848
FOUS11 KWBC 180811
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
311 AM EST TUE FEB 18 2025
VALID 12Z TUE FEB 18 2025 - 12Z FRI FEB 21 2025
..GREAT LAKES
DAYS 1-3...
CYCLONIC FLOW OVER SOUTHERN CANADA AND THE GREAT LAKES ON THE
WESTERN SIDE OF THE ELONGATED UPPER TROUGH AXIS WILL FAVOR A
CONTINUATION OF THE LAKE EFFECT SNOW FOR THE NEXT COUPLE OF DAYS.
WITH 850 TEMPERATURES IN THE -20SC AND NW TO WNW FLOW, MULTI-BANDS
WILL FORM OFF THE UPPER LAKES WITH A STRONG SINGLE BAND OFF LAKE
ONTARIO WITH AN IMPRESSIVE MULTI-LAKE MOISTURE FEED. THE PATTERN
WILL BE SLOW TO UNFOLD, BUT BY EARLY WEDNESDAY A CLOSED LOW WILL
BEGIN TO FORM OVER THE CORN BELT WHICH WILL HELP DISRUPT THE
PATTERN ENOUGH TO DIMINISH THE LAKE EFFECT SNOW, BUT THEN THOSE
HEIGHT FALLS WILL BRING IN A GENERAL/LIGHT SNOW TO THE REGION ON
THURSDAY. WPC PROBABILITIES FOR AT LEAST 8 INCHES OF SNOW OVER THE
NEXT TWO DAYS ARE NEAR 50% OVER THE EASTERN U.P. OF MICHIGAN. OVER
CENTRAL NY BETWEEN ROC-FZY-SYR, THE STRONG SINGLE BAND WILL
CONTINUE TO DUMP SNOW AT 1-3"/HR RATES WITH SIGNIFICANT
ACCUMULATION IN A NARROW SWATH -- PERHAPS MORE THAN 12-18 INCHES
(>60% PROBS). BY DAY 3, SNOWFALL WILL BE LIGHT WITH MOST AREAS
SEEING LESS THAN 4 INCHES OF SNOW.
..PACIFIC NORTHWEST THROUGH THE CENTRAL ROCKIES
DAYS 1-3...
HEIGHT FALLS OVER THE GREAT BASIN THIS MORNING WILL CONTINUE
SOUTHEASTWARD TODAY, GIVING SOME ADDITIONAL SNOW TO THE CO ROCKIES.
TO THE NORTH, ADDITIONAL HEIGHT FALLS OUT OF CANADA WILL DROP
THROUGH CENTRAL MT WITH SOME LIGHT SNOW TO THE CENTRAL ID RANGES,
SOUTHWESTERN MY, AND THE WESTERN WY RANGES WHERE WPC PROBABILITIES
FOR AT LEAST 6 INCHES OF SNOW ARE LOW (<40%) TO THE NORTH BUT HIGH
(>70%) OVER WESTERN WY AND THE HIGH PEAKS OF THE NORTHERN CO
ROCKIES.
BY DAY 2, A PACIFIC SYSTEM WILL START TO MOVE INTO THE NORTHWEST,
SPANNING THE LATITUDES FROM NORCAL UP TO THE CANADIAN BORDER. IVT
WILL BE MODESTLY HIGH (~90TH PERCENTILE) INTO NORCAL/SOUTHERN
OR/NORTHERN NV TOWARD IDAHO, SUPPORTING LIGHT TO MODERATE SNOWS FOR
THE TERRAIN WITH SNOW LEVELS NEAR 3000FT TO THE NORTH AND 5000FT
TO THE SOUTH THAT WILL RISE A BIT AS THE CORE OF THE MOISTURE PLUME
PUSHES THROUGH. THE SYSTEM WILL MOVE STEADILY ALONG AND CLEAR THE
COAST WITH QPF STARTING EARLY THURSDAY, PUSHING INTO NORTHERN
UT/SOUTHERN ID AND INTO THE ROCKIES. HOWEVER, MOISTURE WILL WANE
AND SNOW WILL BECOME LIGHTER OVERALL INTO D3 WITH THE SNOW CONFINED
MAINLY TO THE UNITAS AND HIGHER CO ROCKIES BY THEN. FOR THE 3-DAY
PERIOD, WPC PROBABILITIES FOR AT LEAST 8 INCHES OF SNOW ARE HIGHEST
(>70%) OVER THE HIGHER TERRAIN ABOVE 6000FT CLOSER TO THE COAST,
7000-8000FT OVER THE GREAT BASIN, AND 9000FT OVER CO/WY.
..CENTRAL PLAINS THROUGH THE MID-ATLANTIC STATES
DAYS 1-2...
A SIGNIFICANT WINTER STORM IS UNDERWAY OVER THE CENTRAL PLAINS
WHICH WILL SPREAD EASTWARD THROUGH THE MID-SOUTH INTO THE SOUTHERN
MID-ATLANTIC WITH POTENTIALLY MAJOR IMPACTS INCLUDING HEAVY SNOW
AND SIGNIFICANT ICE.
