Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 260630
QPFHSD

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

VALID 12Z THU APR 26 2018 - 12Z SUN APR 29 2018

...MINNESOTA ARROWHEAD...

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

...RANGES OF NORTHERN CALIFORNIA AND THE CASCADES...

THE MAIN FEATURE OF INTEREST WILL BE A LARGE CLOSED UPPER LOW
SLOWLY PROGRESSING EASTWARD OVER NORTHERN CALIFORNIA AND 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 CASCADES.  THERE SHOULD BE ENOUGH MOISTURE
AND LIFT AVAILABLE TO SUPPORT 1 TO 2 INCH AMOUNTS, AND POSSIBLY
GREATEST FOR THE HIGHEST SUMMITS.

...IDAHO ROCKIES...

WITH THE CLOSED LOW IMPINGING ON THE NORTHERN ROCKIES BY DAY 3
(SATURDAY NIGHT), DEEP LAYER ASCENT AHEAD OF THE LOW WITH A
SHORTWAVE DISTURBANCE PIVOTING AROUND IT IS EXPECTED TO LEAD TO
MODERATE SNOW OVER THE HIGHER ELEVATIONS OF THE SALMON RIVER AND
SAWTOOTH MOUNTAINS, AND SOME ALSO EXTENDING INTO THE BITTERROOT
RANGE.  THIS REGION HAS THE HIGHEST CHANCE OF RECEIVING GREATER
THAN 4 INCHES ANYWHERE NATIONWIDE DURING THE ENTIRE FORECAST
PERIOD, MAINLY ABOVE 6000 FEET.

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

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

HAMRICK







$$





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