHOWERS
WHERE LOW-LEVEL INSTABILITY HAS MAXIMIZED. THESE FLURRIES AND
SNOW SHOWERS ARE EXPECTED TO DRIFT INTO NORTHERN IL AND
NORTHWEST IN OVER THE NEXT 1 TO 3 HOURS AND PERSIST THROUGH AT
LEAST MIDNIGHT BEFORE TAPERING. WHILE ACCUMULATIONS WITH ANY
FLURRIES ARE NOT EXPECTED, THE FINE SNOW GRAINS AND BLUSTERY
WINDS MAY PRODUCE LOCAL VISIBILITY REDUCTIONS IN THE 3 TO 5 MILE
RANGE WITH LOWER VALUES POSSIBLE WITH ANY TRUE SHOWERS.
HOWEVER, SOME SNOW ACCUMULATIONS (GENERALLY UNDER A QUARTER
INCH) MAY OCCUR WITH THE SNOW SHOWERS; ESPECIALLY FOR AREAS
SOUTH OF THE KANKAKEE RIVER WHERE BETTER SHOWER COVERAGE IS
FORECAST. THAT SAID, THOSE PLANNING TO BE OUT AND ABOUT TONIGHT
SHOULD USE CAUTION IN CASE OF SLIPPERY ROADS AND VISIBILITY
CHANGES.
THE BIGGER WEATHER STORY OF THE NIGHT WILL BE THE RETURN OF
BITTERLY COLD TEMPERATURES AND WIND CHILLS AS THE SNOW DEPARTS.
WHILE SOME GUIDANCE IS SHOWING CLOUD COVER PERSISTING OVERNIGHT,
THE THIN NATURE OF ANY CLOUDS SHOULDN'T INHIBIT RADIATIONAL
COOLING MUCH. THEREFORE, EXPECT OVERNIGHT LOWS TO DIP BELOW ZERO
WITH WIND CHILLS EXPECTED TO BOTTOM OUT IN THE -20F TO -30F
RANGE BY DAYBREAK. SINCE THE -30F WIND CHILLS WILL BE MORE
ISOLATED, HAVE DECIDED TO MAINTAIN THE COLD WEATHER ADVISORY FOR
NOW BUT IF MORE WIDESPREAD COVERAGE OF THESE WIND CHILLS OCCUR
AN UPGRADE TO A EXTREME COLD WARNING MAY BE CONSIDERED.
TEMPERATURES WILL REBOUND A BIT ON TUESDAY, BUT DESPITE THE
SUNSHINE HIGHS WILL ONLY TOP OUT IN THE LOW SINGLE DIGITS.
COUPLE THIS WITH THE 15 TO 20 MPH WINDS AND WIND CHILLS WILL
REMAIN IN THE NEGATIVE TEENS THROUGH THE DAY ON TUESDAY.
HOWEVER, AS WINDS TURN MORE SOUTH- SOUTHWESTERLY TUESDAY NIGHT
TEMPERATURES SHOULD GRADUALLY INCREASE HEADING INTO WEDNESDAY
MORNING. THOUGH, LOWS TUESDAY NIGHT WILL STILL BE AROUND ZERO TO
NEGATIVE SINGLE DIGITS BEFORE THIS OCCURS.
YACK
WEDNESDAY THROUGH MONDAY:
SOUTHWESTERLY WARM ADVECTION WILL BE WELL UNDERWAY AT THE
BEGINNING OF THE EXTENDED FORECAST PERIOD WITH THE REGION
SITUATED BETWEEN A 1030+MB HIGH OVER THE MID-ATLANTIC AND LOW
PRESSURE DEVELOPING ACROSS NORTHERN MINNESOTA/SOUTHWEST ONTARIO.
WHILE TEMPERATURES WILL ACCORDINGLY BE INCREASING STEADILY
THROUGHOUT THE DAY, SUB-ZERO WIND CHILLS ARE EXPECTED TO PERSIST
THROUGH WEDNESDAY MORNING DUE TO WINDS GUSTING UP TO 25-30 MPH.
