059
FOUS11 KWBC 152045
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
345 PM EST WED JAN 15 2025
VALID 00Z THU JAN 16 2025 - 00Z SUN JAN 19 2025
..GREAT LAKES & CENTRAL APPALACHIANS
DAYS 1-2...
A TROUGH EXTENDING FROM A LOW MOVING EAST OVER SOUTHERN HUDSON BAY
WILL PUSH ACROSS THE WESTERN GREAT LAKES TONIGHT AND THE EASTERN ON
THURSDAY. AREAS OF LIGHT SNOW CAN BE EXPECTED AHEAD OF THE TROUGH
WITH UP TO 24 HOURS OF MODERATE LAKE EFFECT SNOW BEHIND ON NWLY
FLOW. DAY 1 SNOW PROBABILITIES FOR >4" ARE 30-60% FOR PREFERRED
U.P. AND WESTERN MI SNOWBELTS WITH 50-80% VALUES ON DAY 1.5 EAST OF
LAKE ERIE.
THE BROAD NWLY FLOW ALLOWS IDEAL UPSLOPE FLOW FOR SNOW
SHOWERS IN THE CENTRAL APPALACHIANS. DAY 1.5 SNOW PROBABILITIES FOR
>6" ARE 60-90% FROM THE LAURELS OF PA THROUGH THE ALLEGHENY
HIGHLANDS IN WV.
DAY 3...
STRONG SURFACE LOW DEVELOPMENT SHIFTING EAST ACROSS ONTARIO FRIDAY
IS ON THE LEADING EDGE OF AN ARCTIC PLUNGE (SEE KEY MESSAGES LINKED
BELOW) DOWN THE GREAT PLAINS. BROAD CYCLONIC FLOW UNDER THIS TROUGH
SENDS NOTABLE MOISTURE NORTH FROM THE SOUTHEAST AND OVER THE GREAT
LAKES AND EVENTUALLY NORTHEAST. PRECIP ONSET IN THE CENTRAL
APPALACHIANS IS SATURDAY MORNING. SUFFICIENT COLD AIR SHOULD LINGER
AT THE SURFACE FOR A WINTRY MIX INCLUDING FREEZING RAIN TO OCCUR.
PROBABILITIES FOR SIGNIFICANT FREEZING RAIN ARE CURRENTLY LOW, BUT
THERE IS A THREAT PARTICULARLY IN THE SHELTERED VALLEYS IN VA/WV/MD
INTO PA.
..ROCKIES AND HIGH PLAINS
DAYS 2/3...
A RATHER AMPLIFIED UPPER RIDGE BUILDS ACROSS THE NORTHEASTERN
PACIFIC AND ALASKA THURSDAY INTO FRIDAY WHICH OPENS POLAR AIR TO
PLUNGE SOUTH FROM THE CANADIAN PRAIRIES WITH A STRONG COLD FRONT
("BLUE NORTHER") SWEEPING DOWN THE GREAT PLAINS FRIDAY THROUGH
SATURDAY. THOUGH MOISTURE WILL BE LIMITED, STRONG NLY FLOW AROUND
A 1055MB HIGH THAT PUSHES INTO MT SATURDAY EVENING WILL SUPPORT
UPSLOPE ENHANCEMENT ALONG THE LENGTH OF THE EASTERN SLOPES OF THE
ROCKIES.
AS THE FRONT DIVES SOUTHWARD, STEEPER LAPSE RATES WILL SUPPORT
SNOW SQUALLS ALONG THE FRONT EARLY FRIDAY IN CENTRAL MONTANA
PROGRESSING ACROSS WYOMING AND POSSIBLY NORTHERN COLORADO THROUGH
FRIDAY EVENING. SNOW SQUALL PARAMETER VALUES IN THE 12Z NAM ARE 2
TO 4 OVER THESE AREAS SUGGESTING BURSTS OF SNOW WITH SHARPLY
REDUCED VISIBILITY LEADING TO NEAR WHITEOUT CONDITIONS. CAM
GUIDANCE SHOULD SHED A LITTLE MORE LIGHT ON THE THREAT OVER THE
NEXT TWO DAYS, BUT WE HAVE OUTLINED THIS AREA IN OUR KEY MESSAGES
(SEE BELOW). DAY 2 WPC SNOW PROBABILITIES FOR >4" REMAIN MODERATE
(40-70%) OVER TERRAIN IN CENTRAL MONTANA/NORTHERN WYOMING.
AS THE FRONT RACES SOUTHWARD, ENHANCED LIFT FROM A REINFORCING
SHORTWAVE TROUGH ON THE BACKSIDE OF THE SPRAWLING UPPER TROUGH WILL
ALLOW MORE MODERATE SNOW OVER THE CO FRONT RANGE AND THE I-25
CORRIDOR THROUGH THE DENVER METRO AREA. DAY 3 SNOW PROBABILITIES
FOR >4" ARE HIGH 60-90% IN TERRAIN AND AROUND 50% IN THE FOOTHILLS
TO THE I-25 CORRIDOR FROM SOUTHERN WY THROUGH CO.
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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