Area Forecast Discussion
Issued by NWS Upton, NY

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000
FXUS61 KOKX 012359
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
659 PM EST SUN FEB 1 2015

.SYNOPSIS...
LOW PRESSURE APPROACHES FROM THE OHIO VALLEY TONIGHT AND PASSES
JUST SOUTH OF LONG ISLAND MONDAY. THE LOW TRACKS WELL TO THE EAST
MONDAY NIGHT. A SERIES OF COLD FRONTS WILL MOVE ACROSS THE REGION
THROUGH THE UPCOMING WEEK...THE FIRST WEDNESDAY NIGHT INTO
THURSDAY...AND THEN ANOTHER ON SATURDAY. IN BETWEEN...COLD...POLAR
HIGH PRESSURE WILL BE ACROSS THE AREA. LOW PRESSURE OVER THE GULF
COAST STATES LATE IN THE WEEK STILL LOOKS TO TAKE A TRACK WELL
OFFSHORE.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
SOME VERY LIGHT SNOW ACROSS EASTERN PA WILL SPREAD ACROSS
LOCATIONS NORTH AND WEST OF NYC THE NEXT COUPLE OF HOURS. A
STEADIER SNOW DOES NOT DEVELOP ACROSS THE AREA UNTIL AFTER
MIDNIGHT. POPS WERE ADJUSTED DOWN THIS EVE AND TEMPS WERE BUMPED
UP A COUPLE OF DEGREES BASED ON LATEST OBS AND TRENDS.

MODELS IN GOOD AGREEMENT WITH LOW PRESSURE TAKING SHAPE OVER THE
MID MISSISSIPPI RIVER VALLEY THIS AFTERNOON...TRACKING THROUGH THE
OHIO VALLEY TONIGHT...AND BEGINNING TO REDEVELOP JUST SOUTH OF THE
TRI- STATE MONDAY MORNING.

INCREASING AND LOWERING CLOUDS THIS EVENING...WITH GRADUALLY
INCREASING CHANCES OF LIGHT SNOW FROM W TO E TONIGHT.

TEMPS GENERALLY STEADY IN LOWER 30S-35 ALONG THE COAST FOR MOST OF
THE NIGHT...THEN WETBULBING TO FREEZING WITH START OF HEAVY
SNOW...THEN RISING ABOVE FREEZING LATE ACROSS IMMEDIATE SOUTH AND
EASTERN COASTAL AREAS TO ABOVE FREEZING TOWARDS DAYBREAK. JUST
INTERIOR OF THE IMMEDIATE COAST...ACROSS INTERIOR NE NJ...LOWER
HUDSON VALLEY...AND SOUTHERN CT...TEMPS SHOULD FALL INTO THE TEENS
AND 20S WITH EVAPORATIONAL COOLING ONCE SNOW STARTS AND HOLD
THERE INTO DAYBREAK.

BASED ON APPROACHING COUPLED JET STRUCTURE...TIGHT LOW/MID-LEVEL
THERMAL STRUCTURE...AND 60-70 KT LLJ FEEDING STRONG GULF MOISTURE
FEED OF 2-3 STD PWATS UP OVER THE REGION LATE TONIGHT...EXPECTING
HEAVY SNOW INITIALLY TO DEVELOP ACROSS THE REGION FROM W TO E AFTER
2 TO 4 AM. SNOWFALL RATES OF 1 TO 2 INCHES PER HOUR POSSIBLE.
THIS IS SUPPORTED BY HIGH PROB OF 1" PER HOUR SNOWFALL RATES IN
THE SREF.

