Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 300641
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
241 AM EDT MON MAR 30 2015

.SYNOPSIS...
A FRONTAL BOUNDARY WILL MOVE THROUGH DURING MONDAY, THEN A FAST
MOVING LOW PRESSURE SYSTEM SHOULD SWEEP THROUGH OUR AREA LATE
TUESDAY. HIGH PRESSURE BUILDS INTO THE REGION FOR WEDNESDAY, THEN
MOVES OFFSHORE ON THURSDAY. THE NEXT COLD FRONT WILL ARRIVE LATE
IN THE WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
THE SYNOPTIC SETUP IS COMPRISED OF A FAST FLOW REGIME. THIS WILL
ALLOW A FRONTAL BOUNDARY TO QUICKLY MOVE THROUGH OUR AREA BY MIDDAY.
THIS IS ATTACHED TO LOW PRESSURE THAT WILL TRACK WELL TO OUR NORTH.
THE ASSOCIATED UPPER-LEVEL TROUGH IS FAIRLY STRONG WITH EMBEDDED
SHORT WAVE ENERGY, HOWEVER THERE IS NOT A LOT OF MOISTURE TO WORK
WITH.

THERE ARE SOME HEALTHY LOW-LEVEL JETS AHEAD OF THIS FEATURE. ONE IS
AT 850 MB NEAR 60 KNOTS FROM THE OHIO VALLEY TO THE EASTERN GREAT
LAKES, HOWEVER THIS IS FORECAST TO WEAKEN AS IT TRACKS TO THE NORTH
AND EAST. AT 925 MB, A LOW-LEVEL JET IS SLIDING UP ACROSS THE
DELMARVA AND SOUTHEASTERN NEW JERSEY THIS MORNING. THIS FEATURE
SHOULD WEAKEN SOME THROUGH THE DAY AS IT SHIFTS OFFSHORE DUE TO THE
MAIN SYSTEM LIFTING SO FAR TO OUR NORTH. THESE LOW-LEVEL JETS AND
ASSOCIATED WAA ALOFT IS DRIVING CLOUDINESS ACROSS THE AREA. THIS
SHOULD PERSIST THROUGH AT LEAST THE FIRST HALF OF THE DAY, THEN SOME
THINNING SHOULD TAKE PLACE /ALTHOUGH STRATOCUMULUS MAY HANG ON
LONGER ACROSS THE NORTHWEST ZONES/. THE 925 MB LOW-LEVEL JET APPEARS
TO BE THE MAIN FOCUS FOR SOME ASCENT AND THIS IS WHERE MUCH OF THE
GUIDANCE IS PLACING AN AREA OF LIGHT SHOWERS. THEREFORE, WE WILL
CARRY THE HIGHEST POPS ACROSS THE SOUTHERN ZONES FOR A TIME EARLY
THIS MORNING.

THE FORECAST SOUNDINGS INDICATE LOW-LEVEL DRY AIR, HOWEVER THIS IS
ALLOWING FOR SOME INITIAL EVAPORATIVE COOLING. THEREFORE, SOME SNOW
AND EVEN SOME SLEET HAS BEEN OCCURRING WITH THE INITIAL BAND
ARRIVING FROM THE WEST. THE TEMPERATURES HAVE BEEN INCREASING SOME
PRIOR TO THE PRECIPITATION, THEREFORE ANY SNOW IS EXPECTED TO BE
LIGHT WITH ANY GRASSY ACCUMULATIONS LIMITED.

ONCE THE FRONT SHIFTS EAST THE WINDS SWING AROUND TO THE WEST AND
NORTHEAST FROM ABOUT MIDDAY ON. DESPITE A FRONT MOVING THROUGH, THE
AIRMASS IS EXPECTED TO BE WARMER TODAY COMPARED TO YESTERDAY. THE
FORECAST SOUNDINGS SHOW DECENT BOUNDARY LAYER MIXING DEVELOPING, AND
THEREFORE IT WILL BECOME A BREEZY DAY. AS FOR THE HIGH TEMPERATURES,
WE MAINLY USED AN EVEN GFS/NAM MOS BLEND.

