February 8, 2013 Pre Storm Forecast Discussion New York City

000
FXUS61 KOKX 080540
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
1240 AM EST FRI FEB 8 2013

.SYNOPSIS…
A MAJOR AND POTENTIALLY HISTORIC WINTER STORM WILL IMPACT THE
TRI-STATE AREA TODAY INTO SATURDAY. LOW PRESSURE APPROACHING THE
MID ATLANTIC COAST WILL TRACK NORTHEAST TODAY. THE STORM WILL
THEN RAPIDLY INTENSIFY AS IT TRACKS TO THE SOUTH AND EAST OF LONG
ISLAND TONIGHT INTO SATURDAY. HIGH PRESSURE BUILDS IN
SATURDAY NIGHT INTO SUNDAY AND MOVES OFFSHORE SUNDAY NIGHT. A
FRONTAL SYSTEM WILL THEN MOVE IN ON MONDAY AND OFFSHORE BY MONDAY
NIGHT. WEAK HIGH PRESSURE BUILDS IN THEREAFTER WITH POSSIBLE
DISTURBANCES ALOFT THROUGH MIDWEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/…
FORECAST REMAINS ON TRACK WITH ONLY MINOR ADJUSTMENTS TO HOURLY
T/TD GRIDS BASED ON LATEST OBS/MOD/SAT DATA. ONSET OF PRECIP STILL
LOOKS TO BE AFTER 3 AM OR SO.

LOW PRESSURE ALONG THE EASTERN SEABOARD…WITH ANOTHER LOW PRES
SYSTEM OVER THE OHIO VALLEY. IT IS THE SHORTWAVE ENERGY
ASSOCIATED WITH THIS LATTER FEATURE THAT AMPLIFIES AND EVENTUALLY
PHASES WITH THE COASTAL LOW…RESULTING IN EXPLOSIVE CYCLOGENESIS
FRI INTO SAT.

IN THE MEANTIME…EXPECT LIGHT SNOW TO SPREAD IN FROM THE SOUTH
WITH ANY ACCUMULATIONS REMAINING LIGHT AND LESS THAN AN INCH. E
WINDS CONTINUE TO STRENGTHEN DUE TO A TIGHTENING PRESSURE
GRADIENT BETWEEN THE POLAR HIGH TO THE NORTH AND DEEPENING LOW
PRESSURE TO THE SOUTH.

TEMPS SHOULD MOVE LITTLE FROM HERE ON OUT. 20S IN THE
SUBURBS…AND AROUND FREEZING ACROSS THE NYC METRO.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/…
GLOBAL MODELS HAVE ALL COME INTO OVERWHELMINGLY GOOD AGREEMENT
FOR A MAJOR…IF NOT HISTORIC WINTER STORM ACROSS THE TRI-STATE
AREA FRIDAY INTO SATURDAY. THE HEAVIEST SNOWS AND STRONGEST WINDS
WILL BE FRIDAY NIGHT INTO EARLY SATURDAY MORNING.

LOW PRESSURE ALONG THE MID ATLANTIC COAST ON FRIDAY AFTERNOON WILL
UNDERGO MAJOR INTENSIFICATION AS THE LOW TRACKS TO THE SOUTH AND
EAST OF LONG ISLAND FRIDAY NIGHT. WHILE THERE LOOKS TO BE A BRIEF
CHANGEOVER TO RAIN OR A WINTRY MIX AT THE COAST LATE FRIDAY MORNING
AND AFTERNOON…ALL PRECIPITATION WILL GO BACK TO SNOW BY EVENING.
IN FACT…TRENDS IN THE MODELS HAVE BEEN COLDER…INCLUDING THE MOST
RECENT 18Z NAM WRF. A HEALTHY E/SE FLOW IN THE BOUNDARY LAYER LATE
TONIGHT INTO FRIDAY AFTERNOON WILL LIKELY BE SUFFICIENT ENOUGH TO
BRING IN SOME WARMER AIR AT THE COAST. THE OFFSETTING FACTOR THOUGH IS
THE RAPIDLY DEEPENING LOW AND THE ISALLOBARIC COMPONENT OF THE
WINDS…WHICH COULD ALLOW THE COLD AIR TO DRAIN SOUTH INTO THE
FORECAST AREA EVEN FASTER THAN WHAT MODEL GUIDANCE SUGGESTS. IN
THIS CASE…SNOWFALL TOTALS COULD BE EVEN HIGHER AT THE COAST IF A
CHANGEOVER DOES NOT OCCUR. PREFERENCE WAS TOWARD THE COLDER ECMWF
BASED ON GOOD RUN TO RUN CONTINUITY AND TRENDS IN OTHER MODELS.