A QUICK 2 TO 5 ALONG THE CITY/COAST IS THE MOST LIKELY
(HIGHEST AMOUNTS ACROSS NORTHERN PERIPHERIES WITH LOCALLY 6
INCHES) BEFORE ANY CHANGEOVER TOWARDS DAYBREAK. A GENERAL 4 TO 8
INCHES OF SNOW BY DAYBREAK ACROSS INTERIOR NE NJ...LOWER HUDSON
VALLEY...AND SW CT. 3 TO 5 INCHES ACROSS SE CT. THESE RANGES HAVE
THE POTENTIAL TO BE SHIFTED UP OR DOWN BY 1-2 INCHES...BECAUSE A 1
HOUR DIFFERENCE IN TIMING OF CHANGEOVER WILL MEAN THE DIFFERENCE
IN ALMOST 2 INCHES OF SNOW FROM THE TOTAL! THIS VARIABILITY ISSUE
IS ILLUSTRATED WELL BY THE 10 AND 90 PERCENTILE SNOW TOTAL GRAPHICS
ON OUR WEB PAGE.

FOR THE NYC/NJ METRO AND COAST...ALMOST ALL OF THE SNOWFALL FOR THE
EVENING WILL BE SEEN IN THE EARLY MORNING HOURS. THE EARLY
MORNING COMMUTE WILL BE HEAVILY IMPACTED FOR THE ENTIRE AREA.

THEREAFTER...THE FORECAST CHALLENGE REMAINS IN HOW QUICKLY AND FAR
NORTH WARM AIR RIDES IN ALOFT AS WE APPROACH DAYBREAK MONDAY
MORNING...AND WHERE A COASTAL FRONT SETS UP DEMARCATING A TIGHT
GRADIENT BETWEEN SE WINDS AND 40 DEGREE TEMPS TO THE SE AND
ENE/NE WINDS TO THE NORTH WITH SUB-FREEING TEMPS.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
MODEL GUIDANCE HAS SHIFTED BIT FARTHER NORTH WITH THE 12Z
GUIDANCE...WITH GENERAL AGREEMENT IN COASTAL LOW PRESSURE RE-
DEVELOPING JUST SOUTH OF THE REGION MONDAY MORNING AND SKIRTED THE
LI COAST AS IT TRACKS EAST DURING THE DAY.

00Z SBU ENSEMBLE SENSITIVITY GUIDANCE SHOWED A NUDGE NORTH IN
ENSEMBLE MEANS...WITH A BIT OF VARIANCE EXPLAINED IN FASTER SPEED
AND A BIT FARTHER NORTH TRACK OF LOW. THIS SEEMED TO BEARING OUT
IN THE 12 OPERATIONAL GUIDANCE WITH A BIT WARMER AND QUICKER
MOVEMENT OF THE LOW.

SO WITH GENERAL CONSENSUS ON A FARTHER NORTH TRACK...UNCERTAINTY
STILL LIES IN THE TIGHTNESS OF THE THERMAL GRADIENT ALOFT...SPEED
AND NORTHWARD EXTENT OF CHANGEOVER FROM SNOW TO LIQUID ALOFT. THEN
AT THE SURFACE...COASTAL FRONT SET-UP WILL BE CRITICAL...IN
DIFFERENCE BETWEEN PLAIN RAIN TO SOUTH (MOST LIKELY SOUTH COASTAL
LI/NYC) AND FREEZING RAIN TO THE NORTH.

HIGHEST CONFIDENCE IN REMAINING MAINLY SNOW THROUGH THE EVENT IS
FAR INTERIOR LOWER HUDSON VALLEY...AN ADDITIONAL 3 TO 5 INCHES OF
SNOW LIKELY HERE THROUGH THE AFTERNOON.

A MIX OF SNOW...SLEET AND FREEZING RAIN FROM AFTER DAYBREAK
THROUGH EARLY AFTERNOON LIKELY FOR INTERIOR NE NJ...CENTRAL LOWER
HUDSON VALLEY AND INTERIOR SW CT. AN ADDITIONAL 1 TO 3 INCHES OF
SNOW AND SLEET LIKELY HERE THROUGH THE AFTERNOON...WITH POTENTIAL
FOR 1/4 TO 1/2 INCH OF ICE ALONG SOUTHERN/EASTERN BOUNDARIES. IF
NORTHWARD WARMING TREND CONTINUES...THE SNOW AMOUNTS WOULD BE
LOWER IN THE AFTERNOON WITH INCREASED POTENTIAL TO REACH THE 1/2
INCH ICE AMOUNTS.

