NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Aug 29, 8:30 PM EST, 1 hour 14 minutes earlier.
Area forecast discussion, Aug 29, 8:30 PM EST, 1 hour 14 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
930 PM EDT SAT AUG 29 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE THROUGH THE AREA TONIGHT THEN STALL TO OUR
SOUTH FOR MUCH OF THE FORECAST WHILE HIGH PRESSURE WILL TRY TO
MOVE IN FROM THE NORTHWEST.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
WITH WHAT COULD HAVE BEEN, TODAY ENDED UP TURNING OUT TO BE A PRETTY
NICE DAY AFTER A CLOUDY AND RAINY START, A GOOD PORTION OF THE AREA
SAW SOME BREAKS IN THE CLOUDS BY THE AFTERNOON, WHICH ALLOWED THE
TEMPERATURES TO WARM INTO THE LOW TO MID 80S. SOME ISOLATED TO
SCATTERED SHOWERS HAVE DEVELOPED AND MOVED INTO THE AREA AND SHOULD
CONTINUE INTO THE EVENING AND OVERNIGHT HOURS. A COLD FRONT WILL
MOVE THROUGH OUR AREA TONIGHT WITH SCATTERED SHOWERS, AND POSSIBLY
AN ISOLATED THUNDERSTORM, AHEAD AND ALONG THE BOUNDARY. WHAT WAS
DANNY WILL LIFT TO OUR NORTHEAST TONIGHT AND INTO THE CANADIAN
MARITIMES BY SUNDAY, SO WE SHOULD NOT HAVE ANYMORE EFFECTS FROM THAT.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY NIGHT/...
BY SUNDAY MORNING, THE COLD FRONT SHOULD BE MOVING OFF THE COAST.
THE GFS AND NAM DEVELOP A WEAK WAVE ALONG THE FRONT, BEFORE LIFTING
IT NORTHWARD, WHICH COULD HELP DEVELOP SOME SHOWERS. THE QUESTION IS
WHEN DOES THIS HAPPEN. THE GFS IS FASTER AND HAS IT EARLY IN THE
MORNING, WHILE THE NAM HAS IT LATER IN THE MORNING. ALSO, THERE IS A
SECONDARY SURFACE TROUGH THAT MAY MAKE ITS WAY THROUGH THE AREA
LATER DURING THE DAY. FOR BOTH OF THESE REASONS WE HAVE DECIDED TO
GO WITH A SLIGHT CHANCE OF AN ISOLATED SHOWER OR THUNDERSTORM. EVEN
IF IT TURNS OUT TO BE A CLOUDY AND RAINY START, THINGS SHOULD CLEAR
OUT BY THE AFTERNOON AND COULD WARM UP QUITE NICELY INTO THE LOW TO
MID 80S.
THE FRONT IS FORECAST TO MOVE TO OUR SOUTH AND STALL THERE OVER THE
NEXT SEVERAL DAYS WHILE HIGH PRESSURE TRIES TO BUILD IN FROM THE
NORTHWEST. AT THE SAME TIME, THE MID/UPPER TROUGH REMAINS ENTRENCHED
TO OUR WEST, BEFORE A CLOSED LOW BEGINS TO DEVELOP BY TUESDAY
EVENING. WITH THE PROXIMITY OF THE STALLED FRONTAL BOUNDARY TO OUR
SOUTH AND ANY DISTURBANCES ALOFT THAT MOVE THROUGH THE AREA, THERE
MAY BE SOME SHOWER ACTIVITY FOR THE AREA, MAINLY IN OUR SOUTHERN
ZONES. A WAVE OF LOW PRESSURE MAY DEVELOP ALONG THE STALLED FRONT
LATE MONDAY INTO LATE TUESDAY WHILE A STRONGER SHORT WAVE MAY MOVE
ACROSS THE AREA, WHICH COULD ENHANCE THE POSSIBILITY OF
PRECIPITATION LATE MONDAY INTO TUESDAY.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
EVEN THOUGH HIGH PRESSURE CONTINUES TO TRY TO BUILD IN FROM THE
NORTHWEST, IT LOOKS LIKE THE FRONT WILL HAVE A HARD TIME PUSHING TOO
FAR SOUTH OF THE AREA, AND IT MAY EVEN RETURN BACK NORTHWARD
THURSDAY AS A WAVE MAY DEVELOP ALONG THE BOUNDARY AND LIFT TOWARD
OUR AREA. ALSO, THE CLOSED MID/UPPER LOW WILL SPIN NEAR THE OHIO
RIVER VALLEY THROUGH THURSDAY BEFORE OPENING AND LIFTING INTO THE
NORTHEAST BY FRIDAY. WITH AN AREA OF LOW PRESSURE POSSIBLY
DEVELOPING ALONG THE FRONTAL BOUNDARY, AND ANY SHORT WAVES THAT MOVE
ACROSS THE AREA WITHIN THE SOUTHWEST FLOW ALOFT, THERE IS A CHANE OF
SHOWERS, OR THUNDERSTORMS, FOR A PORTION OF THE AREA THROUGH FRIDAY,
ESPECIALLY THE AREAS FURTHER SOUTH LATE WEDNESDAY THROUGH THURSDAY
LOOKS LIKE THE MOST LIKELY TIME. WITH THE MID/UPPER TROUGH IN PLACE,
TEMPERATURES IN THE EXTENDED COULD START OUT A FEW DEGREES BELOW
NORMAL BEFORE WARMING TO A COUPLE OF DEGREES ABOVE BY THE END OF THE
WEEK ONCE THE TROUGH BEGINS TO LIFT OUT OF THE AREA.
