Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 160816
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
315 AM EST THU FEB 16 2017

VALID 12Z THU FEB 16 2017 - 12Z SUN FEB 19 2017

NORTHWEST/CALIFORNIA/INTERMOUNTAIN WEST...

PROBABILITIES FOR HEAVY SNOW WILL OVERSPREAD MOST OF THE HIGHER
ELEVATIONS OF THE WEST...INCLUDING
THE NORTHWEST/CALIFORNIA/INTERMOUNTAIN WEST...PRIMARILY ABOVE 3 TO
4 THOUSAND FEET THURSDAY THROUGH SATURDAY...AS A SPLITTING UPPER
TROUGH DEVELOPS ACROSS THE REGION. MODEL SPREAD IS QUITE TYPICAL
FOR SUCH A PATTERN...WITH CONFIDENCE IN THE PROBABILITIES HIGHEST
EARLY IN THE FORECAST PERIOD WHEN THE MODEL SPREAD IS SMALL...AND
LOWEST LATE IN THE FORECAST PERIOD WHEN THE MODEL SPREAD IS
HIGHER. THROUGH THURSDAY NIGHT...LOW TO MODERATE PROBABILITIES OF
8 AND 12 INCHES OF SNOW ARE CONFINED TO THE SAWTOOTH RANGE AND
NORTHERN SIERRAS...WITH THE SPREAD EQUALLY DISTRIBUTED AMONG THE
VARIOUS ENSEMBLE SYSTEMS. FOR DAY 2/FRIDAY AND FRIDAY
NIGHT...MODERATE TO HIGH PROBABILITIES OF 12 INCHES CONTINUE
ACROSS THE SIERRAS...MOSTLY ABOVE 4 TO 5 THOUSAND FEET...WITH LOW
TO MODERATE PROBABILITIES OF 4 AND 8 INCHES OF SNOW EXTENDING INTO
THE HIGHER ELEVATIONS OF CENTRAL NEVADA AS WELL AS THE WASATCH
RANGE. THE MODEL SPREAD ALSO GROWS ON DAY 2...WITH THE GEFS
MEMBERS GENERALLY MORE AMPLIFIED WITH THE LEADING EDGE OF THE
UPPER TROUGH ENTERING OREGON...THUS HIGHER WITH SNOW PROBABILITIES
FOR THE OREGON CASCADES...
COMPARED WITH OTHER GUIDANCE THAT SUGGESTS LESS AMPLIFICATION AND
THEREFORE LOWER PROBABILITIES. FOR DAY 3/SATURDAY AND SATURDAY
NIGHT...LOW TO MODERATE PROBABILITIES OF 8 INCHES RETURN TO THE
SAWTOOTH RANGE AND CONTINUE FOR PARTS OF THE WASATCH RANGE...WHILE
LOW TO MODERATE PROBABILITIES OF 4 INCHES CONTINUE FOR THE HIGHER
ELEVATIONS OF THE SIERRAS. REGARDING SPREAD...THE SREF NMMB
MEMBERS WERE SLOWER AND MUCH LESS AMPLIFIED WITH NORTHERN PARTS OF
THE SPLITTING UPPER TROUGH CROSSING THE NORTHWEST RESULTING IN
VERY LOW PROBABILITIES FOR HEAVY SNOW...WHILE THE GEFS MEMBERS
WERE PARTICULARLY AMPLIFIED...RESULTING IN HIGHER PROBABILITIES
FOR HEAVY SNOW. THESE OUTER SOLUTIONS RELATIVE TO THE CONSENSUS
ARE THEN SPLIT BY THE SREF ARW AND ECMWF MEMBERS...WHICH ARE NEAR
THE MIDDLE OF THE ENVELOPE. WHILE THE CONSENSUS APPROACH IS MORE
PREFERRED AT THIS TIME...THE SOLUTION ENVELOPE BECOMES LARGE AT
THIS TIME...THUS ASSOCIATED WITH LOW CONFIDENCE.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT.

JAMES


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