THE NAM WRF AND ECWMF ARE THE MOST AGGRESSIVE SOLUTIONS WITH SEVERAL
INCHES OF LIQUID ACROSS THE AREA. THE GFS WHILE MORE
CONSERVATIVE…ALSO POINTS TO STRONG FRONTOGENESIS IN THE 85-70H
LAYER WITH MID LEVEL DEFORMATION AND INSTABILITY ALOFT…ALL
INGREDIENTS POINTING TOWARD SIGNIFICANT SNOW BANDING SOMEWHERE IN
SOUTHERN NEW ENGLAND. THIS SIGNATURE OFTEN INDICATES VERY HIGH
SNOWFALL TOTALS ASSOCIATED WITH EAST COAST CYCLOGENESIS. IN
ADDITION…WITH STORM CENTRAL PRESSURE SAT MORNING DROPPING TO
AROUND 975 MB NEAR THE BENCHMARK…40N…70W…AND HIGH PRESSURE
OVER EASTERN CANADA AROUND 1040 MB…WINDS WILL BE VERY STRONG.
BLIZZARD CONDITIONS ARE LIKELY FROM NYC AND POINTS EAST…WITH
SLIGHTLY LOWER WINDS TO THE WEST.

AS FOR SNOWFALL ACCUMULATIONS…LOOKING FOR 10 TO 15 INCHES ALONG
THE COAST…12 TO 16 INCHES LOWER HUDSON VALLEY…AND 18 TO 24
INCHES ACROSS CT. THERE COULD BE LOCALIZED HIGHER AMOUNTS WITH
STRONG SNOW BANDS.

THUS…BLIZZARD WARNINGS HAVE BEEN ISSUED FROM NYC METRO AND
POINTS EAST…WITH WINTER STORM WARNINGS TO THE NW. THE WORST
CONDITIONS WILL BE DURING THE NIGHTTIME FRIDAY AND EARLY MORNING
HOURS SATURDAY.

TEMPERATURES ON FRIDAY WILL GET UP INTO THE LOWER AND MID 30S…BUT
THEN RAPIDLY FALL OFF INTO THE 20 FRIDAY EVENING AS WINDS TURN
TOWARD THE NORTH WITH STRONG COLD ADVECTION.

SNOW TAPERS OFF BY SAT AFT WITH GUSTY NW WINDS ON ITS BACKSIDE AND
TEMPS NOT GETTING OUT OF THE 20S. WIND CHILL VALUES WILL DROP INTO
THE SINGLE DIGITS AND LOWER TEENS BY DAYBREAK SAT.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/…
STARTING OUT SATURDAY NIGHT…SNOW WILL HAVE COME TO AN END BUT
GUSTY WINDS AND COLD AIR ADVECTION WILL STILL BE STRONG AS HIGH
PRESSURE STARTS TO BUILD IN FROM THE NORTH AND WEST. THE BACKING OF
WINDS FROM THE NORTHERLY WINDS IN THE LOW LEVELS TO NORTHWESTERLY
WINDS IN THE MID AND UPPER LEVEL PLUS THE CLEARING SKIES AND FRESH
SNOW PACK WILL LEAD TO VERY COLD TEMPERATURES SATURDAY NIGHT. LOWS
ARE FORECAST TO BE IN THE SINGLE DIGITS AND TEENS WITH WIND CHILLS
NEAR TO SEVERAL DEGREES BELOW ZERO.

COLD TEMPERATURES CONTINUE ON SUNDAY WITH MAX TEMPERATURES AT LEAST
A FEW DEGREES BELOW NORMAL AND IN THE 30S…MID TO UPPER 30S CLOSER
TO NEW YORK CITY. DESPITE THE WINDS BECOMING LIGHTER AS HIGH
PRESSURE CENTERS OVER THE REGION WITH NEARLY FULL SUNSHINE…THIS
WILL GO MORE TOWARDS THE LATENT HEAT FLUX OF MELTING THE SNOW.