&&
.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
A BROKEN LINE OF SHOWERS AND SOME THUNDERSTORMS FROM NORTHWESTERN
NEW JERSEY TO THE NORTHERN CHESAPEAKE WAS MOVING SLOWLY EASTWARD
THIS EVENING. THE RESPONSIBLE COLD FRONT WILL MOVE SLOWLY TO THE
COAST OVERNIGHT. INSTABILITY IS NOT AS STRONG AS IT WAS, AND SHOULD
LESSEN OVERNIGHT AS WELL. THUNDERSTORMS MENTIONS WERE KEPT IN FOR
EARLY THIS EVENING FOR THE NORTHERN AND CENTRAL TAF SITES, AND
ACTIVITY WAS FURTHER WEST OF KMIV AND KACY AND SHOULD WEAKEN BEFORE
REACHING THEM LATER ON TONIGHT, IF AT ALL.
THERE DOES NOT APPEAR TO BE A LARGE PUSH FOR THIS FRONTAL BOUNDARY
TO SETTLE TOO FAR SOUTH AND EAST LATE TONIGHT AND SUNDAY. THIS WILL
TEND TO KEEP THE LOW-LEVEL MOISTURE AROUND AND WITH THE CLOUDS
THINNING TONIGHT, SOME FOG MAY BECOME A CONCERN. FOG WAS CARRIED
LATE TONIGHT AND EARLY SUNDAY MORNING AT ALL THE TERMINALS, WITH THE
HIGHER VFR VISIBILITY INDICATED AT KPHL. CONFIDENCE IS NOT TOO HIGH
REGARDING THE VISIBILITIES, HOWEVER AT LEAST SOME FOG IS LIKELY.
SOME FORECAST SOUNDINGS INDICATE A SATURATED SHALLOW LAYER OVERNIGHT
AND EARLY SUNDAY MORNING. IF THIS OCCURS, SOME STRATUS MAY RESULT.
AT THIS TIME, WE DID NOT JUMP ON THIS TOO MUCH, GIVEN LOWER
CONFIDENCE, BUT DID GO WITH A FEW CLOUDS IN THE IFR AND MVFR RANGE.
FOR SUNDAY, ANY LOW CLOUDS/FOG ARE EXPECTED TO DISSIPATE BY 14Z AND
GIVE WAY TO SOME CUMULUS. THE FRONT GRADUALLY COMING THROUGH WITH
POSSIBLY A WEAK AREA OF LOW PRESSURE ON IT COULD SPARK A SHOWER OR
THUNDERSTORM. AT THIS TIME, IT IS THOUGHT TO BE ISOLATED, THEREFORE
THEY WERE NOT INCLUDED AT THE TERMINALS AT THIS TIME. A LIGHT TO
CALM WIND WILL INCREASE TO ABOUT 10 TO 15 KNOTS FROM THE WEST
THROUGH THE MORNING AS VERTICAL MIXING BECOMES MORE ESTABLISHED.
THIS VERTICAL MIXING MAY ALLOW FOR SOME GUSTS TO NEAR 20 KNOTS IN
THE AFTERNOON, BUT FOR NOW WE JUST INCREASED THE SUSTAINED WINDS
SOME.
OUTLOOK...
