053
FOUS11 KWBC 181953
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 PM EST TUE FEB 18 2025
VALID 00Z WED FEB 19 2025 - 00Z SAT FEB 22 2025
..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. SEE THE LATEST KEY MESSAGES LINKED AT THE END
OF THE DISCUSSION.
CURRENT RADAR/SAT COMPOSITE IS PRETTY REVEALING THIS AFTERNOON WITH
THE DEVELOPMENT OF A SIGNIFICANT SWATH OF PRECIP DEVELOPING IN-OF
THE CENTRAL PLAINS INTO THE ADJACENT LOWER TO MID-MISSISSIPPI
VALLEY. SHORTWAVE TROUGH EJECTING OUT OF THE CENTRAL ROCKIES WILL
CONTINUE DOWNSTREAM WITH GENERAL MID-LEVEL ASCENT PATTERN MAXIMIZED
WITHIN THE CORRIDOR EXTENDING FROM SOUTHEAST KS TO POINTS EAST
WITHIN SOUTHERN MO/NORTHERN AR WITH A HEAVY SNOW FOOTPRINT
FORECAST TO ALIGN WITHIN THE ABOVE CORRIDOR. WPC PROB SNOWBANDS AT
THE 12Z UPDATE WAS STILL PRETTY AGGRESSIVE FOR A SEVERAL HR TIME
FRAME OF 1-2"/HR RATES EMBEDDED WITHIN THE PRIMARY PRECIP SHIELD
MOVING ACROSS THE OZARKS UNTIL ABOUT THE THREE-RIVER CONFLUENCE AT
THE MO/TN/AR BORDER. HEAVY SNOWS OVER THE SPAN OF SEVERAL HOURS
WILL PRODUCE TOTAL ACCUMULATIONS GENERALLY >8" ACROSS THAT SAME
EXPANSE FROM KS THROUGH NORTHERN AR AND SOUTHERN MO THROUGH
WEDNESDAY MORNING. HIGH PROBS (50-80%) FOR >4" EXISTS JUST FOR THE
00-12Z WEDNESDAY PERIOD ACROSS SOUTHERN MO, NORTHERN AR, AND FAR
SOUTHWESTERN KY WITH LOWER PROBS (25-50%) EXTENDING FURTHER EAST
THROUGH THE OHIO VALLEY FOR THE REMAINDER OF THE PERIOD.
FURTHER SOUTH INTO CENTRAL AR DOWN THROUGH NORTHERN LA, DOMINANT
PTYPE WILL CONTINUE TO TREND MORE FAVORABLE FOR IP/ZR AS A SHALLOW
WARM LAYER IS PROGGED DUE TO THE MERIDIONAL PUSH OF GULF AIR
ADVECTING OVER TOP THE SHALLOW COLD AIR MASS BEING PUSHED SOUTH ON
THE SOUTHERN FLANK OF THE ARCTIC HIGH DRILLING SOUTH OVER THE
COURSE OF TODAY AND TOMORROW. THANKFULLY THE ASCENT PATTERN IS
STRONGEST FURTHER NORTH, SO ICE ACCUMS ARE NOT ANTICIPATED TO BE
SEVERE, BUT STILL RELATIVELY IMPACTFUL WITH PROBS OF ICE >0.1"
HOLDING BETWEEN 10-30% ACROSS THE AR/LA BORDER OVER THE COURSE OF
THE FORECAST PERIOD. ICE PROBS DECREASE DOWNSTREAM FOR D2, BUT
STILL MAINTAIN SOME LOW PROBS FOR BETWEEN 0.01-0.1" ICE ACCUMS
ACROSS NORTHERN MS/AL/GA FOR MAINLY THE 06-14Z TIME FRAME ON
WEDNESDAY BEFORE PRECIP MOVES OUT OF THE AREA THE SECOND HALF OF
THE D2 PERIOD.
