597
FOUS11 KWBC 170823
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
323 AM EST MON FEB 17 2025
VALID 12Z MON FEB 17 2025 - 12Z THU FEB 20 2025
..GREAT LAKES
DAYS 1-2...
BEHIND THE EXITING WINTER STORM, CYCLONIC FLOW WILL REMAIN OVER
THE GREAT LAKES WITH 805MB TEMPS < -20C. NW TO WNW FLOW WILL FAVOR
THE TYPICAL MI BELT REGIONS BUT WITH AN EMPHASIS OVER THE EASTERN
U.P. DUE TO PERSISTENT LIGHT TO MODERATE SNOW AND ESPECIALLY
DOWNWIND OF LAKE ONTARIO. THERE, AN INTENSE SINGLE BAND MAY SET UP
TODAY INTO OSWEGO AND JUST NORTH OF SYRACUSE WITH SOME WAVERING N-S
INTO TUESDAY. TWO-DAY TOTALS COULD EXCEED 18" (WPC PROBS > 50%)
WITH INTENSE SNOWFALL RATES OF 2-3"/HR. STRONG PRESSURE GRADIENT IN
PLACE WILL KEEP WINDS ELEVATED AS WELL, CREATING BLOWING AND
DRIFTING OF SNOW WITH ESPECIALLY HAZARDOUS WHITEOUT CONDITIONS
WITHIN THE BAND. SNOW WILL GRADUALLY WIND DOWN INTO DAY 3.
..PACIFIC NORTHWEST/ROCKIES/NORTHERN HIGH PLAINS
DAYS 1-2...
AN ACTIVE PACIFIC JET WILL MAINTAIN UNSETTLED WEATHER INTO THE
NORTHWESTERN U.S. FOR THE NEXT 24 HOURS OR SO OVER THE CASCADES
INTO THE NORTHERN ROCKIES. HEIGHT FALLS WILL CONTINUE MOVING INLAND
THIS MORNING WITH MODEST SNOWS FOLLOWING ALONG OUT OF THE CASCADES
AND INTO THE BITTERROOTS/WESTERN MT THIS EVENING. EAST OF THE
CONTINENTAL DIVIDE A VERY COLD AIR MASS WILL BE IN PLACE THANKS TO
HIGH PRESSURE OVER CANADA THAT PUSHES SOUTHWARD THROUGH THE PLAINS,
SETTING UP UPSLOPE FLOW INTO WESTERN MT. SNOW TOTALS WILL BE LIGHT
TO MODEST IN THE HIGHER ELEVATIONS WHERE WPC PROBABILITIES FOR AT
LEAST 8 INCHES OF SNOW ARE >70%. OVER CENTRAL MT, LIGHT SNOW DUE
TO UPSLOPE/EASTERLY FLOW IS EXPECTED FROM BILLINGS TO KALISPELL BUT
WPC PROBABILITIES FOR AN ADDITIONAL 4 INCHES ARE LOW (<40%) IN THE
LOWER ELEVATIONS. AS THE HEIGHT FALLS MOVE INTO THE PLAINS, SNOW
WILL GRADUALLY DIMINISH ON TUESDAY.
DAY 3...
THE NEXT SYSTEM WILL ENTER THE PACIFIC NORTHWEST STARTING TUESDAY
NIGHT WITH SOME PERIODS OF SNOW FOR THE CASCADES, INCLUDING INTO
THE PASSES. MOISTURE PLUME WILL AIM INTO OREGON BUT THEN MOVE
QUICKLY INLAND, HELPING TO SPREAD SNOW INTO THE NORTHERN ROCKIES
THROUGHOUT THE DAY ON WEDNESDAY (ESPECIALLY INTO THE BLUE MOUNTAINS
AND INTO THE CENTRAL IDAHO RANGES). WPC PROBABILITIES FOR >6" OF
SNOWFALL ARE HIGH (>70%) IN THESE AREAS.
..CENTRAL PLAINS/MID-MS VALLEY/MID-SOUTH
DAYS 1-2...
