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Area Forecast Discussion
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000
FXUS61 KPHI 181611
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1211 PM EDT THU SEP 18 2014

.SYNOPSIS...
A WEAK FRONTAL BOUNDARY WILL MOVE THROUGH OUR AREA THIS AFTERNOON
AND EVENING. HIGH PRESSURE WILL THEN BUILD IN TONIGHT INTO FRIDAY,
BEFORE SHIFTING OFFSHORE FRIDAY NIGHT. A WARM FRONT WILL LIFT TO
OUR NORTHWEST SATURDAY, THEN A COLD FRONT IS EXPECTED TO ARRIVE
LATE SUNDAY INTO MONDAY. THIS FRONT WILL SETTLE TO OUR SOUTH AND
EAST DURING MONDAY, THEN AN EXPANSIVE AREA OF HIGH PRESSURE IS
SCHEDULED TO BUILD IN FOR TUESDAY AND WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WITH THE MIDDAY UPDATE, WE ADDED SOME ISOLATED SHOWERS TO THE
FORECAST FOR THE NEXT COUPLE OF HOURS ACROSS PORTIONS OF FAR
SOUTHEASTERN PENNSYLVANIA, FAR NORTHERN DELAWARE, AND CECIL COUNTY
MARYLAND. LATEST RADAR IMAGERY SHOWS A SMALL AREA OF LIGHT SHOWERS
AND SPRINKLES HOLDING TOGETHER AND SLOWLY MOVING EAST INTO THESE
AREAS. IN ADDITION, HOURLY TEMPS AND DEWPOINTS WERE ALSO TWEAKED
THROUGH THE AFTERNOON USING THE LAV/LAMP GUIDANCE TO ACCOUNT FOR
LATEST OBSERVATIONS AND TRENDS. 

OTHERWISE, THE MID-ATLANTIC IS LOCATED TOWARD THE BASE OF AN
UPPER TROUGH AS SEEN ON WATER VAPOR SATELLITE IMAGERY. THIS LARGE-
SCALE TROUGH IS ASSOCIATED WITH AN UPPER LOW LOCATED JUST TO THE
EAST OF HUDSON BAY. A COLD FRONT STRETCHING FROM THE GULF OF ST
LAWRENCE SOUTHEASTWARD INTO UPSTATE NY WAS RATHER DIFFUSE ON THE
13Z SFC ANALYSIS. THE COLD FRONT WILL MOVE SOUTHWARD INTO THE MID-
ATLANTIC REGION THIS AFTERNOON.

12Z IAD, APG AND OKX SOUNDINGS ALL OBSERVED A SHALLOW SATURATED 
LAYER BETWEEN 800-700 MB WITH MOISTURE TRAPPED BELOW THE MID-LEVEL 
SUBSIDENCE INVERSION. MODEST LIFT ASSOCIATED WITH A SHORTWAVE TROUGH 
HAS LEAD TO A BAND OF BKN-OVC STRATOCU OVER EASTERN PA, NORTHWEST NJ 
AND THE EASTERN MD SO FAR THIS MORNING. TRIED TO TIME EASTWARD 
PROGRESSION OF THE TROUGH AND ASSOCIATED STRATOCU IN HOURLY SKY 
GRIDS WITH THE MORNING UPDATE. LATEST RAP MODEL, WHICH HAD
INITIALIZED WELL WITH CURRENT CLOUD COVER, HANGS ON TO THE MORNING
CLOUD THE LONGEST INTO THE AFTERNOON OVER SOUTHEASTERN PA AND THE
DELMARVA.

FORECAST MAX TEMPS TODAY IN THE MID 70S ARE ONLY A COUPLE OF DEGREES 
BELOW CLIMO.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
THE MID-LEVEL TROF AXIS MOVES OFF THE COAST THIS EVENING. A SURFACE 
HIGH BEHIND THE COLD FRONT BEGINS TO BUILD IN ACROSS THE AREA. 

