Area Forecast Discussion
Issued by NWS Upton, NY

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000
FXUS61 KOKX 050259
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
959 PM EST WED MAR 4 2015

.SYNOPSIS...
A COLD FRONT MOVES THROUGH THE REGION LATE TONIGHT...WITH WAVES
OF LOW PRESSURE TRACKING ALONG IT INTO THURSDAY. CANADIAN HIGH
PRESSURE BUILDS IN THURSDAY NIGHT...THEN SLIDES TO OUR SOUTH
THROUGH FRIDAY NIGHT. A SERIES OF WEAK COLD FRONTS CROSS THE
REGION THIS WEEKEND INTO EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
PCPN HAS BECOME MUCH BETTER ORGANIZED IN THE LAST COUPLE OF HOURS
WITH A STEADY RAIN MOVING IN FROM THE SW...IMPACTING MOST AREAS
WITH THE EXCEPTION OF THE FAR INTERIOR OF THE LOWER HUDSON VALLEY
AND SRN CT. DUAL POL RADAR DATA SHOWS A MIXED PCPN PHASE AT ABOUT
4000 TO 5000 FT. IT WILL TAKE SEVERAL MORE HOURS OF VERTICAL
COOLING BEFORE A TRANSITION TO SNOW OCCURS. COLD FRONT REMAINS
JUST NORTH OF THE LOWER HUDSON VALLEY. 00Z NAM WRF HAS TRENDED A
BIT SLOWER WITH THE COLD AIR WORKING IN WHICH MAY DELAY THE
CHANGEOVER AN HOUR OR TWO.

SEVERAL WAVES WILL FORM ALONG THIS FRONTAL ZONE...WHICH WILL BE
SUPPORTED BY A VERY INTENSE UPPER LEVEL JET...BETWEEN 200 AND 215
KT. UPPER LEVEL DIVERGENCE INCREASES OVERNIGHT INTO THURSDAY WITH
THIS JET. TIGHT BAROCLINIC ZONE ALSO SETS UP AS COLD AIR FILTERS
IN OVERNIGHT BEHIND THE FRONT.

EXPECT ANY PRECIPITATION THAT FALLS THIS EVENING TO BE IN THE FORM
OF PLAIN RAIN. AS THE COLDER AIR FILTERS IN FROM THE NORTHWEST
BEHIND THE FRONT...PRECIPITATION TRANSITIONS TO A RAIN...SLEET..AND
SNOW MIX FROM NORTHWEST TO SOUTHEAST LATE THIS EVENING. FEEL THE
ENTIRE AREA WILL BE ALL SNOW BY OR JUST AFTER 06Z. SNOW...MODERATE
TO POSSIBLY HEAVY AT TIMES...IS THEN EXPECTED THROUGH AT LEAST MID
MORNING ACROSS SOUTHERN ZONES. THE SNOWFALL WILL BE A BIT LIGHTER
ACROSS THE INTERIOR ZONES AS THE BEST FRONTOGENESIS AND LIFT WILL
RESIDE ACROSS THE SOUTHERN PORTION OF THE REGION. THE SNOW BEGINS
TO TAPER OFF FROM NORTHWEST TO SOUTHEAST DURING THE AFTERNOON AND
EVENING.

OVERALL MODELS HAVE COME INTO BETTER AGREEMENT WITH THE
GFS..EURO...CMC...CMC REGIONAL...UKMET...GEFS...AND SREF ALL
INDICATE AT LEAST MODERATE SNOW ACROSS SOUTHERN ZONES FROM JUST
AFTER 06Z TO AROUND 18Z THURSDAY. THE NAM APPEARS TO BE AN OUTLIER
AS IT SUPPRESSES MUCH OF THE SNOW SOUTH OF THE REGION AFTER 12Z.
THE 18Z NAM DID SHIFT THE AXIS A BIT FURTHER NORTH HOWEVER
COMPARED TO ITS 12Z RUN. LARGE SCALE SYNOPTIC LIFT SUPPORTS SNOW
CONTINUING LONGER THAN THE NAM IS SHOWING AND THIS THINKING IS
MORE IN LINE WITH THE REST OF THE GUIDANCE. THE FIRST PORTION OF
THE SNOW WILL SEE LOWER SNOW TO LIQUID RATIOS...BUT AS THE COLUMN
COOLS SIGNIFICANTLY EARLY THURS MORNING...EXPECT RATIOS TO INCREASE
A BIT.

