Quantitative Precipitation Forecast
Issued by NWS

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
000
FOUS11 KWBC 260757
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
357 AM EDT THU MAR 26 2015

VALID 12Z THU MAR 26 2015 - 12Z SUN MAR 29 2015


DAYS 1 THROUGH 3...


...MID ATLANTIC/NORTHEAST...

LOW PRESSURE OVER THE OH VALLEY EARLY ON DAY 1 TRACKS
NORTHEAST...CROSSING NEW ENGLAND DURING THE SECOND HALF OF THE
PERIOD BEFORE EXITING THE COAST. LIFT ASSOCIATED WITH A LONG WAVE
TROUGH CROSSING THE EAST COAST BRINGS THE POTENTIAL FOR SNOW
SHOWER ACTIVITY ON DAY 2. THERE APPEARS TO BE AN INCREASING THREAT
FOR WINTRY PRECIPITATION ACROSS A PORTION OF THE MID ATLANTIC INTO
LONG ISLAND NY AS MOISTURE BECOMES FOCUSED ON A LOW LEVEL INVERTED
TROUGH DURING DAY 3. THERE WAS DECENT MODEL AGREEMENT ON DAY
1...THOUGH THE 00Z NAM MAY STILL BE A TAD TOO FAST BRINGING COLD
AIR BACK INTO NORTHERN NEW ENGLAND. TIMING OF THE LIFT WITH THE
LONG WAVE TROUGH IS GOOD AMONG MODEL SOLUTIONS FOR DAY 2. THE 00Z
ECMWF LATCHED ONTO THE IDEA OF MOISTURE ALONG AN INVERTED TROUGH
ON DAY 3...BUT THE PLACEMENT IS STILL UNCERTAIN. A BLEND OF THE
00Z ECMWF/GFS WAS USED HERE.

DAY 1...
LOW PRESSURE TRACKING ALONG A COLD FRONT CROSSING THE OH VALLEY
AND NORTHEAST MOVES OVER NEW ENGLAND LATE ON DAY 1...BEFORE
EXITING OFF THE COAST. LIFT WITH A SHORT WAVE ASSOCIATED WITH THE
SURFACE LOW CROSSES THE OH VALLEY THROUGH UPSTATE NY INTO NORTHERN
NEW ENGLAND. THE BEST LIFT WITH THE SHORT WAVE AFFECTS THE OH
VALLEY AND MUCH OF NY STATE BETWEEN 26/18Z AND 27/00Z. THERE IS
NOW BETTER AGREEMENT AMONG THE 00Z MODEL SUITE MEMBERS TO EITHER
KEEPING COLD AIR IN PLACE ACROSS WESTERN NY (OR BRINGING IN BACK
IN SOONER FROM ONTARIO)...SO THAT MUCH OF THE LIFT THAT OCCURS
BETWEEN 18Z AND 00Z GOES INTO SNOWFLAKE PRODUCTION. MODEL
SOUNDINGS SHOWED MOISTURE AND LIFT IN THE DENDRITIC GROWTH ZONE
(THOUGH THE LIFT WAS COMPARATIVELY SHALLOW IN THIS LAYER) DURING
THIS TIME...WHICH SUPPORTS A SWATH OF 3 TO 6 INCHES OF SNOWFALL
EXTENDING FROM FAR NORTHWEST PA THROUGH MUCH OF WESTERN AND
NORTHERN NY STATE. THESE AMOUNTS ARE WELL SUPPORTED BY MEMBERS OF
BOTH THE 21Z SREF OUTPUT AND THE OUTPUT FROM THE LATEST ECMWF
ENSEMBLE PACKAGE.

FURTHER NORTH ACROSS NORTHERN VT/NORTHERN NH AND MUCH OF WESTERN
AND NORTHERN ME...THERE IS MORE SPREAD IN THE TIMING OF THE
ARRIVAL OF THE COLDER AIR IN THE COLUMN...AND TIMING THE CHANGE
FROM RAIN TO SNOW. THE 00Z GFS HAS THE SUPPORT OF THE 21Z SREF
MEAN AND 12Z ECMWF FOR ITS THERMAL FIELDS...WHICH ARE WARMER THAN
THE 00Z NAM. CONSIDERING THIS ENDS UP BEING AN ANA FRONT
SCENARIO...ELEVATION PLAYS A FACTOR IN THE SNOWFALL
FORECAST...WITH THE HIGHER ELEVATIONS SEEING THE HIGHER SNOWFALL
AMOUNTS. EVEN THE WARMER SOLUTION OF THE ABOVEMENTIONED CONSENSUS
SUGGESTS A SWATH OF 4 TO 6 INCHES ACROSS THESE AREAS (WHILE THE
00Z NAM WOULD IMPLY CLOSER TO 8 INCH AMOUNTS). THESE AMOUNTS TOO
ARE WELL SUPPORTED BY MEMBERS OF BOTH THE 21Z SREF AND LATEST
ECMWF ENSEMBLE OUTPUT. SOUTHEAST OF THE TERRAIN ACROSS
VT/NH/SOUTHWEST AND CENTRAL ME...THE BEST LIFT AND MOISTURE EXIT
BEFORE THE COLUMN COOLS SUFFICIENTLY TO SUPPORT SNOWFALL.

