176
FXUS63 KLOT 161212
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
612 AM CST SUN FEB 16 2025
KEY MESSAGES
- LAKE EFFECT SNOW EXPECTED THIS MORNING IN NORTHWEST IN (MAY
BRUSH THE IMMEDIATE IL LAKESHORE), POTENTIALLY LINGERING INTO
THE AFTERNOON AND EVENING IN PORTER COUNTY, IN. SOME LOCALIZED
TRAVEL IMPACTS ARE POSSIBLE DUE TO SNOW-COVERED ROADS.
PERIODS OF LIGHT SNOW/FLURRIES ARE LIKELY ELSEWHERE TODAY.
- BITTERLY COLD CONDITIONS ARE EXPECTED SUNDAY NIGHT THROUGH
THURSDAY MORNING.
- THERE'S A LOW CHANCE OF ACCUMULATING SNOW WELL SOUTH OF I-80
MONDAY AFTERNOON AND EVENING, THEN A CHANCE OF FLUFFY
ACCUMULATING SNOW AND ASSOCIATED TRAVEL IMPACTS AREAWIDE LATE
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT.
DISCUSSION
ISSUED AT 411 AM CST SUN FEB 16 2025
THROUGH MONDAY:
OVERNIGHT REGIONAL RADAR MOSAIC IMAGERY SHOWS A LAKE EFFECT
SNOW BAND JUST OFF THE WISCONSIN LAKESHORE PIVOTING SOUTHWARD
AND SETTING ITS SIGHTS ON FAR NORTHEAST ILLINOIS AND NORTHWEST
INDIANA. WHILE SOME LIGHT LAKE ENHANCED SNOW/FLURRIES AND EVEN
PATCHES OF FREEZING DRIZZLE HAVE BEEN OBSERVED OUT AHEAD OF THIS
LAKE EFFECT BAND, STEADIER SNOWFALL WILL COMMENCE AS WE
APPROACH DAYBREAK AS INVERSION HEIGHTS CLIMB ABOVE 5000 FT AGL,
STEEPENING LOW-LEVEL LAPSE RATES YIELD 50-100 J/KG OF LAKE-
INDUCED CAPE, AND CLOUD-LAYER TEMPERATURES BECOME MORE FIRMLY
ENTRENCHED WITHIN THE DENDRITIC GROWTH ZONE. WHILE THE LAKE
EFFECT PARAMETER SPACE AS A WHOLE WON'T BE SPECTACULAR BY ANY
MEANS, STRONG LOW-LEVEL CONVERGENCE COULD STILL ALLOW FOR SNOW
TO COME DOWN AT A PRETTY DECENT CLIP WITHIN THE MAIN LAKE EFFECT
BAND -- POSSIBLY BETWEEN 0.5" AND 1"/HOUR AS LAKE EFFECT
PARAMETERS CRESCENDO DURING THE LATE MORNING/EARLY AFTERNOON PER
THE 00Z HREF.
IT STILL LOOKS AS THOUGH THIS LAKE EFFECT BAND SHOULD SCOOT
EASTWARD QUICK ENOUGH DURING THESE PEAK SNOWFALL RATES TO
PREVENT OVERALL SNOW ACCUMULATIONS FROM GETTING TOO OUT OF HAND,
BUT IF IT DOES END PROGRESSING MORE SLOWLY TO THE EAST LATER
THIS MORNING, THEN COULD ENVISION LOCALIZED SNOW TOTALS NEAR 3"
OCCURRING IN A PORTION OF NORTHWEST INDIANA. THE MOST LIKELY
OUTCOME FEATURES SNOW TOTALS UP TO AROUND 1" IN LAKE-ADJACENT
PORTIONS OF NORTHEAST ILLINOIS AND IN THE 1-2" RANGE ACROSS MUCH
OF NORTHWEST INDIANA, SO WILL REISSUE THE GOING SPECIAL WEATHER
STATEMENT TO CONTINUE TO HIGHLIGHT THE LIKELIHOOD OF SLIPPERY
TRAVEL FROM SNOW-COVERED ROADS.
ELSEWHERE TODAY, EXPECT PERIODIC LIGHT SNOW/FLURRIES AS AN
ANOMALOUSLY COLD MID/UPPER-LEVEL TROUGH ENTERS THE REGION. IT
WILL ALSO BE UNPLEASANTLY BLUSTERY WITH NORTHWESTERLY WINDS
GUSTING IN EXCESS OF 30 MPH DUE TO THE PRESENCE OF A TIGHT
PRESSURE GRADIENT BETWEEN A DEPARTING, BUT STILL DEEPENING, LOW
PRESSURE SYSTEM TO OUR SOUTHEAST AND STRONG HIGH PRESSURE TO OUR
NORTHWEST. THESE STRONG WINDS COULD LEAD TO SOME PATCHY BLOWING
SNOW OCCURRING PRIMARILY IN RURAL PORTIONS OF INTERIOR NORTHERN
ILLINOIS WHERE A DEEP ENOUGH SNOWPACK EXISTS, BUT DON'T HAVE A
GOOD FEEL FOR HOW SUSCEPTIBLE THE EXISTING SNOWPACK IS TO BEING
BLOWN AROUND, SO DON'T HAVE ANY PLANS TO MESSAGE THIS
POSSIBILITY MORE PROMINENTLY AT THIS TIME. TEMPERATURES LIKELY
WON'T CLIMB MUCH, IF AT ALL, TODAY DUE TO EXPANSIVE CLOUD COVER
AND COLD AIR ADVECTION OCCURRING OFF OF THE BLUSTERY
NORTHWESTERLY WINDS.