TEMPERATURES WILL SETTLE IN THE LOWER 40S ACROSS THE SOUTHERN 
POCONOS TO THE MID 50S ACROSS THE COASTAL PLAIN. THIS IS A FEW 
DEGREES BELOW NORMAL.

COULD BE A BIT MORE CLOUDINESS ACROSS THE SOUTHERN ZONES, BUT NO 
PRECIPITATION IS EXPECTED. SOME PATCHY FOG IS POSSIBLE TOWARD 
MORNING.

NORTHWEST WINDS ON THE LIGHTER SIDE WILL SHIFT OUT OF THE NORTH OR 
NORTHEAST BY THE FRIDAY SUNRISE.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
THE OVERALL SYNOPTIC SETUP IS COMPRISED OF THE FLOW BECOMING MORE 
ZONAL FRIDAY ACROSS THE NORTHERN HALF OF THE NATION. SOME RIDGE 
DEVELOPMENT THOUGH OUT WEST LOOKS TO ALLOW A SHORT WAVE TO DIVE INTO 
THE MIDWEST SATURDAY, WHICH RESULTS IN A TROUGH AMPLIFYING ACROSS 
THE GREAT LAKES AND NORTHEAST SUNDAY THROUGH MONDAY. THIS TROUGH MAY 
THEN START TO LIFT OUT LATE TUESDAY. IT APPEARS THE MAIN FRONTAL 
PASSAGE OCCURS SUNDAY NIGHT INTO MONDAY, THEN AN EXPANSIVE SURFACE 
HIGH IS SCHEDULED TO BUILD ACROSS THE REGION TUESDAY AND WEDNESDAY. 
WE USED A GENERAL MODEL BLEND FOR FRIDAY THROUGH SUNDAY, THEN 
BLENDED IN THE 00Z WPC GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE 
THEN MADE AFTER ADDITIONAL COLLABORATION WITH OUR SURROUNDING 
OFFICES.

FOR FRIDAY...STRONG SURFACE HIGH PRESSURE SHOULD BE SHIFTING OFF THE 
NEW ENGLAND COAST WITH OUR LOW-LEVEL FLOW TURNING EAST AND 
SOUTHEAST. THERE IS SOME MOISTURE FORECAST TO BE LINGERING WELL 
OFFSHORE ESPECIALLY TO OUR SOUTHEAST, AND THE ONSHORE FLOW INTO OUR 
AREA MAY RESULT IN SOME CLOUDINESS ESPECIALLY AT NIGHT. THE 
POTENTIAL COMPLICATION IS THAT THE LOW-LEVEL FLOW MAY ACTUALLY VEER 
TO MORE SOUTHEAST OR SOUTH THROUGH FRIDAY NIGHT, FOCUSING AN 
INCREASE IN MOISTURE NORTHWEST OF THE FALL LINE. IT IS HERE WHERE 
PERHAPS SOME STRATUS AND/OR FOG DEVELOPS AS THE LOW-LEVEL MOISTURE 
POOLS BENEATH AN INVERSION. AS OF NOW, NOT QUITE SURE HOW MUCH 
STRATUS DEVELOPS DUE TO SOME QUESTION ON HOW QUICK THE LOWER LEVELS 
MOISTEN UP. FOR NOW, WE INCREASED THE CLOUDS ESPECIALLY AT NIGHT A 
BIT MORE. THE COMBINATION OF A NEW AIRMASS AND THE ONSHORE FLOW 
SHOULD RESULT IN A COOL DAY ACROSS THE CWA, AND POTENTIALLY BREEZY 
ALONG THE COAST.