DUE TO INCREASED CONFIDENCE HAVE ADDED MANHATTAN...BRONX...HUDSON...
AND EASTERN ESSEX INTO THE WINTER STORM WARNING...AND REPLACED THE
REST OF THE WATCH WITH ADVISORIES FOR ALL BUT NORTHERN NEW LONDON
WHERE NO HEADLINE IS IN EFFECT. ROCKLAND AND NORTHERN WESTCHESTER
INTO AN ADVISORY. SNOWFALL ACCUMULATIONS OF 4 TO 7 INCHES IN THE
WARNING AND 2 TO 5 INCHES IN THE ADVISORY AREA.

SOME UNCERTAINTIES STILL EXIST INCLUDING THE NORTHERN EXTENT OF
THE SNOW...ESPECIALLY DURING THE DAY ON THURSDAY. IF ANY NORTH SHIFT
NORTH OCCURS...TOTALS COULD BE A BIT HIGHER THAN FORECAST. ON THE
OTHER HAND...IF A SOUTH SHIFT OCCURS...TOTALS COULD END UP LOWER.

TEMPERATURES WILL BEGIN TO FALL THIS EVENING INTO THE 30S AND THEN
BELOW FREEZING AFTER 06Z. EXPECT TEMPERATURES FALLING INTO THE 20S
THURSDAY MORNING AND REMAINING IN THE LOW TO MIDDLE 20S DURING THE
DAY.

&&

.SHORT TERM /THURSDAY NIGHT/...
HIGH PRESSURE BUILDS IN FROM THE WEST THURSDAY NIGHT. SKIES WILL
CLEAR FROM WEST TO EAST. WINDS SHOULD DIMINISH LATE AND WITH DRY
CONDITIONS...EXPECTING AN UNSEASONABLY COLD NIGHT WITH
TEMPERATURES FALLING INTO THE SINGLE DIGITS FOR MOST LOCATIONS AND
LOWER TO MIDDLE TEENS IN THE NYC METRO.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
HIGH PRESSURE RIDGE AXIS WILL BE RIGHT OVER US ON FRIDAY...AND IT
WILL SLOWLY SHIFT OFFSHORE LATE IN THE DAY INTO FRIDAY NIGHT. THIS
HIGH PRESSURE SYSTEM HAS CANADIAN ORIGINS...AND WITH PLENTY OF
SNOWPACK TO THE WEST...IT WON`T HAVE MUCH OF A CHANCE TO MODERATE
BEFORE IT ARRIVES HERE. AFTER A RECORD TO NEAR-RECORD COLD
START...DAYTIME TEMPS WILL ONLY RECOVER INTO THE MID 20S...ABOUT 20
DEGREES BELOW NORMAL.

A FAST FLOW ALOFT FOR THE WEEKEND THROUGH WEDNESDAY LEADS TO
DIFFERENCES AMONG THE GLOBAL MODELS REGARDING THE TIMING OF WEAK
FRONTS/TROUGHS PASSING THROUGH HERE. THIS RELATIVELY FLAT FLOW WILL
AT LEAST KEEP THE ABNORMALLY COLD AIR WE`VE BEEN EXPERIENCING LOCKED
UP TO OUR NORTH. SO WITH THE GIVEN UNCERTAINTY OF THE SURFACE
FEATURES...WILL GO CLOSE TO WPC GUIDANCE FOR THIS PERIOD. THIS KEEPS
MOST OF THE REST OF THE LONG TERM PERIOD DRY. JUST A SLIGHT CHANCE
OF LIGHT SNOW NORTH OF THE CITY SATURDAY NIGHT WHERE MOISTURE AND
LIFT WILL BE BETTER AS LOW PRESSURE PASSES WELL TO THE NORTH. THE
ONLY OTHER CHANCE OF PCPN WILL ARRIVE ON MONDAY AS ANOTHER SYSTEM
PASSES WELL TO THE NORTH. THIS ONE APPEARS TO HAVE MORE MOISTURE
WITH IT...SO HAVE SLIGHT CHC POPS FOR THE ENTIRE AREA. PCPN TYPE
MOST LIKELY SNOW TO START...THEN MIXING WITH RAIN BEFORE CHANGING TO
RAIN IN THE AFTERNOON. WITH THE VERY COLD AIR STAYING NORTH...HIGH
TEMPERATURES WILL GRADUALLY MODERATE FROM THE MID 30S ON SATURDAY TO
THE UPPER 40S ON WEDNESDAY...WHICH IS NORMAL.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
PERIODS OF LIGHT TO LOCALLY MODERATE RAIN WILL CONTINUE TONIGHT AS
LOW PRES TRACKS FROM THE GULF COAST AND MOVES OFF THE MID-ATLANTIC
LATE TONIGHT THROUGH THURSDAY MORNING. MVFR TO IFR CONDS EXPECTED IN
RAIN AND FOG.

