Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 151029 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 629 AM EDT WED APR 15 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD ACROSS OUR REGION TODAY AND TONIGHT, THEN SHIFT OFFSHORE THURSDAY INTO FRIDAY. A COLD FRONT WILL MOVE THROUGH FRIDAY AS LOW PRESSURE DEVELOPS NEAR THE NORTH CAROLINA COAST, THEN A SECONDARY COLD FRONT ARRIVES DURING SATURDAY. HIGH PRESSURE IS SCHEDULED TO BRIEFLY BUILD IN FOR SUNDAY, THEN THE NEXT COLD FRONT AND LOW PRESSURE SYSTEM MOVES IN FOR LATER MONDAY AND TUESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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630 AM UPDATE...MAIN CHANGES WITH THIS UPDATE WERE FOR DEW POINT TEMPERATURES. DEW POINTS HAVE FALLEN A BIT FASTER THAN EXPECTED WITH TEENS AND 20S ALREADY OVER THE POCONOS AND NW NJ. UNDERCUT DEW POINTS SLIGHTLY THROUGH OUT THE DAY, BUT WILL WAIT UNTIL UPSTREAM 12Z SOUNDINGS COME IN BEFORE MAKING ANY SIGNIFICANT CHANGES. PREVIOUS NEAR TERM DISCUSSION...THE COLD FRONT, AND ASSOCIATED LOW, WILL CONTINUE TO SLIDE AWAY FROM THE REGION. IN IT`S WAKE, A COOL AND VERY DRY AIR MASS WILL BUILD IN OVER THE REGION. SEE FIRE WEATHER SECTION BELOW FOR A DISCUSSION OF FIRE WEATHER CONCERNS. DESPITE THE COOLER AIR MASS, TEMPERATURES SHOULD ACTUALLY BE PRETTY CLOSE, IF NOT A BIT ABOVE, NORMAL VALUES TODAY. THE UPPER LEVEL JET IS EXPECTED TO REMAIN JUST NORTHEAST OF THE REGION THROUGH THE DAY TODAY, LEADING TO PERSISTENT THICK CIRRUS CLOUDS, SO WHILE IT WON`T BE COMPLETELY SUNNY, IT SHOULD STILL BE A NICE DAY.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... 500 MB SHORT WAVE RIDGE SLIDES OVER THE REGION, AS THE SURFACE HIGH BUILDS CLOSER. ADDITIONALLY, THE 250MB LEVEL JET SLIDES FURTHER OFF SHORE, ALL OF THIS WILL COMBINE FOR CLEARING SKIES OVERNIGHT. WINDS SHOULD BE LIGHT, AND WITH THE RELATIVELY LOW DEW POINT TEMPERATURES, SHOULD SEE CONSIDERABLE RADIATIONAL COOLING. AS A RESULT, EXPECT LOWS IN THE UPPER 30S TO LOWER 40S. AT THIS TIME, HOWEVER, DO NOT EXPECT FROST ADVISORY CONDITIONS IN LOCATIONS WHERE THE GROWING SEASON HAS ALREADY STARTED (IN THESE AREAS EXPECT LOWS MOSTLY IN THE LOWER 40S). && .LONG TERM /THURSDAY THROUGH TUESDAY/... THE SYNOPTIC SETUP IS COMPRISED OF AN INITIAL RIDGE IN THE EAST THAT TRANSITIONS TO SOME TROUGHING. AS THIS OCCURS, A CLOSED LOW ACROSS THE WEST DROPS EAST-SOUTHEAST EVENTUALLY EJECTING ACROSS THE PLAINS. THIS FEATURE BUILDS SOME RIDGING DOWNSTREAM, HOWEVER IT ALSO FORCES SOME AMPLIFICATION OF THE TROUGH ACROSS THE NORTHEAST FOR A PORTION OF THE WEEKEND. THE CLOSED LOW MAY THEN GET ABSORBED INTO A LARGE SCALE TROUGH FROM THE MIDWEST AS IT UNDERGOES AMPLIFICATION EASTWARD EARLY NEXT WEEK. PRIOR TO THIS OCCURRING, A SURFACE LOW IS FORECAST TO DEVELOP NEAR THE NORTH CAROLINA COAST THURSDAY AND THEN TRACK NORTHEASTWARD. THE DETAILS WITHIN THIS SETUP IS OF LOWER CONFIDENCE AS THE MODEL GUIDANCE IS HAVING