Quantitative Precipitation Forecast
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FOUS11 KWBC 111956
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EST THU DEC 11 2014

VALID 00Z FRI DEC 12 2014 - 00Z MON DEC 15 2014


DAY 1...

...PACIFIC NORTHWEST/CA/GREAT BASIN/NORTHERN ROCKIES...

THE 700 MB TROUGH INITIAL SHORT WAVE OFF THE NORTHERN CA COAST
MOVES ONSHORE IN NORTHERN CA ON DAY 1...FUNNELING LIFT AND DEEP
PACIFIC MOISTURE ACROSS CENTRAL CA. THE STRONG LOW LEVEL FLOW
PROMOTES STRONG UPSLOPE, WITH MOISTURE FLUX ANOMALIES 4-5 STD
DEVIATIONS ABV NORMAL THIS EVENING BEFORE SUBSIDING FRIDAY.
FALLING SNOW LEVELS...STRONG SYNOPTIC SCALE LIFT AND COPIOUS
MOISTURE SUPPORT A LARGE AREA OF HEAVY SNOW WITH A COUPLE OF FEET
OF SNOWFALL ACROSS THE SPINE OF THE SIERRA NEVADA RANGE. THESE
AMOUNTS ARE SUPPORTED BY THE HIGHER RESOLUTION GUIDANCE LIKE THE
SREF MEMBERS AND THE NAM. THE QPF PORTION OF THE FORECAST WAS
BASED ON THE MOST RECENT WPC QPF...WHILE THE THERMAL PORTION OF
THE FORECAST WAS BASED PRIMARILY ON A 12Z GFS/09Z SREF MEAN/12Z
ECMWF/12Z NAM BLEND.   FOR THE NORTHERN CASCADES OF WA... WHILE
THE MOISTURE IS NOT AS BOUNTIFUL AS IT IS ACROSS NORTHERN
CA...THERE SHOULD BE ENOUGH MOISTURE AND LIFT TO SUPPORT A SWATH
OF 3 TO 5 INCHES OF SNOWFALL.

...NORTHEAST...

MODEST MOISTURE AND LIFT ASSOCIATED WITH SHORT WAVES ROUNDING THE
MID LEVEL CLOSED LOW CROSS WESTERN NY STATE AND WESTERN PA DURING
DAY 1. THE SHORT WAVE CROSSES WESTERN NY STATE THIS EVENING...WITH
ANOTHER 1 TO 3 INCHES SNOWFALL EXPECTED.
THE LOW LEVEL FLOW BECOMES UNIDIRECTIONAL FOR A TIME AS
WELL...GENERALLY PERPENDICULAR TO THE SHORT AXIS OF THE LAKE. THE
LAKE ENHANCEMENT SHOULD RESULT IN SEVERAL ADDITIONAL INCHES OF
SNOWFALL IN LEESHORE AREAS. FURTHER EAST...THE COLD MOIST LOW
LEVEL FLOW TURNS UPSLOPE ACROSS THE HIGHER TERRAIN OF VT AND
NORTHERN NH. THE FAVORED LOCATIONS HERE COULD SEE 2 TO 4 INCHES OF
SNOWFALL.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

DAY 2...

...GREAT BASIN/NORTHERN TO CENTRAL ROCKIES...

THE MODELS INDICATE POTENTIAL FOR 2 SEPARATE AREAS OF SNOW WITH
THE NORTHERN AND SOUTHERN STREAM TROUGH.  THE 700 MB WAVE CROSSES
THE NORTHERN ROCKIES ON TO THE PLAINS.  AN UPPER DIVERGENCE MAXIMA
CROSSING THE BLUE MNTNS OF NORTHEAST OR ACROSS THE RANGES OF
CENTRAL ID LEADS TO POTENTIAL FOR SEVERAL INCHES OF SNOW AS THE
UPPER TROUGH DRIFTS EAST ACROSS THE REGION.
THE SYNOPTIC SCALE LIFT AUGMENTED BY UPSLOPE FLOW SUPPORTS A SWATH
OF 6 TO 10 INCHES OF SNOW ACROSS THE RANGES OF CENTRAL ID WITH
LOWER AMOUNTS IN WESTERN MT AS THE ECMWF SHOWS THE 300 MB
DIVERGENCE WEAKENING AS IT CROSSES WESTERN MT.


...NORTHEAST...
THE MID LEVEL FRONT AND DEFORMATION ZONE WEST OF THE LOW LEVEL
CIRCULATION OVER NOV SCOTIA PRESENTS THE THREAT OF ANOTHER ROUND
OF LIGHT TO MODERATE SNOW IN EASTERN MAINE.  THE NAM AND GFS SHOW
ENHANCED SNOWFALL NEAR THE ME/NEW BRUNSWICK BORDER AS MID LEVEL
CONVERGENCE MAXIMA CROSS THE REGION.  REMAINING UNCERTAINTY STEMS
FROM THE TIMING OF THE MID-UPPER LEVEL LOW AS IT STARTS TO MOVE
AWAY FROM NEW ENGLAND...WITH THE NAM LINGERING LONGER THAN OTHER
MODELS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


DAY 3...

...CENTRAL TO SOUTHERN ROCKIES AND HIGH PLAINS...

THE SOUTHERN STREAM TROUGH CROSSES NV INTO UT..WITH A FEW OF THE
MODELS INDICATING AN EMBEDDED 700 MB LOW DEVELOPING WITHIN THE
TROUGH AXIS.  ENHANCED 700 MB CONVERGENCE AND MID LEVEL
DEFORMATION WITH THE FRONT/EMBEDDED CIRCULATIONS LEADS TO SNOW IN
THE UT WASATCH. THE UPPER LEVEL TROUGH TAKES ON A NEGATIVE TILT
ACROSS THE SOUTHERN ROCKIES BEFORE CLOSING OFF NEAR THE END OF THE
PERIOD.

THE SYNOPTIC SCALE LIFT AIDS CYCLOGENESIS THAT OCCURS ON A LOW
LEVEL BAROCLINIC ZONE ACROSS SOUTHEAST CO BY 14/12Z. THE LOW LEVEL
FLOW THAT RESULTS PRODUCES UPSLOPE FLOW ACROSS THE CO AND WY
ROCKIES. THE COMBINATION OF SYNOPTIC SCALE LIFT AND UPSLOPE FLOW
AND SUSTAINED SFC-500 MB RELATIVE HUMIDITY OF 90-99 PERCENT LEADS
TO AREAS OF 6 TO 10 INCHES OF SNOW IN FAVORED TERRAIN FROM WY
THROUGH CO.

THE TIMING OF THE CIRCULATION AND ASSOCIATED LOW LEVEL COOLING
WILL DETERMINE HOW FAR SNOW EXTENDS EAST ON THE HIGH PLAINS.
INITIAL TEMPERATURES ARE TOO WARM FOR SNOW WITH COOLING AS HEIGHTS
LOWER...WITH SNOW DEVELOPING ON THE HIGH PLAINS OF NE AND CO LATER
IN THE PERIOD.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN

$$





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