THE AFOREMENTIONED FRONT IS EXPECTED TO STALL TO OUR SOUTH AND EAST
LATER SUNDAY AND LINGER THROUGH WEDNESDAY. A FEW AREAS OF LOW
PRESSURE MAY TRAVEL ALONG THIS FRONT AND COME NEAR PARTS OF OUR AREA
MONDAY INTO TUESDAY. AS OF NOW, IT APPEARS THE ORGANIZED
PRECIPITATION ASSOCIATED WITH THESE WILL REMAIN SOUTH AND EAST OF
OUR TERMINALS. HIGH PRESSURE IS EXPECTED TO GRADUALLY SETTLE INTO
OUR AREA WEDNESDAY AND THURSDAY.
&&
.MARINE...
A WEAK LOW APPEARS TO BE OVER OUR NORTHERN COASTAL WATERS EARLY THIS
EVENING, HOWEVER A WEAK COLD FRONT WILL APPROACH FROM THE WEST
OVERNIGHT. THERE WERE SOME SHOWERS AND THUNDERSTORMS ALONG AND EAST
OF THE COLD FRONT, BUT THESE ARE EXPECTED TO WEAKEN OVERNIGHT. A
CHANCE OF SHOWERS AND THUNDERSTORMS WILL BE KEPT FOR THE EARLY
OVERNIGHT PERIOD FOR THE COASTAL WATERS.
OVERALL, THE WIND DIRECTION LOOKS A LITTLE PROBLEMATIC OVERNIGHT AND
SUNDAY AS A COLD FRONT GRADUALLY SETTLES INTO AND THROUGH OUR AREA.
THIS FRONT WILL KEEP THE PRESSURE GRADIENT RATHER LOOSE BETWEEN
ITSELF AND THE REMNANTS OF TROPICAL STORM DANNY. OVERALL, THOUGH,
THE WINDS WILL BE ON THE LIGHTER SIDE AND GENERALLY A BLEND OF THE
GFS/SREF WAS USED. THE SEAS HAVE INCREASED WITH BUOY 44009 REPORTING
7 FOOT SEAS. HOWEVER, THESE ARE MORE OF A SWELL DUE TO A PERIOD OF
AROUND 9 SECONDS. THESE ARE EXPECTED TO BE AT THEIR PEAK THIS
EVENING BEFORE GRADUALLY SUBSIDING OVERNIGHT AND SUNDAY. THE LATEST
WAVEWATCH DATA IS PRETTY CLOSE TO WHAT IS HAPPENING, THEREFORE THIS
WAS BLENDED WITH CONTINUITY OVERNIGHT INTO SUNDAY. BASED ON THIS,
THE SMALL CRAFT ADVISORY REMAINS IN EFFECT THROUGH THE DAY SUNDAY,
MAINLY FOR HAZARDOUS SEAS.
A COLD FRONT IS FORECAST TO SETTLE ACROSS OUR AREA SUNDAY, BUT THEN
TEND TO STALL JUST TO THE SOUTH AND EAST THROUGH THE FIRST HALF OF
NEXT WEEK. AS SOME WEAK AREAS OF LOW PRESSURE TRACK ALONG IT, THE
BOUNDARY MAY TRY AND LIFT NORTHWARD SOMEWHAT. FOR NOW, THE ORGANIZED
PRECIPITATION IS FORECAST TO STAY SOUTH AND EAST OF OUR WATERS,
HOWEVER THE SOUTHERN WATERS HAVE A BETTER CHANCE OF SEEING SOME
SHOWERS OR THUNDERSTORMS EARLY NEXT WEEK. THE GFS LOOKS OVERDONE
WITH THE PRESSURE GRADIENT TUESDAY NIGHT THROUGH THURSDAY, WHICH IS
DRIVING HIGHER SEAS IN ITS GUIDANCE. GIVEN THE LOWER CONFIDENCE ON
THIS SOLUTION, WE ONLY INCREASED SEAS AROUND A FOOT. THERE LOOKS TO
BE A PRESSURE GRADIENT IN PLACE DUE TO THE STALLED FRONT AND ALSO
HIGH PRESSURE TO THE NORTH, HOWEVER THE STRENGTH OF THIS IS IN
QUESTION. THE HIGH PRESSURE SYSTEM IS EXPECTED TO GRADUALLY SETTLE
INTO OUR AREA WEDNESDAY AND THURSDAY.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT SUNDAY FOR ANZ450>455.
&&
SYNOPSIS...ROBERTSON
NEAR TERM...ROBERTSON
SHORT TERM...ROBERTSON
LONG TERM...ROBERTSON
AVIATION... / GORSE
MARINE... / GORSE