DAY 2...
AS A MID LEVEL LONG WAVE TROUGH CROSSES THE OH VALLEY AND EAST
COAST...SYNOPTIC SCALE LIFT AND STEEPENING MID LEVEL LAPSE RATES
(WHICH TOP OUT NEAR 6.5 C/KM) MAKE THE MOST OF THE DWINDLING
MOISTURE (AS PRECIPITABLE WATER VALUES DROP STEADILY). THIS SHOULD
RESULT IN AREAS OF AN INCH OR TWO OF SNOW IN THE HIGHER TERRAIN OF
THE APPALACHIANS STRETCHING FROM WV SOUTH THROUGH EASTERN TN AND
WESTERN NC. FURTHER EAST ACROSS PA/MD/DE INTO NJ... SCATTERED SNOW
SHOWERS ARE POSSIBLE WHERE BOUNDARY LAYER TEMPERATURES SUPPORT
THEM (MAINLY IN THE HUGER TERRAIN). ANY STRONGER SNOW SHOWER OR
ORGANIZED SNOW SHOWER CLUSTER COULD PRODUCE A LOCAL INCH OF
SNOW...BUT AT THIS POINT IT IS DIFFICULT TO PINPOINT WHERE.

FURTHER NORTH...CONDITIONS BECOME MORE FAVORABLE FOR LAKE
ENHANCEMENT...MAINLY ACROSS THE LOWER GREAT LAKES. MUCH OF LAKE
ERIE IS STILL FROZEN...SO LAKE CONTRIBUTION THERE IS EXPECTED TO
BE MINIMAL. MODEL SOUNDINGS SHOWED CAPPING INVERSIONS DEEPENING TO
NEAR 700 MB SOUTH OF LAKE ONTARIO...WHERE THE LAKE SURFACE IS
MOISTLY OPEN. THE LAKE ENHANCEMENT COULD RESULT IN LOCAL 2 TO 4
INCH SNOWFALL AMOUNTS SOUTH OF KBUF.

DAY 3...
THERE IS A SIGNAL IN THE 00Z MODEL GUIDANCE THAT AN INVERTED
SURFACE TROUGH EXTENDING FROM DEVELOPING LOW PRESSURE WELL OFF THE
MID ATLANTIC COAST WILL FOCUS MOISTURE TOWARD LAND DURING THE
FIRST HALF OF DAY 3. THERE IS A FAIR AMOUNT OF SPREAD CONCERNING
THE PLACEMENT OF THE INVERTED TROUGH... EXTENDING FROM
DE/NORTHEAST MD ON THE 00Z NAM TO LONG ISLAND NY AND SOUTHERN NEW
ENGLAND ON THE 00Z GFS. FOR NOW...THE 00Z ECMWF POSITION WAS
CHOSEN AS THE CONSENSUS POSITION. BASED ON THAT PLACEMENT...AN
INCH OR TWO OF SNOW IS POSSIBLE ACROSS PORTIONS OF NJ AND LONG
ISLAND NY. HOWEVER... FORECAST CONFIDENCE IS LOW DUE TO THE SPREAD
IN PLACEMENT OF THE FOCUS OF THE MOISTURE...AS WELL AS BOUNDARY
LAYER TEMPERATURE ISSUES.


...NORTHERN PLAINS/GREAT LAKES/MIDWEST...

A SHORT WAVE STREAKING SOUTHEAST FROM THE NORTHERN PLAINS THROUGH
THE MIDWEST ON DAY 2 PRODUCES A SWATH OF WINTRY PRECIPITATION
ALONG ITS PATH. THERE WAS FAIRLY GOOD MODEL AGREEMENT WITH THE
TRACK OF THE SHORT WAVE...AND THE PLACEMENT OF THE SWATH OF
PRECIPITATION...SO THE THERMAL FIELDS WERE BASED ON A MULTI MODEL
BLEND. ON DAY 3...A SHORT WAVE PUSHES A WARM FRONT...THEN A COLD
FRONT ACROSS THE NORTHERN PLAINS AND UPPER GREAT LAKES. THERE WAS
MORE SPREAD WITH THIS SYSTEM...ESPECIALLY CONCERNING TIMING OF THE
FRONTAL BOUNDARIES...WHICH AFFECTS PRECIPITATION TYPE. AT THIS
POINT...THE THERMAL FIELDS WERE BASED ON A BLEND OF THE 00Z
GFS/12Z ECMWF...WHICH REPRESENTED A CONSENSUS APPROACH. THE QPF
PORTION OF THE FORECAST FOR EACH DAY WAS BASED ON THE MOST RECENT
WPC QPF.

