Special Marine Warning 37, NWS Philadelphia/Mount Holly

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
330 PM EDT FRI JUN 26 2009

.SYNOPSIS...
A COLD FRONT WILL MOVE THROUGH OUR REGION THIS EVENING, AND
MOVE SLIGHTLY OFF THE COAST LATE TONIGHT. WEAK HIGH PRESSURE WILL
APPROACH FROM THE WEST SATURDAY AND GENERALLY CONTINUE INTO
SUNDAY, BUT A RETURN TO WEAK LOW PRESSURE COULD OCCUR LATER
SUNDAY. HOWEVER, MORE UNSETTLED WEATHER IS POSSIBLE FOR MUCH OF
THE COMING WEEK AS UPPER LEVEL LOW PRESSURE IS EXPECTED TO
APPROACH SLOWLY FROM THE WEST, AND PERIODIC WEATHER DISTURBANCES
ARE FORECAST TO MOVE THROUGH THE REGION.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A COLD FRONT WAS MOVING INTO AN UNSTABLE AND MOIST AIRMASS OVER
OUR REGION THIS AFTERNOON. CONVECTION WAS FIRING AT MID AFTERNOON,
AND A SEVERE THUNDERSTORM WATCH IS IN EFFECT FOR ALL AREAS UNTIL
10 PM THIS EVENING. THE MAIN THREATS ARE DAMAGING WINDS AND LARGE
HAIL, AS CAPES ARE FORECAST TO BE BETWEEN 2000 AND 3000 J/KG, AND
LIFTED INDICES ARE FORECAST BETWEEN MINUS 4 AND MINUS 7. THE MOST
UNSTABLE AIR APPEARED TO BE OVER OUR SOUTHERN NEW JERSEY ZONES,
BUT DEW POINTS HAVE DROPPED OVER MANY AREAS. EVEN SO, AVAILABLE
MOISTURE IS NOT LACKING. TEMPERATURES WERE HELD DOWN A BIT THIS
AFTERNOON BECAUSE OF THE HIGH CLOUDS FROM EARLIER CONVECTION, BUT
INSTABILITY IS RICH REGARDLESS. THE BEST WINDS FROM THE UPPER JET
STREAK WILL BE AFFECTING OUR NORTHERN ZONES THROUGH THIS EVENING
ALTHOUGH THE DYNAMICS ARE NOT AS GOOD FOR SOUTHERN ZONES, THE
THERMODYNAMICS ARE PROBABLY BETTER SOUTH. PERHAPS CELLS WILL BE
MORE SCATTERED SOUTH, WITH MORE ORGANZIED ACTIVITY NORTH AND
CENTRAL.

THE CONVECTION SHOULD WANE BY LATE THIS EVENING, PERHAPS CARRYING
ON AT LOWER LEVELS FOR OUR SOUTHEASTERN AREAS NEARER TO THE FRONT
AS DIURNAL EFFECTS SUBSIDE.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
WITH THE UPPER LOW MOVING THROUGH OUR AREA SATURDAY MORNING, AND
JUST TO THE EAST WITH A NORTHWEST FLOW SATURDAY AFTERNOON, IT WAS
DECIDED TO KEEP IN ISOLATED PRECIPITATION FOR THE DAY, LEAVING
THUNDER OUT OF THE FORECAST IN THE MORNING. THEN, NO WEATHER WAS
MENTIONED SATURDAY NIGHT AND SUNDAY MORNING, BUT A SLIGHT CHANCE
OF CONVECTION WAS KEPT FOR SUNDAY AFTERNOON IN VIEW OF THE
NORTHWEST FLOW AND FORECASTER DISCRETION IT SEEMS THERE IS A
PROPENSITY FOR A FEW CELLS TO DEVELOP WITH LITTLE PROVOCATION
THESE DAYS.

TEMPERATURES WERE GENERALLY HANDLED SIMILARLY BY THE MOS GUIDANCE
SATURDAY AND SUNDAY, SO THE MAXES AND MINS WERE ACCEPTED WITH
ONLY MINOR CHANGES MADE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
MORE UNSETTLED WEATHER IS EXPECTED, MAINLY IN A DIURNALLY-DRIVEN
FASHION, FOR MONDAY ANS TUESDAY. UPPER LEVEL LOW PRESSURE SETTING
UP AND CLOSING OFF OVER THE EASTERN GREAT LAKES IS LIKELY TO SEND
OCCASIONAL DISTURBANCES THROUGH OUR AREA, AND THEN, AS THE UPPER
TROUGH NEARS OUR AREA LATER IN THE WEEK, CONTINUE TO CAUSE AT
LEAST SCATTERED SHOWERS. TIMING IS UNCERTAIN, SO DIURNALLY-
FAVORED AFTERNOONS AND EVENINGS WERE HIGHLIGHTED AT THIS POINT FOR
CONVECTIVE DEVELOPMENT EARLY IN THE WEEK, THEN SHOWERS WERE BROAD-
BRUSHED FOR WEDNESDAY THROUGH FRIDAY. GENERALLY, HPC GUIDANCE,
INCLUDING TEMPERATURES, WAS FOLLOWED.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

