PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 PM EDT SUN MAY 12 2013

VALID 00Z MON MAY 13 2013 - 00Z THU MAY 16 2013

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

...DAY ONE...

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

...DAY TWO...
CURRENT GUIDANCE REMAINS FAIRLY WELL-CLUSTERED IN SHOWING A
PROGRESSIVE 700 MB WAVE AND 300 MB JET STREAK ACROSS THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES/HIGH PLAINS.
IN THE VICINITY OF THE WAVE IS EXPECTED TO BE A BURST OF 700 MB
CONVERGENCE AND ASCENT UNDERNEATH 300 MB DIVERGENCE. 

DRYING IN THE WAKE OF THE 700 MB WAVE LIMITS POST FRONTAL UPSLOPE
SNOW SHOWERS. THIS COMBINES WITH A 6 HOUR OR LESS DURATION OF 700
MB VERTICAL MOTIONS KEEPS POTENTIAL FOR A HEAVY SNOW EVENT
LIMITED.  GIVEN GOOD MODEL AGREEMENT...USED 09Z SREF MEAN/12Z
GFS/12Z ECMWF QPF/TEMPERATURE PROFILES TO DERIVE LOW TO MODERATE
PROBABILITIES OF 4 INCHES OR MORE OF SNOW ACROSS THE NORTHERN
CASCADES.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


...DAY THREE...

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


PETERSEN