Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 241947 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 347 PM EDT FRI APR 24 2015 .SYNOPSIS...
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HIGH PRESSURE EXTENDING OVER THE GREAT LAKES WILL BRIEFLY BUILD ACROSS OUR REGION SATURDAY. A LOW PRESSURE SYSTEM WILL PASS BY TO OUR SOUTH FROM SATURDAY NIGHT INTO SUNDAY, TRACKING FROM AROUND THE TENNESSEE VALLEY TO OFF THE CAROLINA COAST. AN UPPER LEVEL DISTURBANCE IS EXPECTED TO PASS OVER THE NORTHEAST STATES ON MONDAY, FOLLOWED BY WEAK HIGH PRESSURE AFFECTING THE REGION ON TUESDAY. A DEVELOPING LOW PRESSURE SYSTEM IS THEN FORECAST TO MOVE ACROSS THE NORTHERN GULF OF MEXICO REGION WEDNESDAY BEFORE EMERGING OFF THE SOUTHEASTERN SEABOARD THURSDAY.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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AS THE HIGH BUILDS IN AND THE VERY SLOW MOVING LOW TO OUR NE BEGINS TO FILL, THE PRESSURE GRADIENT ACROSS THE REGION WILL DECREASE CONSIDERABLY...LEADING TO WINDS MOSTLY LESS THAN 10 MPH OVERNIGHT. THIS, COMBINED WITH CLEARING SKIES AND THE RELATIVELY COOL AIR MASS IN PLACE WILL LEAD TO A CHILLY NIGHT ACROSS THE REGION. SHOULD SEE LOWS FROM THE MID 20S IN THE HIGHER TERRAIN TO MID 30S ALONG THE COAST AND FOR MOST OF DELMARVA. THEREFORE, HAVE CHANGED THE FREEZE WATCH TO A FREEZE WARNING, AND HAVE ISSUED A FROST ADVISORY FOR MUCH OF THE REST OF THE REGION. NO FREEZE WARNING ISSUED FOR CARBON AND MONROE COUNTIES AS IT IS STILL EARLIER THAN THE AVERAGE LAST FREEZE FOR THAT AREA.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
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STUCK IN BETWEEN TWO LOWS, THE ONE TO OUR NE WHICH WILL CONTINUE TO FILL, AND THE LOW TO OUR SW, WHICH WILL REMAIN WELL TO OUR WEST TOMORROW, WE WILL CONTINUE TO SEE A RATHER WEAK PRESSURE GRADIENT, AND THUS RATHER LIGHT WINDS THROUGH THE DAY TOMORROW. DECREASED HIGHS SLIGHTLY AS WE`RE ONLY RELYING ON WEAK DOWNSLOPE FLOW FOR ANY WARMING TREND, SO TEMPERATURES SHOULD ONLY BE SLIGHTLY HIGHER THAN TODAY.
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&& .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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A COUPLE OF LOW PRESSURE SYSTEMS ARE EXPECTED TO AFFECT THE REGION DURING THE LONG TERM PERIOD, THE FIRST OF WHICH WILL LIKELY AFFECT MAINLY OUR SOUTHERN CWA AS THIS SYSTEM SWINGS BY TO OUR SOUTH, BUT A POTENTIALLY STRONGER, COASTAL SYSTEM MAY REACH THE AREA FOR THE MIDDLE OF NEXT WEEK. INTO SATURDAY NIGHT, AN AREA OF LOW PRESSURE WILL BE APPROACHING FROM AROUND THE OHIO/TENNESSEE VALLEY REGION. AS THIS SURFACE LOW PROGRESSES EASTWARD THROUGH THE NIGHT, A SECONDARY LOW IS FORECAST TO DEVELOP EAST OFF THE NORTH CAROLINA COAST BY SUNDAY MORNING. THE NORTHERN EDGE OF PRECIPITATION ASSOCIATED WITH THESE SYSTEMS IS EXPECTED TO