&&

.SHORT TERM /TONIGHT/...
AN UPPER-LEVEL TROUGH IS FORECAST TO SWING ACROSS THE AREA THIS
EVENING. THIS MAY MAINTAIN SOME CLOUDS ESPECIALLY ACROSS THE
NORTHERN AREAS, HOWEVER ENOUGH DRYING SHOULD TAKE PLACE FOR THE SKY
TO CLEAR OUT. THE FAST NORTHWEST FLOW WILL THEN DRIVE THE NEXT SHORT
WAVE /CLIPPER SYSTEM/ ACROSS THE GREAT LAKES LATE. THIS WILL BE
TRACKING ALONG A THERMAL GRADIENT ALOFT WITH SOME DOWNSTREAM WAA
OCCURRING. AS A RESULT, SOME INCREASE IN CLOUDS MAY START TO TAKE
PLACE TOWARD MORNING FROM WEST TO EAST. AS A LOW PRESSURE SYSTEM
MOVES FARTHER AWAY TO OUR NORTHEAST, THE PRESSURE GRADIENT WILL
RELAX AND SO WILL THE MIXING. THEREFORE, THE WINDS ARE EXPECTED TO
DIMINISH FAIRLY QUICKLY IN THE EVENING.

AS FOR THE LOW TEMPERATURES, WE USED MAINLY AN EVEN BLEND OF THE
NAM/GFS MOS.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
STILL CONSIDERABLE UNCERTAINTY WITH THIS FORECAST ESPECIALLY AS
THE SPLIT FLOW PATTERN CONTINUES FOR MUCH OF THE WEEK.

TUESDAY AND WEDNESDAY...THE BIG QUESTION THROUGH THIS PERIOD WILL
BE THE TRACK OF THE FAST MOVING CLIPPER SYSTEM TUESDAY INTO
TUESDAY NIGHT. MOST MODELS BRING THE CENTER OF THE SURFACE LOW
ACROSS DELMARVA AND SOUTHERN NJ, WITH THE EXCEPTION OF THE NAM,
WHICH TAKES A NORTHERN TRACK, BRINGING THE CENTER OF THE LOW
ACROSS NORTHERN NJ. WITH MORE MODEL AGREEMENT ON THE SOUTHERN
TRACK, FORECAST FAVORS THE SOUTHERN TRACK, KEEPING HIGHER POPS
ACROSS THE SOUTH AND FAVORING THE COLDER GUIDANCE FOR HIGHS ON
TUESDAY. BY WEDNESDAY, A SURFACE HIGH MOVES IN FOR A BRIEF
APPEARANCE.

THURSDAY THROUGH SATURDAY...THIS CONTINUES TO BE THE MOST
UNCERTAIN PERIOD OF THE FORECAST. THE GFS AND ECMWF CONTINUE TO
SHOW VAST DIFFERENCES IN THE TIMING AND TRACK OF A PAIR OF LOWS.
THE FIRST LOW OVER THE HUDSON BAY REGION LATE IN THE WORK WEEK.
THE QUESTION WILL BE IF AND WHEN THE ASSOCIATED COLD FRONT WILL
TRACK AS FAR SOUTH AS OUR REGION. THE SECOND LOW THE GFS SHOWS
DEVELOPING OVER THE SOUTHERN HIGH PLAINS BY THURSDAY NIGHT AND
SLIDING EAST JUST SOUTH OF REGION THROUGH SATURDAY, KEEPING A
STATIONARY FRONT SOUTH OF US THROUGH THIS TIME. THE ECMWF ON THE
OTHER HAND...SHOWS THE LOW FILLING AND ESSENTIALLY DISAPPEARING
BY FRIDAY. GIVEN THE UNCERTAINTY, STAYED CLOSE TO THE PREVIOUS
FORECAST. HOWEVER, AT THIS POINT, AM CONCERNED THAT THE ECMWF MAY
BE UNDERESTIMATING LEE SIDE CYCLOGENESIS. WITH BOTH SOLUTIONS
THOUGH, THE END RESULT IS THAT IT WILL BE COOLER (40S AND 50S)
FOR THE WEEKEND.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY, AND SURROUNDING AREAS.

