Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 272006
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
305 PM EST FRI FEB 27 2015

VALID 00Z SAT FEB 28 2015 - 00Z TUE MAR 03 2015

DAYS 1 TO 3...

...PACIFIC NORTHWEST/CALIFORNIA/GREAT BASIN/CENTRAL TO SOUTHERN
ROCKIES...

AN UPPER TROUGH WILL AMPLIFY SOUTH AND SOUTHWESTWARD ACROSS THE
WEST COAST OVER THE NEXT 24 HOURS AND WILL PRODUCE A CUT OFF LOW
THAT WILL PERSIST JUST WEST OF THE SOUTHERN CALIFORNIA COAST
THROUGHOUT THE FORECAST PERIOD...EVEN AS ANOTHER TROUGH DIGS
SOUTHWARD ALONG THE WEST COAST OF CANADA ON SUNDAY INTO MONDAY.
THE TROUGH OVER THE SOUTHWEST WILL PRODUCE A LONG PLUME OF
SOUTHWESTERLY UPPER FLOW OVER THE SOUTHWEST AND SOUTHERN TO
CENTRAL ROCKIES AND WILL BE RESPONSIBLE FOR SOME IMPRESSIVE SNOW
TOTALS IN THE MOUNTAINS OF THE SOUTHWEST AND SOUTHERN ROCKIES.

THE AXIS OF THE HEAVIEST SNOW WILL SHIFT SOUTHWARD FROM DAY 1 TO
DAY 2 WITH SNOW ENDING ACROSS PORTIONS OF OREGON AND IDAHO...AS
WELL AS THE NORTHERN SIERRA WHILE THE BULK OF THE HEAVIEST SNOW
FALLS ACROSS NEVADA/UTAH/COLORADO/NORTHERN ARIZONA AND NORTHERN
NEW MEXICO. MULTI DAY TOTALS WILL EXCEED A FOOT IN MANY AREAS AND
COULD EXCEED 4 FEET IN THE SAN JUANS.  WHILE THE NEXT TROUGH
DIVING SOUTHWARD ALONG THE WEST COAST WILL INCREASE SNOWFALL
ACROSS THE CASCADES AND ROCKIES ACROSS NORTHWEST MONTANA...SNOW
WILL CONTINUE ON DAY 3 ESPECIALLY ACROSS NORTHERN ARIZONA/UTAH AND
COLORADO.


...THE SOUTHERN/CENTRAL PLAINS/MID TO UPPER MISSISSIPPI
VALLEY/GREAT LAKES/NORTHEAST...

THE COMBINATION OF SHORTWAVE ENERGY EMANATING FROM THE
SOUTHWESTERN TROUGH AND A DIGGING TROUGH MOVING SOUTH AND EAST
FROM SOUTH CENTRAL CANADA TOWARD THE UPPER MIDWEST WILL PRODUCE AN
EXPANDING AREA OF SNOWFALL SPREADING EASTWARD WITHIN THE SOUTHERLY
FLOW BEHIND THE RETREATING ARCTIC HIGH PRESSURE SYSTEM.  RAPIDLY
BUILDING HEIGHTS ACROSS THE SOUTHEAST US ON DAY 3 WILL HELP CREATE
AN EXPANDING BAROCLINIC ZONE ACROSS THE CENTRAL AND EASTERN US.
WHILE THERE APPEARS TO BE LITTLE INDICATION THAT A STRONG SURFACE
SYSTEM WILL DEVELOP...SIGNIFICANT QPF WILL DEVELOP WITHIN THIS
BAROCLINIC ZONE AND THE BULK OF THE HEAVIEST PRECIPITATION WILL
FALL AS SNOW WHILE RESIDUAL LOW LEVEL COLD AIR OVER THE SOUTHERN
PLAINS AND OVER THE MID MISSISSIPPI VALLEY AND LOWER OHIO VALLEY
COULD LEAD TO SOME FREEZING RAIN/SLEET.

SNOW WILL BEGIN TO EXPAND EASTWARD ACROSS OKLAHOMA/KANSAS AND
MISSOURI ON SATURDAY WITH SOME FREEZING RAIN/DRIZZLE DOWN INTO
TEXAS.  THERE IS A SLIGHT RISK OF 4 INCHES OR MORE ESPECIALLY
ACROSS KANSAS WHILE THE SNOW WILL SPREAD EAST NORTHEASTWARD INTO
SATURDAY NIGHT AND SUNDAY ON DAY 2.  THIS EXPANDING AREA OF
SNOWFALL WILL AFFECT A LARGE SWATH FROM THE MID MISSISSIPPI VALLEY
ACROSS THE UPPER OHIO VALLEY AND THEN INTO THE NORTHERN MID
ATLANTIC STATES AND NEW ENGLAND ON SUNDAY EVENING INTO MONDAY.
THERE WILL A MODERATE TO HIGH LIKELIHOOD OF GREATER THAN 4 INCHES
ACROSS THE UPPER OHIO VALLEY AND THEN SPREADING ACROSS THE
NORTHEAST ESPECIALLY ON DAY 3.

THE OPERATIONAL NAM HAS BEEN VERY AGGRESSIVE IN MOVING QPF MORE
RAPIDLY EASTWARD THAN OTHER MODELS...INDICATING AN ENHANCED THREAT
OF FREEZING RAIN EAST OF THE APPALACHIANS.  WHILE IT IS BELIEVED
THAT THE NAM HAS BEEN OVER DONE...OTHER MODELS HAVE TRENDED
FASTER...THOUGH NOT AS FAST OR AS WET AS THE NAM...WITH SPREADING
QPF EASTWARD INTO THE RETREATING COLD AIR.  WHILE THE SURFACE HIGH
MOVES EASTWARD OFF THE EAST COAST...THE LACK OF A STRONG SYSTEM TO
THE WEST AND VERY COLD CONDITIONS INCREASES THE CHANCES FOR
SNOW/SLEET AND FREEZING RAIN EAST OF THE APPALACHIANS ON DAY
3...ALTHOUGH DIFFERENCES IN SYSTEM SPEED AND QPF AMOUNTS STILL
INDICATES CONSIDERABLE UNCERTAINTY LATER IN THE FORECAST.
HOWEVER...SIGNIFICANT SNOW APPEARS LIKELY FROM MISSOURI EAST
NORTHEASTWARD ACROSS NORTH CENTRAL ILLINOIS/INDIANA/OHIO INTO
PENNSYLVANIA NEW YORK AND NEW ENGLAND.

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

KOCIN

$$




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