Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 301937 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 337 PM EDT SAT MAY 30 2015 .SYNOPSIS...
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LOW PRESSURE ALONG AN ASSOCIATED COLD FRONT ACROSS THE OHIO VALLEY WILL CONTINUE MOVING EASTWARD TONIGHT AND INTO OUR REGION ON SUNDAY. THIS COLD FRONT WILL SLOWLY MOVE ACROSS OUR REGION EARLY NEXT WEEK. HIGH PRESSURE WILL BUILD SOUTHEASTWARD BEHIND IT INTO THE REGION FOR THE MIDDLE AND LATER HALF OF NEXT WEEK. THIS HIGH PRESSURE SYSTEM WILL BE FOLLOWED BY ANOTHER COLD FRONT DROPPING SOUTHEAST INTO THE REGION BY NEXT WEEKEND.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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OUR CWA REMAINS NEAR THE WESTERN PERIPHERY OF AN UPPER-LEVEL RIDGE. THE SOUTHERLY FLOW AROUND THIS FEATURE WILL CONTINUE TO SUPPLY A WARM AND MOIST AIRMASS ACROSS OUR REGION. WHILE MUCH OF THE REGION IS SEEING CUMULUS, SOME THAT ARE SHOWING MORE VERTICAL GROWTH THAN OTHERS, THE SURFACE FLOW HAS BACKED SOME ALONG THE COAST ALLOWING FOR LITTLE TO NO CLOUDS AND A COOLING AFFECT. FARTHER INLAND THOUGH, IT IS DIFFERENT. SOME SUBTLE SHORT WAVES EMBEDDED IN THE FLOW AROUND THE RIDGE IS TEAMING UP WITH INSTABILITY AND TERRAIN TO PRODUCE SOME SHOWERS AND THUNDERSTORMS. THIS IS PROBABLY BEING ENHANCED SOME WEST OF OUR AREA WHERE A MORE PRONOUNCED SHORT WAVE IS MOVING UP THE OHIO VALLEY AND TOWARD THE EASTERN GREAT LAKES THIS AFTERNOON. THIS PLACES OUR WESTERN ZONES IN THE BEST AREA FOR SOME CONVECTION THROUGH PORTIONS OF THE EVENING. AS A RESULT, THE HIGHEST POPS REMAIN IN THESE AREAS, THEN THESE DROP OFF TO NON-MENTIONABLE FARTHER EAST. THE FLOW IS ON THE WEAKER SIDE THEREFORE THE STORM MOTION SHOULD BE SLOW ENOUGH TO ALLOW FOR LOCALLY HEAVY RAIN UNDER STRONGER CONVECTIVE CORES GIVEN THE PW VALUES ARE AROUND 1.50 INCHES. THE SHEAR LOOKS TO BE ON THE WEAK ENOUGH SIDE TO KEEP ORGANIZATION AND STRENGTH IN CHECK, ALTHOUGH A PULSE STORM COULD CONTAIN LOCALLY GUSTY WINDS. THE CHC OF SOME SHOWERS OR THUNDER MAY LINGER MAINLY ACROSS OUR NORTHWEST ZONES THROUGH THE NIGHT, ALTHOUGH THIS WILL DEPEND ON ANY BETTER LARGE SCALE LIFT AFTER SUNSET AS THE INSTABILITY WANES. THE AMOUNT OF LOW-LEVEL MOISTURE SHOULD COMBINE WITH AN INVERSION OVERNIGHT TO PRODUCE SOME LOW CLOUDS. THIS APPEARS TO BE MOST FOCUSED ACROSS OUR NORTHERN AND WESTERN AREAS GIVEN THE FLOW HAS VEERED MORE TO THE SOUTHWEST COMPARED TO YESTERDAY. WE MAY SEE MORE STRATUS THAN FOG, THEREFORE DID NOT INCLUDE FOG ATTM. AS FOR THE LOW TEMPERATURES, WE USED MAINLY AN EVEN BLEND OF THE NAM/GFS MOS.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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A SURFACE COLD FRONT WILL GRADUALLY BE SETTLING CLOSER TO OUR AREA. THIS FEATURE APPEARS TO BE SLOWER AND THEREFORE MUCH LESS OF A CHC OF CONVECTION ACROSS OUR SOUTHERN ZONES THROUGH THE DAY. THE BETTER LIFT AND CONVERGENCE IS ACROSS THE NORTHERN AND WESTERN AREAS AND THIS IS WHERE WE HAVE THE HIGHEST POPS ONCE AGAIN. WE DID TIGHTEN UP THE POP GRADIENT A