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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KOKX 220346
AFDOKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
1146 PM EDT TUE MAY 21 2013

.SYNOPSIS...
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A FRONTAL BOUNDARY WILL MOVE INTO THE AREA OVERNIGHT...THEN
DISSIPATE WEDNESDAY MORNING. A COLD FRONT WILL THEN SLOWLY
APPROACH FROM THE WEST...THEN PASS THROUGH THURSDAY NIGHT INTO
FRIDAY MORNING. CANADIAN HIGH PRESSURE WILL THEN BUILD IN FOR THE
MEMORIAL DAY WEEKEND AND EARLY NEXT WEEK.
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&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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ADVECTION FOG/STRATUS IS EXPANDING INTO ERN-MOST LONG ISLAND SOUND
AND NEARBY LAND AREAS. WILL HOLD THE COURSE WITH DENSE FOG ADVY
FOR THE FORKS OF LONG ISLAND AND COASTAL SE CT...WITH PATCHY
FOG ELSEWHERE.

WATCHING LINE OF CONVECTION OVER CENTRAL NY STATE...WHICH THE RA
AND HRRR SUGGEST COULD MAKE A RIGHT TURN TOWARD THE CWA LATE
TONIGHT INTO EARLY WED MORNING. CONVECTION APPEARS OUTFLOW-
DOMINATED WHICH SUGGESTS EVENTUAL WEAKENING. HOWEVER...SINCE THAT
OUTFLOW IS SOMEWHAT ALIGNED WITH THE BULK 0-3 KM SHEAR...SOME
REDEVELOPMENT COULD OCCUR CLOSER TO THE HUDSON VALLEY AND INTERIOR
SW CT LATE TONIGHT...SO HAVE CARRIED A SLIGHT CHANCE POP FOR ALL
AREAS LATE TONIGHT INTO WED MORNING.

BACK DOOR FRONT ADVANCING WWD INTO SOUTHERN CT AND EASTERN LONG
ISLAND WILL LEAD TO A COOLER NIGHT THAN ORIGINALLY FORECAST...WITH
LOWER 55-60. IT WILL HOWEVER REMAIN WARM AND MUGGY OVER THE
HUDSON VALLEY...NYC METRO AND LONG ISLAND...WITH LOWS IN THE 60S.
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&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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LOOKS LIKE A SIMILAR DAY ON WEDNESDAY AS RIDGE SLOWLY SHIFTS
EAST. BACK DOOR COLD FRONT SHOULD QUICKLY WASH OUT WITH DAYTIME
HEATING...AND MORNING FOG AND STRATUS WILL GIVE WAY TO AT LEAST
PARTIAL SUNSHINE. CONVECTION SHOULD BE SCATTERED AT BEST WITH ONLY
MARGINAL INSTABILITY IN PLACE...LESS THAN TODAY. HIGHS IN THE MID
80S...EXCEPT ALONG THE COAST.
-- End Changed Discussion --

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
THE UPPER TROUGH OVER THE MID SECTION OF THE COUNTRY TRANSLATES
EAST THROUGH THE END OF THE WEEK AND THEN OFFSHORE BY THE WEEKEND.
INTERACTION WITH SHORT WAVE ENERGY IN THE NORTHERN BRANCH OF THE
POLAR JET ACROSS EASTERN CANADA WILL AMPLIFY THE TROUGH ACROSS THE
OH VALLEY AND MID ATLANTIC STATES. THIS AMPLIFICATION RESULTS IN
TIMING ISSUES AMONGST THE GLOBAL MODELS...WITH THE OPERATIONAL 12Z
GFS THE SLOWEST AT THE WESTERN END OF THE ENVELOPE. THE ECMWF AND
GGEM ARE THE QUICKEST WITH SWINGING THE FRONT ACROSS THE COAST BY
FRI MORNING. IN FACT...THE GFS CONTINUES TO BECOME MUCH SLOWER
THAN ALL THE GUIDANCE FRI INTO SAT AS THE UPPER LOW CLOSES OFF
APPROACHING THE MID ATLANTIC STATES...TAKING ON A NEGATIVE TILT
MUCH CLOSER TO THE COAST. THIS WOULD RESULT IN A PROLONGED PERIOD
OF POST-FRONTAL RAIN INTO SAT. PREFERENCE AT THIS TIME WAS TO LEAN
TOWARD THE FASTER MODEL CONSENSUS WITH PCPN SHUTTING DOWN FRI
AFT. SUBSEQUENT MODEL TRENDS WILL NEED TO BE CLOSELY MONITORED TO
SEE IF THE FRONTAL SYSTEM SLOWS DOWN EVEN FURTHER.

