December 29, 2012 Forecast Discussion

000
FXUS61 KALY 291436
AFDALY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
936 AM EST SAT DEC 29 2012

.SYNOPSIS…
AN AREA OF LOW WILL MOVE OFF THE MID ATLANTIC COAST TODAY…THEN
HEAD NORTHEASTWARD TONIGHT PASSING SOUTH OF LONG ISLAND AND CAPE
COD. HIGH PRESSURE WILL BUILD IN FOR SUNDAY AND MONDAY. FROM NEW
YEARS EVE INTO THE FIRST WEEK OF THE NEW YEAR…A SERIES OF
FRONTAL SYSTEMS WILL USHER IN PROGRESSIVELY COLDER AIR AS WELL AS
TRIGGER BOUTS OF SNOW SHOWERS.

&&

.NEAR TERM /THROUGH TONIGHT/…
PRESSURE FALLS ARE OCCURRING OVER THE MID ATLANTIC REGION WITH THE
COASTAL LOW BECOMING THE MAIN LOW. THE ATMOSPHERE IS MOISTEN UP
AND SNOW IS OVERSPREADING AND DEVELOPING ACROSS THE AREA. THE
12Z/ALY SOUNDING INDICATES A DRY LAYER FROM ABOUT 925 TO 750 MB
WITH A DEEPER DRIER LAYER INDICATED ON THE 12Z/OKX SOUNDING. HAVE
MADE ADJUSTMENTS TO TEMPERATURES…DEW POINTS AND WINDS BASED ON
OBSERVATIONAL DATA AND LATEST GUIDANCE.

PREVIOUS DISCUSSION…VIG 500HPA SHORT WV IS EJECTING NE FM MISS
VLY. SFC LOW IN TN VLY AND DEEPER THAN GUID. REST OF NT AND SAT
SERIES OF ADDITIONAL 500HPA SHORT WAVES WILL DEEPEN THIS
TROF…AND INITIATE CYCLOGENESIS ALONG THE CAROLINA COAST. THE
PRIMARY LOW WILL DRIFT TWRD PIT AND DIE IN THE MTNS OF W PA.

AS THE 500HPA TROF TURNS NEGATIVE AND CUTS OFF TODAY…THE SFC LOW
BOMBS…DEEPENING 30MB AS IT MOVES FM NC COAST TO NOVA SCOTIA
12UTC SUN. FORTUNATELY ITS TRACK PASSES ABOUT 150 MI S OF CAPE
COD. THE BEST OF THIS STORM WILL FALL ON THE FISHES. FCA WILL ONLY
BE EXPOSED TO OUTER REACHES OF COLD CONVEYOR BELT PCPN AND MST OF
OUR DYNAMICS ARE FM CUTTING OFF 500HPA SYSTEM.

STILL 00UTC MODEL SUITE CONTINUED TREND TWRD INCRG QPF OF 0.25 TO
0.60 WITH MOST AMOUNTS AROUND A UNIFORM 0.40. WITH 850HPA TEMPS
AROUND -4 TO -8C SNOW TO LIQ RATIO OVER FCA NR NORMAL HERE ABOUT
12. AS A RESULT MOST AREAS WILL SEE WINTER WX ADVISORY LEVEL
SNOW…AND THIS WAS ISSUED BY PRIOR SHIFT.

