December 13, 2013 Forecast Discussion

000
FXUS61 KALY 131128
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
628 AM EST FRI DEC 13 2013

.SYNOPSIS…
AN ARCTIC FRONTAL BOUNDARY WILL GRADUALLY SLIDE ACROSS THE REGION
TODAY. 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.

&&

.NEAR TERM /THROUGH TONIGHT/…
AS OF 600 AM EST…
LITTLE CHANGE TO THE ONGOING FORECAST AS LAKE BAND WAS A BIT
DELAYED WITH THE TRACK FURTHER SOUTH BUT WILL DO SO IN A COUPLE OF
HOURS. INLAND EXTENT REMAINS AROUND 60 MILES WHICH IS STILL IN
EXCELLENT AGREEMENT WITH LOCAL EXPERIMENTAL PROGRAM. DID TWEAK
TEMPS AS VALUES HAVE INCREASED A BIT DUE TO THE CLOUD COVER AND
BEFORE THE ARCTIC FRONT FROPA.

AS OF 300 AM EST…
THE INITIAL CONCERN THIS MORNING IS THE ONGOING LAKE EFFECT
ACTIVITY DOWNWIND OF LAKE ONTARIO. KTYX DOPPLER RADAR SUGGESTS THE
INLAND EXTENT OF THE >20DBZ WAS ACROSS NORTH CENTRAL HERKIMER
COUNTY AROUND 60 MILES INLAND FROM THE LAKE. THIS IS IN EXCELLENT
AGREEMENT WITH THE LOCALLY DEVELOPED CSTAR RESEARCH OF LAKE EFFECT
INLAND EXTENT PROGRAM WHICH KEEPS THIS BAND AROUND THAT 60 MILE
INLAND PENETRATION THROUGH THE REMAINDER OF THIS EARLY FRIDAY
MORNING. AFTER SUNRISE…THE ARCTIC FRONTAL BOUNDARY IS EXPECTED
TO SLIDE TOWARD THE I90 CORRIDOR WHICH WILL SHIFT THE BOUNDARY
LAYER WIND TOWARD A WEST-NORTHWEST THEN NORTHWEST WHICH WILL TAKE
THIS BAND SOUTHWARD. MAIN QUESTION WILL BE HOW MUCH THIS FRONT
WILL INTERACT WITH THE MOISTURE AND TRANSPORT IT DOWNSTREAM INTO
THE MOHAWK VALLEY AND THE CAPITAL REGION. LOCALLY DEVELOP HIRESWRF
AND HRRR REFLECTIVITY FORECASTS SUGGEST A FEW SNOW SHOWERS AND
SQUALLS MAY MAKE IT INTO THESE REGIONS AS WE WILL PLACE A LITTLE
HIGHER POPS THROUGH THE MORNING HOURS. AS THE FLOW CONTINUES TO
BACK IN THE WAKE OF THE FROPA…THIS BAND WILL WEAKEN AS FLOW
TRAJECTORY BECOMES LESS THAN FAVORABLE FOR OUR REGION AND LOWERING
SUBSIDENCE INVERSION AS SURFACE HIGH BUILDS NORTH OF THE GREAT
LAKES REGION AND EXTENDS ITS INFLUENCE OVER LAKE ONTARIO.

CLOUDS WILL BE A CHALLENGE TODAY AS 1000-850MB RH VALUES FROM THE
LATEST RUC13 CONTINUE TO SUPPORT RATHER HIGH VALUES FOR THE
SOUTHERN 2/3RDS OF THE CWA. HOWEVER…THE LOW LEVEL AGEOSTROPHIC
FLOW DOES INCREASE A BIT WHICH SHOULD ASSIST WITH THE DRIER AIR
AND EVENTUAL MECHANICAL MIXING FOR SOME BREAKS TO OCCUR INTO THE
CAPITAL REGION LATER THIS 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
20S ELSEWHERE AS H850 TEMPS DROP BACK WELL INTO THE NEGATIVE TEENS
AND AROUND -20C FOR THE DACKS.

&&

.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 THURSDAY/…
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 /12Z FRIDAY THROUGH TUESDAY/…
VFR CONDITIONS ARE IN PLACE AT ALL TERMINALS THIS MORNING WITH SOME
SCT-BKN STRATOCU CLOUDS AROUND 4 KFT AND A BKN-OVC MID LEVEL DECK
AROUND 10 KFT.

DURING THE LATE MORNING TO EARLY AFTN HOURS…AN ARCTIC FRONTAL
BOUNDARY…AIDED BY SOME MOISTURE OFF LAKE ONTARIO…WILL PASS
THROUGH THE REGION FROM NORTH TO SOUTH. CONVERGENCE ALONG THIS
BOUNDARY MAY ALLOW FOR SOME SNOW SHOWERS OR SQUALLS ACROSS THE
REGION. THE BEST CHANCE WILL BE FOR KALB/KPSF…AS THE SNOW SHOWERS
MAY PASS DOWN THE MOHAWK VALLEY AND TOWARDS THE CAPITAL
REGION/BERKSHIRES. WE HAVE INCLUDED A TEMPO TO ACCOUNT FOR THIS
POSSIBILITY FOR A BRIEF PERIOD OF IFR CONDITIONS WITHIN SNOW
SHOWERS/SQUALLS DURING THE LATE MORNING/EARLY AFTN. OUTSIDE OF SNOW
SHOWERS…CIGS WILL BE BKN AROUND 4 KFT DURING THE LATE MORNING TO
AFTN HOURS. CLOUDS SHOULD START TO CLEAR BY THIS EVENING WITH JUST
FEW-SCT LOW CLOUDS AND SOME PASSING CIRRUS OVERNIGHT.

WINDS WILL BE S-SW AHEAD OF THE BOUNDARY…BECOMING WESTERLY AT
AROUND 10 KTS THIS MORNING. BEHIND THE BOUNDARY…WINDS WILL BE
W-NW AT 10-15 KTS WITH A FEW HIGHER GUSTS…ESP AT
KALB/KPSF…WHERE WINDS MAY GUST AS HIGH AS 25 KTS. WINDS WILL
DIMINISH THIS EVENING WITH THE LOSS OF DAYTIME HEATING…AND WILL BE
NW OVERNIGHT AT 10 KTS OR LESS.

OUTLOOK…

SATURDAY-SUNDAY: HIGH OPERATIONAL IMPACT. DEFINITE SN.
SUNDAY NIGHT-MONDAY: NO OPERATIONAL IMPACT. NO SIG WX.
MONDAY NIGHT-TUESDAY: 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.
LAKE EFFECT SNOW ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR
NYZ033-038.
LAKE EFFECT SNOW WARNING UNTIL 1 PM EST THIS AFTERNOON FOR
NYZ032.
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
NEAR TERM…BGM
SHORT TERM…BGM
LONG TERM…FRUGIS
AVIATION…FRUGIS
HYDROLOGY…BGM

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