Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 260146 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 946 PM EDT MON APR 25 2016 .SYNOPSIS... A QUASI STATIONARY FRONT WILL REMAIN IN NORTHEASTERN PENNSYLVANIA AND NORTHERN NEW JERSEY THROUGH TUESDAY MORNING. AN AREA OF LOW PRESSURE IS EXPECTED TO TRACK ALONG THIS FRONT AND CROSS THE REGION TUESDAY AFTERNOON. THE FRONT WILL FINALLY PROGRESS SOUTHWARD THROUGH THE AREA TUESDAY AFTERNOON AND NIGHT. HIGH PRESSURE BUILDS IN FROM CENTRAL CANADA WEDNESDAY. ANOTHER WAVE OF LOW PRESSURE IS FORECAST TO MOVE ALONG THE FRONT, SLIDING JUST SOUTH OF OUR AREA THURSDAY NIGHT INTO FRIDAY. HIGH PRESSURE RETURNS SATURDAY BEFORE YET ANOTHER LOW PRESSURE SYSTEM APPROACHES FROM THE WEST SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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930 PM ESTF: FEW CHANGES TO THE OVERALL FORECAST. ADJUSTED HOURLY TEMPS AND DEWS. RAISED POPS A FEW PCT NEAR AND N OF I80. GGEM DID BEST FOR ITS 6HR QPF ENDING 00Z, FOLLOWED BY THE ECMWF, NAM AND LASTLY THE GFS. STILL UNCONVINCED ON MID LVL SHOWERS DEVELOPING OVERHEAD NEAR MIDNIGHT- 1AM BUT THEY COULD IN THE WAA PATTERN. OTHERWISE...SHOWERS SHOULD PASS ACROSS MUCH OF THE REGION NEAR AND NORTH OF I-78 OVERNIGHT, WITH A SMALL CHC OF THUNDER. SOME OF THE RAIN MAY BE BRIEFLY MDT OR HEAVY. THIS SHOWER ACTIVITY IS FORMING NEAR AN E-W QSTRY BOUNDARY NEAR I-80. WARM SECTOR AIRMASS STILL A LITTLE ON THE DRY SIDE BUT CONVERGENCE AND LIFT SHOULD YIELD SOME BENEFICIAL RAIN NEAR AND N OF I-80 OVERNIGHT.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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A POSSIBLE CONVECTIVELY ACTIVE END TO THE DAY ACROSS THE AREA. THIS WILL BE DUE TO A STRONG SHORT WAVE SLIDING SOUTHEASTWARD FROM THE GREAT LAKES IN THE AFTERNOON. THIS WILL DRIVE A WEAK SURFACE LOW ALONG A FRONTAL BOUNDARY THAT WILL BE DRAPED EAST-WEST ACROSS MOSTLY OUR NORTHERN ZONES. THE PLACEMENT OF THIS FRONT WILL HAVE AN IMPACT ON TEMPERATURES, AND THERE VERY WELL COULD BE QUITE THE GRADIENT FROM SOUTH TO NORTH IN THE AFTERNOON. AS THE STRONG SHORT WAVE ARRIVES IN THE AFTERNOON, AN AREA OF ENHANCED MID LEVEL FLOW WILL MOVE INTO OUR AREA. THIS COMBINED WITH ENOUGH INSTABILITY /DESPITE SOME CLOUD COVER/ SHOULD RESULT IN AT LEAST SCATTERED CONVECTIVE DEVELOPMENT IN THE AFTERNOON. REWINDING A BIT, THERE COULD BE SOME SHOWERS OR A THUNDERSTORM IN THE EARLY MORNING ESPECIALLY NEAR AND NORTH OF PHILADELPHIA AS A LEAD IMPULSE MOVES THROUGH COMBINED WITH AN UPTICK IN INSTABILITY. BACK TO THE AFTERNOON, THE FORECAST SOUNDINGS SHOW A DEEP UNIDIRECTIONAL WIND PROFILE WHICH WOULD PROMOTE LINE SEGMENTS AND CLUSTERS. GIVEN THE FORECAST FLOW, LOCALLY STRONG WINDS COULD OCCUR ESPECIALLY WITH MORE ORGANIZED LINE SEGMENTS. IF ENOUGH INSTABILITY CAN BE REALIZED, SOME HAIL CANNOT BE RULED OUT. THE AMOUNT OF INSTABILITY THAT CAN BE ACHIEVED THROUGH THE AFTERNOON WILL BE THE MAIN DRIVING PARAMETER FOR THE STRENGTH OF THE CONVECTION. GIVEN THE FLOW AND FORCING DURING THE AFTERNOON, WE ADDED IN A GUSTY WIND MENTION TO THE FORECAST. THIS IS ESPECIALLY FOR ABOUT THE SOUTHERN HALF OF THE CWA WHERE THE BOUNDARY LAYER WILL BE WARMER, AND THE FORECAST SOUNDINGS INDICATE A LOW-LEVEL INVERTED-V