THERE WILL BE A BRIEF TRANSITION TO RAIN/SNOW/SLEET IN THE 04-06Z
TIME FRAME...AND THEN THE WINTRY MIX CHANGES ALL SNOW FROM 06-08Z.
TIMING OF TRANSITION MAY BE OFF BY AN HOUR OR SO.

MODERATE SNOW WILL FALL FROM LATE TONIGHT THROUGH THURSDAY
MORNING...AND THEN PERIODS OF LIGHT TO MODERATE SNOW WILL CONTINUE
INTO THE AFTERNOON BEFORE TAPERING OFF LATE. IFR/LIFR CONDS LATE
TONIGHT THROUGH THURSDAY MORNING WILL GRADUALLY IMPROVE TO MVFR IN
THE AFTERNOON...AND THEN EVENTUALLY TO VFR LATE.

EXPECTED RUNWAY ACCUMULATIONS:
KJFK/KISP...6-8 INCHES.
KLGA/KEWR/KTEB/KHPN/KBDR/KGON...4-6 INCHES.
KSWF...2-3 INCHES.

S WINDS THIS EVENING WILL VEER TO THE NW AT 10 KT OR LESS. N/NW
WINDS WILL INCREASE TO 10-15 KT WITH GUSTS UP TO 20 KT BY THURSDAY
MORNING.

.OUTLOOK FOR 00Z FRIDAY THROUGH MONDAY...
.THURSDAY NIGHT-FRIDAY...IMPROVING TO VFR THURS NIGHT. NW GUSTS
15-20KT POSSIBLE THURSDAY NIGHT.
.SAT/SUN...VFR.
.MON...VFR. GUSTY NW WINDS.

&&

.MARINE...
SCA CONDITIONS ARE EXPECTED TO CONTINUE ACROSS THE OCEAN WITH
THE REMAINING WATERS BELOW SCA THROUGH THURSDAY. WINDS ARE
MARGINAL ON THE OCEAN WATERS...ESPECIALLY TONIGHT WHEN THEY
LIKELY STAY BELOW. SEAS HOWEVER WILL BE ABOVE SCA LEVELS. WINDS
INCREASE ON THURSDAY AND WILL CONTINUE THROUGH THE DAY WITH SEAS
AROUND 5 FEET OVER THE OCEAN. SCA CONDITIONS MAY CONTINUE INTO
THURSDAY NIGHT SO THE ADVISORY MAY NEED TO BE EXTENDED FURTHER.

A PERIOD OF SUB SCA CONDITIONS FOR FRIDAY AND FRIDAY NIGHT
EXPECTED AS A HIGH PRESSURE RIDGE APPROACHES AND PASSES THROUGH
THE WATERS. THE RETURN SW FLOW INCREASES ON SATURDAY...WITH SCA
CONDITIONS DEVELOPING ON THE OCEAN DURING THE MORNING AND LASTING
INTO SATURDAY EVENING. A LACK OF STRONG SURFACE FEATURES
THEREAFTER THROUGH MONDAY WILL PROMOTE SUB-SCA CONDITIONS. HAVE
GONE BELOW WAVEWATCH GUIDANCE FOR SOME OF THIS PERIOD AS IT
APPEARS TO BUILDING TOO MUCH SWELL.

&&

.HYDROLOGY...
1/4 TO 3/4 INCH LIQUID EQUIVALENT PRECIPITATION IS LIKELY
TONIGHT INTO THURSDAY. MOST OF THIS WILL BE FROZEN...SO
HYDROLOGIC IMPACTS ARE NOT EXPECTED.

NO SIGNIFICANT PRECIPITATION IS EXPECTED FROM THURSDAY NIGHT
THROUGH THE MIDDLE OF NEXT WEEK.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR CTZ009>012.
NY...WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR NYZ072>075-
     078>081-176>179.
     WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR NYZ069>071.
NJ...WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR NJZ006-
     106>108.
     WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR NJZ002-004-
     103>105.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THURSDAY FOR ANZ350-353-
     355.

&&

$$

SYNOPSIS...JC/DS/DW
NEAR TERM...DS/DW
SHORT TERM...DS
LONG TERM...JC
AVIATION...MPS
MARINE...JC/DS/DW
HYDROLOGY...JC/DS






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