616
FOUS11 KWBC 172100
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
400 PM EST WED DEC 17 2025
VALID 12Z WED DEC 17 2025 - 12Z SAT DEC 20 2025
..CASCADES AND NORTHERN ROCKIES
DAYS 1-3...
AN ANCHORED -WPO/-PNA TELECONNECTION PATTERN IS THE DRIVER IN THE
SEEMINGLY ENDLESS BARRAGE OF ATMOSPHERIC RIVERS THAT IS DELIVERING
COPIOUS AMOUNTS OF SNOW TO THE MOUNTAINS OF THE PACIFIC NORTHWEST
AND THE NORTHERN ROCKIES. AS A COLDER AIR-MASS BECOMES ENTRENCHED
ACROSS THE COLUMBIA BASIN AND NORTHERN ROCKIES. SNOW LEVELS ARE
BETWEEN 2,500-3,000FT IN THE CASCADES AND AS LOW AS 2,000FT IN THE
LEWIS RANGE AT THE ONSET AS MODERATE PRECIP RATES PERSISTING
BEHIND THIS COLD FRONT TODAY GENERATE IMPACTFUL SNOW BELOW PASS
LEVEL. SNOW LEVELS IN THE CORE OF THIS AR WILL RISE TO OVER 9000FT
IN OR THURSDAY MORNING AND 5000 TO 6000FT IN WA BY THURSDAY
AFTERNOON WITH A POWERFUL COLD FRONT SHIFTING SOUTH OVER WA
THURSDAY NIGHT. FARTHER EAST, SNOW LEVELS WILL RISE TO 6,000T IN
THE BITTERROOTS BY THURSDAY NIGHT AND APPROACH 7,000FT IN THE
SAWTOOTH. BEFORE THE SNOW LEVELS RISE, HOWEVER, STRONG 700MB FGEN
WILL SUPPORT SEVERAL HOURS OF HEAVY SNOW AT ELEVATIONS AS LOW AS
6,000FT IN CENTRAL ID AND 5,000FT IN THE BLUE MOUNTAINS THROUGH
THURSDAY AFTERNOON. FARTHER SOUTH, THE TETONS, ABSAROKA, AND WIND
RIVER RANGES WILL RESIDE CLOSER TO STRONGER 700MB JET AND
ANOMALOUS PWATS, GIVING THESE RANGES BOTH AN ABUNDANCE OF MOISTURE
AND STRONG UPSLOPE ENHANCEMENT TO KEEP HEAVY SNOW IN THE FORECAST
THROUGH SATURDAY MORNING FOR ELEVATION AT AND ABOVE 7,000FT.
PROLONGED PACIFIC MOISTURE FLUX CONTINUES TO BE DIRECTED AT OR AND
INTO THE NORTHERN ROCKIES ON FRIDAY WITH HIGHER SNOW LEVELS THAT
SUPPORT HEAVY SNOW IN THE MORE REMOTE REACHES OF THE CASCADES AND
NORTHERN ROCKIES. THE LONE EXCEPTION WILL BE ONGOING WESTERLY UPSLOPE
FLOW INTO THE WA CASCADES WHERE SNOW LEVELS AS LOW AS 1,500FT ARE
EXPECTED. THE BULK OF THE HEAVIEST SNOWFALL IN THE WA CASCADES AND
OLYMPICS ABOVE 2,500FT. WPC 72-HOUR PROBABILITIES SHOW HIGH CHANCES
PROBABILITIES (>70%) FOR SNOWFALL TOTALS >24" AT ELEVATIONS BETWEEN
3,000-4,000FT, WHILE SIMILAR HIGH CHANCE PROBABILITIES EXIST ABOVE
4,000FT FOR SNOWFALL TOTALS >30". IN THE ROCKIES, HIGH CHANCE
PROBABILITIES (>70%) FOR >12" OF SNOW ARE PRESENT ABOVE 5,000FT IN
THE BLUE MOUNTAINS, BITTERROOTS, AND THE LEWIS RANGE, WHILE THOSE
SAME PROBABILITIES FOR >24" ARE PRESENT ABOVE 6,000FT IN THE
SAWTOOTH. SNOWFALL IN THE TETONS AND WIND RIVER RANGES ARE LIKELY
TO RANGE BETWEEN 1-3 FEET WITH SOME LOCALIZED AMOUNTS APPROACHING
4 FEET IN THE MORE REMOTE REACHES OF THESE RANGES THROUGH
SATURDAY.
..NORTHERN PLAINS, UPPER MIDWEST, GREAT LAKES
DAYS 1-3...
A POTENT SHORTWAVE TROUGH, CURRENTLY LOCATED OVER THE NORTHERN
ROCKIES, IS FORECAST TO AMPLIFY AND CLOSE OFF IN RESPONSE TO A 180
KT EASTERN PACIFIC JET DIGGING SOUTHWARD INTO THE FOUR CORNERS
TODAY. AT THE SURFACE, A STRONG SUB-980 MB LOW PRESSURE CENTER
WILL TRACK SOUTHEASTWARD INTO THE NORTHERN PLAINS, BEFORE AN
EMERGENT TRIPLE- POINT LOW MIGRATES ACROSS THE UPPER MIDWEST
TOMORROW AND FRIDAY.
AS THIS LOW EJECTS EASTWARD TONIGHT, STRENGTHENING THETA-E
ADVECTION FROM THE GULF COMBINED WITH MOIST EASTERN PACIFIC INFLOW
WILL RESULT IN PRECIPITABLE WATER ANOMALIES IN THE 99TH PERCENTILE
UPSTREAM OF A DEVELOPING TROWAL ON THE NORTHWEST FLANK OF THE LOW
CENTER. WITH THE ENTRANCE REGION OF A STRENGTHENING JET STREAK
SITUATED OVER THE CANADIAN PRAIRIE, A HEAVY SNOW BAND IS EXPECTED
TO DEVELOP IN THE COMMA-HEAD REGION ROUGHLY FROM A GLASGOW TO
BEMIDJI LINE. THE PROGRESSIVE NATURE OF THIS SYSTEM WILL CAP
OVERALL HEAVY SNOW POTENTIAL, BUT INTENSE ASCENT SUPERIMPOSED WITH
A DEEP DGZ WILL YIELD AT LEAST A BRIEF WINDOW FOR HEAVY SNOWFALL
TONIGHT AND TOMORROW MORNING. THE LATEST WPC PROBABILITIES FOR >6"
OF SNOW HAVE DIPPED SOMEWHAT COMPARED TO THE LATEST CYCLE, BUT
STILL HIGHLIGHT A 40-50% CHANCE THROUGH DAY 1 IMMEDIATELY ALONG THE
INTERNATIONAL BORDER, WHILE 70-90% PROBABILITIES FOR >2" OF
SNOWFALL ARE NOTED IN ADJACENT AREAS. ALTHOUGH THE TOTAL SNOWFALL
FROM THIS EVENT MAY LOOK MODEST FOR THIS REGION, STRONG WIND GUSTS
UPWARDS OF 70 MPH WILL LEAD TO DANGEROUS TRAVEL DUE TO BLOWING SNOW
AND POTENTIAL BLIZZARD IMPACTS. ALONG THE SAME LINES, SNOW SQUALLS
REMAIN POSSIBLE ALONG THE LEADING EDGE OF A SURGING ARCTIC FRONT
ACROSS EASTERN MONTANA, THE DAKOTAS, AND MINNESOTA THROUGH
TOMORROW.
THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.
MULLINAX/ASHERMAN/JACKSON
...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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