Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 241227 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 827 AM EDT FRI APR 24 2015 .SYNOPSIS... A HIGH PRESSURE SYSTEM OVER THE WESTERN GREAT LAKES WILL BUILD SOUTHEAST AND REACH THE FORECAST AREA ON SATURDAY. A LOW PRESSURE SYSTEM EMERGING FROM THE CENTRAL ROCKIES WILL MOVE EAST THROUGH THE TENNESSEE VALLEY SATURDAY NIGHT AND OFF THE CAROLINA COAST ON SUNDAY. AN UPPER LEVEL DISTURBANCE WILL THEN OVER THE NORTHEAST ON MONDAY. A WEAK HIGH PRESSURE SYSTEM THEN BUILDS OVER THE AREA ON TUESDAY. A LOW PRESSURE SYSTEM WILL THEN MOVE ACROSS THE NORTHERN GULF OF MEXICO ON WEDNESDAY AND IS PREDICTED TO MOVE OFF THE SOUTHERN MIDDLE ATLANTIC STATES WATERS ON THURSDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WE HAVE CANCELLED THE FREEZE WARNING THIS MORNING AS TEMPERATURES ARE ABOVE FREEZING AND THE SUN HAS COME UP, SO TEMPERATURES WILL CONTINUE TO RISE. LOW PRESSURE WILL REMAIN NEARLY STATIONARY NEAR THE EASTERN MAINE/CANADA BORDER TODAY, WHILE HIGH PRESSURE BUILDS TO OUR WEST. THIS WILL KEEP A TIGHT PRESSURE GRADIENT ACROSS THE AREA THROUGH TODAY, LEADING TO BREEZY CONDITIONS. WITH CONTINUED GOOD MIXING TODAY, WE WILL BE ABLE TO MIX DOWN STRONGER WINDS FROM THE LOWEST 2,000-3,000 FEET, LEADING TO GUSTS AROUND 25-30 MPH THROUGH THE DAY. A DIFFUSE SURFACE TROUGH IS FORECAST TO CROSS THE AREA TODAY, WHILE THE CHANNELIZED VORTICITY ALOFT SLIDES ACROSS THE AREA. WITH LIMITED MOISTURE, PW`S LESS THAN ONE-QUARTER OF AN INCH AND LOW RH`S IN THE LOW LEVELS, WE DO NOT EXPECT ANY PRECIPITATION. THERE COULD BE SOME FLURRIES/SPRINKLES ACROSS THE WESTERN AREAS THIS MORNING, BUT DON`T THINK THERE IS ENOUGH COVERAGE TO PUT IN FORECAST. CLOUD COVER WILL CONTINUE THIS MORNING, BUT CLOUDS WILL BEGIN TO SCATTER OUT AND DISSIPATE THROUGH THE DAY WITH SUNSHINE RETURNING BY THE AFTERNOON. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... THE AREA OF LOW PRESSURE REMAINS TO OUR NORTHEAST TONIGHT, BUT BEGINS TO MOVE EASTWARD SOME, WHILE THE HIGH PRESSURE TO OUR WEST BEGINS TO WEAKEN. THE PRESSURE GRADIENT SHOULD BEGIN TO WEAKEN SOME, BUT WE WILL LIKELY CONTINUE TO HAVE A LIGHT BREEZE OVERNIGHT. SKIES ARE EXPECTED TO CLEAR OUT OVERNIGHT, AND WE`LL CONTINUE TO HAVE COLD ADVECTION THROUGH THE NIGHT. TEMPERATURES SHOULD BE ABLE TO FALL MORE TONIGHT THAN THEY DID LAST NIGHT. WE WILL CONTINUE WITH THE FREEZE WATCH WHERE WE EXPECT TEMPERATURES TO REACH 32 OR LOWER, AND KEEP MENTION OF FROST IN THE FORECAST FOR MUCH OF THE AREA AS WELL. WE