MODELS DEPICTING ENOUGH WARMING IN THE 800-950 LAYER ACROSS NYC/NJ
METRO...LI...COASTAL LOWER HUDSON VALLEY...COASTAL SW CT...AND SE CT
FOR A COMPLETE TRANSITION FROM SNOW TO LIQUID ALOFT MONDAY MORNING.
COASTAL FRONT SET-UP WILL BE DIFFERENCE BETWEEN FREEZING RAIN TO THE
NORTH AND PLAIN RAIN TO THE SOUTH. CURRENT TRACK OF SURFACE LOW AND
HIGH RES-GUIDANCE INDICATING COASTAL FRONT LIFTING AS FAR NORTH AS
NORTH SHORE OF LI...N/NW PERIPHERY OF NJ/NYC METRO...AND SE
COASTAL CT DURING THE MORNING BEFORE SINKING BACK SE THROUGH THE
AFTERNOON. THIS WOULD INDICATE POTENTIAL FOR A 20-30 MILE ZONE OF
SIGNIFICANT FREEZING RAIN (1/4 TO 1/2 INCH) JUST TO THE NORTH.


WHILE THE 20-30 MILE ZONE JUST TO THE SE OF THE COASTAL FRONT WILL
LIKELY EXPERIENCE A PERIOD OF PLAIN RAIN AS BOUNDARY LAYER WARMS
ABOVE FREEZING...BEFORE GRADUALLY CHANGING TO FREEZING RAIN (1/10
INCH FZRA)...SLEET AND THEN BACK TO SNOW FROM AROUND MIDDAY INTO
MID AFTERNOON. THIS ZONE MAY INCLUDE FAR NORTHERN PORTIONS OF
NYC/NJ METRO...NORTH SHORE OF WESTERN/CENTRAL LI.

FOR SOUTHERN NASSAU COUNTY...EASTERN LI...SE COASTAL CT AND EVEN
SOUTHERN PORTIONS OF NYC...FAIRLY HIGH PROBABILITY OF SEEING SNOW
CHANGING TO PLAIN RAIN AFTER DAYBREAK WITH BOUNDARY LAYER WARMING.
IN FACT TEMPS COULD RISE INTO THE LOWER 40S ACROSS THIS AREAS IN THE
MORNING. THEN A GRADUAL CHANGE BACK TO FREEZING RAIN/SLEET AND
EVENTUALLY SNOW FROM NW TO SE IN THE AFTERNOON. A FEW HUNDREDTHS TO
A TENTH OF AN INCH OF ICE POSSIBLE HERE IN THE AFTERNOON.

FOR ANY AREA THAT DOES CHANGEOVER FROM SNOW TO RAIN/FREEZING
RAIN...URBAN FLOODING POTENTIAL EXISTS WITH 3/5 TO 1 1/4 INCHES OF
RAIN. SEE HYDROLOGY SECTION FOR DETAILS.

DESPITE A CHANGEOVER TO RAIN...FLASH FREEZE POTENTIAL FOR THE EVENING
COMMUTE FOR THE COAST AS THE LOW PULLS EAST...WINDS TURN NORTHERLY
WITH TEMPS LIKELY DROPPING INTO THE UPPER 20S WITH SOME LIGHT SNOW
BANDING.

WILL MAINTAIN WINTER STORM WARNINGS AS IS FOR THE IMPACT TO MORNING
AND EVENING COMMUTES FOR MUCH OF THE REGION. WILL CHANGE WATCH TO
ADVISORY FOR SOUTHERN AND EASTERN LI WITH LESS POTENTIAL FOR
ICING.