TROUBLE HANDLING THE SPLIT FLOW. THE INTERACTION OF THE EJECTING CLOSED LOW AND THE NORTHERN STREAM TROUGH AND ASSOCIATED ENERGY WILL HAVE AN IMPACT ON THE DOWNSTREAM WEATHER. THIS IS MOST NOTED FOR OUR AREA DURING THE WEEKEND AND ESPECIALLY EARLY NEXT WEEK. GIVEN THE LOWER CONFIDENCE, WE USED A MODEL BLEND WITH CONTINUITY FOR WEDNESDAY THROUGH FRIDAY THEN WENT WITH MOSTLY THE 00Z WPC GUIDANCE /BLEND OF THE MEANS SATURDAY, THEN MOSTLY A NAEFS/ECMWF ENSEMBLE MEAN BLEND THEREAFTER/. SOME ADJUSTMENTS WERE THEM MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR THURSDAY...HIGH PRESSURE AT THE SURFACE IS FORECAST TO SHIFT TO OUR EAST DURING THIS TIME FRAME. THIS WILL SET THE STAGE FOR SOUTHEASTERLY LOW-LEVEL FLOW THAT WILL ALLOW FOR MOISTURE ADVECTION TO INCREASE. IT APPEARS THAT A PRESSURE TROUGH DEVELOPS ALONG THE NORTH CAROLINA COAST AS DEPARTING HIGH PRESSURE WEDGES SOUTHWESTWARD FOR A TIME. AS A RESULT, LOW PRESSURE IS FORECAST TO DEVELOP NEAR OR ALONG THE NORTH CAROLINA COAST. THERE MAY BE A CONDUIT OF MOISTURE PULLED NORTHWESTWARD FROM THIS SURFACE LOW AS IT SLOWLY TRACKS NORTHEASTWARD. OTHERWISE, AN INCOMING COLD FRONT SHOULD ALSO HAVE SOME SHOWERS WITH IT. OVERALL, MUCH OF THIS TIME FRAME SHOULD BE DRY WITH ANY SHOWERS TENDING TO HOLD OFF UNTIL LATER THURSDAY NIGHT AND THIS IS WHEN THE POPS INCREASE. FOR FRIDAY AND SATURDAY...IT MAY START OUT RATHER UNSETTLED FRIDAY AS MOISTURE GETS PULLED NORTHWARD FROM LOW PRESSURE NEAR THE NORTH CAROLINA COAST. THIS FEATURE WILL THEN TRACK FARTHER AWAY FROM THE COAST LATER FRIDAY AND SATURDAY, ALTHOUGH A SECONDARY COLD FRONT SHOULD ARRIVE DURING SATURDAY. THERE IS LESS CONFIDENCE IN THE AMOUNT OF SHOWERS FRIDAY AS IT WILL DEPEND ON HOW MUCH INTERACTION THE SURFACE LOW TO OUR SOUTH HAS WITH ENERGY SLIDING BY FARTHER TO THE NORTH. AS A RESULT, WE KEPT POPS BELOW LIKELY AND WENT WITH SCATTERED WORDING FOR NOW. THE SECONDARY FRONT ON SATURDAY MAY NOT HAVE MUCH MOISTURE LEFT TO WORK WITH, THEREFORE WE KEPT POPS ON THE LOWER SIDE. IT DOES APPEAR THAT THE AIRMASS MODERATES PRIOR TO THE COLD FRONTAL PASSAGE WITH MANY AREAS GETTING TO AROUND 70 DEGREES DURING THE DAY. FOR SUNDAY THROUGH TUESDAY...HIGH PRESSURE AT THE SURFACE SHOULD BUILD IN BRIEFLY SUNDAY. AS ENERGY EJECTS EASTWARD FROM A CLOSED LOW AND ALSO FROM THE MIDWEST, A COMPLEX SYSTEM MAY EVOLVE EASTWARD WITH TIME. WE KEPT SUNDAY DURING THE DAY DRY DUE TO THE PRESENCE OF HIGH PRESSURE, THEN WAA AND MOISTURE ADVECTION BEGINS TO OVERTAKE THE AREA AT NIGHT. THIS MAY ALLOW FOR SOME SHOWERS TO ARRIVE, ALTHOUGH IT STILL LOOKS LIKE THE MORE UNSETTLED TIME FRAME MAY BE MONDAY AND TUESDAY. THIS WILL DEPEND ON THE EVOLUTION OF THE SPLIT FLOW AS IT MAY TURN INTO AN AMPLIFIED UPPER-LEVEL TROUGH IN THE EAST. AS OF NOW, THE HIGHEST POPS ARE FOR MONDAY HOWEVER THIS WILL PROBABLY CHANGE. GIVEN THE UNCERTAINTY WITH THE DETAILS, WE DID NOT GO ANY HIGHER THAN HIGH CHC POPS. SOME COOLER TEMPERATURES SHOULD RESULT, ESPECIALLY IF THE RAIN IS MORE WIDESPREAD. