NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Sep 5, 3:11 PM EST, 1 hour 21 minutes earlier.
Area forecast discussion, Sep 5, 3:11 PM EST, 1 hour 21 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
411 PM EDT WED SEP 5 2012
.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL TRACK ACROSS NEW ENGLAND, WITH AN
ASSOCIATED WEAK COLD FRONT SHIFTING EAST OF OUR AREA THROUGH
TONIGHT. A SECOND COLD FRONT IS THEN FORECAST TO MOVE THROUGH OUR
REGION THURSDAY NIGHT AND FRIDAY BEFORE STALLING. AN AREA OF LOW
PRESSURE THEN DEVELOPS IN THE OHIO VALLEY AND TRACKS EASTWARD
SATURDAY INTO SUNDAY. HIGH PRESSURE IS THEN FORECAST TO SETTLE
ACROSS THE REGION MONDAY THROUGH WEDNESDAY. TROPICAL CYCLONE LESLIE
IS FORECAST TO PASS WELL EAST OF THE MID ATLANTIC COAST LATE IN THE
WEEKEND INTO EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A WEAK FRONT IS GRADUALLY PROGRESSING SOUTHEASTWARD THROUGH OUR
REGION LATE THIS AFTERNOON, WITH SOME SHWR/TSTORM ACTIVITY JUST
AHEAD OF THE FRONT MOVING ACROSS SOUTHERN NJ AND THROUGH PORTIONS OF
THE DELMARVA. SCATTERED CONVECTIVE ACTIVITY IS IN STORE FOR THE NEXT
FEW HOURS INTO THIS EVENING FOR THESE AREAS WITH THE ACTIVITY
GRADUALLY TAPERING OFF FROM NORTHWEST TO SOUTHEAST. AS THE FRONT HAS
CLEARED THE GREATER PHILADELPHIA METRO AREA AND WINDS HAVE SHIFTED
AROUND TO THE NORTHWEST, THE THREAT FOR HEAVY RAINFALL WITH
SHWR/TSTORMS HAS ENDED. THUS, THE FLASH FLOOD WATCH HAS BEEN
CANCELLED WITH THE AFTERNOON FCST PACKAGE. ELSEWHERE, PRECIPITABLE
WATER VALUES REMAIN HIGH ACROSS SOUTHERN NJ AND THE DELMARVA, AND
LOCALLY HEAVY DOWNPOURS ARE POSSIBLE WITH CONVECTIVE ACTIVITY
ASSOCIATED WITH THE FRONT.
THE WEAK FRONT WILL GRADUALLY SETTLE JUST TO THE SOUTH OF OUR AREA
DURING THE OVERNIGHT, WITH ONLY A SLIGHT CHANCE OF PRECIPITATION
MAINTAINED FOR OUR FAR SOUTHERN AREAS DURING THE EARLY MORNING
HOURS. ELSEWHERE, THERE MAY BE ENOUGH REMAINING LOW LEVEL MOISTURE
TO ALLOW FOR SOME PATCHY FOG IN SPOTS, WITH LIGHT WINDS DURING THE
OVERNIGHT. HOWEVER, THIS IS NOT EXPECTED TO BE WIDESPREAD.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
A WEAK SURFACE FRONT WILL REMAIN STALLED JUST TO THE SOUTH OF OUR
AREA DURING THE DAY. MEANWHILE, WEAK HIGH PRESSURE TO OUR WEST WILL
BEGIN TO INFLUENCE THE REGION. MUCH OF THE FORECAST AREA WILL HAVE
DRY WEATHER FOR THE DAY, BUT A FEW ISOLATED/SCATTERED SHOWERS OR
THUNDERSTORMS CANNOT BE RULED OUT DURING THE AFTERNOON TO EARLY
EVENING. WITH THE SURFACE FRONT TO OUR SOUTH AND ENOUGH LINGERING
MOISTURE, FORECAST SOUNDINGS SHOW SUFFICIENT INSTABILITY FOR SOME
CONVECTIVE DEVELOPMENT. THIS IS NOT EXPECTED TO BE WIDESPREAD AT
THIS TIME, AND SLIGHT CHANCE POPS HAVE BEEN MAINTAINED.