SNOW TAPERS OFF IN THE EVENING FROM W TO E AS UPPER TROUGH AND
DEFORMATION BAND SWING THROUGH. WINDY AND FRIGID CONDITIONS MONDAY
NIGHT IN THE WAKE OF LOW PRESSURE. WIND GUSTS OF 35 TO 40 MPH LIKELY
MONDAY EVENING/NIGHT WITH LOW POTENTIAL FOR WIND ADVISORY GUSTS UP
TO 50 MPH. LOW TEMPERATURES FALLING INTO THE TEENS COAST AND SINGLE
DIGITS INTERIOR...WITH WINDCHILL OF 10 TO 15 BELOW ZERO ACROSS
INTERIOR AND AROUND 5 BELOW ZERO ALONG THE COAST.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
THE MAIN THEME CONTINUES TO BE A PROGRESSIVE NW FLOW ACROSS THE NRN
TIER OF THE COUNTRY WITH THE MEAN UPPER TROF SITUATED FROM WESTERN
CANADA SE TO THE EASTERN SEABOARD. THIS TYPE OF FLOW OF LATE HAS
CAUSED CHALLENGES WITH THE AMPLIFICATION OF PAC SHORTWAVE ENERGY
MOVING INTO THE EASTERN U.S. THIS THEME LOOKS TO CONTINUE THROUGH
THE EXTENDED FORECAST.

FOR THE MOST PART...THE 12Z GUIDANCE IS ON BOARD WITH A SERIES OF
POLAR COLD FRONTS MOVING THROUGH THE AREA...THE FIRST WED NIGHT INTO
THU...AND THEN ANOTHER NEXT SAT. IN BETWEEN...POLAR HIGH PRESSURE
AND UNSEASONABLY COLD CONDITIONS LOOK TO PREVAIL. ONCE AGAIN...THE
ASSOCIATED SHORT WAVE ENERGY WITH THESE FRONTS IS IN A CONSTANT
STATE OF FLUX WITH THE AMOUNT OF AMPLIFICATION AS THE ENERGY MOVES
IN FROM WESTERN CANADA. THE 12Z GGEM AND ECMWF ARE TRENDING BACK
TOWARD MORE AMPLIFICATION WITH THE LONGWAVE TROF ON THU ACROSS THE
EASTERN U.S. THIS IS ALLOWING A FRONTAL WAVE OFF THE SE COAST THU TO
TAKE A MORE WESTERN TRACK...PLACING THE FORECAST AREA ON THE NW
PERIPHERY OF LIGHT PCPN. RIGHT NOW...WILL JUST MAINTAIN LOW CHANCES
OF SNOW WITH BOTH COLD FRONTAL SYSTEMS AND SEE HOW FUTURE RUNS
HANDLE THE OFFSHORE LOW. ONCE AGAIN THOUGH...BASED ON RECENT MODEL
PERFORMANCE...THIS IS SOMETHING TO STILL WATCH.

TUE AND FRI LOOK TO TO BE THE COLDEST DAYS OF THE WEEK WITH HIGHS
LIKELY NOT GETTING OUT OF THE 20S...WITH THE WARMEST DAY COMING
ON WED AHEAD OF THE NEXT COLD FRONTAL SYSTEM....IN THE LOW 30S
INLAND TO THE UPPER 30S AT THE COAST. VERTICAL TEMP PROFILES ARE
SUPPORTIVE OF SNOW DURING THE PERIOD.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
**HIGH IMPACT EVENT TONIGHT THROUGH MONDAY**

LOW PRESSURE WAS CENTERED OVER THE OHIO VALLEY AT 23Z WITH A WARM
FRONT EXTENDING EAST THROUGH VIRGINIA TO THE DELMARVA. THE LOW
TRACKS EAST TONIGHT WITH THE WARM FRONT IN THE VICINITY. THE LOW
THEN TRACKS OVER OR NEAR LONG ISLAND MONDAY WITH THE WARM FRONT
LIKELY PUSHING SLIGHTLY NORTH INTO THE REGION. THE LOW THEN MOVES TO
EAST OF CAPE COD BY THE END OF THE FORECAST PERIOD.