BY EARLY WEDNESDAY MORNING, INCREASED JET DYNAMICS OVER THE
SOUTHEAST AND MID-ATLANTIC WILL AID IN GENERATING A SURFACE LOW
ALONG THE CENTRAL GULF COAST, PROPAGATING EAST-NORTHEAST OVER THE
COURSE OF WEDNESDAY WITH A SURFACE LOW LOCATED OFF THE NC COAST BY
EARLY THURSDAY MORNING. THE PRIMARY DISTURBANCE TO THE WEST WILL
STILL MOTION ACROSS THE OHIO VALLEY INTO THE MOUNTAINS OF THE
CENTRAL AND SOUTHERN MID-ATLANTIC LEADING TO MODERATE SNOW
ACCUMULATIONS ON D2 ACROSS EASTERN KY/SOUTHERN WV/SOUTHWESTERN VA
LEADING TO PROBS AROUND 30-50% FOR AT LEAST 4" OF SNOWFALL IN THOSE
LOCALES DURING THE 12Z WEDNESDAY TO 12Z THURSDAY PERIOD FALLING
IN-BETWEEN BOTH D1 AND D2. FURTHER EAST INTO THE COASTAL SOUTHERN
MID-ATLANTIC, OUR AFOREMENTIONED SURFACE CYCLONE OVER THE GULF INTO
THE WESTERN ATLANTIC WILL LEAD TO THE GREATEST QPF FOOTPRINT FOR
THE D2 PERIOD WITH HEAVY SYNOPTIC BASED PRECIPITATION OVER PLACES
LIKE THE TIDEWATER OF VA DOWN INTO NORTHEASTERN NC, MAINLY IN THE
FORM OF SNOW. MODERATE PRECIP FOCUS WILL ALIGN WITHIN THE NC
PIEDMONT ACROSS INTO SOUTHEASTERN NC WITH A MIXED PTYPE REGIME
LIKELY TO CAUSE SOME FORMIDABLE ICE ACCUMS IN THE FORM OF SLEET
(IP) AND FREEZING RAIN (ZR). THE AREA ACROSS THE VA TIDEWATER WILL
BE THE EPICENTER FOR THE MOST SIGNIFICANT SNOWFALL FORECAST WITH
TOTALS BETWEEN 6-12" EXPECTED FOR AREAS LIKE NORFOLK UP THROUGH THE
U13 CORRIDOR BETWEEN VA BEACH/CHINCOTEAGUE, WELL-DOCUMENTED WITH
THE LATEST >4" PROBS A SOLID 80+% WITHIN THAT ENTIRE ZONE AND >8"
PROBS UP INTO THE 40-60% RANGE. MODEST PROBS FOR >4" ALSO EXTEND
SOUTH INTO NORTHEASTERN NC WITH A DECENT AREA OF 40-70% PROBS
EXISTING FROM ELIZABETH CITY AND POINTS NORTHWEST.
FREEZING RAIN PROSPECTS EXIST ACROSS A GOOD PORTION OF EASTERN NC
AND THE NORTHERN PIEDMONT OF SC WITH THE HEAVIEST TOTALS LIKELY TO
FALL OVER AREAS ALONG AND EAST OF I-95. WPC PROBABILITIES BETWEEN
50-80% ARE FORECAST FOR >0.1" ICE ACCRETION ACROSS PORTIONS OF
EASTERN NC WITH LOW PROBS (10-30%) FOR THE NORTHERN MOST PORTION OF
THE SC PIEDMONT. 10-30% PROBS ALSO EXIST FOR AS MUCH AS 0.25" OF
ICE ACCRETION OVER EASTERN NC AS WELL, ALTHOUGH THE DETERRENT FOR
THE THREAT IS THE HEAVIEST PRECIP FALLING WITHIN MARGINALLY COLD
ENOUGH AIR AT THE SURFACE (30-32F) WITH PERIODS OF HEAVIER PRECIP
FALLING DURING THE DAY TIME WHICH HISTORICALLY CURBS ICE ACCRETION
RATES, ESPECIALLY AT THESE LATITUDES.