TODAY...MOSTLY VFR CEILINGS. A FRONTAL BOUNDARY WILL CROSS THE
REGION BY ABOUT MIDDAY WITH SOME RAIN OR SNOW SHOWERS. NO
RESTRICTIONS WERE INCLUDED IN THE TAFS AT THIS TIME AS MUCH OF IT IS
EXPECTED TO BE RATHER LIGHT, HOWEVER SOME ICE PELLETS HAVE BEEN
MIXING IN AT THE ONSET WITH THE INITIAL BAND OF SHOWERS MOVING
EASTWARD. SOUTH-SOUTHWEST WINDS 5-10 KNOTS WILL INCREASE TO 15 KNOTS
WITH GUSTS TO ABOUT 25 KNOTS FROM LATE MORNING ON, AND ALSO SHIFT TO
THE WEST AND NORTHWEST.

TONIGHT...VFR, WITH NORTHWEST WINDS QUICKLY DIMINISHING TO ABOUT 4-8
KNOTS DURING THE EVENING.

OUTLOOK...
TUESDAY...CEILINGS AND VISIBILITIES DECREASING TO MVFR, POSSIBLY
IFR, WITH INCOMING RAIN. SNOW POSSIBLE IN HIGHER TERRAIN.

WEDNESDAY...MOSTLY VFR CONDITIONS.

THURSDAY AND FRIDAY...MOSTLY VFR, CHANCE FOR RA AND SLIGHT CHANCE
FOR TSRA. WITH PRECIPITATION, MVFR CONDITIONS POSSIBLE.

&&

.MARINE...
OVERNIGHT - MONDAY...SUB-SCA EXPECTED ACROSS THE WATERS THROUGH
THE LATE EVENING HOURS. THEN WINDS BACK TOWARDS THE SOUTH-
SOUTHWEST AND THE SEAS BEGIN TO INCREASE AGAIN. THE PRESSURE
GRADIENT TIGHTENS WITH SOME ENHANCED MIXING AND GUSTS CLOSE TO 30
KNOTS RIGHT AROUND A COLD FRONT PASSAGE. WINDS VEER TOWARDS THE
WEST- SOUTHWEST BEHIND THE FRONT AND CONTINUE TO GUST FOR A
PERIOD. THE GUSTS ON THE BAY AND OCEAN SHOULD DROP BY MONDAY
EVENING WHILE THE SEAS REMAIN SOMEWHAT ELEVATED ALONG THE
OCEANFRONT. SCA IS GOOD FROM 6Z TONIGHT TO 6Z TUESDAY NIGHT.

OUTLOOK...
TUESDAY...ONCE WAVES DECREASE BELOW 5 FT EARLY TUESDAY MORNING,
WINDS AND SEAS SHOULD REMAIN BELOW SCA CRITERIA FOR THE REST OF
THE DAY.

TUESDAY NIGHT AND WEDNESDAY...WINDS SHOULD REMAIN BELOW SCA
CRITERIA UNLESS THE LOW IS STRONGER THAN FORECAST. SEAS WILL BE
DEPENDENT ON THE WIND FORECAST BUT AT THIS POINT ARE GENERALLY
EXPECTED TO REMAIN NEAR OR BELOW 5 FT.

THURSDAY AND FRIDAY...SOUTHERLY AND SOUTHWESTERLY WINDS WILL
LIKELY INCREASE ABOVE 25 KT FOR AT LEAST PART OF THIS PERIOD. SEAS
WILL LIKELY INCREASE ABOVE SCA CRITERIA AS WELL.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT TUESDAY FOR ANZ450>455.
     SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ430-
     431.

&&

$$
SYNOPSIS...GORSE/JOHNSON
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...JOHNSON
AVIATION...GORSE/JOHNSON
MARINE...HEAVENER/JOHNSON



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