AS FOR THE SENSIBLE WEATHER...COLD FRONT APPROACHES FROM THE WEST
THU...PASSING ACROSS THE REGION THU NIGHT INTO FRI. HIGH PW
VALUES AND MODERATE INSTABILITY WILL LEAD TO THE DEVELOPMENT OF
WIDESPREAD SHOWERS AND THUNDERSTORMS THAT WORK WEST TO EAST
DURING THIS TIME. THE ISOLATED SEVERE THREAT APPEARS LOW AT THIS
TIME WITH THE LOW-LEVEL JET DISPLACED EAST OF THE AREA AND
MARGINAL DEEP LAYER SHEAR. UNIDIRECTIONAL WIND PROFILES SUPPORT
SOME BOWING LINE SEGMENTS WITH GUSTY WINDS. WET-BULB ZERO VALUES ARE
WARM...SUPPORTING ONLY SMALL HAIL. THE MAIN THREAT LOOKS TO BE
THE POTENTIAL FOR HEAVY RAINFALL...ESPECIALLY IF THE UPPER FLOW
BACKS FURTHER WITH THE AMPLIFICATION OF THE UPPER TROF TO THE
WEST. AVERAGE BASIN RAINFALL SHOULD BE CLOSE TO AN INCH...WITH
LOCALIZED HIGHER AMOUNTS.

A DRIER NW FLOW SET UPS FRI NIGHT WITH STRONG COLD ADVECTION. HIGH
PRESSURE BUILDS ACROSS THE GREAT LAKES AND INTO THE MID ATLANTIC
STATES THROUGH EARLY NEXT WEEK WITH TEMPERATURES SEVERAL DEGREES
BELOW SEASONABLE LEVELS.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
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A NEARLY STATIONARY FRONT WILL REMAIN NORTH ACROSS THE LOWER HUDSON
VALLEY WHILE FARTHER EAST THE FRONT WAS MOVING WESTWARD AS A COLD
FRONT. THE FRONT WILL MAKE IT TO AROUND NEW YORK CITY BY MORNING
BEFORE MOVING BACK NORTH DURING THE MORNING.

STRATUS AND FOG WAS BEGINNING TO MOVE IN FROM THE EAST AND WILL MOVE
INTO THE NYC AREA TERMINALS FROM 08Z TO 10Z. CEILINGS AND
VISIBILITIES BECOME IFR AND AS LOW AS VLIFR AT THE COASTAL TERMINALS
ESPECIALLY AFTER 07Z. CONDITIONS IMPROVE EARLY WEDNESDAY
MORNING...13Z TO 15Z. TIMING OF IMPROVEMENT AND CONDITIONS
UNCERTAIN. WIND WILL BE LIGHT FROM THE SOUTH THROUGH THE NIGHT THEN
INCREASE TO 10 TO 15 KT DURING WEDNESDAY.

SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE AFTER 16Z MAINLY NORTH
AND WEST OF THE NEW YORK TERMINALS.