&&
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
THE OVERALL SYNOPTIC SETUP IS COMPRISED OF A ZONAL FLOW TO START
WHICH THEN TRANSITIONS TO A LARGE UPPER-LEVEL TROUGH DEVELOPING AND
ARRIVING OVER THE WEEKEND. THE AMPLIFICATION OF THIS UPPER-LEVEL
TROUGH MAY NOT BE ENOUGH TO COMPLETELY CLOSE OFF DUE TO SHORT WAVE
VARIATIONS. AS THIS AMPLIFICATION OCCURS, A SURFACE LOW DEVELOPS
ACROSS THE OHIO AND TENNESSEE VALLEYS THEN MOVES EASTWARD. THIS
MAY TURN OUR WEATHER ACTIVE FOR AT LEAST A PORTION OF THE WEEKEND
BEFORE DRYING ARRIVES DURING THE FIRST HALF OF NEXT WEEK. IS APPEARS
THAT THE MODEL GUIDANCE HAS BACKED OFF OF THE LARGE CLOSED LOW IDEA,
AS SHEARED ENERGY FROM A SYSTEM NEAR THE PACIFIC NORTHWEST THIS
WEEKEND IMPACTS THE NORTHERN PORTION OF THE RIDGING IN THE ROCKIES.
THIS RESULTS IN NO LONGER ALLOWING FOR THE EXTRA DIGGING NEEDED TO
CLOSE OFF THE LOW. OTHERWISE, TROPICAL CYCLONE LESLIE LOOKS TO TRACK
SOMEWHERE BETWEEN THE EAST COAST OF THE U.S. AND BERMUDA, BUT REMAIN
WELL EAST OF OUR COAST LATER SUNDAY INTO MONDAY. WE WENT WITH A
MODEL BLEND THROUGH SATURDAY, THEN MOSTLY HPC GUIDANCE THEREAFTER.
HPC WENT WITH A BLEND OF THE UKMET, GFS AND ECMWF THROUGH MONDAY,
THEN TRANSITIONED TO A BLEND OF THE GFS/ECMWF FOR TUESDAY AND
WEDNESDAY.
FOR THURSDAY NIGHT, AS LOW PRESSURE TRACKS INTO THE CANADIAN
MARITIMES AN ASSOCIATED WEAK COLD FRONT OR WIND SHIFT WILL
ARRIVE. ANY CONVECTION TIED TO THIS FRONT MAY DISSIPATE BEFORE
ARRIVING. WE WILL KEEP SOME SLIGHT CHC TO LOW CHC POPS IN THE
EVENING AS SOME CONVECTION MAY BE LEFTOVER FROM THE DAYTIME.
FOR FRIDAY, A WEAK COLD FRONT SHOULD BE SETTLING SOUTHEAST OF THE
REGION BEFORE STALLING. THE AIRMASS IS FORECAST TO WARM A BIT WITH
850 MB TEMPERATURES RISING TO ABOUT +17C TO +19C, THEREFORE A HOT
DAY IS IN STORE ESPECIALLY FOR THE URBAN CENTERS. AS A TROUGH
AMPLIFIES WELL TO OUR WEST, A WEAK COLD FRONT OR WIND SHIFT LOOKS TO
SETTLE INTO OUR AREA BUT THIS SHOULD TEND TO SLOW OR STALL AS THE
MID AND UPPER FLOW BACKS IN RESPONSE TO THE AFOREMENTIONED TROUGH
AMPLIFYING. THERE DOES NOT APPEAR TO BE A WEALTH OF MOISTURE OR
FOCUS FOR CONVECTION WITH THIS FRONT, THEREFORE JUST WENT WITH
SLIGHT CHC POPS FOR NOW AS SOME ISOLATED ACTIVITY CANNOT BE RULED
OUT. ANY CONVECTION THAT CAN DEVELOP, SHOULD DISSIPATE BY LATE
EVENING WITH IT PROBABLY MAINLY TIED TO DAYTIME HEATING. THE
AFOREMENTIONED BOUNDARY MAY THEN BECOME A WARM FRONT LATE AS WAA
GETS UNDERWAY ON THE EAST SIDE OF THE AMPLIFYING UPPER-LEVEL TROUGH.
