Quantitative Precipitation Forecast
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FOUS11 KWBC 261946
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 PM EDT THU APR 26 2018

VALID 00Z FRI APR 27 2018 - 00Z MON APR 30 2018


...RANGES OF NORTHERN CALIFORNIA AND THE CA/OR/WA CASCADES...

A LARGE CLOSED UPPER LOW IS FORECAST TO SLOWLY PROGRESS EASTWARD
OVER OREGON FRIDAY NIGHT AND INTO SATURDAY.  COLD AIR ADVECTION
AND STEEP LAPSE RATES OWING TO RAPIDLY COOLING 500-700MB
TEMPERATURES WILL RESULT IN SNOW LEVELS FALLING TO 4000 TO 6000
FEET, AND THE RESULT WILL BE CONVECTIVE SNOW SHOWERS FOR THE
HIGHEST ELEVATIONS OF THE SISKIYOUS, SHASTA, AND CA/OR/WA
CASCADES.  THERE SHOULD BE ENOUGH MOISTURE AND LIFT AVAILABLE TO
SUPPORT 1 TO 3 INCH AMOUNTS, WITH SEVERAL INCHES POSSIBLE IN
ISOLATED PEAKS.

...NORTHERN ROCKIES...

WITH THE 700 MB CLOSED LOW CROSSING THE NORTHERN ROCKIES SATURDAY
NIGHT AND SUNDAY, DEEP LAYER ASCENT AHEAD OF THE LOW WITH A
SHORTWAVE DISTURBANCE PIVOTING AROUND IT IS EXPECTED TO LEAD TO
SEVERAL INCHES OF SNOW OVER THE HIGHER ELEVATIONS OF THE SALMON
RIVER AND SAWTOOTH MOUNTAINS, CONTINUING ACROSS THE BITTERROOT
RANGE AND EVENTUALLY INTO THE RANGES OF NORTHWEST MT.  THIS REGION
HAS THE HIGHEST CHANCE OF RECEIVING GREATER THAN 4 INCHES. THERE
ARE STILL LATITUDINAL DIFFERENCES WITH THE TRACK OF THE
CIRCULATION WITH THE NAM AND UKMET TRENDING NORTH TOWARDS THE GFS
AND ECMWF SOLUTIONS.

ELSEWHERE, THERE IS ALSO MODEL SIGNAL FOR LIGHT SNOW OVER THE
HIGHEST ELEVATIONS OF THE SAN JUAN MOUNTAINS OF COLORADO FROM
FRIDAY NIGHT THROUGH SATURDAY.

...NEW YORK ADIRONDACKS...

THE MODELS FORECAST A MID-UPPER LEVEL LOW TO CROSS THE GREAT LAKES
SAT AND NEW YORK-NORTHERN NEW ENGLAND SUNDAY.  AS THE LOW MOVES
EAST....FALLING HEIGHTS/TEMPS ALLOW PRECIP TO CHANGE OVER TO SNOW
IN THE NY ADIRONDACK MOUNTAINS.  A FEW INCHES ARE EXPECTED SUN AS
POST-FRONTAL NORTHWEST WINDS PROVIDE UPSLOPE FLOW IN WINDWARD
FACING TERRAIN.  THE MODELS ARE COMING INTO BETTER AGREEMENT ON
THE TIMING OF THE 700-500 MB LOW SO WEIGHTING AMONG SOLUTIONS WAS
SIMILAR.

...MINNESOTA ARROWHEAD...

A MID LEVEL TROUGH AND AN ASSOCIATED SURFACE COLD FRONT WILL MOVE
ACROSS NORTHERN MN, WITH POST-FRONTAL COLD ADVECTION CHANGING
PRECIPITATION OVER TO WET SNOW.  SOME LIGHT ACCUMULATIONS NEAR AN
INCH ARE POSSIBLE ON GRASSY SURFACES IN THE NORTHERN PORTION OF
THE MINNESOTA ARROWHEAD REGION TONIGHT.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT FOR DAY 1 THROUGH 3.

PETERSEN









$$





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