THE 18Z TAF FORECASTS WILL INDICATE THE POSSIBILITY OF SHOWERS AND
TSTMS INTO THE EVENING, THEN A BREAK WITH A RETURN CHANCE OF
SHOWERS AROUND MIDNIGHT.

VFR CONDITIONS COVERED THE REGION AT 18Z WITH ISOLATED SHOWERS
DEVELOPING IN CENTRAL PA AND SOME SCATTERED SHOWERS OVER NRN NJ.
THE AREA WITH TSTMS WAS CONFINED TO NY STATE AND EXTREME NRN PA.

ALTHOUGH I CANNOT RULE OUT A POP UP SHOWER OR TSTMS AT ANYTIME THIS
AFTN/EVENING DUE TO THE UNSTABLE AIR IN PLACE. HOWEVER, THE BEST
TIME FOR SHOWERS AND TSTMS IS MID AFTN AT ABE/RDG AND LATE AFTN
AND EARLY THIS EVENING FARTHER SOUTH. COVERAGE OF SHOWERS AND
TSTMS IS EXPECTED TO BE GREATER AROUND ABE/RDG THAN FARTHER TO THE
SOUTH. THE FORECAST AND TIMING OF THE AFTN/EVENING TSTMS IS BASED
ON AN UPPER SHORT WAVE AS DEPICTED BY THE NAM.

THERE SHOULD BE A LULL IN ANY CONVECTIVE ACTIVITY FOR A FEW HOURS
DURING THE EVENING, BEFORE THE THREAT OF SHOWERS RETURNS AS A COLD
FRONT MOVES THROUGH FROM THE NORTHWEST. IF WE HAVE ANY LEFTOVER
UNSTABLE AIR IN PLACE, THIS COULD ALLOW FOR TSTM DEVELOPMENT, BUT
FOR NOW I ONLY MENTION SHOWERS WITH CB DUE TO THE FRONTAL TIMING
AND LOSS OF DAYTIME HEATING.

DRIER AIR RETURNS LATE TONIGHT WITH A NW FLOW DEVELOPING. AREAS
THAT GET RAIN OVERNIGHT COULD SEE SOME LIGHT FOG EARLY IN THE
MORNING. FOR NOW, I ONLY WILL MENTION THE VSBY RESTRICTIONS AS
MVFR AT RDG/ABE AND LEAVE OTHER AREAS VFR SINCE IT WOULD CLEAR OUT
LATER FARTHER SOUTH.

ON SATURDAY...DAYTIME HEATING SHOULD ALLOW GOOD MIXING DURING THE
DAY AND GUSTY NW WINDS OF 20 KTS SHOULD DEVELOP IN THE AFTN. VFR
CONDITIONS ARE FORECAST. AN ISOLATED TSTM COULD DEVELOP IN THE
AFTERNOON BUT MOST AREAS SHOULD MISS THEM.

OUTLOOK...
THERE IS THE THREAT FOR SCATTERED SHOWERS AND TSTMS FROM SUNDAY
THROUGH THE EARLY PART OF THE WEEK WITH THE BEST CHC DURING THE
AFTN OR EVENING HRS.

&&

.MARINE...
A COLD FRONT WILL MOVE THROUGH FROM THE NORTHWEST TONIGHT. SCATTERED
SHOWERS AND TSTMS ARE POSSIBLE THIS EVENING WELL AHEAD OF THE FRONT
AND THEN A SECOND ROUND OF SHOWERS IS POSSIBLE DURING THE MIDDLE OF
THE NIGHT WITH THE ACTUAL COLD FRONTAL PASSAGE.

ANOTHER COLD FRONT IS EXPECTED TO MOVE THROUGH EARLY MONDAY.

EVEN WITH THE TWO COLD FRONTS IN THE FORECAST, WE ARE EXPECTING
CONDITIONS TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH
WEDNESDAY. THE ONLY EXCEPTION IS THE POSSIBILITY OF STRONG WIND
GUSTS WITH THIS EVENINGS THUNDERSTORMS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

SYNOPSIS.../
NEAR TERM.../
SHORT TERM.../
LONG TERM.../
AVIATION...STAUBER
MARINE...STAUBER

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