December 13, 2013 Forecast Discussion

000
FXUS61 KALY 131732
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
1232 PM EST FRI DEC 13 2013

.SYNOPSIS…
AN ARCTIC COLD FRONT WILL GRADUALLY MOVE ACROSS THE REGION THIS
AFTERNOON. IN ITS WAKE…HIGH PRESSURE WILL ATTEMPT TO BUILD OVER
THE NORTHERN HALF OF THE REGION TONIGHT. A WINTER STORM WILL TAKE
SHAPE AND IMPACT THE REGION THIS WEEKEND WITH MODERATE TO
SIGNIFICANT AMOUNTS OF SNOW. THE PRECIPITATION SHOULD TAPER OFF BY
SUNDAY AFTERNOON.

&&

.NEAR TERM /THROUGH TONIGHT/…
AS OF 1115 AM…THE LAKE EFFECT BAND EAST OF LAKE ONTARIO HAS
DIMINISHED TO NOTHING MORE THAN FLURRIES WHILE THE LAST REMNANTS
OF MORE SIGNIFICANT SNOW SHOWERS MOVE DOWN THE MOHAWK
VALLEY…THROUGH THE CAPITAL DISTRICT AND INTO THE TACONICS AND
BERKSHIRES. CURRENT FORECAST HAS THIS COVERED FAIRLY WELL AND HAVE
ONLY MADE ADJUSTMENTS TO THE TEMP GRIDS. THIS BAND AHEAD OF THE
ARCTIC COLD FRONT WILL GRADUALLY SHIFT SOUTHWARD THROUGH THE
AFTERNOON. THE BEST REFLECTIVITY RETURNS HAVE BEEN OVER THE
CAPITAL REGION…CNTRL MOHAWK VALLEY…NRN TACONICS…AND NRN
BERKSHIRES WHERE A COATING TO AN INCH WILL BE POSSIBLE.

THE LATEST GFS SHOWS AN AREA OF SHADOWING OR DOWNSLOPING OFF THE
SRN GREENS/BERKS WITH STRONG EAST/SOUTHEASTERLIES SATURDAY NIGHT
WHICH MAY CUT DOWN ON THE QPF FOR PARTS OF THE UPPER HUDSON RIVER
VALLEY AND CAPITAL REGION. THE NAM SHOWS LESS OF THIS EFFECT. THE
WATCH WILL CONTINUE THIS AFTERNOON…AS WE WILL PERUSE THE INCOMING
ECMWF…CANADIAN…ENSEMBLES AND WPC GUIDANCE BEFORE DECISIONS FOR
WARNINGS AND ADVISORIES IN THE MID TO LATE AFTERNOON.

THE COLD ADVECTION TODAY ALONG WITH THE CLOUD COVER AND A VERY
LOW SUN ANGLE SHOULD KEEP AFTERNOON HIGHS RATHER CHILLY INTO THE
TEENS FOR THE TERRAIN AND L20S OVER THE SRN DACK/SRN GREENS….AS
H850 TEMPS DROP BACK WELL INTO THE NEGATIVE TEENS AND AROUND -20C
FOR THE DACKS. HIGHS WILL BE IN THE M20S AND U20S IN MOST OTHER
LOCATIONS. A FEW L30S ARE POSSIBLE IN THE MID HUDSON VALLEY.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/…
WINTER STORM WATCH FOR THE ENTIRE REGION…

EXTENSIVE COLLABORATION WITH NEIGHBORING WFOS AND WPC THIS MORNING
AS 00Z GUIDANCE IS SLOWLY COMING TO AN AGREEMENT WITH A
SIGNIFICANT IMPACT FROM THIS DEVELOPING WINTER STORM. THIS STORM
IS MORE OF A MILLER TYPE `B` AS REDEVELOPMENT WILL COMMENCE FROM
THE OHIO VALLEY SYSTEM TO THE MID ATLANTIC REGION.

THE MAIN PLAYER WITH THIS UPCOMING EVENT WAS SITUATED OVER THE
FOUR CORNERS REGION PER THE H2O VAPOR LOOP ANALYSIS.
MEANWHILE…PACIFIC MOISTURE WAS ADVANCING AHEAD OF THIS SYSTEM
ACROSS THE SOUTHERN PLAINS AND LOWER MISSISSIPPI RIVER VALLEY. A
POTENT UPPER JET WAS DIVING INTO THE NORTHERN TIER OF THE CONUS AS
THESE SYSTEMS WILL ATTEMPT TO PHASE OVER THE MID ATLANTIC INTO THE
NORTHEAST CORRIDOR ON SATURDAY.