DAY 2...
A SHORT WAVE TRACKS SOUTHEAST FROM MANITOBA THROUGH ND/MN INTO IA
AND MO ON DAY 2. THERE IS SOME MOISTURE IN THE COLUMN AHEAD OF THE
SHORT WAVE (AS MODEL SOUNDINGS SHOWED PRECIPITABLE WATER VALUES
NEAR 0.50 INCHES)...SO QPF IS EXPECTED ALONG THE TRACK OF THE
SHORT WAVE. THE MID LEVEL THERMAL RIBBON RUNS ALONG THE TRACK OF
THE SHORT WAVE...WHICH SUGGESTS THAT THE COLUMN CAN SUPPORT
SNOWFLAKE PRODUCTION. HOWEVER...THE LOWER LEVELS MAY WARM EAST OF
THE THERMAL RIBBON...WHICH INTRODUCES BOUNDARY LAYER ISSUES FOR
PRECIPITATION TYPE. WITH THIS IN MIND...A LONG AXIS OF AN INCH OR
TWO OF SNOW WAS INTRODUCED FROM SOUTHEAST ND ACROSS WESTERN MN
INTO WEST CENTRAL IA.

DAY 3...
A STRONG SHORT WAVE COMING ASHORE OVER THE PACIFIC NORTHWEST ON
DAY 2 CROSSES THE NORTHERN PLAINS AND UPPER GREAT LAKES DURING THE
SECOND HALF OF DAY 3. THE SHORT WAVE PUSHES A WARM FRONT ACROSS
ND/MN...AND THE LIFT ASSOCIATED WITH THIS COULD PRODUCE AN INCH OR
TWO OF SNOWFALL ACROSS NORTHERN MN AND NORTHWEST WI. AFTER THE
WARM AIR ADVECTION ENDS...THE CLOUD LAYER LOSES ITS ICE...SO
PRECIPITATION COULD END AS A PERIOD OF LIGHT FREEZING RAIN OR
FREEZING DRIZZLE. THE LIFT WITH THE SHORT WAVE AHEAD OF THE COLD
FRONT OCCURS MAINLY ACROSS SOUTHWEST ONTARIO...BUT THERE COULD BE
ENOUGH LIFT AND MOISTURE FOR AN ADDITIONAL INCH OR TWO OF SNOW
ACROSS THE ARROWHEAD OF MN.


...PACIFIC NORTHWEST/NORTHERN ROCKIES...

A SHORT WAVE CHOPS DOWN THE TOP OF MID LEVEL RIDGE OVER THE WEST
COAST AS IT CROSSES THE PACIFIC NORTHWEST LATE ON DAY 2...AND THE
NORTHERN ROCKIES DURING DAY 3. THERE IS SOME SPREAD CONCERNING THE
TIMING AND STRENGTH OF THE SHORT WAVE AS IT CROSSES THE REGION.
THE 12Z ECMWF APPEARS TO SLOW THE SHORT WAVE DOWN TOO MUCH (AS
COMPARED TO THE MODEL CONSENSUS). THE 00Z GFS/NAM APPEAR TO FORM
THE BEST TIMING FOR THE SHORT WAVE...SO THESE MODELS WERE USED AS
A BASIS FOR THE THERMAL PORTION OF THE FORECAST. THE QPF PORTION
OF THE FORECAST WAS BASED ON THE MOST RECENT WPC QPF.

DAY 2...
THE SHORT WAVE APPROACHES THE PACIFIC NORTHWEST COAST BETWEEN
28/06Z AND 28/12Z. AHEAD OF THE SHORT WAVE...THE LOW LEVEL FLOW
TRANSPORTS 0.75 INCH PRECIPITABLE WATER TO THE COAST...AND FOCUSES
IT ON THE HIGHER TERRAIN IN FORM OF UPSLOPE. IN THE WARM AIR
ADVECTION AHEAD OF THE SHORT WAVE... FREEZING LEVELS RISE TO
BETWEEN 7000 AND 8000 FEET...SO SNOWFALL ACCUMULATIONS OF 2 TO 4
INCHES OF LIMITED TO THE HIGHER TERRAIN OF THE WA CASCADES.

DAY 3...
AS THE SHORT WAVE CROSSES THE NORTHERN ROCKIES...IT LOSES SOME OF
THE MOISTURE AVAILABLE ACROSS THE PACIFIC NORTHWEST.
HOWEVER...SYNOPTIC SCALE LIFT AND UPSLOPE FLOW HELP TO PRODUCE 2
TO 4 INCHES OF SNOWFALL ABOVE 7000 FEET ACROSS THE BITTERROOT
RANGE IN ID.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT FOR
THE ENTIRE PERIOD.

HAYES

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.