PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
312 PM EDT TUE MAY 05 2009
 
VALID 00Z WED MAY 06 2009 - 00Z SAT MAY 09 2009
 

DAYS 1 THROUGH 3...

NORTHWEST...
A SUCCESSION OF PACIFIC SHORTWAVES IN ZONAL FLOW WILL BRING A MUCH
COLDER AIRMASS ALOFT INTO THE NORTHWEST US...BRINGING A SLIGHT
RISK OF 4+ INCH SNOWFALLS TO PORTIONS OF THE WASHINGTON CASCADES
AND NORTHERN ROCKIES OF IDAHO...MONTANA AND WYOMING THROUGH FRIDAY
EVENING. LATER TONIGHT AND EARLY WEDNESDAY MORNING...THERMAL
PROFILES SUGGEST A GRADUAL LOWERING OF THE LEVEL WHERE
ACCUMULATING SNOWFALL WILL TAKE PLACE ACROSS THE NORTHERN CASCADES
OF WASHINGTON...WITH UP TO 8 INCHES OF SNOWFALL FORECASTED ABOVE
THE 4500FT MSL LEVEL INVOF MT BAKER AND 4+ INCHES INVOF MT
RAINIER. THE LOW SNOW LEVELS FOR EARLY MAY REMAIN IN PLACE ACROSS
THE CASCADES OF WASHINGTON THROUGH THURSDAY MORNING PER THE
CURRENT MODEL SUITE. 

DOWNSTREAM...THE TETONS AND BITTERROOT RANGES AND THEIR ADJACENT
SLOPES/VALLEYS AT/ABOVE 7000 FT MSL WILL LIKELY RECEIVE PERIODS OF
LIGHT SNOWFALL BASED ON THE GFS/NAM THERMAL PROFILES AND HPC/ECMWF
QPFS...BETWEEN WEDNESDAY NIGHT AND FRIDAY MORNING. A SLIGHT RISK
OF 4+ INCHES FORECASTED ACROSS THE CENTRAL TETONS...SOUTHERN
BITTERROOTS AND PORTIONS OF THE IDAHO PANHANDLE.

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