THE AFOREMENTIONED ARCTIC FRONTAL BOUNDARY WILL BECOME QUASI-
STATIONARY ALONG OR JUST SOUTH OF THE NY STATE LINE TONIGHT WITH
BROAD ISENTROPIC LIFT EVOLVING OVER WESTERN AND CENTRAL NY. THIS
WILL SPELL OUT LIGHT SNOW DEVELOPING FROM WEST TO EAST AND COULD
EXTEND AS FAR EAST AS THE CATSKILLS OVERNIGHT. FOR THE REMAINDER
OF THE REGION…EXPECTING A MAINLY DRY OVERNIGHT AS THAT ARCTIC
DRY AIRMASS ADVECTS SOUTHWARD THROUGH THE HUDSON RIVER VALLEY.
OVERNIGHT LOWS WILL DROP WELL BELOW ZERO ACROSS THE DACKS WHERE
THE BETTER CHANCE FOR CLEARING SKIES AND TEENS ELSEWHERE AS THE
H850 TEMPS DROP TO BELOW -20C ACROSS THE NORTH AND NEGATIVE MID
TEENS ELSEWHERE.

IN FACT…THIS AGEOSTROPIC LOW LEVEL COMPONENT WHILE WEAK IN
MAGNITUDE IS RATHER PERSISTENT THROUGH THE DAY SATURDAY INTO
SATURDAY EVENING. THIS WILL KEEP THE PRECIP ALL SNOW AS ISENTROPIC
LIFT INCREASES AND LIGHT SNOW SPREADS ACROSS MOST THE REGION FROM
SOUTH TO NORTH THROUGH THE DAY. ACCUMULATIONS DURING SATURDAY WILL
LIKELY RANGE FROM AROUND 1 INCH ACROSS THE NORTHERN PORTIONS OF
THE REGION WITH AROUND 3 INCHES FOR THE SOUTH AND SOUTHWEST
PORTIONS OF THE REGION. HIGH TEMPERATURES WILL STRUGGLE TO GET OUT
OF THE TEENS.

SATURDAY NIGHT…THIS WILL BE THE MAIN EVENT FOR THE REGION AS
INCREASING LOW LEVEL SOUTH-SOUTHEAST JET GREATER THAN 50KTS
DEVELOPS AS SECONDARY DEVELOPMENT OF THE COASTAL LOW TAKES SHAPE.
THERE WILL BE AN ENHANCED REGION OF 2-D FGEN FORCING PER THE NCEP
MODEL SUITE ACROSS THE SOUTHERN AREAS /MAINLY JUST SOUTH OF THE
CAPITAL REGION/ WHERE SNOWFALL RATES COULD BE ENHANCED. THE
COMBINATION OF THIS SNOWFALL BAND AND THOSE WINDS COULD
POTENTIALLY BRING NEAR BLIZZARD CONDITIONS FOR THE HIGHER TERRAIN
FOR A PERIOD OF TIME. THE REMAINDER THE REGION…SNOW WILL BE
ONGOING WITH LATEST PLUME DIAGRAMS POINTING TOWARD 0.90" H2O
EQUIVALENT FROM THE GEFS/SREF. CROSS SECTIONS REVEAL THE BEST LIFT
FOR THE MOST OF THE REGION WILL OCCUR JUST BELOW THE BEST
DENDRITIC ICE GROWTH WHILE CLOSER TO THE 2D FGEN BANDS THAT WE
EFFECTIVELY TAP INTO THAT DENDRITIC ICE GROWTH. HERE…COULD SEE
SNOWFALL RATES APPROACHING UP TO 2 INCHES PER HOUR. THE ONLY SMALL
ISSUE TO THESE SNOWFALL RATES WILL BE THE DEGREE OF WARM AIR
ADVECTING NORTHWARD. SEEMS SOUTHERN PORTIONS OF DUTCHESS AND
LITCHFIELD COUNTIES COULD SEE A PERIOD OF SLEET/FZRA PER TOP-DOWN
THERMAL APPROACH FROM AN ENSEMBLE TREND OF THE NCEP MODELS.

