Probability Of 4 Inches Of Snow - National USData: MapDiscussion

FOUS11 KWBC 081958
QPFHSD
 
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
258 PM EST WED FEB 08 2012
 
VALID 00Z THU FEB 09 2012 - 00Z SUN FEB 12 2012
 

DAY 1...

THE PROBABILITY OF SIGNIFICANT ICING AND/OR HEAVY SNOW IS LESS
THAN 10 PERCENT.

DAYS 2/3...

...WASHINGTON CASCADES/NORTHERN ROCKIES...

   WARM ADVECTION PRECIPITATION WILL BE THE KEY INGREDIENT FOR
SNOWFALL ACCUMULATIONS IN THE NORTHERN WASHINGTON CASCADES AND
NORTHERN ROCKIES OF IDAHO...WESTERN MONTANA AND NORTHWEST WYOMING.
PACIFIC TROUGH AND ATTENDANT SURFACE LOW MOVING NORTHWARD INSIDE
OF 130 W...SPREADS A BROAD WARM FRONT...WITH ISENTROPIC LIFT
GENERATING AREAS OF SNOWFALL ABOVE 4500-5000FT MSL ACROSS
WASHINGTON. DOWNSTREAM...VERY LITTLE COLD AIR TO WORK WITH WEST OF
THE DIVIDE...WITH SNOWFALL GENERALLY AT/ABOVE 6000FT MSL IN
IDAHO...NORTHERN NEVADA AND WESTERN MONTANA. ACROSS THE
NORTHWEST...GIVEN THE PRIMARY SURFACE TRACK STAYS OFFSHORE ALONG
THE PAC NW COAST AND INTO BC...LIMITED MOISTURE STREAMS
DOWNWIND...CURBING TOTAL SNOWFALL ACCUMULATIONS...TO A MAXIMA OF
2-4 INCHES FOR EACH 24 HOUR PERIOD. SMALL AREAS OF 4+ INCH AMOUNTS
CLOSELY FOLLOWED THE NAM/SREF AND ECMWF THERMAL SOLUTIONS WITH THE
ENSEMBLES IDENTIFYING THE MT BAKER AREA ABOVE 5500FT MSL FOR 4-8
INCHES. 
   EAST OF THE DIVIDE...A MUCH COLDER LOW-LEVEL AIRMASS WITH
ORIGINS IN CANADA WILL BE IN PLACE AS MID-LEVEL WARM ADVECTION
ADVANCES EASTWARD AND LIGHT SNOWFALLS DEVELOP IN TOP-DOWN
FASHION...TO VALLEY FLOORS. MUCH OF THE COLD ADVECTION BEGINS TO
MOVE SEWD INTO NW MONTANA THURSDAY EVENING...SPREADING INTO
CENTRAL/EASTERN MONTANA AND NORTHERN WYOMING ON FRIDAY AND
COLORADO ON SATURDAY. MUCH OF THE EAST SIDE SNOWFALL OCCURRING IN
EAST CENTRAL/SOUTHERN MONTANA...CENTRAL WYOMING AND EASTERN
COLORADO WILL BE GENERATED BY MECHANICAL LIFT/TURBULENT MIXING
FROM A RATHER BROAD UPSLOPE FLOW COMPONENT AND AXIS OF H85-H7
FRONTOGENESIS.

...GREAT LAKES AND CENTRAL APPALACHIANS...

   VERY COLD UPPER-LEVEL VORTEX AND EMBEDDED SHORTWAVE ENERGY
ANCHORS OVER HUDSON BAY AND EASTERN CANADA ON DAY 2/3 AND SLOWLY
SLIPS SOUTHWARD INTO THE NORTHEAST AND EASTERN GREAT LAKES.
SHORTWAVE ENERGY ROTATING THROUGH THE BASE OF THE TROUGH...SPREADS
ACROSS THE UPPER GREAT LAKES AND ALONG THE ST LAWRENCE VALLEY INTO
NORTHERN NEW ENGLAND...WITH LAKE-EFFECT SNOW SHOWERS ACROSS
PORTIONS OF MICHIGAN...WESTERN NEW YORK AND DOWNWIND OF LAKE ERIE.
BY FRIDAY NIGHT AND SATURDAY...BROAD UPSLOPE NORTHWEST FLOW WILL
BE GENERATING SNOWFALLS ACROSS THE APPALACHIANS OF WESTERN
PENNSYLVANIA...EASTERN OHIO...FAR WESTERN MARYLAND AND PORTIONS OF
EASTERN WEST VIRGINIA/SOUTHWESTERN VIRGINIA.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.
VOJTESAK
$$