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. ONLY LINGERING HIGH CIRRUS CLOUDS ARE POSSIBLE, PRIMARILY THROUGH 00Z. NORTHERLY WINDS MAY BRIEFLY GUST NEAR 20 KT THROUGH 21Z, BUT OTHERWISE WINDS SHOULD BE NEAR OR BELOW 10KT. WINDS ARE EXPECTED TO GRADUALLY SHIFT TO EAST NORTHEASTERLY OVERNIGHT TONIGHT. OUTLOOK... THURSDAY THROUGH SATURDAY...VFR THURSDAY WITH INCREASING CLOUDS, THEN CONDITIONS TENDING TO LOWER TO MVFR WITH SCATTERED SHOWERS LATER THURSDAY NIGHT AND FRIDAY. OUR CONFIDENCE IS ON THE LOWER SIDE WITH THE TIMING AND HOW MUCH RAIN OCCURS. A SECONDARY COLD FRONT MOVES THROUGH DURING SATURDAY, HOWEVER THIS MAY HAVE LIMITED MOISTURE WITH IT. SUNDAY...OVERALL VFR AS HIGH PRESSURE BRIEFLY BUILD IN.
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&& .MARINE...
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SMALL CRAFT ADVISORY HAS BEEN CANCELLED. WINDS AND SEAS HAVE DROPPED BELOW CRITERIA. A FEW GUSTS NEAR 20 KT WILL BE POSSIBLE THROUGH THE DAY ON THE COASTAL WATERS, BUT SHOULD REMAIN BELOW SCA CRITERIA. OUTLOOK... THURSDAY AND FRIDAY...THE WINDS AND SEAS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA AS THE FLOW OVERALL IS FORECAST TO BE LIGHT ENOUGH. SATURDAY AND SUNDAY...A COLD FRONT MOVES THROUGH DURING SATURDAY THEN HIGH PRESSURE ARRIVES BRIEFLY FOR SUNDAY. THE WINDS APPEAR TO REMAIN BELOW ADVISORY CRITERIA, HOWEVER THE SEAS COULD NEAR 5 FEET FOR A TIME ON THE OCEAN MAINLY IF THE NORTHERLY FLOW AHEAD OF HIGH PRESSURE LASTS LONG ENOUGH AND IS A BIT STRONGER.
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&& .FIRE WEATHER... ALMOST ALL OF THE REGION (WITH THE EXCEPTION OF A FEW COASTAL LOCATIONS) WILL SEE MINIMUM RELATIVE HUMIDITY VALUES NEAR OR BELOW 20 PERCENT. HOWEVER, BOTH FUEL MOISTURE AND WINDS WILL BE LIMITING FACTORS FOR THE FIRE WEATHER CONCERNS TODAY. MUCH OF DELMARVA AND FAR SOUTHERN NJ HAD RAIN TOTALS NEAR OR ABOVE 1 INCH YESTERDAY, LEADING TO HIGHER FUEL MOISTURES. FOR THE REST OF THE REGION HOWEVER, THE LIGHT RAIN YESTERDAY MAY NOT HAVE MADE A SIGNIFICANT IMPACT ON FUEL MOISTURE. AS FOR WINDS, A FEW GUSTS NEAR 20 KT ARE POSSIBLE ACROSS THE REGION. HOWEVER, THE TIGHTEST PRESSURE GRADIENT, AND THUS THE STRONGEST WINDS ARE EXPECTED IN THE MORNING AND NOT WITH THE LOWEST RELATIVE HUMIDITY VALUES. WE WILL CONTINUE TO MONITOR THIS CLOSELY THROUGH THE DAY, BUT FOR NOW WILL HOLD OFF ON ISSUING AN SPS. FOR THURSDAY, THE RELATIVE HUMIDITY VALUES ARE FORECAST TO DROP TO 25-35 PERCENT IN THE AFTERNOON MAINLY FOR NEW JERSEY /AWAY FROM THE COAST/ AND EASTERN PENNSYLVANIA, HOWEVER THE WINDS ARE CURRENTLY FORECAST TO BE 15 MPH OR LESS. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...GORSE NEAR TERM...JOHNSON SHORT TERM...JOHNSON LONG TERM...GORSE AVIATION...GORSE/JOHNSON MARINE...GORSE/JOHNSON FIRE WEATHER...GORSE/JOHNSON

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