CONTINUED COLD AIR ADVECTION OVER AN APPRECIABLE SNOWPACK THAT
IS DEEPEST TO OUR NORTHWEST WILL RESULT IN BITTERLY COLD
CONDITIONS RETURNING TO THE AREA TONIGHT. LOW TEMPERATURES
TONIGHT/MONDAY MORNING ACROSS OUR FORECAST AREA LOOK TO END UP
BOTTOMING OUT IN THE SINGLE DIGITS ON EITHER SIDE OF 0F, COLDEST
FARTHER NORTHWEST. WHILE THE NORTHWESTERLY WINDS SHOULD
DIMINISH SLIGHTLY TONIGHT, THEY WILL REMAIN BLUSTERY ENOUGH TO
PUSH WIND CHILLS WELL BELOW ZERO AND LIKELY BELOW OUR -20F COLD
WEATHER ADVISORY CRITERIA IN INTERIOR PORTIONS OF NORTHERN
ILLINOIS. SHOULD NOTE THAT THERE IS SOME UNCERTAINTY REGARDING
THE EXTENT TO WHICH OUR OVERHEAD CLOUD DECK WILL CLEAR OUT
TONIGHT, AND IF THE CLOUDS HANG ON FOR LONGER THAN PRESENTLY
EXPECTED, THEN LOWS AND MINIMUM WIND CHILLS MAY END UP BEING NOT
AS COLD AS PRESENTLY FORECASTED. THOUGH, REGARDLESS OF WHETHER
WIND CHILLS REACH -20F OR END UP CLOSER TO -10F TONIGHT, IT WILL
UNDOUBTEDLY BE A COLD START TO WHAT'S LOOKING TO BE A FRIGID
WORKWEEK.
DAYTIME TEMPERATURES ON MONDAY LOOK TO ONLY REBOUND INTO THE
TEENS AT BEST AND COULD REMAIN IN THE SINGLE DIGITS AT WORST AS
WEST-NORTHWESTERLY WINDS REMAIN BLUSTERY. ADDITIONALLY, MID-
LEVEL FRONTOGENESIS AND A PAIR OF MID-LEVEL IMPULSES WILL LIKELY
INDUCE A BAND OF SNOW IN THE MID-MISSISSIPPI RIVER VALLEY ON
MONDAY. THE LATEST MODEL GUIDANCE SUGGESTS THAT THIS BAND SHOULD
LARGELY REMAIN TO OUR SOUTH, BUT COULD STILL AT LEAST GET CLOSE
TO OUR SOUTHERN COUNTIES MONDAY AFTERNOON AND/OR EVENING. GIVEN
THAT EVEN A DUSTING OF SNOW CAN CAUSE NOTABLE TRAVEL PROBLEMS
WHEN TEMPERATURES ARE IN THE TEENS AND SINGLE DIGITS, OPTED TO
MAINTAIN A SLIVER OF SLIGHT CHANCE POPS ACROSS OUR FAR SOUTHERN
CWA IN THE EVENT THAT THE BAND WERE TO SHIFT A LITTLE FARTHER TO
THE NORTH THAN WHAT THE LATEST GUIDANCE AS A WHOLE SUGGESTS.
OGOREK
MONDAY NIGHT THROUGH SATURDAY:
THE EXTENDED PERIOD OF BITTERLY COLD TEMPERATURES WILL CONTINUE
THROUGH THE WORKWEEK. THE COLDEST CONDITIONS ARE EXPECTED
MONDAY NIGHT INTO TUESDAY MORNING WHEN WIND CHILLS ARE EXPECTED
TO DROP INTO THE -15 TO -25F DEGREE RANGE. IF SUFFICIENT
CLEARING OCCURS, PARTICULARLY ACROSS INTERIOR NORTHERN ILLINOIS,
-30F WIND CHILLS COULD OCCUR. HOWEVER, THERE COULD BE LINGERING
CLOUD COVER EXTENDING NORTH OF SOME LIGHT SNOW MOVING ACROSS
CENTRAL IL/IN WHICH COULD RESULT IN A COATING OF FLUFFY SNOW
FALLING ACROSS OUR FAR SOUTHERN COUNTIES (NEAR SOUTH OF A
PONTIAC TO RENSSELAER LINE). THUS, CONFIDENCE WAS NOT HIGH
ENOUGH TO ISSUE A EXTREME COLD WATCH ON THIS SHIFT, THOUGH IT IS
POSSIBLE WARNING LEVEL HEADLINES END UP BEING NEEDED DURING
THIS TIME FOR AT LEAST PARTS OF THE AREA.
