102
FOUS11 KWBC 162056
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
356 PM EST TUE DEC 16 2025
VALID 00Z WED DEC 17 2025 - 00Z SAT DEC 20 2025
..CASCADES AND NORTHERN ROCKIES
DAYS 1-3...
AN ACTIVE PERIOD OF WINTER WEATHER PERSISTS ACROSS THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES AS PINCHED ONSHORE FLOW PUSHES
CONSIDERABLE MOISTURE ONSHORE AS AN ATMOSPHERIC RIVER (AR). THERE
ARE SOME NOTABLE TIMING DIFFERENCES AMONGST THE VARIOUS GLOBAL
ENSEMBLES AS TO WHEN THE MOST IMPRESSIVE IVT WILL MOVE ONSHORE, BUT
IN GENERAL A CORE OF ELEVATED IVT (>80% CHANCE TO EXCEED 750
KG/M/S) WILL LIFT INTO WA/OR D2 AHEAD OF A SECONDARY FRONT.
BEFORE THIS OCCURS, A COLD FRONT WILL BE MOVING ACROSS THE PACIFIC
NORTHWEST WITHIN ANOTHER AXIS OF ELEVATED IVT D1, SPREADING
MOISTURE FROM THE COASTAL REGIONS, ACROSS THE CASCADES, AND AS FAR
EAST AS THE NORTHERN ROCKIES BEFORE 00Z THURSDAY. IMPRESSIVE ASCENT
WITHIN THE STRONG PACIFIC JET WILL COMBINE WITH INTENSIFYING 700MB
FGEN AND PERIODS OF UPSLOPE FLOW TO PRODUCE HEAVY PRECIPITATION
ACROSS THE TERRAIN. SNOW LEVELS DURING THIS TIME WILL RISE AHEAD OF
THE COLD FRONT FROM AROUND 4000 FT TO 6000 FT, BUT THEN DROP
RAPIDLY IN ITS WAKE TO AS LOW AS 2000 FT. THE HEAVIEST SNOW IS
LIKELY AHEAD OF THE COLD FRONT SO THE MOST IMPACTFUL SNOW WILL BE
ABOVE PASS LEVELS, BUT IMPACTFUL SNOW IS LIKELY AT THE CASCADE
PASSES BEHIND THE COLD FRONT. WPC PROBABILITIES D1 FOR 6+ INCHES
ARE EXPANSIVE ACROSS THE OLYMPICS, CASCADES, NORTHERN ROCKIES FROM
GLACIER NP THROUGH THE SALMON RIVER/SAWTOOTH RANGE, AND AROUND
YELLOWSTONE NP, REACHING ABOVE 70% ACROSS MOST OF THESE AREAS WITH
SNOW LEVELS VARYING FROM ABOVE 5000 FT EAST, TO JUST 2000-3000 FT
WEST.
MOISTURE BRIEFLY DECREASES EARLY D1 BEHIND THE FIRST WAVE, BUT THEN
INCREASING RAPIDLY AGAIN AS THE SECOND AND MORE IMPRESSIVE IVT
SURGE LIFT E/NE INTO THE AREA. THIS WILL AGAIN BE ACCOMPANIED BY A
FRONTAL WAVE SO SNOW LEVELS WILL RISE RAPIDLY, REACHING 6000-8000
FT WITHIN THE STRONGEST WAA/AR ACROSS OR/SOUTHERN ID/SOUTHERN
MT/WY, WHILE REMAINING LOW AT 2000-4000 FT FARTHER NORTH. WHILE
SNOW LEVELS WILL BE LOWER NORTH, THE HEAVIEST PRECIPITATION IS
EXPECTED SOUTH/ALONG THE APPROACHING FRONT, WITH A HEAVY AND WET
SNOW IMPACTING MUCH OF THE AREA BEFORE SNOW LEVELS RISE. THIS
COULD BE IMPACTFUL DESPITE THE RISING SNOW LEVELS DUE TO THE SNOW
LOAD POTENTIAL OF A SUB-CLIMO SLR SNOW EVENT WITHIN THE AR, SO
ALTHOUGH THE HEAVIEST SNOW ACCUMULATIONS ARE LIKELY ABOVE 7000 FT,
NOTABLE IMPACTS ARE LIKELY WELL BELOW THAT ELEVATION. WPC
PROBABILITIES D2 ARE HIGH (>70%) FOR 6+ INCHES OF SNOW IN THE
CASCADES, OLYMPICS, AND BLUES, EXPANDING INTO MUCH OF THE NW
TERRAIN FROM THE CASCADES THROUGH THE AREA AROUND YELLOWSTONE NP IN
NW WYOMING D3. 3-DAY TOTAL SNOWFALL OF 3-4 FEET IS LIKELY IN THE
HIGHER TERRAIN OF MUCH OF THE NW, WITH LOCALLY MORE THAN 6 FEET IN
THE HIGHEST CASCADES LIKELY.
..NORTHERN PLAINS, UPPER MIDWEST, GREAT LAKES
DAYS 2-3...
A STRONG LOW PRESSURE MOVING ALONG OR NEAR THE BORDERLANDS OF
ND/MN/CANADA WILL BRING IMPACTFUL WINTER WEATHER (AS WELL AS A
VARIETY OF OTHER HAZARDS) TO THE REGION THROUGH LATE WEEK.
