Severe Thunderstorm Warning 84, NWS New York, NY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW YORK NY
900 AM EDT WED JUL 29 2009

.SYNOPSIS...
A COLD FRONT APPROACHING FROM THE LOWER GREAT LAKES AND AN UPPER
LEVEL DISTURBANCE APPROACHING FROM THE CENTRAL APPALACHIANS WILL
SPARK NUMEROUS SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND
TONIGHT IN THE VERY HUMID AND UNSTABLE AIR MASS IN PLACE ACROSS
THE REGION. THE FRONT WILL MOVE SLOWLY EAST OF THE AREA ON
FRIDAY...FOLLOWED BY BUILDING HIGH PRESSURE FRIDAY NIGHT INTO
SATURDAY NIGHT. A WARM FRONT WILL APPROACH FROM THE SOUTH SUNDAY
INTO SUNDAY NIGHT...THEN LIFT NORTH THROUGH THE REGION MONDAY. A
COLD FRONT WILL FOLLOW FROM MONDAY NIGHT INTO TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
LOW STRATUS AND FOG COVERING MOST OF SOUTHERN CT...LONG
ISLAND AND PARTS OF THE NYC METRO AREA...WILL TAKE SOME TIME TO
BURN OFF THIS MORNING AS SUNSHINE IS FILTERED THROUGH BROKEN HIGH
CLOUDS EMANATING FROM UPSTREAM CONVECTION WITH THE MID LEVEL
DISTURBANCE APPROACHING FROM THE CENTRAL APPALACHIANS.
THIS FILTERED SUNSHINE IN COMBINATION WITH A VERY SOUPY AIR
MASS...WITH DEWPOINTS IN THE LOWER 70S...WILL INCREASE
INSTABILITY...WITH AN AXIS OF MLCAPE/SBCAPE OF UP TO 1500/2000
J/KG SETTING UP ACROSS THE LOWER HUDSON VALLEY AND THE NYC METRO
AREA BY AFTERNOON. MEANWHILE DEEP LAYER SW FLOW INCREASES TO 40-45
KT AT H5 AND AROUND 30 KT AT H8 THIS AFTERNOON PER 00Z GFS...
BRINGING MBE VECTORS TO UNDER 10 KT AS PW INCREASES TO AROUND
2 INCHES.

IN A NUTSHELL...THESE INGREDIENTS INDICATE POTENTIAL FOR SEVERE
WX AND FLOODING THIS AFTERNOON MAINLY FROM NYC NORTH/WEST...THEN
EASTWARD INTO MUCH OF THE REST OF THE CWA THIS EVENING.
HAVE RAISED FLASH FLOOD WATCH FOR AREAS THAT HAVE RECEIVED THE
HEAVIEST RAINFALL FROM SCATTERED CONVECTION OVER THE PAST COUPLE
OF DAYS AND WHERE FFG VALUES ARE LOW...AND DEPENDING ON EVOLUTION
OF CONVECTION THIS AFTERNOON...THE WATCH COULD BE EXPANDED TO
INCLUDE THE REST OF THE NYC METRO AREA AND SOUTHWEST CT. SPC HAS
INCLUDED NEARLY ALL THE CWA IN A SLIGHT RISK FOR SEVERE TSTMS.
MAIN THREAT APPEARS TO BE DAMAGING WINDS VIA WET MICROBURSTS...
EVEN AN ISOLATED TORNADO GIVEN STRENGTHENING LOW LEVEL WIND
FIELDS...0-3 KM CAPE OF UP TO 300 J/KG AND LOW LCL HEIGHTS THIS
AFTERNOON AND EARLY EVENING.

CONVECTION SHOULD HANG ON INTO THE NIGHT AS THE SFC FRONT MOVES
EASTWARD...VIA LOW LEVEL CONVERGENCE AHEAD OF THE ADVANCING
FRONT...PLUS MID/UPPER LEVEL SUPPORT VIA H5 VORT AND RIGHT REAR
QUADRANT OF H3 JET STREAK LIFTING NE INTO UPSTATE NY AND
NEW ENGLAND.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
COLD FRONT WILL BE SLOW TO CLEAR THE AREA ON THU...SO HAVE STARTED
OFF WITH LIKELY POP IN THE MORNING FROM NYC EAST...AND THEN STILL
A CHANCE DURING THE AFTERNOON AND EARLY EVENING VIA DAYTIME
HEATING. LATER THURSDAY NIGHT SHOULD BE DRY...WITH RIDGING
BUILDING IN AND LOWS SLIGHTLY ABOVE NORMAL.