A PACIFIC NORTHWEST ORIGINATING SHORTWAVE TRAVERSING THE SOUTH
CENTRAL PLAINS MAY ATTEMPT TO INTERACT WITH AN UPPER LEVEL
SHORTWAVE/CLOSED LOW EXPECTED TO MOVE ACROSS THE UPPER MIDWEST
COULD BRING ACCUMULATING SNOW TO THE REST OF THE AREA DURING THE
LATE TUESDAY NIGHT THROUGH WEDNESDAY TIMEFRAME (20-30% CHANCE).
WHILE QPF IS EXPECTED TO BE LIGHT, WITH SUCH A COLD AIRMASS IN
PLACE, ANY SNOW THAT FALLS SHOULD END UP FAIRLY HIGH RATIO (I.E.
FLUFFY) AND READILY COAT ROADWAYS. WE WILL ALSO HAVE TO KEEP AN
EYE ON MORE ROBUST LAKE EFFECT SNOW POTENTIALLY DRIFTING WEST
INTO LAKE AND PORTER COUNTIES IN INDIANA DURING THIS TIME
IF/WHEN WIND DIRECTIONS BECOME MORE NNW VERSUS WNW.
WHILE NOT EXPECTED TO BE AS COLD AS MONDAY NIGHT, WIND CHILLS
ARE FORECAST TO REMAIN NEAR TO BELOW ZERO THROUGH WEDNESDAY
MORNING AS THEY VERY SLOWLY WARM EACH DAY THROUGH THE LATTER
HALF OF THE WEEK, WITH HIGHS BACK IN THE 20S FORECAST AREAWIDE
BY SATURDAY. A QUICK LOOK AT ENSEMBLE METEOGRAMS FOR
TEMPERATURES BEYOND THIS WEEK SUGGESTS TEMPERATURES COULD
GRADUALLY WARM BACK ABOVE FREEZING AND CLOSER TO NORMAL FOR THE
LAST WEEK OF FEBRUARY (TYPICALLY UPPER 30S TO AROUND 40).
PETR
AVIATION /12Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 610 AM CST SUN FEB 16 2025
- PERIODS OF LIGHT SNOW/FLURRIES THROUGH THIS AFTERNOON WITH
MVFR VSBYS AT TIMES (A DUSTING POSSIBLE)
- LAKE EFFECT SNOW EXPECTED AT OR VERY NEAR GYY THROUGH EARLY
AFTERNOON WITH LIFR VSBYS POSSIBLE (1-2" ACCUMS POSSIBLE)
- NW WINDS GUSTING TO 25-30 KT THROUGH THIS AFTERNOON
LIGHT SNOW HAS OVERSPREAD THE AREA THIS MORNING. THIS MAY
RESULT IN BRIEF MVFR VSBY REDUCTIONS THROUGH MID MORNING.
ADDITIONAL WAVES OF LIGHT SNOW/FLURRIES ARE POSSIBLE THROUGH THE
REST OF THE DAY. CAN'T RULE OUT OCCASIONAL MVFR VSBYS AND A
LIGHT DUSTING FROM MID MORNING THROUGH MID AFTERNOON. OPTED TO
ACCOUNT FOR THIS WITH PROB30 GROUPS DUE TO LOWER CONFIDENCE.
RADAR TRENDS SUGGEST THAT THE LAKE EFFECT SNOW BAND WILL REMAIN
EAST OF ORD AND MDW THIS MORNING AND HAVE ACCORDINGLY TRENDED
LESS PESSIMISTIC WITH THIS UPDATE. WE WILL STILL HAVE TO WATCH
IT CLOSELY THROUGH THE MORNING HOURS. GYY WILL BE VERY CLOSE TO
WHERE THE BAND SETS UP, HOWEVER, AND HAVE MAINTAINED A BRIEF
WINDOW OF LIFR VSBYS THROUGH MID-MORNING IN BURSTS OF SNOW. A
QUICK 1 TO 2" OF SNOW WILL BE POSSIBLE BEFORE THE BAND SHIFTS
EAST INTO PORTER COUNTY.
WINDS WILL BE STRONG THROUGH THIS AFTERNOON OUT OF THE NORTHWEST
WITH GUSTS TO 25 TO 30 KT. WINDS THEN EASE SLIGHTLY THIS EVENING
AND OVERNIGHT GRADUALLY TURNING MORE WEST NORTHWESTERLY. THIS
COULD RESULT IN PATCHY BLOWING SNOW, PARTICULARLY OUT TOWARD RFD
WHERE THERE IS A DEEPER SNOWPACK.
PETR
LOT WATCHES/WARNINGS/ADVISORIES
IL...COLD WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM CST
MONDAY FOR ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ103.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 6 AM CST MONDAY FOR THE IL
NEARSHORE WATERS.
SMALL CRAFT ADVISORY UNTIL 6 AM CST EARLY THIS MORNING FOR THE
IN NEARSHORE WATERS.
GALE WARNING UNTIL MIDNIGHT CST TONIGHT FOR THE IN NEARSHORE
WATERS.
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