BIT FROM NORTHWEST TO SOUTHEAST, HOWEVER THE HIGHER POPS DO EDGE TO INTERSTATE 95 TOWARD LATE AFTERNOON. AS THE FRONT NEARS OUR NORTHERN ZONES DURING THE AFTERNOON, SOME SHOWERS AND THUNDERSTORMS ARE EXPECTED TO OCCUR. THERE IS LESS CERTAINTY REGARDING THE AMOUNT OF INSTABILITY DURING THE COURSE OF THE DAY, GIVEN THE PROSPECTS OF LOW CLOUDS TO START THEN CONVECTIVE TEMPERATURES BEING REACHED TO PROMOTE A DECENT AMOUNT OF CUMULUS DEVELOPMENT. THE AREAS CLOSER TO THE INCOMING FRONT WILL TEND TO HAVE SOME INCREASE IN THE SHEAR TO PROMOTE ORGANIZED STORMS AND THIS COULD POSE A LOCALIZED DAMAGING WIND THREAT. GIVEN THE LOW CONFIDENCE IN THE CONVECTIVE EVOLUTION/STRENGTH THIS FAR OUT, WE DID NOT ADD ENHANCED WORDING TO THE FORECAST. LOCALLY VERY HEAVY RAIN HOWEVER CAN OCCUR GIVEN HIGH PW VALUES AHEAD OF THE FRONT AND ALSO THE CHC OF SOME TRAINING OF CELLS TO OCCUR. THIS OVERALL LOOKS LOCALIZED AT THIS POINT HOWEVER WE DID ADD A HEAVY RAIN MENTION TO THE FAR NORTHERN AND WESTERN AREAS. AS FOR THE HIGH TEMPERATURES, WE USED A NAM/GFS MOS BLEND WITH SOME ADJUSTMENTS THEN MADE. SINCE THE FRONTAL BOUNDARY ARRIVAL IS SLOWER, MUCH OF THE AREA WILL REMAIN IN THE WARM SECTOR AND THEREFORE HIGHS WERE BUMPED UP SOME ESPECIALLY THE SOUTHERN AREAS /COOLER ALONG THE COAST/.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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SUNDAY NIGHT THROUGH TUESDAY NIGHT: LOW PRESSURE ACROSS THE GREAT LAKES WILL TRACK NORTHEAST OF THE REGION AS A COLD FRONT BEGINS TO DRIFT SOUTHEAST TOWARD THE REGION. SHOWERS AND SOME THUNDERSTORMS ARE LIKELY TO BE ONGOING. THE HIGHEST CONCENTRATION WILL BE ACROSS THE NORTHERN PARTS OF THE REGION CLOSER TO THE SURFACE LOW AND FRONTAL BOUNDARY. THIS EVENT WILL LIKELY TRANSITION FROM THE THUNDERSTORMS TO A HEAVY RAIN THREAT. A STRONG STORM OR TWO CONTAINING GUSTY WINDS AND SMALL HAIL CAN NOT BE RULED OUT EARLY IN THE EVENING SUNDAY WITH MODEST INSTABILITY 500-1500 J/KG CAPE AND STEEP LOW LEVEL LAPSE RATES. INSTABILITY WILL DECREASE HEADING INTO MONDAY WITH THE FRONT SAGGING SOUTHEAST TOWARD THE REGION. MID-LEVEL FLOW WILL SLOW DOWN CONSIDERABLY BY MONDAY, ALMOST ALLOWING THE FRONT TO STALL OUT. SEVERAL FACTORS SUGGEST HEAVY, POTENTIALLY TRAINING SHOWERS AND A FEW THUNDERSTORMS WILL OCCUR AT TIMES LATE SUNDAY NIGHT INTO TUESDAY AS MID-LEVEL DISTURBANCES PASS THROUGH THE REGION. MOISTURE WILL CONTINUE TO STREAM NORTHWARD AHEAD OF THE FRONT LEADING TO SURGING PW VALUES CLOSE TO 2 INCHES. A TALL SKINNY CAPE PROFILE IS ALSO MODELED ALONG WITH VERY SLOW STORM MOTIONS. WITH MORE IN THE WAY OF SHOWERS OVERALL, LOWER INSTABILITY WILL LEAD TO A MORE ISOLATED THREAT FOR ANY STRONG THUNDERSTORMS. THE HIGHEST CHANCES FOR RAIN WILL GRADUALLY SHIFT SOUTHEASTWARD MONDAY AND MONDAY NIGHT AND DEPEND ON THE EXACT TRACK OF PASSING MID- LEVEL DISTURBANCES. THE FRONTAL BOUNDARY SHOULD BEGIN TO TRANSITION EASTWARD ON TUESDAY WITH GRADUALLY DECREASING CHANCES OF RAIN FROM NORTHWEST TO SOUTHEAST. TOTAL RAINFALL IS LIKELY TO RANGE FROM 1 TO 3 INCHES WITH LOCALLY HIGHER AMOUNTS. THERE IS SOME