262
FOUS11 KWBC 041812
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 PM EDT SAT OCT 4 2025
VALID 00Z SUN OCT 05 2025 - 00Z WED OCT 08 2025
..NORTHERN ROCKIES
DAYS 1-2...
UPPER LEVEL PROGRESSION REMAINS STEADFAST FROM PREVIOUS FORECASTS
WITH THE CLOSED UPPER REFLECTION NOW ANALYZED AS A VIGOROUS OPEN
WAVE TAKING ON A NEGATIVE TILT AS IT MIGRATES NORTHEAST OUT OF THE
GREAT BASIN INTO THE ADJACENT NORTHERN ROCKIES. CONSENSUS ON HEAVY
SNOW BEGINNING ACROSS THE HIGHER TERRAIN OF SOUTHWEST MT INTO
NORTHWEST WY LATER THIS AFTERNOON REMAINS WITH SOME OF THE RIDGES
LIKELY TO HAVE SWITCHED OVER IN THE PAST FEW HRS. AS HEIGHTS
CONTINUE TO FALL PRECIPITOUSLY WITH THE UPPER LEVEL PROGRESSION. AT
THE SURFACE, A STRONG SURFACE REFLECTION IS ANALYZED OVER THE UT/CO
BORDER WITH AN EXPECTED PROGRESSION TO THE NORTH-NORTHEAST OVER THE
NEXT 24 HRS. THE COMBINATION OF A FAVORABLE UPPER LEVEL
PROGRESSION AND STRENGTHENING AXIS OF DEFORMATION OVER SOUTHERN MT
AND NORTHERN WY WILL LEAD TO A SIGNIFICANT HEAVY SNOW EVENT, THE
FIRST OF THE SEASON ACROSS THE ABSAROKA/BEARTOOTH/WIND RIVER RANGES
WITH THE BIG HORNS GETTING INTO THE HEAVY SNOW THREAT A LITTLE
LATER THIS EVENING AS THE HEIGHT FALLS SHIFT EAST. HEAVY SNOW IS
LIKELY OVER THESE RANGES OVERNIGHT INTO EARLY TOMORROW MORNING
LEADING TO RATES BETWEEN 1-2"/HR AT TIMES GENERATING A SWATH OF 6+"
TOTALS A LIKELIHOOD BY THE TIME WE REACH SUNRISE TOMORROW.
BEHIND THIS FIRST, STRONGER SHORTWAVE, A SECOND SHORTWAVE WILL
DIVE SOUTH OUT OF ALBERTA AND INTO THE NORTHERN ROCKIES ON SUNDAY.
THE PRESENCE OF THIS SECOND SHORTWAVE WILL SUPPORT MAINTAINING
HEAVY SNOW INTO NORTHERN MT, ESPECIALLY GLACIER NP. THIS DIGGING
SECOND SHORTWAVE WILL ALLOW THE LARGER LONGWAVE TROUGH TO REMAIN IN
PLACE, EVEN EXPANDING AND GROWING SOUTH AND WEST. SIMILARLY
IMPORTANT TO THE PRESENCE OF THESE 2 SHORTWAVES MOVING THROUGH THE
FLOW AND TAKING ADVANTAGE OF THE ABUNDANT LOW LEVEL MOISTURE, A
LARGE POLAR SURFACE HIGH WILL EFFECTIVELY END THE WINTRY THREAT
FROM NORTH TO SOUTH. THIS IS BECAUSE THE POLAR HIGH WILL ALSO BE
QUITE DRY, SO IT WILL MOVE THE MOISTURE FEEDING THE SNOW ON TOWARDS
THE NORTH AND EAST. WITH THAT POLAR LOW IN PLACE, EXPECT
TEMPERATURES TO TUMBLE WELL DOWN INTO THE 30S. THUS, AS IS VERY
COMMON IN THE WINTERTIME, THE LIMITED TIME BETWEEN THE ADVANCING
COLD/DRY AIR AND THE RETREATING ATMOSPHERIC MOISTURE WILL FAVOR
CERTAIN AREAS, SUCH AS THE BEARTOOTH RANGE, WHILE KEEPING MANY
OTHERS ON THE PLAINS BONE DRY. WITH THE ADVANCING COLD AIR, SNOW
LEVELS WILL FALL TO AS LOW AS 5,000 FT, BUT THE DRYNESS SHOULD HOLD
ANY HEAVY SNOW OCCURRING TO SUNDAY MORNING, BEFORE THE SNOW ENDS
FROM NORTH TO SOUTH.
WPC PROBABILITIES FOR 6 INCHES OR MORE OF SNOW REMAIN ELEVATED BETWEEN
50 AND 90% FOR THE BEARTOOTH, ABSAROKAS, AND BIG HORN RANGES WHILE
PROBABILITIES ARE A BIT LOWER, BETWEEN 60 AND 80% FOR THE WIND
RIVER RANGE.
THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.
WEGMAN/KLEEBAUER
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