IN ADDITION TO THE WARMING TEMPERATURES AND GUSTY WINDS, THERE
IS THE POTENTIAL FOR ACCUMULATING SNOW WEDNESDAY MORNING THROUGH
THE EVENING. A PAIR OF SHORTWAVES ARE FORECAST TO MOVE THROUGH
THE BROADER REGION DURING THIS TIME, ONE PAIRED WITH THE
AFOREMENTIONED SURFACE LOW ACROSS THE NORTHWEST GREAT LAKES AND
A SEPARATE SHEARED OUT WAVE PIVOTING OUT OF THE CENTRAL PLAINS.
WHILE THESE FEATURES DON'T APPEAR TO PHASE FULLY (AT LEAST AT
THIS RANGE), ASCENT ASSOCIATED WITH THEM SHOULD BE SUFFICIENT
FOR SNOW.
MODELED VERTICAL PROFILES SHOW A STOUT BUT DRY LAYER IN THE
LOWEST LEVELS, AT LEAST INITIALLY WEDNESDAY MORNING. STEADY
SATURATION IN THE MID-LEVELS IS EXPECTED, WHICH BECOMES QUITE
DEEP THROUGH THE DGZ (2-3+ KM) AT TIMES WHICH WOULD SUPPORT
LARGE ENOUGH DENDRITES TO PUNCH THROUGH THIS DRY LAYER. WHILE
IT WILL BE NOTABLY WARMER THAN THE FIRST PART OF THE WEEK, AIR
TEMPERATURES STILL IN THE TEENS AND LOWER 20S WOULD ALLOW SNOW
TO READILY ACCUMULATE ON UNTREATED SURFACES. MODELS CONTINUE TO
SUPPORT A MOSTLY LIGHTER QPF SCENARIO WITH THIS SYSTEM, WITH
SNOWFALL AMOUNTS GENERALLY IN THE 1" OR LESS RANGE, JUST ENOUGH
TO MAKE UNTREATED ROADS SLIPPERY. FOR NOW HAVE MAINTAINED
MAINLY 30-40 PERCENT CHANCES FOR SNOW WITH THIS SYSTEM. WOULD
LIKE TO SEE HOW SOME OF THE HI-RES GUIDANCE HANDLES THINGS
BEFORE INTRODUCING "LIKELY" OR HIGHER POPS (55%+), BUT SUSPECT
THAT IS WHERE THINGS ARE HEADED.
THE COLD FRONT EVENTUALLY MOVES THROUGH LATE WEDNESDAY NIGHT
INTO THURSDAY MORNING, TEMPORARILY STALLING OUR WARMING TREND ON
WITH HIGHS IN MID-UPPER 20S. LAKE EFFECT SNOW MAY LINGER IN
NORTHEAST PORTER COUNTY, OTHERWISE DRY CONDITIONS ARE FORECAST
THROUGH THE END OF THE WEEK WITH TEMPERATURES GRADUALLY
MODERATING EACH DAY BACK TO ABOVE FREEZING ON SATURDAY. WHILE A
QUICK HIT OF LIGHT SNOW CAN'T BE RULED OUT AT TIMES, ENSEMBLE
TRENDS FAVOR GENERALLY DRIER CONDITIONS CONTINUING.
PETR
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1142 AM CST MON JAN 20 2025
SCATTERED LOW-END VFR STRATOCUMULUS THIS AFTERNOON WILL
INCREASE IN COVERAGE AND DEEPEN EARLY THIS EVENING AS A MID-
LEVEL WAVE CROSSES THE REGION. FLURRIES CAN BE EXPECTED
THROUGHOUT THE EVENING, WITH ISOLATED TO SCATTERED SHSN CAPABLE
OF BRIEFLY REDUCING VISIBILITY TO MVFR LEVELS DUE THE NATURE OF
SMALL SNOWFLAKES IN ARCTIC AIRMASSES. W WINDS GUSTING TO AROUND
25 KNOTS THIS AFTERNOON WILL VEER WNW THIS EVENING AMID STRONG
COLD AIR ADVECTION.
SCATTERED MVFR CLOUDS MAY PERSIST OVERNIGHT, BUT SKC CONDITIONS
ARE EXPECTED THROUGH MUCH OF DAYTIME HOURS ON TUESDAY. WINDS
WILL REMAIN W/WNW WITH GUSTS OVER 20 KNOTS THROUGH THE DAY.
KLUBER
LOT WATCHES/WARNINGS/ADVISORIES
IL...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 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.
VISIT US AT WEATHER.GOV/CHICAGO
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