NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Sep 9, 7:20 AM EST, 20 minutes earlier.
Area forecast discussion, Sep 9, 7:20 AM EST, 20 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
820 AM EDT TUE SEP 9 2008
.SYNOPSIS...
A COLD FRONT WILL MOVE SOUTHEAST FROM THE GREAT LAKES REGION AND
CROSS THE REGION LATE THIS AFTERNOON AND EARLY TONIGHT. COOL HIGH
PRESSURE WILL THEN DOMINATE THE WEATHER WEDNESDAY AND THURSDAY
THURSDAY BEFORE SLIDING OFF TO THE EAST ON FRIDAY. A COUPLE OF
FRONTAL SYSTEMS WILL THEN CROSS THE REGION THROUGH NEXT WEEKEND
AND EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AN AREA OF SHOWERS AND THUNDERSTORMS EXTENDED FROM SOUTHERN NEW YORK
STATE ACROSS SUSSEX COUNTY NJ INTO CARBON AND MONROE COUNTIES IN PA
AND SOUTHWESTWARD (MAINLY JUST TO THE W OF OUR CWA). THE AREA OF
PRECIPITATION IS MOVING TO THE NE, BUT APPEARS TO BE MAKING MORE NWD
PROGRESS THAN EWD. NEVERTHELESS, DUE TO ITS PROXIMITY AND SOME
DECENT RAINS OVER THE POCONOS ALREADY, HAVE UPPED POPS ACROSS NERN
PA AND NRN NJ. MADE A FEW ADJUSTMENTS TO CLOUD COVER.
OTHERWISE...
A COLD FRONT DROPPING DOWN FROM THE NW SHOULD REACH PHL THIS
EVENING. THIS FRONT ALONG WITH JET INDUCED DYNAMICS AND
INSTABILITY WILL ALLOW SHOWERS AND TSTMS TO FORM AND MOVE THROUGH
THE REGION.
THE STORM PREDICTION CENTER HAS PLACED THE ENTIRE AREA UNDER A
SLIGHT RISK FOR SEVERE THUNDERSTORMS. THIS IS SUPPORTED BY FCST
CAPES FROM THE GFS BUFR DATA OF 2000-3500 G/KG, THEN NAM ALSO HAS
HIGH CAPES FCST, BUT NOT QUITE AS HIGH AS FROM THE GFS. ALSO,
THERE WILL BE A JET MOVING BY TO THE NORTH, PUTTING THE REGION IN
THE FAVORED RIGHT REAR QUADRANT. AN LASTLY, WE HAVE H8 WINDS OF 30
TO 40 KTS. ALL-IN-ALL, THIS SUPPORTS THE SLIGHT RISK FCST BY SPC.
HOWEVER, ALL IS NOT THAT SIMPLE. WE DO HAVE COMPLICATING FACTORS.
FIRST, IT IS SEPTEMBER AND CLOUDS CAN EASILY LIMIT HOW WARM WE GET
TODAY. THE PREVIOUSLY MENTIONED LOW LEVEL JET AROUND 925 MB HAS
ALLOWED CLOUDS TO DEVELOP THROUGH MOST OF THE REGION AND HAS
ALLOWED SHOWERS/TSTMS TO FORM TO THE WEST. IF THEY MOVE AND BECOME
WIDESPREAD FARTHER TO THE EAST, THE THREAT OF SVR WILL BE LESS.
AS THE CAPE AVBL FOR TSTMS WILL BE SPREAD THROUGH MORE CONVECTIVE
CELLS, THEREBY LIMITING THEIR SEVERITY.
NOW THAT I GAVE THE PLUSES AND MINUSES ABOVE, I DO THINK SEVERE IS
POSSIBLE, ESPECIALLY CONSIDERING THE WINDS ALOFT AND JET
ASSOCIATED DYNAMICS, BUT CONFIDENCE IS NOT HIGH. EVEN SO, I WILL
KEEP THE ENHANCED TSTM WORDING IN THE ZFP.
LASTLY, THE GRIDDED FFG FROM RFC SHOWS SOME AREAS THAT ONLY NEED 1
INCH OF RAIN IN 1 HR TO GET FLOODING. THESE LOW VALUES ARE IN THE
AREAS THAT GOT THE MOST RAIN FROM HANNA.
I DONT EXPECT STATIONARY OR SLOW MOVING TSTMS TODAY DUE TO THE
STRONG WINDS ALOFT, BUT IF TSTMS DO DECIDE TO TRAIN, THEN FLOODING
IS POSSIBLE. I WILL LET THE DAY CREW RE-EVALUATE AND ISSUE AN FFA
IF NEEDED.