FOR SATURDAY AND SUNDAY...HIGH PRESSURE BECOMES ELONGATED INTO THE 
MID ATLANTIC AS IT WEAKENS AND SHIFTS FARTHER OFFSHORE. THIS OCCURS 
AS SOME WAA GETS UNDERWAY AHEAD OF THE NEXT SYSTEM AND HEIGHTS RISE 
SOME. THIS SHOULD RESULT IN A NORTHBOUND WARM FRONT THAT MOSTLY 
SLIDES JUST TO OUR NORTHWEST, AND WARMER AIR ARRIVES ACROSS OUR CWA 
ESPECIALLY SUNDAY WITH A MORE SOUTHWESTERLY LOW-LEVEL FLOW. A SHORT 
WAVE DIVING ACROSS THE GREAT LAKES WILL DRIVE A SURFACE LOW 
EASTWARD. THE AMPLIFICATION OF THE UPPER-LEVEL TROUGH SHOULD TAKE 
THE MAIN SURFACE LOW WELL TO OUR NORTH THOUGH DURING SUNDAY. THE 
ASSOCIATED COLD FRONT HOWEVER WILL ARRIVE INTO OUR AREA LATE SUNDAY 
WITH SOME SHOWERS. A BAND OF SHOWERS MAY END UP WEAKENING WITH A
SOUTHEASTERN EXTENT DUE TO MUCH OF THE LARGE SCALE LIFT PEELING
AWAY TO THE NORTH. THE INSTABILITY LOOKS LOW THEREFORE WE
CONTINUED WITH NO THUNDER MENTION ATTM. WE GENERALLY FAVORED A
BLEND OF CONTINUITY AND WPC GUIDANCE, WHICH PAINTS SLIGHT CHC TO
LOW CHC POPS ACROSS THE CWA MAINLY SUNDAY NIGHT. MEANWHILE, A LEAD
SHORT WAVE NEAR THE CAROLINAS MAY ORGANIZE A SURFACE LOW ALONG AN
OLD BAROCLINIC ZONE. THIS FEATURE SHOULD TRACK NORTHEAST AND HAVE
NO REAL AFFECT ON OUR SENSIBLE WEATHER.

FOR MONDAY AND TUESDAY...THE MAIN UPPER-LEVEL TROUGH MAY AMPLIFY 
SOME MORE ACROSS THE NORTHEAST AND MID ATLANTIC REGIONS MONDAY. 
BASED ON SOME RIDGING ENTERING THE PLAINS, AN EXPANSIVE SURFACE HIGH 
IS FORECAST TO BUILD ACROSS THE MIDWEST AND GREAT LAKES LATER MONDAY 
INTO TUESDAY, WITH THIS FEATURE ARRIVING INTO OUR AREA DURING 
TUESDAY. SOME GUIDANCE SHOWS SOME INSTABILITY TYPE SHOWERS OCCURRING 
JUST TO OUR NORTH TUESDAY AS ANOTHER SHORT WAVE ROTATES AROUND THE 
BASE OF THE UPPER-LEVEL TROUGH. REGARDING POPS, KEPT SOME SLIGHT CHC 
TO LOW CHC POPS ESPECIALLY MONDAY MORNING WITH THE DEPARTING COLD 
FRONT. WE CARRIED A DRY FORECAST FOR TUESDAY AS THE UPPER-LEVEL 
TROUGH MAY START TO LIFT OUT SOME WITH ANY FOCUS GENERALLY TO OUR 
NORTH.

FOR WEDNESDAY...AS A RIDGE SLIDES ACROSS THE GREAT LAKES, A 
POTENTIALLY STRONG SURFACE HIGH BUILDS ACROSS THE NORTHEAST AND MID 
ATLANTIC REGIONS. IF THE CENTER OF THIS HIGH ENDS UP ACROSS NEW 
ENGLAND, THEN WE WILL HAVE AN ONSHORE FLOW ONCE AGAIN. AS OF NOW, 
LEANED MUCH CLOSER TO THE 00Z WPC GUIDANCE FOR ALL WEATHER ELEMENTS.

&&

.AVIATION /16Z THURSDAY THROUGH MONDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS

VFR TDA AND TNGT. STRATOCU BETWEEN 5-9 KFT PROGRESSES EASTWARD
ACROSS THE TERMINALS TDA. NW WINDS UNDER 10 KT TODAY WILL VEER TO
THE N THIS EVE AND NE BY EARLY FRI MRNG.