LIGHT SNOW IS POSSIBLE AN HOUR OR TWO AS INDICATED IN TAFS...BUT
STEADY AND MORE WIDESPREAD SNOW PUSHES INTO WESTERN TERMINALS FROM
00-02Z MONDAY AND INTO EASTERN TERMINALS FROM 02-04Z. SNOW MAY BE
HEAVY AT TIMES DURING THE OVERNIGHT HOURS.

SNOW CHANGES TO A MIXTURE OF SNOW AND FREEZING RAIN MONDAY MORNING
FOR KISP AND THE NJ/CITY TERMINALS...BEFORE CHANGING TO PLAIN RAIN
FOR PART OF THE MORNING AND AFTERNOON. RAIN THEN CHANGES BACK TO
FREEZING RAIN AND SNOW. BRIEF SLEET IS ALSO POSSIBLE DURING THE
TIMES OF CHANGE TO LIQUID...AND THEN BACK TO FROZEN PCPN. SEE TAFS
FOR TIMING. OTHER TERMINALS WILL SEE MORE IN THE WAY OF SNOW...BUT
STILL SOME MIXED PCPN EXCEPT KSWF WILL BE MAINLY SNOW. A CHANGE TO
ALL SNOW FOR A COUPLE OF HOURS IS POSSIBLE BEFORE THE PRECIPITATION
ENDS. THERE STILL IS SOME UNCERTAINTY WITH THE TIMING OF THE
PRECIPITATION CHANGEOVERS BOTH IN THE MORNING AND AFTERNOON AND WILL
BE DEPENDENT ON HOW FAR AND QUICKLY WARM AIR MOVES IN IN THE
MORNING...AND THE COLD AIR BEHIND THE LOW IN THE AFTERNOON.

LIGHT AND VARIABLE WIND WILL BECOME EAST TO SOUTHEAST AROUND
04Z...THEN AS THE LOW PASSES THROUGH THE WIND SHIFTS TO THE NORTH
AND NORTHEAST MONDAY AFTERNOON AND BECOMES GUSTY.

RUNWAY ACCUMULATIONS:
KTEB/KEWR/KLGA/KJFK/KISP: 2-4" OF SNOW BEFORE CHANGEOVER MON MORNING
WITH UP TO ANOTHER INCH OF SNOW POSSIBLE MON AFTN-EVE. TRACE TO ONE
QUARTER INCH OF ICE DURING MON MORNING AND AFTN.

KHPN/KBDR: 4-7" OF SNOW. ALSO...A QUARTER TO HALF INCH OF ICE DURING
MON MORNING AND AFTN.

KGON:3-6" OF SNOW. ALSO...A TRACE TO A QUARTER INCH OF ICE DURING
MON MORNING AND AFTN.

KSWF: 8-12" OF SNOW. POSSIBLY A LITTLE SLEET MIXED IN LATE MON
MORNING.

.OUTLOOK FOR 00Z TUESDAY THROUGH FRIDAY...
.MONDAY NIGHT...ANY LINGERING SNOW SHOWERS END EARLY...AND
CONDITIONS IMPROVE TO VFR. NW WINDS 15-20 KT WITH 25-35 KT GUSTS.
.TUESDAY...VFR.
.WEDNESDAY...VFR. A CHANCE OF SNOW SHOWERS WEDNESDAY AFTERNOON AND
WEDNESDAY NIGHT WITH LOCALLY MVFR TO IFR CONDITIONS.
.THURSDAY...VFR. NW GUSTS 20 KT.
.FRIDAY...VFR.