EXTEND MAINLY INTO OUR SOUTHERN CWA, ESPECIALLY ACROSS OUR DELMARVA ZONES AND SOUTHERN NEW JERSEY, AND WE HAVE CHANCE TO LIKELY POPS FROM NORTH TO SOUTH SATURDAY NIGHT FOR THESE AREAS. THE LOW PRESSURE WILL THEN EXIT EAST AND OUT TO SEA THROUGH THE COURSE OF SUNDAY, BUT THERE COULD BE SOME LEFTOVER PRECIP THAT LINGERS OVER THE DELMARVA INTO SUNDAY MORNING, AND WE GRADUALLY DIMINISH POPS TO CHANCE AND THEN LOWER THROUGH THIS PERIOD. ELSEWHERE THROUGH THE FORECAST AREA, A DRY SUNDAY IS ANTICIPATED WITH SOME CLOUDS AND GENERALLY LIGHT NORTHERLY WINDS. MONDAY COULD PRESENT A FEW SHOWERS FOR OUR AREA AS AN UPPER DISTURBANCE/UPPER LOW LINGERS AROUND THE NORTHEAST STATES OR JUST TO THEIR EAST. MODEL FORECAST SOUNDINGS PREDICT CONVECTIVE TEMPERATURES TO BE REACHED MONDAY, SO THERE WILL BE INCREASING CLOUDS THROUGH THE DAY ALONG WITH SOME ISOLATED/SCATTERED SHOWERS EXPECTED AS COOLER AIR ALOFT ASSOCIATED WITH THE UPPER LOW LINGERS NEARBY. THE UPPER LOW PULLS AWAY OUT TO SEA INTO TUESDAY, AND WEAK HIGH PRESSURE FROM THE WEST GRADUALLY BUILDS ACROSS OUR REGION, LASTING THROUGH THE DAYTIME WEDNESDAY. WE HAVE KEPT A DRY FORECAST THROUGH THIS PERIOD, WITH RATHER LIGHT NORTHERLY WINDS AND NEAR AVERAGE END OF APRIL TEMPERATURES. THE TRICKY AND HIGHLY UNCERTAIN PART OF THE FORECAST THEN INVOLVES THE DEVELOPMENT AND TRACK OF A POTENTIALLY STRONG COASTAL SYSTEM THAT MAY BEGIN TO AFFECT OUR REGION WEDNESDAY NIGHT AND LASTING THROUGH THURSDAY TO THURSDAY NIGHT. THERE CONTINUES TO BE A WIDE RANGE OF SOLUTIONS FROM THE OPERATIONAL MODELS TO VARIOUS ENSEMBLE DATA REGARDING THE TRACK, EVOLUTION, AND INTENSIFICATION OF LOW PRESSURE, MOST LIKELY FROM AROUND THE NORTHERN GULF OF MEXICO REGION WEDNESDAY BEFORE ITS POTENTIAL EMERGENCE OFF THE EAST COAST THURSDAY. WITH THE GREATER UNCERTAINTY THROUGH THIS PERIOD, WE LEANED MORE TOWARD WPC GUIDANCE FOR MOST ELEMENTS, INCLUDING TEMPERATURES, WINDS, AND POPS, WITH ADDITIONAL COLLABORATION WITH NEIGHBORING OFFICES.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE TAF PERIOD. GUSTY NORTHWESTERLY WINDS SHOULD DECREASE BETWEEN 00Z AND 03Z, AND THEN REMAIN AROUND 10KT OR LESS THROUGH THE OVERNIGHT HOURS. WINDS MAY INCREASE AFTER SUNRISE TOMORROW, WITH WIND GUSTS AROUND 15KT POSSIBLE, BUT WIND SPEEDS SHOULD BE LESS THAN TODAY/S WINDS. OUTLOOK... SATURDAY NIGHT...PRIMARILY VFR CONDITIONS, EXCEPT SOME RAIN AND SUB- VFR POSSIBLE MAINLY SOUTH OF A KILG/KACY LINE, INCLUDING THE DELMARVA. SUNDAY...MAINLY VFR CONDITIONS, AS ANY SUB-VFR IN RAIN TO START ACROSS SOUTHERN AREAS WILL IMPROVE BACK TO VFR. MONDAY...MAINLY VFR CONDITIONS; ALTHOUGH, SOME ISOLATED SHOWERS ARE POSSIBLE. GUSTY NORTH TO NORTHWEST WINDS, WITH GUSTS TO 20 KNOTS. TUESDAY AND WEDNESDAY...MAINLY VFR EXPECTED; ALTHOUGH, CONDITIONS MAY DETERIORATE LATE WEDNESDAY NIGHT DEPENDING ON THE TIMING AND TRACK OF A POSSIBLE COASTAL LOW PRESSURE.