OUTLOOK...
FRIDAY...VFR THROUGH THE DAY, HOWEVER SOME LOW CLOUDS OR EVEN SOME 
FOG COULD DEVELOP OVERNIGHT WITHIN AN ONSHORE FLOW. OUR CONFIDENCE 
IS ON THE LOWER SIDE.

SATURDAY AND SUNDAY...SOME LOW CLOUDS AND/OR SOME FOG TO START EACH 
DAY, OTHERWISE MOSTLY VFR. A COLD FRONT ARRIVES SUNDAY NIGHT WITH 
POSSIBLE SHOWERS AND LOCAL SUB-VFR CONDITIONS.

MONDAY...SOME SHOWERS POSSIBLE ESPECIALLY IN THE MORNING, OTHERWISE 
MOSTLY VFR WITH A WIND SHIFT TO THE NORTHWEST.

&&

.MARINE...
BUOY 44065 CAME BACK ON LINE ABOUT 10 PM LAST NIGHT. HOPEFULLY BUOY 
44025 WILL NOT BE FAR BEHIND.

TODAY...LONG PERIOD SWELLS GENERATED BY EDOUARD CONTINUE TO REACH
THE EAST COAST TODAY. LATEST OBS SHOW 13-14 SEC WAVE PERIODS THIS
MORNING. SEAS EXPECTED TO REMAIN JUST BELOW SCA LEVELS WIT WAVE
HEIGHTS ARE 4 FT WHILE NORTHERLY WINDS WILL BE AROUND 10 KT
(GUSTING TO 20 KT LATE IN THE DAY).

TONIGHT...SWELLS ARE STILL FORECAST TO BE WITH US THROUGH TONIGHT. 
SEAS WILL BE LESS THAN 4 FEET. LIGHT NORTHERLY WINDS WILL INCREASE 
TO 20 KT OVERNIGHT ESPECIALLY ACROSS THE NORTHERN WATERS.  

OUTLOOK...
FRIDAY...A NORTHEASTERLY WIND SURGE WITH AN INITIAL TIGHTENING OF 
THE PRESSURE GRADIENT AND CAA SHOULD THEN EASE SOME AS THE WINDS 
TURN EAST-SOUTHEAST BY LATE IN THE DAY AND AT NIGHT. THE SURGE COULD 
BE ENOUGH FOR SOME 25-KNOT GUSTS AND SEAS BUILDING TO 5 FEET ON THE 
COASTAL WATERS FOR A TIME. AS OF NOW THE WINDS AND SEAS ARE 
MARGINAL AND THEREFORE WILL HOLD OFF ON AN ADVISORY.

SATURDAY AND SUNDAY...THE WINDS SHOULD TURN FROM THE SOUTH DURING 
THIS TIME FRAME AS HIGH PRESSURE DEPARTS TO THE EAST. THE NEXT COLD 
FRONT ARRIVES SUNDAY NIGHT, HOWEVER AN INCREASE IN THE WINDS SHOULD 
OCCUR AHEAD OF IT BUT THEY SHOULD BE BELOW ADVISORY CRITERIA. THE 
SEAS HOWEVER COULD BE RIGHT NEAR 5 FEET SATURDAY FROM THE EARLIER
ONSHORE COMPONENT. 

MONDAY...THE CONDITIONS SHOULD BE BELOW ADVISORY CRITERIA OVERALL AS 
WINDS SHIFT FROM THE NORTH AS HIGH PRESSURE STARTS TO BUILD IN LATE.

&&

.RIP CURRENTS...
IN HOUSE GUIDANCE SUGGESTS A MODERATE RISK TODAY FOR NJ/DE BECAUSE OF
LONG PERIOD SWELLS GENERATED BY EDOUARD.

&&

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

&&

$$
SYNOPSIS...GORSE
NEAR TERM...KLEIN/KLINE
SHORT TERM...KRUZDLO
LONG TERM...GORSE
AVIATION...GORSE/KLEIN/KRUZDLO
MARINE...GORSE/KLEIN/KRUZDLO
RIP CURRENTS...KRUZDLO/KLEIN






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