THE ANOMALOUS IVT RESPONSIBLE FOR PERIODS OF HEAVY SNOW IN THE
ROCKIES WILL ACCOMPANY A PERIOD OF 700MB WAA OVER THE CENTRAL
PLAINS. THE COMBINATION OF 700MB FGEN AND AN ACCELERATING 250MB JET
ALOFT WILL SUPPORT A STRIPE OF LIGHT/MODERATE SNOW FROM THE BLACK
HILLS SOUTHEASTWARD THROUGH NE AND INTO THE LOWER MISSOURI RIVER
VALLEY TODAY, WEAKENING LATER TODAY. THEN TONIGHT, THE STRONGER
500MB SHORTWAVE TROUGH TRACKING ACROSS THE CENTRAL ROCKIES WILL
GRADUALLY DEEPEN WHILE UPPER-LEVEL DIFFLUENCE INCREASES AT THE NOSE
OF A 250MB JET STREAK ROUNDING THE BASE OF THE CENTRAL ROCKIES
TROUGH, SETTING UP ANOTHER AREA OF SNOW FROM NW TO SE. BY EARLY
TUESDAY MORNING, KS WILL BE WITHIN THE ENTRANCE REGION OF THE UPPER
JET WHICH WILL HELP PROMOTE AN AREA OF SNOW ACROSS CENTRAL KS
WHERE LOWER-LEVEL FGEN IS MAXIMIZED. TEMPERATURES WILL BE COLD
BEHIND AN ARCTIC FRONT, WHICH SHOULD ALLOW FOR SLRS ~15:1
ESPECIALLY IN HEALTHIER BANDS. THIS AREA OF SNOW WILL MOVE
SOUTHEASTWARD AND INCREASE IN INTENSITY INTO SOUTHEASTERN KS AND
SOUTHERN MO LATE TUE AFTERNOON/EVENING WHERE THE 00Z CAM GUIDANCE
SHOWS THE POTENTIAL FOR 1-1.5"/HR RATES (PER WPC SNOWBAND TOOL). BY
EARLY WEDNESDAY THE SNOW MAY DIMINISH IN INTENSITY INTO KY AS THE
UPPER JET REORIENTS ITSELF AND SHIFTS FOCUS TO THE GULF COAST,
SETTING UP THE COASTAL PART OF THIS EVENT FARTHER EAST. WPC
PROBABILITIES OF AT LEAST 4 INCHES OF SNOW ARE HIGH (>70%) FROM
CENTRAL KS EASTWARD INTO MO AND EXTREME SOUTHERN IL. WITHIN THIS
REGION, WPC PROBABILITIES FOR AT LEAST 8 INCHES OF SNOW ARE
MODERATE (40-70%), ESPECIALLY OVER SOUTHERN MO.
TO THE SOUTH OF THIS SWATH OF SNOW, COLD SURFACE TEMPERATURES
BENEATH >0C AIR ALOFT WILL PROMOTE AN AREA OF SLEET AND FREEZING
RAIN OVER CENTRAL OK EASTWARD INTO AR. A FEW HUNDREDTHS OF AN INCH
OF ICING IS POSSIBLE, ESPECIALLY INTO THE OUACHITA MOUNTAINS.
..CENTRAL/SOUTHERN APPALACHIANS/MID-ATLANTIC
DAY 3...
THE NEXT PHASE OF THE SYSTEM MOVING OUT OF THE MID-MS VALLEY HAS
BEEN IN QUITE A BIT OF FLUX. QUESTION REVOLVES AROUND THE TIMING
AND AMOUNT OF INTERACTION BETWEEN THE SHORTWAVE RESPONSIBLE FOR THE
SNOW ACROSS KY/NORTHERN TN AND THE LEAD HEIGHT FALLS AHEAD OF THE
UPPER LOW OVER THE WESTERN GREAT LAKES/CORN BELT. A SURFACE WAVE
SHOULD DEVELOP NEAR THE GULF COAST BY EARLY WED AND TRACK EASTWARD
THEN EAST-NORTHEASTWARD JUST OFF THE SOUTHEAST COAST TO BECOME THE
NEW FOCUS FOR QPF. MODELS HAVE BEEN WAVERING QUITE A BIT ON THE
AMOUNT OF DEVELOPMENT AND HOW CLOSE TO THE COAST THIS MAY BE,
INFLUENCING HOW MUCH QPF TO SURGE INTO THE SOUTHERN MID-ATLANTIC.
OVERALL TREND CONTINUES TO BE A FLATTER AND DRIER SYSTEM AND HAVE
TRENDED THAT WAY TONIGHT.
NEVERTHELESS, THERE IS CONFIDENCE IN THE WAVE DEVELOPMENT AND AT
LEAST LIGHT TO MODERATE QPF THAT WILL SPREAD INTO THE SOUTHEAST AND
SOUTHERN MID-ATLANTIC FROM THE SYSTEM. THE RESULT WILL BE A SWATH
OF SNOW OVER SOUTHERN AND SOUTHEASTERN VA AND NORTHERN NC WITH AN
AREA OF SLEET AND POTENTIALLY SIGNIFICANT FREEZING RAIN TO THE
SOUTH OVER EASTERN NC WHERE QPF WILL BE PLENTIFUL. WPC
PROBABILITIES FOR AT LEAST 4 INCHES OF SNOW ARE >50% ACROSS
SOUTHERN/SOUTHEASTERN VA. OVER NC, WHERE THE COLD AIR IN PLACE
BEHIND THE DEPARTING SYSTEM SUNDAY WILL BE OVERRUN WITH >0C AIR
ALOFT, THE ICING POTENTIAL IS SIGNIFICANT. WPC PROBABILITIES FOR AT
LEAST 0.25" ICE ARE AT LEAST 30% BUT MAY RISE IN FUTURE UPDATES.
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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