LIKELY POP RETURNS FRIDAY AFTERNOON WITH THE APPROACH OF THE NEXT
FRONTAL SYSTEM. ONCE AGAIN...NUMEROUS SHOWERS AND THUNDERSTORMS
COULD PRODUCE VERY HEAVY RAINFALL AND MULTI-MODE SEVERE WX IN A
SETUP SIMILAR TO THAT OF TODAY...AND WITH BETTER UPPER SUPPORT
VIA RR QUAD OF 80-KT H3 JET STREAK JUST TO THE NORTH/WEST OF
THE CWA.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
COLD FRONT MOVES THROUGH SATURDAY MORNING WITH CLOUDS AND SHOWERS
POSSIBLY LINGERING INTO MIDDAY. MUCH SHARPER HIGH PRESSURE RIDGE
FOLLOWS THIS WAVE ON SATURDAY AFTERNOON...SO EXPECT A FAIRLY RAPID
DRYING. H8 THICKNESS VALUES DO NOT DROP ALL THAT MUCH BEHIND THE
FRONT...BUT GIVEN THE SOURCE REGION OF THE AIRMASS WOULD EXPECT A
DROP IN DEWPOINTS.

THE FRONT APPEARS TO NOT MAKE NOT MORE THAN ABOUT 100 MILES SOUTH OF
LONG ISLAND BEFORE STALLING OUT AGAINST THE BERMUDA HIGH.

LEANING TOWARD DRY FORECAST SUNDAY...HOWEVER THERE ARE INDICATIONS
OF A WAVE MOVING ALONG THE STALLED FRONT TO THE SOUTH.

THE 28/12Z GFS WAS DEPICTING A FAIRLY STRONG COLD FRONT MONDAY
NIGHT...WHICH IF IT WORKS OUT WOULD DELIVER NOTICEABLY COOLER AIR
(H10-5 THICKNESS 560 DAM).

TEMPS REMAIN NEAR TO SLIGHTLY BELOW NORMAL DURING THE DAY AND
SLIGHTLY ABOVE NORMAL AT NIGHT.

&&

.AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
LOW LEVEL STRATUS (MAINLY MVFR TO IFR WITH POCKETS LIFR/VLIFR)
ALONG WITH MVFR/VFR FOG (WITH POCKETS LIFR) HAVE OVERSPREAD ALL
TERMINALS (ONLY THE FOG AT KSWF). THIS IS MORE PERVASIVE THAN
GUIDANCE HAD SUGGESTED. BASED ON VERY MOIST LOW LEVELS WITH
LIMITED MIXING EXPECTED UNTIL MID MORNING (AT BEST)...HAVE GONE
AHEAD AND HAVE TAFS REFLECT CONDITIONAL CLIMATOLOGY AT EACH
LOCATION...BASICALLY EXPECT IFR OR WORSE THROUGH MID MORNING THEN
MVFR THROUGH MIDDAY. VFR ONCE MIXED OUT UNTIL CONVECTION ARRIVES
IN THE LATE AFTERNOON.

PER LATEST GUIDANCE HAVE SLOWED DOWN TIMING OF CONVECTION.
APPEARS COULD SEE AN INITIAL BATCH OVER CITY AND WESTERN TERMINALS
EARLY IN THE AFTERNOON (CB IN TEMPO GROUP)...WITH MAIN BATCH OF
CONVECTION OVER WESTERN TERMINALS ARRIVING DURING THE EVENING PUSH
(TEMPO TSRA) AND CONTINUING INTO THE OVERNIGHT. EASTERN TERMINALS
SHOULD NOT SEE ANY CONVECTION/THUNDER UNTIL LATE EVENING AT THE
EARLIEST.

WITH SLOWER ARRIVAL OF CONVECTION...BELIEVE WILL SEE STRATUS/FOG
AT EASTERN TERMINALS THIS EVENING.

AS FOR WINDS...MAINLY LIGHT AND VARIABLE...BECOMING SOUTHEAST 5-10KT
THIS MORNING...INCREASING SLIGHTLY THIS AFTERNOON...THEN VEERING
TO SW OVERNIGHT.

OUTLOOK FOR 12Z THURSDAY THROUGH SUNDAY...
LEFTOVER SUB-VFR CIGS/VSBYS IN THUNDERSTORM ACTIVITY INTO
THURSDAY MORNING. VFR WEATHER CONDITIONS EXPECTED TO RETURN
THURSDAY AFTERNOON/NIGHT. PERIODIC SUB-VFR IN SCATTERED SHOWERS
AND THUNDERSTORMS FRIDAY AFTERNOON AND NIGHT...AND THEN AGAIN ON
SUNDAY.

&&

.MARINE...
SHOWERS AND TSTMS CURRENTLY MOVING ACROSS THE OCEAN WATERS. WILL
UPDATE THE CWF TO INCLUDE MENTION OF STORMS THIS MORNING. HEAVY
RAIN AND FREQUENT LIGHTNING WILL OCCUR WITH THESE STORMS.

PRESSURE GRADIENT SHOULD TIGHTEN ENOUGH OVER THE COASTAL OCEAN
WATERS TO PRODUCE GUSTS TO 25 KT THIS EVENING...PLUS BUILD SEAS TO
4 TO 6 FT...SO HAVE SCA THERE. OVER THE REMAINDER OF THE WATERS
GUSTS SHOULD TOP OUT AT 20 KT...SO HAVE CANCELLED THE SCA OUTSIDE
THE COASTAL OCEAN WATERS. SEAS SHOULD REMAIN UP ON COASTAL WATERS
LIKELY INTO THURSDAY NIGHT (AND POSSIBLY BEYOND)...ONLY HAVE 80
PCT CONFIDENCE THROUGH THURSDAY SO DID NOT EXTEND SCA AT THIS
TIME.