FOR SATURDAY THROUGH SUNDAY, A SHARPENING UPPER-LEVEL TROUGH WILL BE
APPROACHING FROM THE WEST SATURDAY. THIS FEATURE WAS FORECAST TO
CLOSE OFF, HOWEVER THE MAIN SHORT WAVE LOOKS TO BE POSITIONED TO NOT
ALLOW THIS TO HAPPEN. AS A RESULT, AN AMPLIFYING TROUGH BECOMES MORE
PROGRESSIVE. THE SHARPNESS OF THE TROUGH WILL HELP TO INDUCE A
SURFACE LOW IN THE OHIO VALLEY WHICH THEN TRACKS TO THE EAST AND
NORTHEAST. A DECENT AMOUNT OF INCREASING ASCENT ARRIVING FROM THE
WEST SHOULD RESULT IN SOME SHOWERS AND EVEN THUNDERSTORMS
DEVELOPING. THE TIMING ON SATURDAY MAY BE SLOW ENOUGH DEPENDING ON
HOW SHARP THE UPPER-LEVEL TROUGH GETS. IN ADDITION, TROPICAL CYCLONE
LESLIE IS FORECAST TO BE TRACKING NORTHWARD BETWEEN THE EAST COAST
OF THE U.S. AND BERMUDA. DEPENDING ON HOW STRONG THIS SYSTEM IS,
SUBSIDENCE ON ITS WEST SIDE MAY HINDER CONVECTIVE DEVELOPMENT ACROSS
A PART OF OUR AREA. AS A RESULT, WE SLOWED DOWN THE POPS SOME WITH
MORE OF A FOCUS ACROSS THE WESTERN ZONES IN THE AFTERNOON.
THE ENTIRE SYSTEM THEN MOVES IN SATURDAY NIGHT WITH A HIGHER CHANCE
OF SHOWERS AND PERHAPS SOME THUNDER. A PLUME OF HIGHER PW VALUES
NEAR 2.0 INCHES IS FORECAST TO MOVE ACROSS OUR AREA LATE IN THE DAY
SATURDAY AND AT NIGHT. THIS MAY RESULT IN SOME LOCALLY HEAVY
RAINFALL. THIS SYSTEM MAY BE STEADY IN ITS FORWARD MOTION, ALTHOUGH
THE 12Z ECMWF IS A LITTLE SLOWER IN CLEARING IT ON SUNDAY. WE
FAVORED LOW END LIKELY POPS FOR THE FIRST HALF OF SATURDAY NIGHT,
THEN TAPERED TO CHC. THE COLD FRONT SHOULD BE CLEARING THE COAST
SUNDAY MORNING WITH PERHAPS SOME LINGERING SHOWERS SUNDAY AS THE
TROUGH AXIS ARRIVES.
FOR MONDAY THROUGH WEDNESDAY, THE UPPER-LEVEL TROUGH TENDS TO LIFT
OUT DURING THIS TIME FRAME ALLOWING HIGH PRESSURE TO EVENTUALLY
SETTLE RIGHT OVER OUR REGION. THIS SURFACE HIGH MAY THEN BEGIN
SHIFTING TO OUR SOUTH AND EAST DURING WEDNESDAY WITH THE POTENTIAL
FOR A WARM FRONT ORGANIZING WELL TO OUR WEST. DUE TO A NORTHERLY
FLOW AND A COOLER AIRMASS, TEMPERATURES WILL BE ON THE LOWER SIDE
ALONG WITH DEW POINTS MAINLY IN THE 50S.
&&
.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
SHWR/TSTORMS ASSOCIATED WITH A WEAK FRONT ARE PUSHING SOUTHEASTWARD
THROUGH PORTIONS OF SOUTHERN NJ AND DELAWARE. THIS ACTIVITY WILL
LIKELY REACH KACY AND KMIV BETWEEN 20Z AND 23Z. ELSEWHERE, THE FRONT
AND ASSOCIATED CONVECTIVE ACTIVITY IS ALREADY TO THE SOUTH OF OUR
OTHER TERMINALS, AND VFR CONDITIONS ARE EXPECTED FOR THESE AREAS
THROUGH THE EVENING.
WINDS WILL GRADUALLY DIMINISH AND BE UNDER 10 KNOTS FOR ALL AREAS
DURING TONIGHT. WITH THE LIGHT WINDS AND ENOUGH LINGERING LOW LEVEL
MOISTURE, SOME LOW CLOUDS OR PATCHY FOG MAY BE POSSIBLE DURING THE
EARLY MORNING HOURS AND UP THROUGH DAYBREAK. THIS IS HINTED AT IN
THE TAFS AND WILL BE REVISITED BY THE NEXT SHIFT.
VFR AND SOME MID-LEVEL CLOUDS EXPECTED THURSDAY, WITH WINDS AT OR
UNDER 10 KNOTS. ISOLATED SHWR/TSTORM ACTIVITY MAY BE POSSIBLE IN THE
AFTERNOON, BUT IS NOT IN THE TAFS AT THIS TIME.
