Severe Thunderstorm Warning 58, NWS New York, NY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE UPTON NY
426 PM EDT THU JUL 19 2007

.SYNOPSIS...
A STRONG UPPER TROUGH WILL MOVE THROUGH THE GREAT LAKES AND
NORTHEAST STATES THROUGH TONIGHT...THEN HEAD INTO NEW ENGLAND ON
FRIDAY. AN ASSOCIATED PRE-FRONTAL TROUGH WILL MOVE THROUGH THE AREA
THIS EVENING AND SPARK STRONG TO SEVERE THUNDERSTORMS INTO THIS
EVENING. A TRAILING COLD FRONT WILL FOLLOW LATE TONIGHT INTO FRIDAY
MORNING. HIGH PRESSURE WILL MOVE IN AT THE SURFACE...BUT A STRONG
DISTURBANCE DIGGING INTO THE BACK SIDE OF THE UPPER TROUGH WILL
EVENTUALLY CARVE OUT A LARGE UPPER LEVEL LOW PRESSURE SYSTEM OVER
THE MID ATLANTIC REGION...WHICH WILL THEN MOVE SLOWLY KEEP
TEMPERATURES NEAR OR JUST A TOUCH BELOW NORMAL THROUGH TUESDAY. MORE
TYPICAL SUMMERTIME HEAT AND HUMIDITY WILL RETURN BY MID WEEK AS THIS
LOW WEAKENS AND MOVES AWAY FROM THE AREA.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
SPC MESOANALYSIS SHOWED SBCAPE ONLY ABOUT 1000 J/KG AND MLCAPE ABOUT
HALF THAT...BUT WITH STRONG EFFECTIVE 0-6 KM SHEAR OF 50-55 KT...0-1
KM SHEAR OF 20-25 KT...AND LOW LCL HEIGHTS...STORMS OVER
PUTNAM/FAIRFIELD HAVE BEEN QUICKLY DEVELOPING STRONG LOW LEVEL
MESOCYCLONES WITH DAMAGING WIND. AN ISOLATED TORNADO CANNOT BE RULED
OUT. ADDITIONAL ACTIVITY MAY DEVELOP SOUTH AND WEST INTO THIS
EVENING...AND ALSO AFFECT NORTHEAST NJ AND NEW YORK CITY...HENCE THE
SEVERE TSTM WATCHES IN EFFECT FOR MOST OF THE CWA EXCEPT ORANGE
COUNTY...LONG ISLAND AND NEARBY COASTAL WATERS. MARINE LAYER SHOULD
KEEP LONG ISLAND AND COASTAL SOUTHEAST CT SAFE SHOULD ANY STORMS MAE
IT TO THE COAST...BUT GIVEN WHAT HAPPENED WITH YESTERDAY/S SPINNING
STORMS CONFIDENCE NOT VERY HIGH HERE. PWAT NEAR 2 INCHES MEANS
STORMS COULD BE CAPABLE OF PRODUCING VERY HEAVY RAIN AS WELL.

ACTIVITY SHOULD WIND DOWN LATE THIS EVENING...BUT STILL COULD SEE
SHOWERS/TSTMS THROUGH THE NIGHT AS SURFACE COLD FRONT STILL WEST OF
THE AREA AND DEEP MOISTURE STILL IN PLACE.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/...
12Z NAM/GFS WERE BOTH MORE OPTIMISTIC FOR FRI MORNING...SO HAVE
GRADUALLY TAPERED DOWN FROM CHANCE MORNING POP TO DRY CONDITIONS
THROUGHOUT BY 18Z.  APCHG SHORTWAVE ROTATING AROUND UPPER TROUGH
LATE FRI AFTERNOON AND EARLY EVE...WITH PRECEDING H8 POSITIVE
THETA-E ADVECTION...SFC TROUGH STILL AROUND AND AREA UNDERNEATH
UPPER JET RIGHT ENTRANCE REGION...LOOKS WORTHY OF A SLIGHT CHANCE
POP MOST PLACES EXCEPT LONG ISLAND AND FAR SOUTHEAST CT.