THE AIRMASS WILL BEGIN TO MODERATE SUNDAY NIGHT AS HIGH PRESSURE
SLIDES OFFSHORE AND LIGHT WINDS BECOME MORE SOUTHERLY AT THE
SURFACE. STILL…LOWS WILL BE VERY COLD AND NEAR TO A LITTLE BELOW
NORMAL WITH VALUES IN THE UPPER TEENS TO 20S. AN UPPER LEVEL LOW
OVER THE GREAT LAKES APPROACHES MONDAY WITH A WARM FRONT MOVING
THROUGH DURING THE DAY WITH A COLD FRONT MOVING THROUGH MONDAY
NIGHT…AFTER WHICH WINDS WILL TURN MORE WESTERLY. MODELS HAVE
PRETTY GOOD AGREEMENT WITH PRECIP…STARTING AS SNOW LATE SUNDAY
NIGHT INTO MONDAY…MIXING WITH AND CHANGING TO RAIN FROM SOUTH TO
NORTH DURING THE DAY WITH CONTINUED SOUTHERLY FLOW.

CANNOT RULE OUT CONTINUED SHOWER ACTIVITY MONDAY NIGHT AND TUESDAY
AS THE UPPER LEVEL LOW BECOMES MORE ELONGATED AND ITS AXIS MOVES
INTO THE REGION. ASSOCIATED POSITIVE VORTICITY ADVECTION WITH
EMBEDDED SHORTWAVES ALOFT WILL ENHANCE THE POPS FOR SHOWERS…WHICH
WOULD BE MORE SNOW SHOWERS ACROSS INTERIOR AND RAIN TOWARDS THE
COAST. WEAK HIGH PRESSURE AT THE SURFACE…BUT WILL HAVE SLIGHT
CHANCE POPS DUE TO DYNAMICS ALOFT. CONTINUED WESTERLY FLOW WITH
PARENT LOW PRESSURE MOVING OFF INTO THE CANADIAN MARITIMES WILL
STILL ENABLE A RELATIVELY MORE MILD DAY…HIGHS IN THE LOW TO MID
40S. FOLLOWED MORE OF THE ECMWF WED-FRI AND NOT SO MUCH THE GFS
WHICH HAS A LOW PRESSURE SYSTEM DEVELOPING AND MOVING ACROSS THE
REGION ON WED. IN ANY CASE…ALOFT IT WILL STILL REMAIN UNSETTLED
WITH STILL A TROUGH PATTERN THROUGH THU ALTHOUGH THE WAVELENGTH WILL
BE GETTING LARGER. CHANCES FOR SHOWERS BETWEEN 20 AND 30
PERCENT…MORE SNOW SHOWERS FOR INTERIOR AND SNOW SHOWERS AT THE
COAST LATER WED NIGHT.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/…
* HIGH IMPACT AVIATION WEATHER EVENT TODAY AND SATURDAY*

HIGH PRESSURE TO THE NE DRIFTS FARTHER OFFSHORE EARLY THIS MORNING.
STRONG LOW PRESSURE REACHES CAPE HATTERAS LATER THIS MORNING…AND
TRAVELS SOUTH OF THE TERMINALS TONIGHT.

WINDS MOSTLY NE TO ENE OVERNIGHT WITH SPEEDS INCREASING TO AROUND 15
KT EARLY THIS MORNING…SLIGHTLY LOWER OUTSIDE OF NYC. DURING THE
DAY TODAY…WIND SPEEDS GRADUALLY INCREASE WITH GUSTS DEVELOPING
TOWARD MID-LATE MORNING. GUSTS OVER THE CITY TERMINALS INCREASING TO
35 TO 40 KT BY EVENING. WINDS BACK TO THE NE DURING THE AFTERNOON.
STRONG GUSTS CONTINUE THROUGH THE NIGHT WITH OCCASIONAL GUSTS TO 50
KT POSSIBLE.