SNOW IS ALREADY UNDERWAY ACROSS KS INTO MO THIS MORNING, DRIVEN BY
LEAD SHORTWAVES AHEAD OF THE ROCKIES TROUGH. THROUGH THIS MORNING,
AS THE STRONGER HEIGHT FALLS APPROACH THE REGION, SNOW WILL EXPAND
OVER THE CENTRAL AND SOUTHERN PLAINS EASTWARD BENEATH THE RRQ OF
THE UPPER JET AND ATOP THE ARCTIC AIR MASS DRIVEN IN BY THE STRONG
COLD FRONT OVERNIGHT. WITH SUFFICIENT MOISTURE INFLUX FROM THE
GULF, SNOW RATES WILL INCREASE OVER SOUTHERN KS INTO SOUTHERN MS
LATER THIS MORNING INTO THE AFTERNOON WITH >1"/HR RATES AT TIMES
PER THE WPC SNOWBAND TOOL AND HREF PROBS. SNOW WILL ADVANCE
EASTWARD INTO THE MID-SOUTH LATER THIS EVENING AND OVERNIGHT BUT
LIKELY DIMINISH SOMEWHAT IN INTENSITY. TO THE SOUTH, THE SHALLOW
ARCTIC AIR MASS WILL CONTINUE SOUTHWARD BUT SOUTHERLY FLOW ALOFT
WILL MAINTAIN >0C TEMPERATURES, FAVORING A MIX OF SLEET AND
FREEZING RAIN OVER PARTS OF OK INTO AR, NORTHERN LA, AND WESTERN
MS. FOR THE D1 PERIOD, WPC PROBABILITIES OF AT LEAST 4 INCHES OF
SNOW ARE HIGH (>70%) FROM SOUTHEASTERN KS AND NORTHEASTERN OK
EASTWARD TO WESTERN KY. WITHIN THIS REGION, PROBABILITIES OF AT
LEAST 8 INCHES OF SNOW ARE >60% NEAR JOPLIN TO SPRINGFIELD, MO.
ICING TO THE SOUTH SHOULD GENERALLY BE LIGHT BUT THERE IS A LOW
CHANGE (10-30%) OF AT LEAST 0.10" ACCRETION NEAR THE OACHITA
MOUNTAINS IN AR.
BY WEDNESDAY MORNING, THE NEXT PHASE OF THE SYSTEM WILL TAKE SHAPE
OVER THE NORTHERN GULF AS THE ENTRANCE REGION OF THE UPPER JET
TOUCHES THE LA/MS COAST, HELPING TO FAVOR CYCLOGENESIS. THE
NORTHERN PART OF THE SYSTEM WILL STILL SPREAD SNOW ACROSS THE MID-
SOUTH EASTWARD TO THE CENTRAL APPALACHIANS WHERE SOME OROGRAPHIC
LIFT WILL HELP WRING OUT SEVERAL INCHES OF SNOW INTO EASTERN
KY/SOUTHERN WV/SOUTHWESTERN VA. THE LARGER QPF-MAKER WILL BE THE
FORMING GULF LOW THAT IS FORECAST TO TRACK ENE TO NE ACROSS NORTH
FL BEFORE TURNING NORTHEASTWARD ALONG THE GULF STREAM JUST OFF THE
SC/NC COASTS. WITH THE COLD AIR MASS IN PLACE THROUGH THE EAST,
THIS SETS UP A SOUTHERN SLIDER SNOW EVENT WITH AN AXIS OF HEAVY
SNOW ALONG THE VA/NC BORDER INTO THE TIDEWATER AND SOUTHERN
DELMARVA. THE INCOMING NORTHERN STREAM UPPER LOW WILL LAG BEHIND
JUST ENOUGH TO NOT PHASE UNTIL FARTHER DOWNSTREAM, BUT ENOUGH
INGREDIENTS WILL BE COMING INTO PLACE IN THE FORMATIVE STAGES OF
THIS SYSTEM TO YIELD A MODEST TO HEAVY SNOWFALL FOR PARTS OF THE
SOUTHERN MID-ATLANTIC, WITH A CUTOFF NEAR A LINE ALONG I-66/I-95
INTO SOUTHERN NJ. WPC PROBABILITIES FOR AT LEAST 6 INCHES OF SNOW
ARE HIGHEST OVER SOUTHEASTERN VA AND NORTHEASTERN NC, SQUARELY
THROUGH THE NORFOLK AREA.
LIKE PLACES FARTHER WEST, THE >0C AIR ALOFT WILL RISE UP AND OVER
THE COLD SURFACE TEMPERATURES OVER EASTERN NC, SETTING UP A
FREEZING RAIN EVENT THAT MAY BE SIGNIFICANT ALONG AND EAST OF I-95
BETWEEN THE VA BORDER AND INTO NORTHEASTERN SC. THERE, WPC
PROBABILITIES FOR AT LEAST 0.10" ICING ARE >50% WITH SOME AREAS
RECEIVING MORE THAN 0.25" ACCRETION.
..SOUTHEASTERN MASS
DAY 3...
THE EXITING SYSTEM FROM THE SOUTHEAST/SOUTHERN MID-ATLANTIC WILL
TRACK NORTHEASTWARD, AND MAY CLIP SOUTHEASTERN MA/CAPE COD D3 ON
ITS WAY INTO ATLANTIC CANADA. THE QUESTION REVOLVES AROUND THE
SPEED OF THE INCOMING NORTHERN STREAM UPPER LOW AND HOW MUCH IT CAN
CAPTURE THE EXITING SYSTEM. GIVEN THE UNCERTAINTY LEADING INTO THE
EVENT IN THE SOUTHEAST/MID-ATLANTIC, THERE ARE STILL A WIDE RANGE
OF SOLUTIONS FROM ZERO TO MODERATE SNOW OVER PART OF THE REGION.
FOR NOW, THERE ARE LOW (10-40%) PROBABILITIES OF AT LEAST 4 INCHES
OF SNOW OVER CAPE COD AND THE ISLANDS.
FRACASSO
...WINTER STORM KEY MESSAGES ARE IN EFFECT. PLEASE SEE CURRENT
KEY MESSAGES BELOW...
HTTPS://WWW.WPC.NCEP.NOAA.GOV/KEY_MESSAGES/LATESTKEYMESSAGE_2.PNG
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