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&& .MARINE...
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SMALL CRAFT ADVISORY CONDITIONS WILL CONTINUE EVERYWHERE THROUGH EARLY EVENING. AFTER SUNSET, WINDS AND SEAS SHOULD BEGIN TO SLOWLY DECREASE. EXPECT SUB SCA CONDITIONS ON THE DE BAY BY THIS EVENING. ON THE OCEAN WATERS, SCA CONDITIONS MAY LINGER INTO THE EARLY MORNING HOURS ON SATURDAY. ONCE CONDITIONS FALL BELOW SCA CRITERIA, SUB SCA CONDITIONS ARE EXPECTED THROUGH THE DAY TOMORROW. OUTLOOK... SATURDAY NIGHT AND SUNDAY...SUB-ADVISORY CONDITIONS ARE EXPECTED AT THIS TIME. AN AREA OF LOW PRESSURE IS FORECAST TO PASS BY TO OUR SOUTH, BUT IT SHOULD NOT BE CLOSE ENOUGH TO RAISE WINDS OR SEAS TO SCA LEVELS. MONDAY...CONTINUED MAINLY SUB-SCA CONDITIONS; ALTHOUGH, SOME WIND GUSTS TO AROUND 20 KNOTS PLUS ARE POSSIBLE. TUESDAY AND WEDNESDAY...MOSTLY SUB-ADVISORY CONDITIONS THROUGH THIS PERIOD; ALTHOUGH, SOME HIGHER WINDS AND SEAS MAY BEGIN TO OCCUR LATE WEDNESDAY NIGHT DEPENDING ON THE TIMING AND TRACK OF POSSIBLE COASTAL LOW PRESSURE. LOW CONFIDENCE.
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&& .FIRE WEATHER...
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RELATIVE HUMIDITY VALUES AS OF 3 PM WERE GENERALLY BETWEEN 20 AND 30 PERCENT ACROSS THE REGION. EXPECT THIS TO CONTINUE INTO THE LATE AFTERNOON AND EARLY EVENING HOURS, SO WILL LET THE SPS CONTINUE THROUGH 8 PM EDT. DRY CONDITIONS ARE EXPECTED ONCE AGAIN TOMORROW, WITH MINIMUM RH VALUES ONCE AGAIN RANGING FROM 20 TO 35 PERCENT. HOWEVER, WINDS WILL BE CONSIDERABLY LIGHTER TOMORROW, WITH WIND GUSTS GENERALLY NEAR OR BELOW 15 MPH THROUGH THE DAY TOMORROW.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...FREEZE WARNING FROM 2 AM TO 8 AM EDT SATURDAY FOR PAZ060>062- 101>106. FROST ADVISORY FROM 2 AM TO 8 AM EDT SATURDAY FOR PAZ070-071. NJ...FREEZE WARNING FROM 2 AM TO 8 AM EDT SATURDAY FOR NJZ001- 007>010-012-013-015>022-027. FROST ADVISORY FROM 2 AM TO 8 AM EDT SATURDAY FOR NJZ014- 023>026. DE...FROST ADVISORY FROM 2 AM TO 8 AM EDT SATURDAY FOR DEZ001>004. MD...FREEZE WARNING FROM 2 AM TO 8 AM EDT SATURDAY FOR MDZ008. FROST ADVISORY FROM 2 AM TO 8 AM EDT SATURDAY FOR MDZ012-015- 019-020. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT SATURDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ430- 431.
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&& $$ SYNOPSIS...KLINE NEAR TERM...JOHNSON SHORT TERM...JOHNSON LONG TERM...KLINE AVIATION...JOHNSON/KLINE MARINE...JOHNSON/KLINE FIRE WEATHER...JOHNSON

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