KLEEBAUER
..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 UNWIND, 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 HEAVY LAKE EFFECT SNOW, BUT THEN
THOSE HEIGHT FALLS WILL BRING IN A GENERAL/LIGHT SNOW TO THE REGION
ON THURSDAY AND FRIDAY. WPC PROBABILITIES FOR AT LEAST 8 INCHES OF
SNOW ONLY EXIST ON DAY 1 (WEDNESDAY) PARTS OF THE MICHIGAN U.P.
AND OFF SOUTHERN LAKE ONTARIO. FOR CENTRAL NY BETWEEN ROC- FZY-
SYR, THE STRONG SINGLE BAND WILL STEAL THE SHOW AND CONTINUE TO
DUMP SNOW AT 1-3"/HR RATES WITH SIGNIFICANT ACCUMULATION IN A
NARROW SWATH -- PERHAPS MORE THAN 12 INCHES OF ADDITIONAL SNOW
(10-20% PROBS). BY DAYS 2 AND 3, SNOWFALL WILL BE LIGHT WITH MOST
AREAS SEEING LESS THAN 4 INCHES OF SNOW. THE GREATEST POTENTIAL FOR
ADDITIONAL SNOWFALL OVER 4 INCHES (20-50%) IS FORECAST OFF LAKE
MICHIGAN INTO WESTERN L.P. AND FAR NORTHERN INDIANA ON THURSDAY,
POSITIONED ALONG THE EASTERN AND NORTHERN PERIPHERY OF THE UPPER
LOW.
..PACIFIC NORTHWEST THROUGH THE CENTRAL ROCKIES
DAYS 1-3...
INITIALLY FOR TONIGHT, ADDITIONAL HEIGHT FALLS OUT OF CANADA WILL
DROP THROUGH CENTRAL MT WITH SOME LIGHT SNOW TO THE CENTRAL ID
RANGES, SOUTHWESTERN MT, AND THE WESTERN WY RANGES WHERE WPC
PROBABILITIES FOR AN ADDITIONAL 6 INCHES OF SNOW ARE LOW (<40%) TO
THE NORTH BUT HIGH (>70%) OVER SOUTHERN WY AND THE HIGH PEAKS OF
THE NORTHERN CO ROCKIES.
BY EARLY WEDNESDAY, A POTENT BUT PROGRESSIVE 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 THE END OF D2 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. THE NEXT SYSTEM BEGINS
TO ENTER THE NORTHWEST BY THE END OF D3 WITH LIGHTER SNOW ENTERING
THE NORTHERN CASCADES.
..SOUTHEASTERN MASS
DAY 2-3...
THE EXITING SYSTEM FROM THE SOUTHEAST/SOUTHERN MID-ATLANTIC WILL
TRACK NORTHEASTWARD, AND MAY CLIP SOUTHEASTERN MA/CAPE COD ON
THURSDAY 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 AND PUMP UP THE DOWNSTREAM
RIDGE. RECENT 12Z GUIDANCE HAS NUDGED NORTHWARD, WHICH IS COMMON IN
THE SHORT RANGE WITH DEVELOPING LOW PRESSURE SYSTEMS OFF THE COAST
AS CAMS INCORPORATE LATENT HEAT RELEASE AND STRONGER WAA IN
RELATION TO CONVECTION IN THE WARM SECTOR OF THE SYSTEM. HOWEVER,
THE BEST CHANCES FOR SNOWFALL OVER 4 INCHES REMAINS OVER NANTUCKET
(70-80%) AS WELL AS BOTH MARTHA'S VINEYARD AND CAPE COD (40-60%),
WITH LOW PROBS (10-20%) CLIPPING FAR EASTERN LONG ISLAND, SOUTHERN
CT AND THE REMAINDER OF SOUTHEAST MA.
FRACASSO/SNELL
...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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