.OUTLOOK FOR 00Z THURSDAY THROUGH SUNDAY...
.WEDNESDAY NIGHT...SCT SHRA AND TSTMS POSSIBLE. IFR POSSIBLE IN FOG
AND STRATUS.
.THURSDAY-FRIDAY...NUMEROUS SHRA AND TSTMS POSSIBLE. IFR POSSIBLE IN
FOG AND STRATUS.
.SATURDAY...RESIDUAL SHRA BEHIND A COLD FRONT WITH MVFR. BECOMING VFR
WITH NW WINDS INCREASING TO 20-30KT.
.SUNDAY...VFR WITH NW WINDS 20-25KT.
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&&

.MARINE...
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DENSE FOG BEGINNING TO DEVELOP ACROSS THE EASTERN WATERS.
THIS ADVECTION FOG IS EXPECTED TO EXPAND BACK WEST OVERNIGHT.

SHALLOW BACK DOOR COLD FRONT SHOULD BRING SE-E WINDS OVERNIGHT TO
THE ERN-MOST OCEAN WATERS...ALSO LONG ISLAND SOUND AND THE BAYS OF
LONG ISLAND. OTHERWISE...S-SW SUB SCA WINDS SHOULD CONTINUE
THROUGH WED NIGHT. SEAS SHOULD SLOWLY BUILD ON WED...BUT HAVE
UNDERCUT WAVEWATCH TO PREVENT REACHING SCA CRITERIA UNTIL
WEDNESDAY NIGHT. THINKING WITH STRONG INVERSION THAT WIND FORCING
WAS OVERDONE IN THE WW3 FORECAST.

A COLD FRONT WILL MOVE ACROSS THE AREA WATERS FRIDAY MORNING...WITH
HIGH PRESSURE BUILDING THROUGH THE WEEKEND. WINDS COULD BE BELOW
SCA LEVELS BY FRIDAY MORNING...WITH SEAS ON THE OCEAN REMAINING
ABOVE SCA CRITERIA THROUGH MUCH SATURDAY MORNING. UNDERCUT
WAVEWATCH BY A FOOT DURING THIS TIME AS IT WAS SLOWER BRINGING THE
FRONTAL SYSTEM ACROSS THE AREA. THERE IS THOUGH SOME UNCERTAINTY
WITH THE SEAS DUE TO THE TIMING DIFFERENCES AMONGST THE MODELS.
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&&

.HYDROLOGY...
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SLIGHT CHANCE FOR SOME SHOWERS/TSTMS TO ENTER THE AREA LATE
TONIGHT INTO EARLY WED MORNING. SCT SHOWERS/TSTMS LATER WED WILL
BE CAPABLE OF PRODUCING LOCALLY HEAVY RAINFALL...WITH THE BEST
CHANCES NORTH/WEST OF NYC. TOTAL BASIN AVG QPF FOR WED-THU COULD
BE 1/4 TO 1/2 INCH...WITH LOCALLY HIGHER AMTS IN TSTMS.

A MORE ORGANIZED EVENT LATE THU INTO FRI SHOULD PRODUCE AVERAGE
BASIN RAINFALL AMOUNTS CLOSE TO AN INCH...WITH LOCALIZED HIGHER
AMOUNTS. THERE IS THE POTENTIAL FOR TRAINING OF THUNDERSTORMS
WHICH COULD RESULT IN FLASH FLOODING.

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.
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&&

.OKX WATCHES/WARNINGS/ADVISORIES...
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CT...DENSE FOG ADVISORY UNTIL 10 AM EDT WEDNESDAY FOR CTZ011-012.
NY...DENSE FOG ADVISORY UNTIL 10 AM EDT WEDNESDAY FOR NYZ079.
     DENSE FOG ADVISORY UNTIL 10 AM EDT WEDNESDAY FOR NYZ081.
NJ...NONE.
MARINE...DENSE FOG ADVISORY UNTIL 10 AM EDT WEDNESDAY FOR ANZ330-340.
     DENSE FOG ADVISORY UNTIL 10 AM EDT WEDNESDAY FOR ANZ345-350-
     353.
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&&

$$