MVFR TO IFR WITH -SN LIKELY DEVELOPING BY THE MORNING PUSH. ALONG
THE COAST…SNOW IS EXPECTED TO MIX WITH OR CHANGE OVER TO RAIN MID
TO LATE MORNING. CIGS LOWER TO IFR. AWAY FROM THE
COAST…PRECIPITATION SHOULD STAY ALL SNOW OR MIX WITH SLEET.

COASTAL TERMINALS EXPECTED TO HAVE 10 TO 15 INCHES OF
SNOWFALL…WITH 12 TO 18 INCHES NORTH OF THE CITY. SNOWFALL AMOUNTS
OF 3 INCHES PER HOUR WILL BE POSSIBLE FRIDAY NIGHT…ESPECIALLY IN
THE EVENING HOURS. STRONG WINDS WILL RESULT IN BLOWING AND DRIFTING
OF SNOW INTO SATURDAY.

.OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY…
.FRIDAY NIGHT-SATURDAY…WINTER STORM WITH ACCUMULATING SNOW
CONTINUES THROUGH SATURDAY MORNING. HEAVIEST SNOW MORE LIKELY TO
OCCUR FRIDAY NIGHT. IFR-LIFR CONDS WITH 50+KT PSBL FRIDAY NIGHT-SAT
MORNING.
.SUNDAY…VFR.
.MONDAY…SUB VFR POSSIBLE IN PRECIPITATION.
.TUESDAY…VFR.

&&

.MARINE…
EAST WINDS INCREASE QUICKLY THIS MORNING. A HURRICANE FORCE WIND
WARNING REMAINS UP FOR THE OCEAN E OF MORICHES INLET BY EVENING
AS A 70-80 KT NORTHEASTERLY LOW LEVEL JET PASSES OHD WITH GOOD
POTENTIAL TO MIX THESE WINDS TO THE SFC…AND STORM WARNINGS FOR
MOST OTHER WATERS.

STILL UNCERTAIN ENOUGH AS TO WHETHER WRN LONG ISLAND SOUND AND NY
HARBOR WILL SEE STORM FORCE GUSTS…SO KEPT THE STORM WATCH GOING
THERE. THIS WILL STILL BE PRECEDED BY A GALE WARNING FOR LATE FRI
MORNING INTO FRI AFTERNOON.

FCST SEAS FRI INTO SAT ARE WAY ABOVE WAVEWATCH…WITH MAX OCEAN SEAS
19-24 FT FRI NIGHT AT THE HEIGHT OF THE STORM. CENTRAL/EASTERN LONG
ISLAND SOUND COULD SEE 10-FOOTERS AS WELL.

GALES FORECAST TO LOWER TO SCA BY LATE SAT NIGHT WITH RESIDUAL
SCA ON OCEAN EARLY SUNDAY. CONDITIONS BELOW SCA THEREAFTER UNTIL
MON AFTERNOON…WHEN CONTINUED SOUTHERLY FETCH LEADS TO HIGHER
WAVES. SCA THEN IS FORECAST MON AFTERNOON THROUGH REST OF FORECAST
PERIOD FOR OCEAN.

&&

.HYDROLOGY…
SIGNIFICANT PRECIPITATION OF 1-2 INCHES LIQUID EQUIVALENT QPF IS
EXPECTED TODAY THROUGH SAT MORNING…WITH POTENTIAL FOR
HIGHER AMOUNTS UP TO 2.5 INCHES QPF IN BANDING. PRECIP WILL LIKELY
START OUT AS SNOW FRIDAY MORNING AND THEN CHANGE TO RAIN OR MIX WITH
RAIN AT THE COAST CHANGING BACK TO SNOW FRIDAY NIGHT/EARLY SAT.

LIQUID AMOUNTS 1/4 TO 1/2 INCH POSSIBLE WITH FRONTAL SYSTEM LATE
SUNDAY NIGHT THROUGH MONDAY.

&&

.TIDES/COASTAL FLOODING…
COASTAL FLOOD WARNINGS AND ADVISORIES HAVE BEEN ISSUED FOR THE
ENTIRE COASTAL AREA.

