Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 240851
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
350 AM EST TUE JAN 24 2017

VALID 12Z TUE JAN 24 2017 - 12Z FRI JAN 27 2017


DAYS 1 THROUGH 3...


...ROCKIES/WEST COAST...

LONG WAVE TROUGHING CROSSING THE ROCKIES AND WESTERN COAST DURING
THE NEXT THREE DAYS WILL PROVIDE SYNOPTIC SCALE ASCENT FOR
PRECIPITATION. HOWEVER...THE COLUMN IS EXPECTED TO BE VERY DRY
DURING THIS TIME...SO ACCUMULATING SNOWFALL IS EXPECTED ONLY OVER
THE HIGHER TERRAIN. THERE WAS FAIRLY GOOD AGREEMENT WITH RESPECT
TO THE SYNOPTIC SETUP...SO THE THERMAL FIELDS WERE BASED ON A
MULTI MODEL BLEND. THE QPF PORTION OF THE FORECAST WAS BASED ON
THE MOST RECENT WPC QPF.

SYNOPTIC SCALE LIFT ASSOCIATED WITH A LONG WAVE TROUGH EXITING THE
ROCKIES AND SOUTHWEST STATES...COMBINED WITH UPSLOPE FLOW...WILL
MAKE THE MOST OF A SEASONABLY DRY COLUMN ACROSS THE ROCKIES AND
AND THE HIGHER TERRAIN OF THE SOUTHWEST STATES DURING DAY 1. THE
BEST UPSLOPE IS FOCUSED ON THE ROCKIES IN CO AND NORTHERN CENTRAL
NM...WHERE 2 TO 4 INCHES OF SNOWFALL IS EXPECTED. LOCAL 2 TO 4
INCH SNOWFALL AMOUNTS ARE ALSO POSSIBLE OVER THE WASATCH RANGE IN
UT...AS WELL AS THE GRAND TETONS IN WY.

LONG WAVE TROUGHS CROSSING THE REGION DURING DAYS 2 AND 3 CONTINUE
TO PROVIDE BROAD SYNOPTIC SCALE ASCENT ACROSS MUCH OF THE WEST
COAST INTO THE ROCKIES. AGAIN...MOISTURE IS THE LIMITING FACTOR
FOR SNOWFALL...AND UPSLOPE LOW WILL RESULT IN LOCAL 2 TO 4 INCHES
OF SNOWFALL IN THE HIGHER TERRAIN ACROSS THE REGION.


...NORTHERN AND CENTRAL PLAINS/UPPER MS VALLEY/UPPER GREAT LAKES...

A LONG WAVE TROUGH OVER THE ROCKIES EARLY ON DAY 1 CLOSES OFF OVER
THE CENTRAL PLAINS LATE ON DAY 1. THE MID LEVEL SYSTEM SPINS UP A
SURFACE LOW OVER WESTERN KS EARLY...AND THE SURFACE LOW FOLLOWS A
SIMILAR TRACK. AHEAD OF THE SURFACE AND MID LEVEL SYSTEMS...STRONG
INFLOW INFUSES MOISTURE INTO A DEVELOPING MID LEVEL LIFT TO
PRODUCE A SWATH OF HEAVY SNOWFALL ACROSS THE CENTRAL PLAINS INTO
THE MS VALLEY. THE SURFACE AND MID LEVEL SYSTEMS WEAKEN AS THEY
TRACK ACROSS THE UPPER GREAT LAKES DURING DAY 2. THE THERMAL
PORTION OF THE FORECAST WAS BASED PRIMARILY ON A BLEND OF THE 00Z
ECMWF/00Z NAM...WHILE THE QPF PORTION OF THE FORECAST WAS BASED ON
THE MOST RECENT WPC QPF.

THE LATEST IR LOOP SHOWED COOLING TOPS NEAR THE EASTERN EDGE OF
THE BETTER LIFT ASSOCIATED WITH THE LONG WAVE TROUGH CROSSING THE
ROCKIES EARLY THIS MORNING. AS THE MID LEVEL SYSTEM TRACKS
EAST...A DEVELOPING LOW LEVEL INFLOW IS LIFTED IN THE
STRENGTHENING UPGLIDE...WHICH INTRODUCES HIGHER MOISTURE ACROSS
THE NORTHERN AND CENTRAL PLAINS DURING THE FIRST HALF OF DAY 1. AS
THE MID LEVEL SYSTEM BEGINS TO CLOSE OFF OVER NE/IA...THE MOISTURE
AND LIFT BECOME ORGANIZED INTO A FRONTOGENETICALLY FORCED BAND
STRETCHING FROM SOUTHWEST SD ACROSS NORTHEAST NE INTO FAR SOUTHERN
MN AND NORTHERN IA. THERE IS A MULTI MODEL SIGNAL FOR THE BEST
LIFT TO OCCUR BETWEEN 25/00Z AND 25/06Z...DURING WHICH TIME MODEL
SOUNDINGS INDICATED ELEVATED INSTABILITY (INTRODUCING THE
POSSIBILITY OF CONVECTION IN THE BANDING).