SUNDAY…THE MAIN STORM CENTER NOW REFORMS AND INTENSIFIES OVER
THE GULF OF MAINE SUNDAY MORNING. THERE COULD BE A PERIOD OF THE
MOHAWK VALLEY CONVERGENCE PER CSTAR RESEARCH WHICH WILL NEED TO BE
MONITORED. OTHERWISE…SNOW WILL GRADUALLY DIMINISH IN COVERAGE
AND INTENSITY THROUGH THE DAY AS WE TRANSITION TO LIGHT SNOW
SHOWERS AND UPSLOPE FAVORED LOCATIONS FOR SOME ADDITIONAL SNOW
ACCUMULATIONS.

AT THE END OF THIS EVENT…COULD SEE VALUES OF 6-12 INCHES ACROSS
THE REGION HENCE THE WINTER STORM WATCH IN EFFECT FOR THE ENTIRE
REGION.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/…
THE DEPARTING WINTER STORM WILL CONTINUE TO LIFT NORTHEAST TOWARDS
ATLANTIC CANADA…WITH COLD CYCLONIC FLOW IN PLACE OVER THE
NORTHEASTERN US IN ITS WAKE. SOME LINGERING LAKE ENHANCED SNOW
SHOWERS WILL AFFECT THE WESTERN ADIRONDACKS AND WESTERN MOHAWK
VALLEY ON SUNDAY NIGHT WITH VERY COLD TEMPS…THANKS TO THE FRESH
SNOW COVER AND DIMINISHING WINDS. MOST AREAS LOOK TO DROP INTO THE
SINGLE DIGITS…WITH BELOW ZERO READINGS POSSIBLE OVER THE HIGH
TERRAIN…ESP IN THE ADIRONDACKS.

HIGH PRESSURE WILL PASS OVER THE REGION ON MONDAY…ALLOWING FOR DRY
WEATHER WITH BELOW NORMAL TEMPS. HIGHS WILL ONLY REACH THE TEENS TO
LOW 20S WITH PARTIAL SUNSHINE.

CLOUDS WILL QUICKLY INCREASE FOR MONDAY NIGHT AS A CLIPPER SYSTEM
DIVES FROM SOUTHERN CANADA TOWARDS THE GREAT LAKES. THERE IS GOOD
MODEL AGREEMENT THAT THIS SYSTEM WILL SLIDE ACROSS THE NORTHEAST FOR
LATE MONDAY NIGHT INTO TUESDAY. AS A RESULT…A SEVERAL HOUR PERIOD
OF LIGHT SNOW LOOKS TO MOVE ACROSS THE REGION. MOISTURE WILL BE
LIMITED…AND ANY SNOWFALL LOOKS TO BE LESS THAN ADVISORY LEVEL
AMOUNTS. TEMPS WILL CONTINUE TO BE VERY COLD…WITH SINGLE DIGITS
MONDAY NIGHT…AND MAINLY 20S ON TUESDAY.

BEHIND THIS SYSTEM…ANOTHER ROUND OF LAKE EFFECT SNOW LOOKS TO
IMPACT THE WESTERN ADIRONDACKS FOR TUESDAY NIGHT THROUGH WEDNESDAY
NIGHT. MEANWHILE…DRY WEATHER BUT BELOW NORMAL TEMPS WILL CONTINUE
ACROSS THE REMAINDER OF THE FORECAST AREA. MIN TEMPS TUESDAY NIGHT
WILL BE IN THE TEENS TO NEAR 20…WITH 20S TO LOW 30S DURING THE DAY
WEDNESDAY…AND TEENS AGAIN ON WED NIGHT.

THE LAKE EFFECT SHOULD SHUT OFF SOMETIME THURSDAY…AS A LARGE AREA
OF HIGH PRESSURE PASSES OVER THE AREA. SOME MODERATION IN TEMPS
WILL START TO OCCUR…AS A TROUGH BEGINS TO GET CARVED OUT ACROSS
THE WESTERN US AND RIDGING DEVELOPS ACROSS THE SOUTHEASTERN US. THIS
WILL PUT OUR REGION IN A SW FLOW ALOFT. TEMPS ON THURSDAY MAY
FINALLY REACH THE FREEZING MARK IN THE CAPITAL REGION…ALTHOUGH
HIGH TERRAIN AREAS WILL STILL BE IN THE 20S. THE WARMING TREND
APPEARS TO CONTINUE RIGHT INTO THE UPCOMING WEEKEND.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/…
LINGERING LAKE EFFECT SNOW SHOWERS WILL RESULT IN PERIODIC
REDUCTIONS IN FLYING CONDITIONS EARLY IN THE TAF PERIOD…BEFORE VFR
CONDITIONS RETURN AHEAD OF AN APPROACHING WINTER STORM THAT WILL
IMPACT THE REGION PRIMARILY LATE-SATURDAY INTO SUNDAY.