WILL LET LATER SHIFTS LOOK AT FUTURE GUIDANCE TO DETERMINE IF AND WHERE WE WOULD NEED FREEZE WARNINGS/FROST ADVISORY OVERNIGHT. && .LONG TERM /SATURDAY THROUGH THURSDAY/... A BLOCKY WEATHER PATTERN WITH A POSSIBLE NOR`EASTER AT THE END OF THE LONG TERM CONTINUES IN THIS LONG TERM PERIOD. WHILE MODELING CONSENSUS REMAINS CONSISTENT ABOUT A RELATIVELY BENIGN PASSAGE OF A SFC LOW OFF THE CAROLINA COAST ON SUNDAY, THERE CONTINUES TO BE VIOLENT MODEL SOLUTION SWINGS WITH THE END OF THE LONG TERM COASTAL SYSTEM. THE ECMWF HAS GONE FROM A ROBUST NOR`EASTER TO FUGETABOUTIT TO ROBUST NOR`EASTER IN THREE SUCCESSIVE 00Z SOUNDING MODEL RUNS. INDICATIONS OF A DOUBLE TELECONNECTION SWITCH FAVORS A ROBUST EAST COAST SOLUTION. THE QUESTION WILL BE DOWN THE ROAD HOW ROBUST FOR US. WHILE LAST NIGHT`S OP ECMWF RUN WAS REFUTED BY ITS ENSEMBLE BRETHREN, THIS ONE WE SUSPECT WILL GET SOME ENSEMBLE SUPPORT. THE OTHER MEDIUM RANGE MODELS ALSO HAVE A LOW PRESSURE SYSTEM GOING OFF THE EAST COAST, BUT ARE NOT AS STRONG AS THE ECMWF. BOTH THE OP GFS AND CAN GGEM RUNS WERE CLOSE TO THE MIDDLE OF THE PACK SOLUTIONS OF THEIR ENSEMBLE MEMBERS. ONCE AGAIN MODELING DIFFERENCES HAVE MORE TO DO WITH THE UPSTREAM WRN NOAM RIDGING COMING FROM THE BERING SEA CLOSED LOW AND NOT AS MUCH WITH THE CLOSED LOW IN THE WESTERN ATLANTIC. STAY TUNED. ITS A SIMILAR INITIALIZATION SCHEME TONIGHT WITH THE GFS BETTER AT 500MB WEST AND THE WRF/NAM BETTER EAST. ALSO THE WRF WAS SLIGHTLY BETTER AT 850MB AND 925MB WITH THE GFS HAVING MORE NEGATIVE (COLD BIAS) INITIALIZATION ERRORS. THE DP/DT WITH THE SAT NGT SYSTEM WITH THE GFS IS DEFINITELY MORE SUBDUED WITH THE UKMET NOW ASSUMING THE HONOR OF THE WETTEST/NORTHERNMOST SOLUTION. THE DP/DT IS ALSO BLOCKIER SUGGESTING THAT OUR CURRENT CLOSED LOW SHOULD NOT GET OUT OF THE WAY (THUS A MORE SUPPRESSED TRACK WITH LOW NUMBER ONE). LIKE LAST NIGHT WE USED THE GFS DIAG TO ADJUST THE FCST AND THIS COMES CLOSEST TO THE CAN GGEM OUTPUT IN OUR CWA. SREF ENSEMBLE MEAN SUGGESTS THE OP WRF/NAM IS TOO SUPPRESSED. EXCEPT FOR THE UKMET, ALL OTHER MODELS ARE DRY FOR SATURDAY DAY. THE 250MB JET POSN PREDICTED BY THE UKMET LOOKS TO BE IN MODE CONFLICT WITH PCPN ARRIVING. SO POPS WERE KEPT OUT OF OUR CWA THRU SATURDAY AFTERNOON. THE POSN OF THE JET WHILE TOO CLOSE NORMALLY FOR PCPN COULD HELP GENERATE THICKER CIRRUS ACROSS OUR CWA AS CLOUDS OVERALL INCREASE. GREATER CONFIDENCE ABOUT MAX TEMPS BEING REACHED NORTHEAST THAN SOUTHWEST. WITH THE SFC HIGH IN CLOSE PROXIMITY, WINDS OVERALL WILL BE LIGHTER. NOT