Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 252009
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
408 PM EDT WED APR 25 2018

VALID 00Z THU APR 26 2018 - 00Z SUN APR 29 2018

..DAY 1...

...WY BIGHORN MOUNTAINS TO NORTHERN LARAMIE MOUNTAINS...

LIGHT SNOW IS EXPECTED OVER THE BIGHORN MOUNTAINS OF WYOMING LATER
THIS EVENING DOWN INTO THE NORTHERN LARAMIE MOUNTAINS AS AN
UPSTREAM SHORTWAVE APPROACHES THE REGION....WITH SYNOPTIC SCALE
LIFT AIDED BY 300 MB DIVERGENCE IN THE LEFT EXIT REGION OF THE JET
STREAM.  THIS COINCIDES WITH MODEST LOW LEVEL CONVERGENCE WITH THE
FRONT AND POST-FRONTAL UPSLOPE FLOW AS WINDS VEER TO THE
NORTHWEST. THE SNOW SHOULD TAPER THU AS THE JET AND MOISTURE POOL
MOVES AWAY FROM THE REGION.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT.

...DAY 2...

...MINNESOTA ARROWHEAD...

A MID LEVEL TROUGH AND AN ASSOCIATED SURFACE COLD FRONT WILL MOVE
ACROSS SOUTHERN CANADA...WITH POST-FRONTAL COLD ADVECTION CHANGING
PRECIP OVER TO SNOW.  LIGHT ACCUMULATIONS ARE POSSIBLE ON GRASSY
SURFACES IN THE NORTHERN PORTION OF THE MINNESOTA ARROWHEAD
THURSDAY EVENING.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT.

...DAY 3...

...RANGES OF NORTHERN CA/OR/WA...

LIGHT SNOW IS POSSIBLE AT THE HIGHER ELEVATIONS OF THE
SHASTA/SISKIYOU RANGE NORTHWARD INTO THE OR AND WA CASCADES AS A
CLOSED LOW OVER THE EASTERN NORTH PACIFIC DRIFTS ONSHORE AND THEN
INLAND.  THIS WILL RESULT IN LOWERING HEIGHTS/THICKNESSES ACROSS
THE AREA.
WITH COOLING TEMPERATURES...SNOW ELEVATIONS GRADUALLY LOWER.  THE
MODELS INDICATE MOIST CONDITIONS REMAIN IN PLACE AFTER THE FRONTAL
PASSAGE IN THE MOUNTAINS OF NORTHWEST CA/ OR-WA CASCADES...WITH A
WEST COMPONENT TO THE LOW-MID LEVEL FLOW LEADING TO OROGRAPHIC
ENHANCEMENT IN WINDWARD TERRAIN.  SEVERAL INCHES OF SNOW ARE
POSSIBLE AT HIGHER ELEVATIONS WHERE A LONGER PERIOD OF SNOW IS
FORECAST.

...SAN JUAN RANGE OF SOUTHWEST COLORADO...

THE MODELS SHOW FLOW BACKING TOWARDS THE SOUTHWEST ACROSS
SOUTHEAST UT AND SOUTHWESTERN CO...WHICH FACILITATES WARM/MOISTURE
ADVECTION INTO THE SAN JUAN MOUNTAINS...WITH TERRAIN FACING
TOWARDS THE FLOW AIDING IN PRODUCING LIFT ACROSS THE REGION. DEEP
LAYER MOISTURE WITH RELATIVE HUMIDITY INCREASING TO 90 PERCENT
FROM 600 TO 400 MB SUPPORT SOW DEVELOPING IN THE SAN JUANS.  THERE
IS A SIGNAL IN THE MODELS FOR A SLIGHT RISK OF 4 INCH SNOWFALL
AMOUNTS IN THE SAN JUAN MOUNTAINS FRIDAY NIGHT AND EARLY SATURDAY
MORNING.  SNOWFALL SHOULD BE CONFINED TO THE HIGHEST ELEVATIONS OF
THE MOUNTAIN RANGE...GIVEN VALLEY AREAS ARE FORECAST TO BE TOO
WARM FOR SNOW.

THE PROBABILITY OF ICING GREATER THAN 0.25 INCHES IS LESS THAN 10
PERCENT.

PETERSEN







$$





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