ALONG THE ABOVEMENTIONED AXIS...MOISTURE AND LIFT ARE INTRODUCED
INTO THE DENDRITIC GROWTH ZONE...RESULTING IN HIGHER SNOW TO
LIQUID RATIO VALUES. THERE IS A MULTI MODEL SIGNAL FOR AN AXIS OF
8 TO 14 INCHES OF SNOWFALL... WHICH IS CLOSER TO THE 00Z ECMWF/NAM
POSITION. THESE SNOWFALL AMOUNTS REPRESENT A MODERATE PROBABILITY
OF 12+ INCHES OF SNOWFALL...CENTERED OVER NORTHEAST NE AND FAR
SOUTHWEST SD. THE SOUTHERN AND EDGE OF THE 4+ INCH SNOWFALL AREA
WAS DETERMINED BY THE LOW LEVEL INFLOW AHEAD OF THE SURFACE
LOW...WHICH ALLOWS BOUNDARY LAYER TEMPERATURES TO RISE ABOVE
FREEZING AS THE SURFACE LOW PASSES. THIS RESULTS IN A FAIRLY SHARP
SNOWFALL GRADIENT EXTENDING FROM SOUTHERN NE INTO SOUTHEAST IA AND
FAR SOUTHERN WI.

THE MID LEVEL SYSTEM AND SURFACE LOW SLOWLY WEAKEN DURING DAY 2 AS
THEY CROSS THE UPPER GREAT LAKES. THERE IS STILL ENOUGH MOISTURE
AND LIFT ASSOCIATED WITH THE WEAKENING MID LEVEL FRONTOGENETIC
BANDING TO PRODUCE A STRIPE OF 2 TO 4 INCHES OF SNOWFALL FROM
NORTHEAST IA ACROSS SOUTHERN WI AND THE NORTHERN LP OF MI. MODEL
SOUNDINGS SHOWED NEARLY ISOTHERMAL PROFILES NEAR FREEZING...SO
LOCALLY HIGHER AMOUNTS ARE POSSIBLE. THE PROBABILITY OF 4+ INCHES
OF SNOWFALL IN THIS SCENARIO IS CONSIDERED SLIGHT.


...MID ATLANTIC/NORTHEAST...

A STRONG MID LEVEL SYSTEM AND SURFACE LOW OFF THE MID ATLANTIC
COAST EARLY ON DAY 1 TRACK OFF THE NORTHEAST COAST DURING DAY
1...REACHING WESTERN NOVA SCOTIA DURING DAY 2. UPSLOPE FLOW BEHIND
THE MID LEVEL SYSTEM COULD RESULT IN UPSLOPE SNOWFALL ACROSS
PORTIONS OF SOUTHERN APPALACHIANS DURING DAY 3. THERE WAS
GENERALLY GOOD MODEL AGREEMENT WITH RESPECT TO THE TRACK OF THE
SURFACE AND MID LEVEL SYSTEMS...SO THE THERMAL PORTION OF THE
FORECAST WAS BASED ON THE 00Z ECMWF/00Z NAM...WHILE THE QPF
PORTION OF THE FORECAST WAS BASED ON THE MOST RECENT WPC QPF

THE LATEST IR LOOP SHOWED A STRONG MOISTURE CHANNEL STREAMING
NORTH...PARALLELING THE SOUTHEAST NEW ENGLAND COAST. A MID LEVEL
CLOSED LOW JUST OFF THE MID ATLANTIC COAST IS FEEDING WARMER AIR
IN THE MID LEVELS ACROSS EASTERN NY STATE AND MUCH OF NEW ENGLAND.
00Z MODEL SOUNDINGS ACROSS THIS AREA SHOWED A PRONOUNCED WARM NOSE
BETWEEN 4500 AND 6000 FEET...WHERE TEMPERATURES TOP OUT BETWEEN
+2/+4 CELSIUS IN THIS LAYER. THE WARMING RESULTED IN SLEET AND
FREEZING RAIN HERE...AND THIS AIRMASS WILL ARRIVE OVER THE
REMAINDER OF NEW ENGLAND DURING THE MORNING HOURS.