SNOW WILL OVERSPREAD FCA DURING THE LATE THIS MORNING AND CONTINUE
THROUGH THE EVENING…DIMINISHING TO -SNSH LATE AT NIGHT AS
STRONG CAA FOLLOWS IN STORMS WAKE. NW FLOW AND MOIST LLVL WILL
MAKE -SHSN MORE PERSISTENT LATE AT NIGHT OVER HIR TRRN.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/…
SFC LOW PRESSURE WILL CONTINUE TO RAPIDLY DEEPEN ACROSS ATLANTIC
CANADA ON SUNDAY AS IT MOVES NORTHEASTWARD AND AWAY FROM THE REGION.
THE COMBINATION OF CYCLONIC FLOW AROUND THIS STRONG STACKED STORM
SYSTEM AND NW UPSLOPE FLOW WILL ALLOW FOR SOME ADDITIONAL SNOW
SHOWERS ON SUNDAY ACROSS THE HIGHER TERRAIN…MAINLY THE SRN
ADIRONDACKS/SRN GREEN MTNS…WITH SOME ADDITIONAL LIGHT ACCUMULATION
POSSIBLE. THE HUDSON VALLEY AREA LOOKS TO REMAIN DRY. SOME LAKE
ENHANCED SNOW SHOWERS WILL ALSO IMPACT PORTIONS OF THE WESTERN
ADIRONDACKS/WESTERN MOHAWK VALLEY…ALTHOUGH THE FLOW SHOULD KEEP
THE WORST OF THIS ACTIVITY TO THE WEST OF OUR AREA. THE THREAT FOR
ANY SNOW SHOWERS WILL DIMINISH FOR THE AFTN/EVE HOURS…AS WEAK
RIDGING OVER THE OHIO VALLEY BEGINS TO BUILD INTO THE AREA. CHILLY
AIR POURING IN BEHIND THE STORM WILL ALLOW FOR COLD TEMPS ON
SUNDAY…WITH 20S ACROSS MUCH OF THE AREA…AND TEENS FOR THE
GREENS/ADIRONDACKS. ALONG WITH THE GUSTY NW WINDS…THIS WILL MAKE
FOR A RATHER WINTRY DAY.

THE WIND WILL START TO DIMINISH FOR SUNDAY NIGHT AS HIGH PRESSURE
MOVES IN JUST SOUTH OF THE REGION ACROSS THE MID ATLANTIC STATE.
WITH CLEARING SKIES…TEMPS WILL DROP TO COLDEST LEVELS OF THE
WINTER SO FAR…WITH SINGLE DIGITS TO TEENS OVER MUCH OF THE
AREA…AND EVEN A FEW BELOW ZERO READINGS ACROSS NORTHERN PARTS OF
THE AREA.

THE FLOW AT 500 HPA WILL FLATTEN OUT AND BECOME A BIT MORE ZONAL FOR
MONDAY INTO TUESDAY. A FAST MOVING SFC BOUNDARY LOOKS TO MOVE
THROUGH AT SOME POINT DURING THE DAY TUESDAY. TEMPS WILL CONTINUE TO
RUN A LITTLE BELOW NORMAL…ESP IN THE WAKE OF THE BOUNDARY FOR LATE
TUESDAY/TUESDAY NIGHT. WITH THIS SYSTEM BEING A NORTHERN STREAM
SYSTEM…IT/S QUITE MOISTURE STARVED…SO IT SHOULD BE MAINLY DRY
OVER THE MAJORITY OF THE AREA WITH JUST ISOLD SNOW SHOWERS/FLURRIES.
THE EXCEPTION WILL BE ACROSS PORTIONS OF THE WESTERN
ADIRONDACKS…WHERE THE FLOW OFF LAKE ONTARIO MAY ALLOW FOR SOME
ADDITIONAL LAKE ENHANCED/UPSLOPE SNOW SHOWERS…ESP JUST AHEAD AND
WITH THE PASSAGE OF THE BOUNDARY. MAX TEMPS ON MONDAY WILL BE IN THE
20S…WITH TEENS FOR VALLEY AREAS FOR MONDAY NIGHT. MAX TEMPS WILL
ONCE AGAIN BE IN THE 20S AHEAD OF THE BOUNDARY FOR TUESDAY
MORNING…BUT TEMPS LOOK TO DROP INTO THE SINGLE DIGITS ACROSS MUCH
OF THE AREA FOR TUESDAY NIGHT…WITH SOME BELOW ZERO READINGS ACROSS
THE HIGH TERRAIN.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/…
COLD TEMPERATURES WILL BE IN PLACE FOR MUCH OF THE EXTENDED
PERIOD…AS AN ARCTIC BOUNDARY AND A STRONG PUSH OF COLD AIR MOVES
ACROSS THE REGION. THE MODELS ARE IN SOME DISAGREEMENT REGARDING
THE EXACT TIMING. HOWEVER…BOTH THE LATEST 00Z ECMWF AND GFS ALL
SHOW 850 HPA TEMPS OF -20 TO -24 DEGREES C MAKING ITS WAY ACROSS
OUR AREA BY SOME POINT DURING THE LATE WEEK PERIOD. THIS WILL
ALLOW FOR TEMPS TO ONLY REACH THE TEENS AT MOST IN VALLEYS FOR MAX
TEMPS…WITH SINGLE DIGITS ACROSS THE HIGH TERRAIN. IN
ADDITION…OVERNIGHT LOWS WILL BE NEAR ZERO IN VALLEY AREAS AND -5
TO -15 DEGREES F OVERNIGHT FOR THE HIGH TERRAIN AND TYPICAL
SHELTERED AREAS. WITH THIS BEING AN ADVECTIVE COLD…SOME WIND MAY
ACCOMPANY THE COLD TEMPS…SO WIND CHILLS COULD APPROACH OR EXCEED
ADVISORY CRITERIA IN PORTIONS OF THE AREA AS WELL. WE WILL INCLUDE
MENTION OF THIS IN THE HWO AT THIS TIME. IT SHOULD BE FAIRLY DRY
MOST OF THE TIME…ALTHOUGH SOME SNOW SHOWERS/SQUALLS COULD
ACCOMPANY ANY SFC BOUNDARY. WILL MANLY ONLY GO WITH SLIGHT CHC
POPS FOR SNOW SHOWERS ACROSS MOST OF THE AREA…WITH LOW CHC POPS
IN AREAS DOWNWIND OF LAKE ONTARIO.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/…
PRESSURE FALLS ARE OCCURRING OVER THE MID ATLANTIC REGION WITH THE
COASTAL LOW BECOMING THE MAIN LOW. THE ATMOSPHERE IS MOISTEN UP
AND SNOW IS OVERSPREADING AND DEVELOPING ACROSS THE AREA. THE
12Z/ALY SOUNDING INDICATES A DRY LAYER FROM ABOUT 925 TO 750 MB
WITH A DEEPER DRIER LAYER INDICATED ON THE 12Z/OKX SOUNDING.