AS FAR AS TEMPS GO, I WENT WITH A BLEND OF THE MET/MAV NUMBERS.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
I EXPECT THE FRONT TO MOVE OFF THE COAST BY MIDNIGHT WITH TSTM
ACTIVITY MOVING EAST WITH THE FRONT. COOL HIGH PRESSURE THEN
BRINGS COOLER AND DRIER AIR TO THE REGION LATE TONIGHT. HOWEVER,
THE FLOW BECOMES NE OVER THE FAR SOUTHERN ZONES AND THE DRY AIR
COULD TEMPORARILY BE DLAD THERE AND SHOWERS MIGHT LINGER INTO WED
MORNING. ONCE THE DRY AIR ARRIVES, SKIES WILL CLEAR AND REMAIN
MOSTLY CLEAR THROUGH THURSDAY. THIS AIRMASS IS VERY COOL AS
IDENTIFIED BY THE 1000-850 THICKNESSES OF 1340 NORTH TO 1375 SOUTH
WED AM. THE MAV MINS LOOK OK OR SLIGHTLY HIGH CONSIDERING THE CAA
LATE TONIGHT. FOR WEDNESDAY, IT WILL FEEL SOMEWHAT LIKE AUTUMN AND
TEMPERATURES SHOULD ONLY REACH THE LOW 70S WHILE REMAINING THE MID
TO UPPER 60S IN THE POCONOS. THE LOWS WED NIGHT WILL BE MOSTLY IN
THE 40S, EXCEPT FOR SOME LOWER AND MIDDLE 50S EXTREME SOUTH AND
ALONG THE COAST. THURSDAY SHOULD SEE TEMPS COOL ONCE AGAIN WITH
READINGS SIMILAR OR SLIGHT ABOVE WED.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
THE HIGH THAT WILL HAVE BROUGHT THE COOL DRY WEATHER TO THE AREA
FOR WED AND THURSDAY WILL MOVE OFFSHORE FRIDAY. THIS WILL ALLOW
MOISTURE TO RETURN TO THE REGION DURING FRIDAY. THEN A SERIES OF
FRONTAL SYSTEMS WILL MOVE OVER THE REGION AND STALL THROUGH
MONDAY, MEANING POSSIBLE SHOWERS EACH DAY. THUNDERSTORMS WERE
INCLUDED ONLY FOR SUNDAY AS THAT IS THE TIMEFRAME WHEN THE AIRMASS
LOOKS WARMEST AND MOST UNSTABLE. OTHERWISE, THE HPC FCST HAS BEEN
ACCEPTED.
&&
.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
AN APPROACHING COLD FRONT WILL CAUSE A DOWNTURN IN FLYING CONDITIONS
DURING TODAY. IN FACT, THERE ARE EVEN SOME HINTS THAT THERE COULD BE
SOME SHOWERS THIS MORNING OVER OUR CENTRAL AND NORTHWESTERN AREAS,
BUT THIS WILL BE TRANSPARENT IN THE TAFS FOR NOW. SCATTERED TO
BROKEN STRATOCUMULUS HAD FORMED OVER THE CENTRAL AND NORTHWESTERN
TAF SITES AS OF 06Z, APPARENTLY IN RESPONSE TO WARM ADVECTION LIFT
ASSOCIATED WITH A LOW LEVEL JET. THESE SHOULD TEND TO REMAIN ABOVE 3
THOUSAND FEET, BUT THERE MAY BE A FEW LOWER CEILINGS FLOATING AROUND
EARLY THIS MORNING. OTHERWISE, THESE STRATOCUMULUS SHOULD TEND TO
BREAK UP SOMEWHAT AFTER SUNRISE. THEN, THE MORE SIGNIFICANT CLOUDS,
AS WELL AS SHOWERS AND THUNDERSTORMS, APPEAR TO BE COMING IN FOR THE
AFTERNOON. THE GFS IS STILL A LITTLE FASTER THAN THE NAM, BUT
FRONTAL PASSAGE ALONG THE LOWER DELAWARE RIVER VALLEY LOOKS LIKE 22Z
TO 23Z OR SO, WITH LITTLE OR NO PRECIPITATION AND GRADUAL CLEARING
IN THE WAKE OF THE FRONT THROUGH 02Z TO 04Z. CONDITIONS WILL LOWER
TO MARGINAL VFR, AND LOCALLY IFR, IN CONVECTION THIS AFTERNOON, WITH
VFR CONDITIONS RETURNING THIS EVENING AND PERSISTING OVERNIGHT.
FOR THE OUTLOOK BEYOND 12Z TUESDAY, BUILDING HIGH PRESSURE WILL LEAD
TO VFR FLYING WEATHER WEDNESDAY THROUGH FRIDAY. ANOTHER FRONT IS
SHOWN BY THE MODELS TO APPROACH FRIDAY, WITH LOWER CONDITIONS AT
TIMES POSSIBLE AS EARLY AS FRIDAY NIGHT, PERHAPS PERSISTING SATURDAY
AND MAYBE EVEN INTO SUNDAY. TROPICAL WEATHER MAY INVADE THE AREA
WITH THE REMNANTS OF IKE EARLY NEXT WEEK, IF THE 00Z GFS CAN BE
BELIEVED THIS FAR OUT.
&&
.MARINE...
A SHARP LATE SUMMER (OR EARLY AUTUMN, IF YOU PREFER) COLD FRONT WILL
APPROACH THE COAST FROM THE NORTHWEST TODAY AND PASS OFF THE COAST
LATE TODAY AND THIS EVENING. CONDITIONS MAY APPROACH SMALL CRAFT
ADVISORY CRITERIA TODAY. THE NAM 925 WINDS ARE A TOUCH STRONGER THAN
THE GFS. WELL SIDE WITH THE GFS, BUT EVEN SO, WELL MENTION A FEW
GUSTS TO 25 KT ON THE OCEAN TODAY.
WITH A NORTH TO NORTHEAST FLOW WEDNESDAY, WAVEWATCH HAS BUILT SEAS
TO 5 FEET. ITS TRUE THAT THE GRADIENT SEEMS TO RELAX IN THE
AFTERNOON A BIT, BUT WITH A NORTH TO NORTHEAST FLOW OF 15 TO 20
KNOTS, WITH GUSTS UP TO 25 KNOTS, WAVES MAY MAKE IT TO 5 FEET.
BEYOND WEDNESDAY, HIGH PRESSURE SHOULD SUPPORT MARINE ACTIVITIES
WEDNESDAY AND THURSDAY, AND PROBABLY INTO FRIDAY AS WELL.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 6 PM EDT WEDNESDAY FOR
ANZ431-450>455.
&&
SYNOPSIS...STAUBER
NEAR TERM...STAUBER
SHORT TERM...STAUBER
LONG TERM...STAUBER
AVIATION...
MARINE...