SIGNATURE DEVELOPING. THE PW VALUES ARE FORECAST TO BE IN THE 1.2-1.5 INCH RANGE, THEREFORE LOCAL DOWNPOURS WILL ACCOMPANY THE CONVECTION. TT BEING MODELED INTO THE LOWER 50S MAY PERMIT SOME SMALL HAIL. ONE SMALL ARGUMENT AGAINST WIDESPREAD AFTN CONVECTION SE PA AND S NJ IS THE STIFF WLY FLOW AT 850 MB. AS FOR THE HIGH TEMPERATURES, WE USED A MOS BLEND TO START THEN BUMP THESE UP A BIT ESPECIALLY ACROSS THE SOUTHERN AREAS WHERE BETTER HEATING MAY TAKE PLACE. GIVEN MORE CLOUD COVER AND A NEARBY BOUNDARY, LOWERED TEMPERATURES A BIT ACROSS THE FAR NORTHERN LOCALS.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... THE COLD FRONT WILL CONTINUE TO PROGRESS SOUTHWARD THROUGH THE FORECAST AREA TUESDAY EVENING. ALTHOUGH ENHANCED LIFT ASSOCIATED WITH THE MID-LEVEL SHORTWAVE TROUGH IS FORECAST TO MOVE OFFSHORE BY SUNSET, SHOWERS AND THUNDERSTORMS WILL PERSIST LATER INTO THE EVENING AS ADDITIONAL FORCING ACROSS THE SOUTHERN HALF OF THE FORECAST AREA IS FAVORED IN THE RIGHT-ENTRANCE REGION OF AN UPPER- LEVEL JET STREAK. THE THREAT OF STRONG TO SEVERE THREAT MAY PERSIST THE FIRST HALF OF THE EVENING ACROSS FAR SE PA/S NJ AND THE DELMARVA, ESPECIALLY IF THE UNSTABLE WARM SECTOR SOUTH OF THE FRONT HAS NOT BEEN WORKED OVER. THE COLD FRONT WILL MOVE SOUTH OF THE DELMARVA LATE TUESDAY NIGHT AND THEN BECOME STATIONARY NEAR THE NC-VA BORDER WEDNESDAY. DRIER AND COOLER AIR WILL WORKS ITS WAY INTO THE REGION AS CANADIAN HIGH PRESSURE CENTERED NEAR THE NORTHWEST PASSAGES RIDGES DOWN TOWARD US. HOWEVER, THE DRIER AIR MAY STRUGGLE TO MAKE IT INTO OUR FAR SOUTHERN ZONES, RESULTING IN CLOUDY SKIES THAT PERSIST INTO MOST OF WEDNESDAY ACROSS THE DELMARVA. LEE CYCLOGENESIS IS CURRENTLY TAKING PLACE IN THE CO FRONT RANGE OF THE ROCKIES. THIS SURFACE LOW WILL MEANDER OVER THE CENTRAL PLAINS FOR THE NEXT FEW DAYS AS THE UPPER TROUGH TIED TO THE SURFACE LOW REMAINS CUTS OFF. THE CUTOFF LOW IS FORECAST TO EVENTUALLY WEAKEN AND BECOME AN OPEN WAVE BY THURSDAY. IN RESPONSE TO THE EVOLVING UPPER PATTERN, THE SURFACE LOW WILL PROGRESS EASTWARD ALONG THE STATIONARY BOUNDARY TO OUR SOUTH ON THURSDAY. A SECONDARY WAVE OF LOW PRESSURE MAY DEVELOP AND RIDE THE FRONT ON FRIDAY. OVERRUNNING PRECIP SHOULD EXPAND NORTHWARD LATE WEDNESDAY NIGHT INTO THURSDAY AS THE FLOW BACKS MORE OUT OF THE SOUTH AHEAD OF THE LOW AND ISENTROPIC LIFT STRENGTHENS ALONG AND ON THE COOL SIDE OF THE BOUNDARY. THERE IS STILL UNCERTAINTY REGARDING HOW FAR NORTH THE FRONT AND PRECIP ADVANCES WITH DRIER AIR BEING REINFORCED BY HIGH PRESSURE ANCHORED TO OUR NORTH. THERE IS SOME EVIDENCE FROM GUIDANCE THAT EVAPORATIVE COOLING AT THE ONSET COULD LEAD TO A COLD AIR DAMMING PATTERN IF THERE IS ENOUGH LOW-LEVEL DRY AIR IN PLACE WHEN THE OVERRUNNING PRECIP MOVES IN. THIS WOULD KEEP THE FORECAST AREA ON THE COLD SIDE OF THE BOUNDARY. WE WILL CONTINUE TO SHOW THE HIGHEST POPS ACROSS OUR SOUTHERN AREAS DUE TO THE PROXIMITY OF THE FRONT. SATURDAY LOOKS DRY AS HIGH PRESSURE BRIEFLY BUILDS BACK INTO THE MID ATLANTIC. SHOWERS MAY RETURN SUNDAY INTO MONDAY AS YET ANOTHER WAVE OF LOW PRESSURE IS EXPECTED TO ORGANIZE OVER THE GREAT PLAINS AND TRACK EASTWARD ALONG THE STATIONARY FRONT. