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FOUS11 KWBC 122017
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
316 PM EST FRI MAR 12 2010

VALID 00Z SAT MAR 13 2010 - 00Z TUE MAR 16 2010

...WEST...
ON DAY ONE...AN UPPER TROUGH AND ASSOCIATED STRONG THERMAL
BOUNDARY WILL BARREL INTO THE WEST COAST BEFORE MOVING INLAND AND
DECAYING. THE NRN STREAM WILL THEN DAMPEN OUT ACROSS THE NW INTO
THE NRN ROCKIES ON SAT. THE HVY SNOWFALL ON DAY ONE WILL WILL
IMPACT THE RANGES OF ID SOUTH INTO NORTHERN NV AND THE
SIERRA...ALIGNING WITH THE STRONGEST MID-UPPER LEVEL JET AND MAX
PAC MOISTURE TRANSPORT WILL CONCENTRATE FOR ENHANCED VERTICAL
LIFT... LARGE QPF AMOUNTS AND HVY SNOW.  THE MODELS/ENSEMBLE
MEMBERS SHOW HIGHER AMOUNTS IN THE TERRAIN OVER THE BLUES AND
BOISE/SAWTOOTH RANGES AND SIERRA.

ON DAY TWO...THE SNOWFALL THREAT AREA THEN SHIFTS OUT OF NV INTO
UT AND SOUTHWEST CO ALONG THE PATH OF THE CLOSED MID LEVEL
CIRCULATION AND GREATEST LIFT RESULTING FROM UPPER
DIVERGENCE/LOWER CONVERGENCE MAXIMA IN THE WASATCH/UINTAS/SAN
JUANS.  LIGHT SNOW EXTENDS INTO THE RANGES OF WESTERN WY ALONG THE
UPPER LEVEL TROUGH AXIS...WHERE CONDITIONS REMAIN MOIST WITH AREAS
OF SFC-500 MB RH OVER 90 PERCENT MOST OF THIS PERIOD.

ON DAY THREE... THE HEAVIEST SNOW WILL SHIFT INTO TOWARDS THE SRN
ROCKIES WITH THE HEAVIEST SNOWFALL ALONG THE SANGRE DE CRISTO
RANGE. THE MID-UPPER LEVEL CROSSES NEW MEXICO...TRIGGERING THE
GREATEST UPPER DIVERGENCE/LOW CONVERGENCE COUPLET. AS ON DAY
TWO...SNOW IS ENHANCED WHERE UPSLOPE FLOW OCCURS.  THE MODELS SHOW
ON THE ORDER OF AN INCH LIQUID EQUIVALENT...WITH HIGHER AMOUNTS IN
THE NAM RESULTING FROM A SLOWER MOVEMENT OF THE MID LEVEL LOW IN
SOUTHWEST CO/ADJACENT NM.  THE SNOW RATIOS FROM THE MODEL SUGGEST
ON THE ORDER OF THE LOWER TEENS TO ONE DURING THE HEAVIER
PRECIP..SO AN INCH LIQUID EQUIVALENT TRANSLATES TO ABOUT A FOOT OF
SNOW IN THE SANGRE DE CRISTOS ON DAY THREE.
MANUAL PROGS USED A BLEND OF THE ECMWF AND 09Z SREF MEAN FOR ALL
THREE DAYS...WITH LESS WEIGHT ON THE NAM/GFS/GEFS MEAN.

...INTERIOR NEW YORK/NEW ENGLAND...

THE CLOSED LOW SFC/ALOFT WILL DRIFT SLOWLY NORTH AND THEN EAST
NORTHEAST FROM THE THE MID ATLANTIC COAST INTO THE COASTAL WATERS
OVER THE NEXT COUPLE OF DAYS. THE IMPRESSIVE ERLY MOISTURE SURGE
FROM THE ATLANTIC WILL INUNDATE THE REGION. INITIALLY THERMAL
PROFILES ACROSS THE REGION WILL BE ABV FREEZING ON DAY ONE.  ON
DAY TWO...THE MODEL GUIDANCE SUGGESTS ENOUGH COLD AIR ADVECTED
SOUTH FROM A SURFACE RIDGE OVER THE CANADIAN MARITIMES AND A
TREMENDOUS UPSLOPE COMPONENT ENHANCING THE VERTICAL LIFT TO COOL
TEMPERATURE PROFILES SO THERE IS A MIXTURE OF SNOW AND FREEZING
RAIN IN THE BERKSHIRES/CATSKILLS/ADIRONDACKS.  MODEL/ENSEMBLE QPF
AMOUNTS ARE HIGH AND DIFFERENCES IN TEMPERATURE PROFILES FROM
MODEL TO MODEL LEAD TO LARGE UNCERTAINTIES AND LOW CONFIDENCE.
MANUAL PROGS FOLLOWED A BLEND OF THE ECMWF/09Z SREF MEAN FOR QPF
AND THERMAL PROFILES...WITH LESS WEIGHTING ON THE 12Z NAM/GFS
THROUGH THE FORECAST CYCLE FOR PROBS OF  SNOW/ICING ACROSS THE
FAVORED TERRAIN OF INTERIOR NY/NEW ENGLAND.

THE PROBABILITY OF SIGNIFICANT ICING ON DAY ONE IS LESS THAN 10
PERCENT.

PETERSEN
$$