THIS AFTERNOON…LINGERING LAKE EFFECT SNOW SHOWERS WILL CONTINUE
FOR THE NEXT COUPLE OF HOURS AT KALB…KGFL AND KPSF RESULTING IN
INTERMITTENT PERIODS OF IFR/MVFR FLYING CONDITIONS. HAVE ADDRESSED
THESE SNOW SHOWERS WITH TEMPO GROUPS WITH THE SNOW SHOWERS EXPECTED
TO TAPER OFF BY 20Z WITH LITTLE TO NO ACCUMULATION. AN ARCTIC FRONT
WILL SLIDE THROUGH THE REGION THIS AFTERNOON AS WELL ALLOWING THE
WINDS TO BECOME NORTHWESTERLY AROUND 10 KNOTS WITH OCCASIONAL GUSTS
UP TO 20 KNOTS POSSIBLE ESPECIALLY AT KALB AND KPSF.

TONIGHT INTO SATURDAY…HIGH PRESSURE WILL ATTEMPT TO RIDGE IN
ACROSS THE REGION RESULTING IN A BRIEF PERIOD OF DRY WEATHER
OVERNIGHT. THE ATTENTION THEN SHIFTS TO A SIGNIFICANT WINTER STORM
THAT WILL BE TAKING SHAPE ACROSS THE GREAT LAKES AND MID-ATLANTIC
REGIONS…MAINLY AFFECTING THE REGION BEYOND THIS TAF PERIOD.

REGARDLESS…HIGH-LEVEL CLOUDS WILL CONTINUE TO SPILL NORTHWARDS
ACROSS THE REGION AND INCREASE THROUGH THE NIGHT…GRADUALLY
LOWERING TOWARDS DAYBREAK…BUT REMAINING AT VFR LEVELS. SCATTERED
LIGHT SNOW SHOWERS WILL BEGIN TO DEVELOP BY THE END OF THE TAF
PERIOD…WITH THE HEAVIEST SHOWERS AND POTENTIAL MVFR/IFR FLYING
CONDITIONS OCCURRING AT KPOU/KPSF. WINDS WILL BECOME NORTHEASTERLY
SATURDAY GENERALLY AROUND 5-10 KNOTS.

OUTLOOK…

SATURDAY-SUNDAY: HIGH OPERATIONAL IMPACT. DEFINITE SN.
SUNDAY NIGHT-MONDAY: NO OPERATIONAL IMPACT. NO SIG WX.
MONDAY NIGHT-WEDNESDAY: MODERATE OPERATIONAL IMPACT. CHANCE OF SHSN.

&&

.HYDROLOGY…
NO HYDRO RELATED CONCERNS ARE EXPECTED THROUGH EARLY NEXT WEEK.
MAINLY SNOW WILL FALL THIS WEEKEND AND TEMPERATURES WILL BE WELL
BELOW NORMAL AND ICE WILL CONTINUE TO FORM ON AREA RIVERS…STREAMS
AND PARTICULARLY LAKES THROUGH EARLY NEXT WEEK.

FOR DETAILS ON SPECIFIC AREA RIVERS AND LAKES…INCLUDING OBSERVED
AND FORECAST RIVER STAGES AND LAKE ELEVATIONS…PLEASE VISIT THE
ADVANCED HYDROLOGIC PREDICTION SERVICE /AHPS/ GRAPHS ON OUR WEBSITE.

&&

.ALY WATCHES/WARNINGS/ADVISORIES…
CT…WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY
MORNING FOR CTZ001-013.
NY…WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY
MORNING FOR NYZ032-033-038>043-047>054-058>061-063>066-
082>084.
MA…WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY
MORNING FOR MAZ001-025.
VT…WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY
MORNING FOR VTZ013>015.

&&

$$
SYNOPSIS…BGM/WASULA
NEAR TERM…BGM/WASULA
SHORT TERM…BGM
LONG TERM…FRUGIS
AVIATION…IRL
HYDROLOGY…BGM

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