&&

.MARINE...
WINDS PICK UP FROM THE SE AND E LATE TONIGHT WITH SCA CONDS
DEVELOPING ACROSS ALL WATERS. THERE IS EVEN A CHANCE OF A FEW GUSTS
UP TO GALE FORCE FOR A SHORT PERIOD LATE TONIGHT INTO EARLY MON
MORNING ON THE OCEAN WATERS. THINKING IS THAT SCA IS THE BEST WAY TO
GO WITH THIS.

LOW PRES CENTER THEN PASSES THROUGH THE WATERS MON MORNING INTO
EARLY AFTN WITH A LULL IN WINDS AS WELL AS A SHIFT TO N...THEN NW ON
THE BACK SIDE OF THE LOW. WINDS INCREASE THROUGH THE AFTERNOON AND
EVENING WITH GALES EXPECTED ON ALL WATERS MON NIGHT. IN
ADDITION...VESSEL ICING IS EXPECTED TO MODERATE...SO A FREEZING
SPRAY ADVISORY HAS BEEN ISSUED AS WELL FOR MONDAY NIGHT.

SMALL CRAFT CONDITIONS WILL LIKELY CONTINUE ON ALL WATERS INTO
THE FIRST HALF OF TUESDAY WITH IMPROVING CONDITIONS AS HIGH PRESSURE
BUILD ACROSS THE WATERS. THERE IS THEN THE POTENTIAL FOR SCA
CONDITIONS ON THE OCEAN WATERS IN THE SW FLOW AHEAD OF A COLD FRONT
WED INTO WED NIGHT...AND THEN THU INTO THU NIGHT IN THE POST-FRONTAL
NLY FLOW. HIGH PRESSURE RETURNS AT THE END OF WEEK.

&&

.HYDROLOGY...
GENERALLY 1 TO 1 1/2 INCHES OF LIQUID FORECAST WITH THE SYSTEM
TONIGHT THROUGH MONDAY. LOW POTENTIAL FOR 2 INCHES ACROSS LI. MUCH
OF THIS WILL BE SNOW AND SLEET ACROSS INTERIOR NORTHERN NE
NJ...LOWER HUDSON VALLEY AND CT.

ACROSS METRO NYC/NJ...LI...AND EVEN COASTAL CT/LOWER HUDSON
VALLEY...A PERIOD OF HEAVY RAIN/FREEZING RAIN LIKELY WITH WHICH WOULD
CAUSE SOME URBAN FLOODING ISSUES DUE TO SNOW CLOGGED DRAINAGE. RISES
ON FLASHY NE NJ...COASTAL LOWER HUDSON VALLEY AND SW CT SMALL
STREAMS CLOSER TO THE COAST ARE ALSO POSSIBLE.

NO SIGNIFICANT WIDESPREAD PCPN IS FORECAST FOR THE REMAINDER OF THE
PERIOD.

&&

.TIDES/COASTAL FLOODING...
AT THIS TIME IT APPEARS THAT FOR THE HIGH TIDE MONDAY MORNING...THAT
DEPARTURES WILL REMAIN BELOW THE 1.5-2 FT REQUIRED FOR MINOR
COASTAL FLOODING.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR CTZ005>012.
NY...WINTER WEATHER ADVISORY UNTIL 6 PM EST MONDAY FOR NYZ079>081-
     179.
     WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR NYZ067>075-078-
     176>178.
NJ...WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR NJZ002-004-006-
     103>108.
MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EST MONDAY
     FOR ANZ330-335-338-340-345-350-353-355.
     FREEZING SPRAY ADVISORY FROM 10 PM MONDAY TO 6 AM EST TUESDAY
     FOR ANZ330-335-338-340-345-350-353-355.
     GALE WARNING FROM 6 PM MONDAY TO 6 AM EST TUESDAY FOR ANZ330-
     335-338-340-345-350-353-355.

&&

$$

SYNOPSIS...NV/DW
NEAR TERM...NV/DW
SHORT TERM...NV
LONG TERM...DW
AVIATION...MET
MARINE...JC/NV
HYDROLOGY...NV/DW
TIDES/COASTAL FLOODING...






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