Quantitative Precipitation Forecast
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FOUS11 KWBC 212205
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
504 PM EST WED JAN 21 2015

VALID 00Z THU JAN 22 2015 - 00Z SUN JAN 25 2015


...DAY 1...

...MIDDLE ATLANTIC/SOUTHERN NEW ENGLAND...

A MODEST TROUGH OVER THE OH VALLEY AND THE APPALACHIAN WILL
CONTINUE TO SCOOT EASTWARD AND OUT TO SEA LATER THIS EVENING.  A
WEAK SURFACE LOW MOVING NORTHEAST OFF THE COAST OF VA WILL BE SOME
225 MILES EAST SOUTHEAST OF NANTUCKET BY 12Z ON THURSDAY.

MOST OF THE SNOW WHICH HAD BEEN GENERATED BY THE MODEST TROF IN
THE LOW/MID LEVELS AND SUPPORTED BY A JET STREAK ALOFT SHOULD BE
SWEPT OUT TO SEA...WITH THE MAIN EXCEPTION BEING FROM SOUTHERN NY
AND ACROSS FAR SOUTHERN NEW ENGLAND GIVEN THE PROXIMITY OF THE
VORT CENTER AS IT MOVES AWAY.  DETERMINISTICALLY...NOT EXPECTING
MORE THAN AN INCH OR TWO BASED ON THE OPERATIONAL RUNS OF THE
GFS/NAM...BUT THERE WAS ENOUGH SUPPORT FROM THE ENSEMBLES TO
SUGGEST A SLIGHT RISK OF SNOW BEING WARRANTED ACROSS PARTS OF THE
SOUTHERN LONG ISLAND COASTLINE BEFORE SNOW TAPERS OFF ALL
TOGETHER.

IN GENERAL...THE PREFERRED BLEND OF THE MODELS FROM THE 12Z CYCLE
WAS THE GFS AND ECMWF.


...DAYS 1 TO 3...

...SOUTHERN ROCKIES/SOUTHWEST/SOUTHERN HIGH PLAINS/TENNESSEE
VALLEY/APPALACHIANS/MID ATLANTIC/SOUTHERN NEW ENGLAND...

A POTENTIALLY HIGH IMPACT STORM FIRST AFFECTING THE SOUTHERN
ROCKIES/SOUTHWEST AND SOUTHERN PLAINS ON FROM TONIGHT INTO
THURSDAY BECOMES A SNOW/ICE THREAT FOR THE TENNESSEE
VALLEY/APPALACHIANS/MID ATLANTIC FROM LATE THURSDAY INTO FRIDAY.

TWO TROUGHS...ONE OF THE THE DESERT SOUTHWEST AND THE OTHER DIVING
SOUTHWARD FROM THE NORTHERN ROCKIES WILL CONTINUE TO JOIN FORCES
LATER TONIGHT AND ON THURSDAY FORM INTO A SIGNIFICANT UPPER TROUGH
OVER THE SOUTHWEST. SNOW WILL SPREAD SOUTHWARD ACROSS SOUTHERN
COLORADO/MUCH OF CENTRAL/NORTHERN AND EASTERN NEW MEXICO/SOUTHWEST
KANSAS/THE PANHANDLES OF OKLAHOMA AND TEXAS/WESTERN
OKLAHOMA/WESTERN TEXAS AND AN AREA ALONG THE RED RIVER VALLEY
BETWEEN OKLAHOMA AND TEXAS.  THE HEAVIEST SNOW IS EXPECTED TO
DEVELOP ALONG THE FRONT SLOPES OF THE ROCKIES FROM CENTRAL AND
SOUTHERN COLORADO ACROSS PARTS OF THE SAN JUAN AND SANGRE DE
CRISTO RANGES...WHERE THERE IS A HIGH PROBABILITY OF AT LEAST 8 TO
12 INCHES OF SNOW.  AMOUNTS IN EXCESS OF A FOOT OF SNOW ARE
POSSIBLE IN PORTIONS OF SOUTHERN COLORADO/NORTHEAST NEW MEXICO AND
THE WESTERN PANHANDLES OF TEXAS AND OKLAHOMA.

AS THE TROUGH MOVES EASTWARD AS A POSITIVELY TILTED TROUGH ON
THURSDAY INTO EARLY FRIDAY...SNOW WILL LINGER ACROSS SOUTHEASTERN
NEW MEXICO AND WESTERN TEXAS AND BEGIN TO SPREAD EASTWARD ALONG
THE RED RIVER VALLEY BETWEEN OKLAHOMA AND TEXAS. AS THIS
HAPPENS...THE COMPUTER MODELS DIVERGE ON HOW THE TRACK OF THE SNOW
WITH THE NAM TAKING THE BULK OF THE SNOW EASTWARD INTO OK WHILE
THE ECMWF/GFS WERE MORE INCLINED TO SLIDE THE ENERGY SOUTH.  ONCE
AGAIN OUR PREFERENCE WAS MORE TOWARDS A WEAKER SOLN THAN THE NAM.

ON DAY 3/FRIDAY INTO EARLY SATURDAY...THE POSITIVELY TILTED TROUGH
MOVES EASTWARD AND THEN BEGINS TO EVOLVE INTO AN INCREASINGLY
NEUTRAL AND THEN NEGATIVELY TROUGH MOVING ALONG THE GULF COAST
BEFORE STARTING TO HEAD NORTHEASTWARD ALONG THE ATLANTIC COAST.
WHILE AN AREA OF CONFLUENCE OVER THE EASTERN US IS ASSOCIATED WITH
RISING PRESSURES ALONG THE EASTERN US AHEAD OF THIS
SYSTEM...ALLOWING COLDER AIR TO PRECEDED THE STORM BEFORE MOVING
UP ALONG THE EAST COAST...THE CONFLUENCE SUBSIDES AND HIGH
PRESSURE MOVES OFF THE EAST COAST.

THE BIG QUESTION REVOLVES AROUND THE THERMAL FIELDS ASSOCIATED
WITH THE SYSTEM.  COLD AIR MAY BE IN PLACE AT THE BEGINNING OF THE
EVENT SOME SNOW/SLEET AND SOME FREEZING RAIN.  WITHOUT AN ARCTIC
HIGH IN PLACE...A TRANSITION TO RAIN ACROSS THE MID ATLANTIC
REGION AND NORTHEASTERN STATES WILL BE POSSIBLE.  LOOKING AT THE
AMOUNT OF QPF PER PTYPE SHOWS MOST PLACES HAVE SOME POTENTIAL FOR
RAIN OR SNOW WITH THE BEST FOR FREEZING PCPN POTENTIAL IN THE
HIGHER ELEVATION OF THE APPALACHIAN CHAIN.  ONCE AGAIN FELT THAT
THERE WOULD BE A GREATER RISK OF 0.25 INCHES OF RAIN IF THERE WAS
ARCTIC HIGH PRESSURE TO THE NORTH.  IN TERMS OF SNOW...THE HIGHEST
TOTALS ARE EXPECTED TO BE IN THE 4 TO 8 INCH RANGE OVER THE
ELEVATED TERRAIN OF EASTERN WEST VIRGINIA AND WESTERN VIRGINIA BY
SATURDAY MORNING.  SNOW SHOULD THEN TRACK NORTH AND
EAST...IMPACTING PARTS OF THE NORTHEAST AND NEW ENGLAND BY LATE
SATURDAY/EARLY SUNDAY.

GAVE MOST WEIGHT TO THE GFS/ECMWF SOLNS.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT.

BANN

$$




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