VARIABILITY WITHIN THE GEFS, NAEFS AND OPERATIONAL MODELS ON THE EXACT PLACEMENT OF THE HIGHEST TOTALS DUE TO VARIABILITY IN THE FEATURES. A GENERAL CONSENSUS AT THIS TIME YIELDS THE HIGHEST RAINFALL TOTALS ACROSS FAR EASTERN PA, NORTHERN NJ AND THE EASTERN SHORE OF MD WITH ONLY MODERATE CONFIDENCE IN THIS PLACEMENT. QPF GRIDS ARE MORE GENERALIZED TO ACCOUNT FOR THE UNCERTAINTY. HIGH TEMPERATURES ARE ALSO FORECASTED A LITTLE COOLER THAN SOME OF THE STATISTICAL AND ENSEMBLE GUIDANCE NUMBERS DUE TO THE RAIN CHANCES AS WELL. WEDNESDAY THROUGH FRIDAY NIGHT: HIGH PRESSURE BUILDS OVER THEN PASSES EAST OF THE REGION FOR THE MIDDLE AND LATER HALF OF THE WEEK. COOL REFRESHING AIRMASS TO START THEN WARMER AND MUGGY BY WEEKS END. THE GFS AND THE GEFS ARE TRYING TO KEY ON ANOTHER LOW PRESSURE FEATURE TO OUR SOUTH WHICH COULD RESULT IN ANOTHER SHOWER CHANCE. HOWEVER, GIVEN THE LACK OF SUPPORT FROM THE OTHER MODELS ATTM IMPACTS FROM THIS FEATURE ARE NOT THAT LIKELY. FORECAST WILL JUST FEATURE PARTLY TO MOSTLY SUNNY SKIES. SATURDAY: ANOTHER COLD FRONT IS LIKELY TO MOVE INTO THE REGION. WARM AND MORE HUMID CONDITIONS MAY PRECEDE THE FRONT. POTENTIAL IS PRESENT FOR ENSEMBLE GUIDANCE TO BE A LITTLE LOW WITH HIGH TEMPERATURES GIVEN SOUTHERLY FLOW AND INCREASING 925 MB TEMPERATURES. SOME SCATTERED THUNDERSTORMS MAY FORM AHEAD OF THE FRONT AS WELL. OPTED FOR LOW CHANCE POPS ATTM.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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&& .MARINE...
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A SOUTHERLY FLOW WILL BE MAINTAINED THROUGH SUNDAY WELL AHEAD OF A COLD FRONT. THIS FLOW SHOULD INCREASE AT TIMES, ESPECIALLY NEARSHORE AND ALSO ACROSS THE NORTHERN COASTAL WATERS HOWEVER WE ARE ANTICIPATING THE BULK OF THE GUSTS TO REMAIN UNDER 25 KNOTS. THE SOUTHERLY FLOW WILL MAINTAIN ELEVATED SEAS ON THE COASTAL WATERS, HOWEVER THESE ARE ANTICIPATED TO BE NO HIGHER THAN 4 FEET OVERALL. THERE COULD BE SOME FOG OVERNIGHT AND EARLY SUNDAY MORNING NEARSHORE, HOWEVER WITH THE FLOW MORE FROM THE SOUTHWEST ABOVE THE SURFACE WE ANTICIPATE IT NOT TO BE WIDESPREAD AND IT WAS NOT INCLUDED ATTM. OUTLOOK... SUNDAY NIGHT THROUGH TUESDAY MORNING: SEAS AROUND FOUR FEET WITH WIND GUSTS BELOW 20 KNOTS. TUESDAY AFTERNOON THROUGH THURSDAY: SEAS AROUND FIVE FEET, DECREASING BY A FOOT OR TWO FROM NORTH TO SOUTH ON THURSDAY. ANY WIND GUSTS UNDER 20 KNOTS. WAVEWATCH COULD BE TO HIGH IN THIS PERIOD WITH WAVE HEIGHTS GIVEN THE GFS MODEL HAS MORE IN THE WAY OF LOW PRESSURE TO OUR SOUTHEAST.
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&& .RIP CURRENTS...
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THE RIP CURRENT RISK FOR THE JERSEY SHORE REMAINS AT MODERATE THROUGH THIS EVENING, DUE TO SOME STRONGER SOUTHERLY NEARSHORE WINDS COMBINED WITH A LONGER WAVE PERIOD.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GAINES NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GAINES AVIATION...GAINES/GORSE MARINE...GAINES/GORSE RIP CURRENTS...GORSE

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