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REMAINDER OF TONIGHT...VFR OVERALL, WITH CEILINGS DEVELOPING AND LOWERING TO 5000 FT, ESPECIALLY LATE. SOME SHOWERS AND PERHAPS A THUNDERSTORM MAINLY AFTER MIDNIGHT ESPECIALLY ALONG AND NORTH OF A KRDG TO KTTN LINE. SOUTHWEST TO LOCALLY SOUTH- SOUTHEAST WINDS LESS THAN 10 KNOTS. TUESDAY...A FEW SHOWERS AND POSSIBLY A THUNDERSTORM AROUND EARLY IN THE MORNING, ESPECIALLY NNJ. ADDITIONAL SHOWERS WITH SCATTERED THUNDERSTORMS ARE EXPECTED BY LATE AFTERNOON. SOME THUNDERSTORMS COULD PRODUCE LOCALLY BRIEF STRONG WIND GUSTS. THE VISIBILITY WILL BE REDUCED DURING SOME SHOWERS AND THUNDERSTORMS DUE TO DOWNPOURS. GIVEN SOME UNCERTAINTY WITH THE TIMING, DID NOT SIGNIFICANTLY LOWER THE VISIBILITY AT THIS TIME. SOUTHWESTERLY WINDS INCREASE TO 10-15 KNOTS, WITH SOME LOCALLY HIGHER GUSTS TO 25 KT ESPECIALLY FROM THE KPHL AREA ON SOUTH AND EAST. OUTLOOK... TUESDAY NIGHT...THE THREAT OF SHRA AND TSRA SHOULD PERSIST INTO THE EVE FOR THE PHILA TERMINALS AND ESPECIALLY SOUTH. THE CONVECTION WILL BE ASSOCIATED WITH A COLD FRONT THAT IS MOVING SWD THRU THE TERMINALS DURING THE EVENING. FROPA WILL BE MARKED BY A WIND SHIFT FROM W-SW TO N-NE. EXPECT RESTRICTIONS MVFR OR LOWER BRIEFLY WHEN THESE STORMS MOVE THRU. IMPROVING TO VFR OVERNIGHT. WEDNESDAY AND WEDNESDAY NIGHT...MAINLY VFR. THURSDAY THROUGH FRIDAY...SHOWERS RETURN. BEST CHANCE FOR SHOWERS AND MVFR RESTRICTIONS WOULD BE ACROSS THE SRN TERMINALS.
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&& .MARINE... A SOUTHERLY FLOW IS ANTICIPATED THROUGH TUESDAY WITH SOME INCREASE ESPECIALLY DURING THE DAY TUESDAY. A FRONTAL ZONE HOWEVER WILL BE DRAPED NEAR OUR NORTHERN ATLANTIC COASTAL WATERS THROUGH TUESDAY THAT COULD AFFECT THE WINDS TO SOME EXTENT. THE INCREASE THROUGH TUESDAY SHOULD BE ENOUGH TO BUILD SEAS TO 5 FEET ON THE ATLANTIC COASTAL WATERS, AND WITH WARMER AIR OVER THE COOLER WATERS WINDS SHOULD MOSTLY BE LESS THAN 25 KNOTS. HOWEVER THERE SHOULD BE ENOUGH MIXING ESPECIALLY NEARSHORE ON TUESDAY TO PROMOTE GUSTS TO ABOUT 25 KNOTS. THEREFORE, THE SMALL CRAFT ADVISORY REMAINS IN EFFECT STARTING LATER TONIGHT. WE WILL HOLD OFF ON ADDING AN ADVISORY FOR DELAWARE BAY ATTM AS THE SOUTHWEST WIND DIRECTION SHOULD LIMIT ANY 25-KNOT GUSTS TO JUST NEARSHORE. SOME THUNDERSTORMS TUESDAY ESPECIALLY LATE IN THE AFTERNOON COULD PRODUCE LOCALLY STRONG WIND GUSTS. OUTLOOK... TUESDAY NIGHT...SCA EXTENDED THRU ALL OF TUESDAY NIGHT FOR THE COASTAL WATERS WITH NELY WINDS GUSTING TO NEAR 25 KT AND SEAS NEAR 5 FT. WEDNESDAY THROUGH FRIDAY...WINDS AND SEAS BELOW SCA THRESHOLDS. && .FIRE WEATHER...
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WE CONTINUE TO PROVIDE WEATHER SUPPORT FOR THE LARGE WILDFIRE BURNING IN PORTIONS OF NORTHERN MONROE COUNTY THAT HAS SPREAD INTO PIKE COUNTY. HIGHER DEW POINTS OVERNIGHT AND TUESDAY ALONG WITH SHOWERS WILL HELP WITH MOISTURE LEVELS AND HOPEFULLY PUT A DAMPER ON THE FIRE. NEAR AND N OF I-80 COULD SEE ONE QUARTER INCH OVERNIGHT.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR ANZ450>455.
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&& $$ SYNOPSIS...DRAG/KLEIN NEAR TERM...DRAG/GORSE 946 SHORT TERM...DRAG/GORSE 946 LONG TERM...KLEIN AVIATION...DRAG/GORSE/KLEIN 946 MARINE...GORSE/KLEIN FIRE WEATHER...

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