MUCH OF A CHANGE TO POPS FOR SATURDAY NIGHT WITH THE CUT-OFF RIGHT AROUND THE LATITUDE OF PHL AND THE ACY EXPRESSWAY. THE LIKELY POPS IN DELMARVA WERE DETERMINED BY WHERE THE GFS HAS PREDICTED LLVL THETA E CONVERGENCE, MID LEVEL WAA AND WEAK 300K ISENTROPIC LIFT. THE DEEPER PREDICTED QVEC CONVERGENCE CUT-OFF HAS PHL NOW ON THE NORTHERN EDGE (WAS THRUT OUR CWA LAST NIGHT). WOULD EXPECT CLOUDS TO KEEP MIN TEMPS UP VS THE MUCH CHILLIER NIGHT TONIGHT. AS THE SURFACE LOW MOVES EASTWARD IN THE TENNESSEE VALLEY A SECONDARY IS PREDICTED TO FORM EAST OF NORTH CAROLINA AND BECOME "THE LOW". SOME REMNANT PCPN FROM THE PRIMARY LOW COULD LINGER IN DELMARVA ON SUNDAY. WE EDGED POPS SOUTHWARD AND LOWER AS THE DAY PROGRESSES. MENTION IS IN DELMARVA ONLY. FARTHER NORTH THE CONVECTIVE TEMP IS PREDICTED TO BE REACHED, SO PARTIAL SUNSHINE WILL SUFFICE. WE ARE ASSUMING THE GFS FAST BIAS IS IN FORCE WITH THE APPROACHING SHORT WAVE TO THE NORTH, SO NO POPS. MAX TEMPS BASED ON PREDICTED 925MB TEMPS. ONCE AGAIN BETTER CONFIDENCE NORTH THAN SOUTH. WE KEPT SUNDAY NIGHT DRY, BANKING ON THE LACK OF DAYTIME HEATING WILL NEGATE SHOWERS FROM DEVELOPING. BUT ON MONDAY WITH THE COLD POCKET STILL CLOSE TO OUR CWA AND CONVECTIVE TEMPS WITHIN REACH, WE KEPT IN THE CHANCE FOR SHOWERS. AN INCREASING GRADIENT FROM THE OFFSHORE LOW SHOULD ALSO MAKE IT BREEZIER. WITH WEAK HIGH PRESSURE BUILDING INTO OUR CWA, WE KEEP TUESDAY THROUGH WEDNESDAY DAY DRY. THEN WE ARE CLOSE TO WPC GUIDANCE FOR WEDNESDAY NIGHT AND THURSDAY. THIS COASTAL SYSTEM HAS THE POTENTIAL TO HAVE AN IMPACT ON OUR CWA, PENDING ITS FINAL TRACK AND INTENSIFICATION RATE. BUT THE FACT THAT BOTH THE PNA AND NAO WILL BE IN THE CORRECT LOADING POSN PRIOR TO THIS SYSTEM DOES ADD HIGHER CONFIDENCE OF IT OCCURRING. OF COURSE IF THE WRN ATLC CLOSED LOW REMAINS TOO CLOSE TO THE NOAM COAST, THIS NEXT SYSTEM TOO MAY NOT BE ABLE TO MAKE A SHARP TURN UP THE EAST COAST. && .AVIATION /13Z FRIDAY THROUGH TUESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS WILL PREVAIL ACROSS THE TAF SITES THROUGH THE PERIOD. CLOUD COVER THIS MORNING WILL BEGIN TO SCATTER OUT AND DISSIPATE THROUGH THE DAY WITH MOSTLY CLEAR SKIES RETURNING BY THIS AFTERNOON. WINDS WILL BE THE MAIN CONCERN AGAIN TODAY AS WINDS GUSTS WILL ONCE AGAIN GUST MID TO UPPER 20 KNOT RANGE AT TIMES TODAY. THE GUSTS SHOULD DROP OFF AFTER SUNSET AND OVERNIGHT, ALTHOUGH A STEADY BREEZE SHOULD REMAIN FOR MOST AREAS. OUTLOOK... SATURDAY...MAINLY VFR. SATURDAY NIGHT...MAINLY VFR CONDITIONS NORTHERN AIRPORTS