DRY AIR IN PLACE ACROSS NORTHERN NEW ENGLAND WILL MITIGATE THE
WARM AIR TO SOME DEGREE...AND THE MOISTENING COLUMN SHOULD ALLOW
THE PRECIPITATION TO FALL AS SNOW ACROSS MUCH OF THE AREA DURING
THE MORNING HOURS. A LOW LEVEL EASTERLY FLOW AHEAD OF THE DEEP
SURFACE LOW ASSOCIATED WITH THE MID LEVEL SYSTEM HAS WARMED
COASTAL NEW ENGLAND ENOUGH SO THAT FREEZING OR FROZEN
PRECIPITATION BECOMES LESS OF AN ISSUE.

FURTHER INLAND...STRETCHING FROM INTERIOR NORTHERN MA INTO NH AND
INTERIOR WESTERN ME...THE WARM NOSE WILL OCCUR WHERE THE COLD AIR
REMAINS IN PLACE...MAINLY DURING THE MORNING HOURS. THIS WILL
RESULT IN A PERIOD OF SNOW HERE...TRANSITIONING TO A PERIOD OF
FREEZING RAIN. THE LATEST FRAM ICE ACCRETION OUTPUT...AS WELL AS
THE 00Z NAM...SUGGEST THAT 0.10 TO 0.25 INCHES OF QPF ARE POSSIBLE
EXTENDING ACROSS MUCH OF NH INTO WESTERN ME...AS WELL AS
NORTHERNMOST ME. THE 00Z NAM IS COLDER IN THESE AREAS...SO THERE
IS A SMALL CHANCE FOR LOCAL 0.50 INCH ICE ACCUMULATION AMOUNTS
ACROSS PORTIONS OF NORTHERN NEW ENGLAND AND NEARBY WESTERN ME. AT
THIS POINT...THE THREAT FOR 0.25+ INCHES OF ICE IS CONSIDERED
MODERATE ACROSS FAR NORTHWEST ME...AND SLIGHT ACROSS THE REST OF
THIS AREA.

THE COLUMN REMAINS COLD ENOUGH FOR SNOW ACROSS NORTHERN ME DURING
DAY 1. THE 00Z GFS IS MUCH COOLER ACROSS FAR NORTHERN ME...AND ITS
GUIDANCE IS MUCH HIGHER WITH RESPECT TO SNOWFALL AMOUNTS HERE.
USING A 00Z ECMWF/NAM BLEND RESULTS IN A LOWER SNOWFALL
AMOUNT...WITH GENERALLY 6 TO 10 INCHES OF SNOWFALL ACROSS FAR
NORTHERN ME. GIVEN THE MODEL SPREAD IN TEMPERATURES HERE...THE
PROBABILITY OF 12+ INCHES OF SNOW ACROSS FAR NORTHERN ME IS
CONSIDERED SLIGHT.

AS THE MID LEVEL SYSTEM PASSES...COLDER AIR RETURNING WILL RESULT
IN A CHANGE OF PRECIPITATION TYPE TO SNOW ACROSS MUCH OF NY STATE
INTO NORTHERN PA...FAR NORTHWEST NJ AND A PORTION OF THE LOWER AND
MID LEVEL HUDSON VALLEY. MOST LOCATIONS SHOULD SEE 1 TO 3 INCHES
OF SNOWFALL AFTER THE CHANGEOVER.

ADDITIONAL SNOWFALL IS POSSIBLE ACROSS THE NORTHERNMOST PORTION OF
ME DURING DAY 2...AS THE BEST MID LEVEL LIFT EXITS. UPSLOPE FLOW
COULD RESULT IN AN ADDITIONAL 1 TO 2 INCHES OF SNOWFALL IN THE
FAVORED LOCATIONS IN VT/NH AND WESTERN ME DURING DAY 2.

AS THE LOW TO MID LEVEL FLOW BECOMES MORE CYCLONIC FLOW ACROSS NY
STATE AND NEW ENGLAND...CONDITIONS BECOME MORE FAVORABLE FOR LAKE
EFFECT CIRCULATIONS TO DEVELOP DURING DAY 3. THE BOUNDARY LAYER
FLOW ACROSS LAKES ERIE AND ONTARIO BECOME BETTER ALIGNED WITH THE
LONG AXIS OF THE LAKE...AND MODEL SOUNDINGS SHOWED THE CAPPING
INVERSION RISING TO NEAR 700 MB FOR A TIME. THIS SHOULD ALLOW FOR
SOME DEVELOPMENT OF CELLS IN THE LAKE EFFECT
CIRCULATIONS...RESULTING IN 3 TO 6 INCH SNOWFALL AMOUNTS DOWNWIND
OF EACH LAKE DURING DAY 3. THESE SNOWFALL AMOUNTS SUGGEST A
MODERATE PROBABILITY OF 4+ INCHES OF SNOW IN THE FAVORED LOCATIONS
EAST OF EACH LAKE.


HAYES


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