THE NEXT COLD FRONT APPROACHING FRIDAY...THEN CROSSING THE WATERS
FRIDAY NIGHT/SATURDAY MORNING SHOULD AT LEAST PRODUCE SCA WIND
GUSTS OVER THE COASTAL OCEAN WATERS AND POSSIBLY THE REMAINDER AS
WELL (THOUGH NOT CONFIDENT ENOUGH TO PUT GUSTS TO SCA LEVELS OVER
THE NON-COASTAL OCEAN WATERS AT THIS TIME). HIGH PRESSURE BUILDING
IN BEHIND THE FRONT SHOULD ALLOW FOR PRESSURE GRADIENT TO RELAX
ENOUGH...AND HENCE WINDS DECREASE ENOUGH THAT SEAS ON THE COASTAL
OCEAN ZONES SHOULD FALL BELOW SCA LEVELS DURING THE DAY ON
SATURDAY...AND REMAIN SO THROUGH THE REMAINDER OF THE WEEKEND.

&&

.HYDROLOGY...
POTENTIAL FOR WIDESPREAD RAINFALL AMOUNTS BETWEEN 1-2 INCHES...
WITH LOCALIZED TOTALS OF UP TO 4 INCHES...EXISTS THIS AFTERNOON
INTO THURSDAY MORNING...ESPECIALLY NORTH/WEST OF NYC. FLASH FLOOD
WATCH HAS BEEN RAISED FOR AREAS MOST VULNERABLE TO FLASH FLOODING
GIVEN ANTECEDENT RAINFALL/SATURATED GROUNDS AND 1-3 HR FFG VALUES
OF 1-2 INCHES...BUT THE WATCH COULD BE EXTENDED SOUTHWARD TO
INCLUDE THE NYC METRO AREA AND SW CT DEPENDING ON EVOLUTION OF
CONVECTION THIS AFTERNOON.

ANOTHER ROUND OF LOCALLY HEAVY RAINFALL IS POSSIBLE WITH SHOWERS
AND THUNDERSTORMS AHEAD OF A COLD FRONT FRI AND FRI NIGHT.

&&

.CLIMATE...
ON TUE...THE AVERAGE TEMPERATURE AT CENTRAL PARK REACHED ABOVE
NORMAL FOR THE FIRST TIME SINCE JUNE 12TH. SEE PUBLIC INFORMATION
STATEMENT FOR OTHER STATISTICS ON THE UNUSUALLY COOL JULY AND
SUMMER SEASON THUS FAR.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
NY...FLASH FLOOD WATCH FROM 2 PM EDT THIS AFTERNOON THROUGH LATE
     TONIGHT FOR NYZ067>069.
NJ...FLASH FLOOD WATCH FROM 2 PM EDT THIS AFTERNOON THROUGH LATE
     TONIGHT FOR NJZ002>004.
MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM EDT
     THURSDAY FOR ANZ350-353-355.

&&

SYNOPSIS...BG
NEAR TERM...BG
SHORT TERM...BG
LONG TERM...BS
AVIATION...PFM
MARINE...MPS/PFM
HYDROLOGY...BG
CLIMATE...

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NEW YORK NY
1241 PM EDT WED JUL 29 2009

NJZ002>005-011-291745-
BERGEN-EASTERN PASSAIC-ESSEX-UNION-WESTERN PASSAIC-
1241 PM EDT WED JUL 29 2009

...DEVELOPING THUNDERSTORMS WILL IMPACT ESSEX...NORTHERN BERGEN...
NORTHERN UNION AND PASSAIC COUNTIES...

AT 1239 PM EDT...SATELLITE IMAGERY AND NATIONAL WEATHER SERVICE
DOPPLER RADAR INDICATED THAT THUNDERSTORMS WERE RAPIDLY DEVELOPING
NEAR FLORHAM PARK...OR NEAR EAST HANOVER...AND MOVING NORTHEAST AT 15
MPH.

PEOPLE IN ESSEX...NORTHERN BERGEN...NORTHERN UNION AND PASSAIC
COUNTIES...INCLUDING MILLBURN...CALDWELL...FAIRFIELD...WAYNE...
PATERSON...POMPTON LAKES AND HAWTHORNE...SHOULD MONITOR THE WEATHER
SITUATION CLOSELY. LISTEN FOR POSSIBLE WARNINGS AND BE PREPARED TO
TAKE APPROPRIATE ACTION SHOULD SEVERE WEATHER THREATEN.

SMALL HAIL...AND GUSTY WINDS UP TO 50 MPH ARE EXPECTED WITH THESE
STORMS. IN ADDITION...VERY HEAVY RAIN IS OCCURRING WITH THESE
STORMS. THIS COULD CAUSE PONDING OF WATER ON ROADWAYS...AND MINOR
FLOODING OF POOR DRAINAGE AREAS.

LIGHTNING IS ONE OF NATURES NUMBER ONE KILLERS. REMEMBER...IF YOU CAN
HEAR THUNDER...YOU ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING. MOVE
TO SAFE SHELTER IMMEDIATELY.

JMC