A POTENT SHORTWAVE EMERGING FROM THE PACIFIC NORTHWEST/BRITISH
COLUMBIA WEDNESDAY AFTERNOON WILL BE THE DRIVER OF THIS DEVELOPING
SYSTEM AS IT TRACKS RAPIDLY EASTWARD EMBEDDED WITHIN PINCHED ZONAL
FLOW. THIS SHORTWAVE WILL AMPLIFY AS IT DIVES INTO THE NORTHERN
HIGH PLAINS, CLOSING OFF TO MANIFEST AS 700-500MB HEIGHT ANOMALIES
FALLING BELOW THE 1ST PERCENTILE ACCORDING TO NAEFS. AS THIS LOW
TRACKS EAST IT WILL INTERACT WITH A POWERFUL 160KT PACIFIC JET
STREAK DIVING ACROSS THE NORTHERN ROCKIES TO CREATE AN INTENSE
SURFACE LOW PRESSURE. WHILE THERE CONTINUES TO BE SOME INTENSITY
AND LATITUDINAL SPREAD AMONG THE ENSEMBLE SYSTEMS OF THIS SURFACE
LOW (ECENS NORTH AND STRONG, GEFS/CMCE FARTHER SOUTH AND A BIT
WEAKER) THE GENERAL TREND IS FOR A STRONG LOW MOVING ALONG THE
CANADIAN BORDER FROM WEDNESDAY AFTN THROUGH FRIDAY MORNING.
DOWNSTREAM OF THIS SURFACE LOW, IMPRESSIVE THETA-E ADVECTION WILL
SURGE NORTHWARD FROM THE GULF, WITH A MODEST TROWAL POTENTIALLY
DEVELOPING AS MOISTURE CURLS BACK TO THE NW OF THE SYSTEM AND LIFTS
ISENTROPICALLY. BENEATH THIS MODEST TROWAL, WHICH WILL BE WELL
POSITIONED INTO THE LFQ OF THE STRONG JET STREAK, A BAND OF HEAVY
SNOW IS POSSIBLE FROM NORTH-CENTRAL MT THROUGH FAR NORTHERN MN. THE
PROGRESSIVE NATURE OF THIS SYSTEM WILL LIMIT THE POTENTIAL FOR
HEAVY SNOW, BUT INTENSE ASCENT INTO A DEEP DGZ WILL RESULT IN AT
LEAST A SHORT PERIOD OF HEAVY SNOW WITHIN A POSSIBLE FGEN-FORCED
BAND. THIS WILL RESULT IN AN AXIS OF AT LEAST 2" OF SNOW, BUT THE
GREATEST POTENTIAL FOR 4+ INCHES WILL BE FROM FAR NORTHERN ND INTO
THE ARROWHEAD OF MN D2, AND THEN ACROSS THE U.P. OF MI D3 WHERE WPC
PROBABILITIES EXCEEDING 50%.
ALTHOUGH THE TOTAL SNOWFALL FROM THIS EVENT WILL BE MODEST.
INCREASINGLY STRONG WINDS, WHICH WILL LIKELY ECLIPSE 50 MPH IN
GUSTS, WILL CREATE DANGEROUS TRAVEL DUE TO BLOWING-SNOW OR EVEN
NEAR-BLIZZARD IMPACTS. ADDITIONALLY, THE NAM SNSQ PARAMETER IS
ELEVATED ALONG A COLD FRONT CROSSING MT AND THE DAKOTAS, PRODUCING
ADDITIONAL DANGEROUS TRAVEL WHERE ANY SNOW SQUALLS DEVELOP LATE
WEDNESDAY AND THURSDAY.
..GREAT LAKES
DAY 3...
SECONDARY LOW PRESSURE DEVELOPING ACROSS WISCONSIN WILL RAPIDLY
STRENGTHEN AND LIFT PROGRESSIVELY NORTHEAST THROUGH MI AND INTO
CANADA ON FRIDAY. THE INTENSITY OF THIS LOW WILL RESULT IN AN
IMPRESSIVE SURGE OF WAA AND PRECIPITATION DOWNSTREAM, BUT THIS WILL
ALL FALL AS RAIN IN THE WARMING COLUMN. IN THE WAKE OF THIS LOW,
HOWEVER, STRONG CAA LEADING TO RAPID COLUMN COOLING WILL MOVE
ACROSS THE GREAT LAKES TO PRODUCE PERIODS OF LAKE EFFECT SNOW (LES)
ESPECIALLY ACROSS THE EASTERN U.P., NORTHWEST L.P., AND EAST OF
LAKES ERIE AND ONTARIO. INVERSION DEPTHS ARE FORECAST TO BE
GENERALLY MODEST (850MB) AND PLENTIFUL MOISTURE WILL BE SOMEWHAT
TRANSIENT. STILL, EFFICIENT FORCING INTO THE DGZ WILL LIKELY
PRODUCE AT LEAST SHORT PERIODS OF HEAVY LES, REFLECTED BY WPC
PROBABILITIES THAT REACH 30-50% FOR 4+ INCHES EAST OF ERIE/ONTARIO,
AND 10-30% IN THE OTHER FAVORED N/NW SNOW BELTS.
THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.
WEISS
...WINTER STORM KEY MESSAGES ARE IN EFFECT. PLEASE SEE CURRENT
KEY MESSAGES BELOW...
HTTPS://WWW.WPC.NCEP.NOAA.GOV/KEY_MESSAGES/LATESTKEYMESSAGE_1.PNG
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