UP TO 3 TO 5 FT OR SURGE IS EXPECTED DURING THE TIMES OF HIGH TIDE
FRIDAY EVENING ALONG WESTERN LONG ISLAND SOUND…THE TWIN FORKS OF
LI…AND GREAT SOUTH BAY…WITH WIDESPREAD MODERATE COASTAL
FLOODING. INUNDATION ACROSS N AND NE FACING COASTAL AREAS OF
WESTERN LONG ISLAND SOUND WILL LIKELY BE EXACERBATED BY 3 TO 5 FT
SURF. THE SURF COULD BE DAMAGING ALONG THE UNPROTECTED N AND NE
FACING SHORELINES OF THE TWIN FORKS OF LI WITH POTENTIAL FOR 4 TO
8 FT BREAKING WAVES.

ALONG NY HARBOR AND SE COASTAL CT…2 TO 4 FT OF SURGE DURING THE
TIMES OF HIGH TIDE WILL LIKELY RESULT IN MINOR TO LOCALLY MODERATE
COASTAL FLOODING DURING THE TIMES OF HIGH TIDE FRIDAY EVENING.

THE LARGE SPREAD IN SURGE IS DUE TO THE UNCERTAINTY ON THE EXACT
WIND DIRECTION (N VS NE) FRIDAY EVENING…WHICH WILL MAKE A BIG
DIFFERENCE IN AMOUNT OF SURGE.

SIGNIFICANT BEACH EROSION IS ALSO LIKELY WITH THIS STORM SYSTEM
LATE FRIDAY THROUGH SATURDAY MORNING…WITH PARTICULAR CONCERN FOR
THE TWIN FORKS OF LONG ISLAND. ALONG THE OCEAN BEACHES…BREAKING
WAVE OF 9 TO 13 FT ARE POSSIBLE.

&&

.OKX WATCHES/WARNINGS/ADVISORIES…
CT…COASTAL FLOOD WARNING FROM 6 PM THIS EVENING TO MIDNIGHT EST
TONIGHT FOR CTZ009.
BLIZZARD WARNING FROM 6 AM THIS MORNING TO 1 PM EST SATURDAY
FOR CTZ005>012.
COASTAL FLOOD ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT EST
TONIGHT FOR CTZ010>012.
NY…COASTAL FLOOD WARNING FROM 6 PM THIS EVENING TO MIDNIGHT EST
TONIGHT FOR NYZ071-073-078>081-176-177.
BLIZZARD WARNING FROM 6 AM THIS MORNING TO 1 PM EST SATURDAY
FOR NYZ071>075-078>081-176>179.
COASTAL FLOOD ADVISORY FROM 4 PM THIS AFTERNOON TO 8 PM EST
THIS EVENING FOR NYZ072-074-075-178.
WINTER STORM WARNING FROM 7 AM THIS MORNING TO 1 PM EST
SATURDAY FOR NYZ067>070.
COASTAL FLOOD WARNING FROM 4 PM THIS AFTERNOON TO 8 PM EST
THIS EVENING FOR NYZ179.
NJ…BLIZZARD WARNING FROM 6 AM THIS MORNING TO 1 PM EST SATURDAY
FOR NJZ006-104-106-108.
WINTER STORM WARNING FROM 6 AM THIS MORNING TO 1 PM EST
SATURDAY FOR NJZ002-004-103-105-107.
COASTAL FLOOD ADVISORY FROM 4 PM THIS AFTERNOON TO 8 PM EST
THIS EVENING FOR NJZ006-106-108.
MARINE…STORM WARNING FROM 6 AM THIS MORNING TO NOON EST SATURDAY FOR
ANZ330-340-345-353-355.
STORM WATCH FROM THIS EVENING THROUGH SATURDAY MORNING FOR
ANZ335-338.
GALE WARNING FROM 10 AM THIS MORNING TO 6 PM EST THIS EVENING
FOR ANZ335-338.
STORM WARNING FROM 6 AM THIS MORNING TO 6 PM EST THIS EVENING
FOR ANZ350.
HURRICANE FORCE WIND WARNING FROM 6 PM THIS EVENING TO
MIDNIGHT EST TONIGHT FOR ANZ350.

&&

$$
SYNOPSIS…JM/DW
NEAR TERM…DW/PW
SHORT TERM…DW
LONG TERM…JM
AVIATION…BC
MARINE…GOODMAN/PW
HYDROLOGY…JM/DW
TIDES/COASTAL FLOODING…BG

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