DRY CONDITIONS RETURN FRI NIGHT THROUGH SUN MORNING. ANOMALOUS UPPER
LOW OVER THE MID ATLANTIC REGION SHOULD SPAWN AN OFFSHORE LOW THAT
WILL STAY WELL SOUTH/EAST OF THE AREA...BUT A WEAK SFC TROUGH
EXTENDING NW FROM THE LOW OVER THE AREA...PLUS COLD POOL ALOFT
ASSOCIATED WITH THE UPPER LOW...MAY SPARK WIDELY SCATTERED
SHOWERS/TSTMS SUN AFTERNOON MAINLY OVER THE INTERIOR.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
ANOMALOUS UPPER LOW AND ASSOCIATED MID LEVEL COLD POOL WILL REMAIN
OVER THE AREA THROUGH AT LEAST TUE...WITH TEMPS NEAR OR JUST A TOUCH
BELOW NORMAL...AND SLIGHT CHANCE OF DIURNALLY DRIVEN WIDELY
SCATTERED CONVECTION EACH DAY. UPPER LOW BEGINS TO WEAKEN/MOVE AWAY
BY WED WHILE BERMUDA HIGH BECOMES RE-ESTABLISHED IN THE WESTERN
ATLANTIC...WITH MORE SUMMERLIKE HEAT/HUMIDITY RETURNING FOR WED/THU.
LATEST ECMWF NOT SOLD ON THIS IDEA AND KEEPS UPPER LOW IN THE AREA
THROUGH THU...SO FORECAST CONFIDENCE FOR WED/BEYOND NOT VERY HIGH.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
PRIMARILY VFR TO MVFR CONDITIONS BEFORE THE BULK OF THE SHOWER
ACTIVITY AND POTENTIAL THUNDERSTORMS LATER ON THIS AFTERNOON AND
EVENING. SHOWERS CURRENTLY AT SWF...WITH ISOLATED SHOWERS INVOF THE
CITY TERMINALS. NONE OF THESE ISOLATED SHOWERS HAVE ANY HISTORY OF
LIGHTNING AS OF YET. I HAVE PUSHED BACK MENTION OF CB FOR THE CITY
TERMINALS TO AROUND 20Z...BUT NOW HAVE BEST CHANCE OF TSRA (IN TEMPO
GROUP) IN THE 23Z-01Z TIME FRAME HERE...AND OCCURRING AND HOUR OR
TWO LATER FARTHER EAST. LOOKING AT MVFR TO IFR CONDITIONS DURING ANY
TSTMS.

FROPA WILL OCCUR IN THE 06Z-09Z TIME FRAME FOR MOST TERMINALS...
ENDING THE THREAT OF ANY CONVECTION. LINGERING SHOWERS ARE STILL
POSSIBLE EAST OF THE CITY INTO EARLY FRIDAY MORNING...BUT NOT
SIGNIFICANT ENOUGH TO MENTION IN TAFS. KISP...HUDSON VALLEY...AND CT
TERMINALS HAVE BEEN KEPT AT MVFR IN BR THROUGH MID-MORNING FRIDAY
EVEN AFTER FROPA. ALTHOUGH WINDS WILL BE OFFSHORE...RAPID LOW LEVEL
DRYING NOT ANTICIPATED. OTHERWISE...VFR CONDITIONS ELSEWHERE
AFTER FROPA.

OUTLOOK FROM 18Z FRIDAY THROUGH SUNDAY...MAINLY VFR CONDITIONS WILL
PREVAIL FOR FRIDAY...WITH LOCALIZED/BRIEF SUB-VFR CONDITIONS
REMAINING POSSIBLE IN ASSOCIATION WITH ISOLATED SHOWER ACTIVITY
FRIDAY AFTERNOON INTO EVENING. OTHERWISE...VFR CONDITIONS EXPECTED
FOR FRI NIGHT THROUGH SUN WITH HIGH PRESSURE ACROSS THE REGION.

&&

.MARINE...
AS S WINDS CONTINUE TO INCREASE WITH THE APPROACH OF THE COLD
FRONT...SEAS WILL GRADUALLY BUILD...RISING TO AN AVG OF 5 FT BY THIS
EVENING...MAINLY E OF FIRE ISLAND INLET. THE SMALL CRAFT ADVISORY
FOR THIS AREA WILL BE MAINTAINED.

AS THE FRONT MOVES OVER THE AREA...THE WIND GRADIENT WILL DECREASE
AND SEAS WILL GRADUALLY SUBSIDE BELOW 5 FT BY FRIDAY AFTERNOON.

THIS FRONT IS FORECAST TO STALL JUST OFFSHORE AS A LOW PRESSURE
SYSTEM DEVELOPS OVER THE SOUTHERN MID ATLANTIC STATES. THIS LOW IS
FORECAST TO TRACK NE DURING FRIDAY AND MOVE SE OF LONG ISLAND DURING
SATURDAY. A PERSISTENT PERIOD OF NE WINDS WILL DEVELOP FRIDAY INTO
SATURDAY...CAUSING SEAS TO GRADUALLY BUILD FROM E TO W ACROSS THE
ATLANTIC OCEAN BY SAT.

HIGH PRES WILL MOVE TOWARD THE REGION MONDAY INTO TUESDAY.

&&

.HYDROLOGY...
DEEP MOISTURE WITH PRECIPITABLE WATER VALUES AROUND 2 INCHES THROUGH
TONIGHT WILL LEAD TO THE POSSIBILITY OF ADDITIONAL HEAVY RAINFALL
DURING THE PERIOD. THERE WILL BE THE POTENTIAL FOR LOCALIZED SMALL
STREAM FLOODING DEPENDING ON WHERE LOCALIZED HEAVY RAINFALL FALLS.
URBAN...POOR DRAINAGE...AND LOW LYING FLOODING WILL ALSO BE POSSIBLE
DURING THIS TIME FRAME.

&&

.EQUIPMENT...
UPPER AIR OPERATIONS MAY RETURN TO SERVICE IN TIME FOR THE 00Z
LAUNCH.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
NY...NONE.
NJ...NONE.
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 PM EDT
     FRIDAY FOR ANZ350-353.

&&

PUBLIC/HYDRO...GOODMAN
AVIATION...JC
MARINE...GC

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