OUTLOOK...
THURSDAY NIGHT THROUGH FRIDAY NIGHT...MOSTLY VFR. A SHOWER OR
THUNDERSTORM IS POSSIBLE THURSDAY EVENING AND AGAIN FRIDAY
AFTERNOON, HOWEVER THE COVERAGE LOOKS LIMITED. LOCALIZED EARLY
FRIDAY MORNING FOG IS POSSIBLE.
SATURDAY THROUGH SUNDAY...TIMES OF SUB-VFR CONDITIONS POSSIBLE
ESPECIALLY WITH SOME SHOWERS AND THUNDERSTORMS. THE GREATER CHANCE
APPEARS TO BE LATE SATURDAY AFTERNOON AND AT NIGHT.
MONDAY...VFR WITH POSSIBLY A GUSTY NORTHERLY WIND.
&&
.MARINE...
A SMALL CRAFT ADVISORY WILL CONTINUE FOR OUR WATERS /THROUGH THURSDAY
NIGHT/, WITH A LONG PERIOD SOUTHEASTERLY SWELL. WAVE HEIGHTS WILL
CONTINUE TO BE IN THE 4 TO 6 FOOT RANGE. MEANWHILE, WAVE HEIGHTS ON
DELAWARE BAY ARE FORECAST TO BE MAINLY IN THE 1 TO 3 FOOT RANGE.
WINDS ON OUR WATERS WILL AVERAGE BETWEEN 10 TO 15 KNOTS THROUGH
TONIGHT AND THURSDAY.
OUTLOOK...
THE WINDS ARE ANTICIPATED TO REMAIN UNDER SMALL CRAFT ADVISORY
CRITERIA THURSDAY NIGHT AND FRIDAY AS A WEAK COLD FRONT SETTLES
THROUGH. THE NEXT FRONT AND LOW PRESSURE SYSTEM ARRIVES LATER
SATURDAY AND SHOULD CLEAR THE REGION SUNDAY MORNING. HIGH PRESSURE
WITH A NORTHERLY FLOW THEN SETTLES IN FOR LATER SUNDAY AND EARLY
NEXT WEEK. THE NORTHERLY FLOW OF COOLER AND DRIER AIR OVER THE
WARMER WATERS MAY ALLOW FOR THE WINDS TO INCREASE TO NEAR ADVISORY
LEVELS FOR A TIME EARLY NEXT WEEK. OTHERWISE, LONG PERIOD SWELLS
WILL LIKELY CONTINUE INTO EARLY NEXT WEEK ON THE OCEAN. THESE WILL
BUILD SOME MORE DUE TO DISTANT TROPICAL CYCLONE LESLIE, AND FOR NOW
THE SMALL CRAFT ADVISORY WAS EXTENDED THROUGH THURSDAY NIGHT. THE
CONDITIONS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA ON
DELAWARE BAY /EXCEPT PERHAPS SOME GUSTINESS LATE SUNDAY AND MONDAY/,
WITH SOME HIGHER SWELLS NEAR THE MOUTH OF THE BAY.
&&
.RIP CURRENTS...
A HIGH RISK OF RIP CURRENTS CONTINUES THROUGH TONIGHT.
LONG PERIOD SWELLS FROM DISTANT TROPICAL CYCLONE LESLIE WILL
CONTINUE TO AFFECT OUR ATLANTIC COAST THROUGH EARLY NEXT WEEK. THE
BUILDING OF THE SWELLS WITHIN THE SURF ZONE WILL CONTINUE TO RESULT
IN A MODERATE TO HIGH RISK OF RIP CURRENTS FOR THE NEXT SEVERAL
DAYS. DEPENDING ON THE STRENGTH OF LESLIE AND HOW HIGH THE SEAS GET,
A HIGH SURF ADVISORY MAY BE NEEDED LATER IN THE WEEKEND INTO EARLY
NEXT WEEK.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...HIGH RIP CURRENT RISK UNTIL 10 PM EDT THIS EVENING FOR NJZ014-
024>026.
DE...HIGH RIP CURRENT RISK UNTIL 10 PM EDT THIS EVENING FOR DEZ004.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR ANZ450>455.
&&
SYNOPSIS...GORSE
NEAR TERM...KLINE
SHORT TERM...KLINE
LONG TERM...GORSE
AVIATION...GORSE/KLINE
MARINE...GORSE/KLINE
RIP CURRENTS...GORSE