WIDESPREAD IFR CONDITIONS ARE EXPECTED TO DEVELOP IN THE SNOW.
CONDITIONS ARE EXPECTED TO IMPROVE TO MVFR AFTER MIDNIGHT AS THE
COAST LOW MOVES OFF TO EAST.

NORTHEAST TO NORTH WINDS 5 TO 10 MPH SHIFTING TO NORTHWEST TONIGHT.

OUTLOOK…
SUN…IMPROVING TO VFR. DECREASING CHC POPS IN THE MORNING.
SUN NIGHT-MON…VFR. NO SIG WX.
MON NIGHT-WED…MAINLY VFR. SLIGHT CHC -SHSN.

&&

.HYDROLOGY…
ALL PCPN NEXT 5 DAYS WILL FALL AS SNOW. LIQ EQUIV OF 0.25 TO 0.60
EXPECTED THROUGH TONIGHT. AMOUNTS OF ANOTHER 0.25 TO 0.40 COULD
FALL DURING THE NEXT WEEK.

SOME RIVER GAGES ARE ALREADY SHOWING SIGNS OF ICE EFFECTS AND
SOME RIVER LEVEL READINGS LOOK UNREPRESENTATIVE. STEADILY COLDER
AIR MASSES MOVE INTO THE REGION THIS WEEK AND ICE WILL FORM AND
THICKEN ON THE WATERWAYS IN THE ALY HSA.

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 WEATHER ADVISORY UNTIL 4 AM EST SUNDAY FOR CTZ001-013.
NY…WINTER WEATHER ADVISORY UNTIL 4 AM EST SUNDAY FOR NYZ032-033-
038>043-047>054-058>061-063>066-082>084.
MA…WINTER WEATHER ADVISORY UNTIL 4 AM EST SUNDAY FOR MAZ001-025.
VT…WINTER WEATHER ADVISORY UNTIL 4 AM EST SUNDAY FOR VTZ013>015.

&&

$$
SYNOPSIS…IAA/SNYDER
NEAR TERM…IAA/SNYDER
SHORT TERM…FRUGIS
LONG TERM…FRUGIS
AVIATION…IAA/SNYDER
HYDROLOGY…SNYDER

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