AND TERMINALS. SOME RAIN AND SUB-VFR CONDITIONS ARE POSSIBLE, MAINLY SOUTH OF A KILG/KACY LINE. SUNDAY AND SUNDAY NIGHT...BECOMING VFR DELMARVA AIRPORTS SUNDAY DAY AND MAINLY VFR REMAINING AIRPORTS AND TERMINALS. MONDAY...MAINLY VFR WITH SOME GUSTY NORTH TO NORTHWEST WINDS. SOME ISOLATED SHOWERS OCCURRING. MONDAY NIGHT AND TUESDAY...MAINLY VFR WITH LESS OF A WIND IMPACT, && .MARINE... WINDS ON THE BAY WHICH WERE GUSTING NEAR GALE CONDITIONS EARLY THIS MORNING HAD BEEN ON A DOWNWARD TREND BUT OVER THE LAST HALF HOUR HAVE STARTED TRENDING UPWARD AGAIN. THUS...ISSUED A GALE WARNING ON THE BAY THROUGH 5 PM EDT. THE SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR TODAY AND TONIGHT ON THE OCEAN AS WINDS WILL REMAIN ELEVATED WITH THE PRESSURE GRADIENT REMAINING ACROSS THE AREA AND SOME WINDS FROM ALOFT MIXING DOWN TO THE SURFACE. WITH THE NORTHWEST FLOW, SEAS ARE NOT EXPECTED TO BUILD SIGNIFICANTLY AND SHOULD BE AROUND 3-6 FEET. OUTLOOK... SATURDAY THROUGH SUNDAY...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED. THE LOW PRESSURE SYSTEM SHOULD PASS TOO FAR TO THE SOUTH TO GENERATE HIGHER SEAS OR WINDS. LOWEST CONFIDENCE ON DELAWARE OCEAN WATERS. SUNDAY NIGHT THROUGH MONDAY...NEAR SCA CRITERIA AS THE GRADIENT TIGHTENS BETWEEN THE OFFSHORE LOW AND APPROACHING HIGH PRESSURE SYSTEM. MONDAY NIGHT AND TUESDAY...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED. && .FIRE WEATHER... DRY AND GUSTY CONDITIONS ARE EXPECTED TODAY WITH RH VALUES EXPECTED TO DIP INTO THE LOW/MID 20S AND WINDS GUSTING AROUND 25-30 MPH. THE QUESTION REMAINS HOW MOIST THE FUELS ARE. NOT SURE HOW MUCH DRYING OCCURRED YESTERDAY WITH THE CLOUD COVER AND RELATIVELY HIGH HUMIDITY VALUES. WE PLAN TO ISSUE AN SPS THIS MORNING FOR ENHANCED FIRE SPREAD CONCERNS AND LET THE DAY SHIFT CONTACT STATE PARTNERS AGAIN TO ASCERTAIN FUEL MOISTURE CONDITIONS FOR TODAY AND SEE IF AN UPGRADE IS NEEDED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR PAZ060>062-101>106. NJ...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR NJZ001-007>010-012-013-015>022-027. DE...NONE. MD...FREEZE WATCH FROM LATE TONIGHT THROUGH SATURDAY MORNING FOR MDZ008. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT SATURDAY FOR ANZ450>455. GALE WARNING UNTIL 5 PM EDT THIS AFTERNOON FOR ANZ430-431. && $$ SYNOPSIS...GIGI NEAR TERM...ROBERTSON SHORT TERM...ROBERTSON LONG TERM...GIGI AVIATION...GIGI/JOHNSON/ROBERTSON MARINE...GIGI/JOHNSON/ROBERTSON FIRE WEATHER...ROBERTSON

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