Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 230123 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 923 PM EDT TUE APR 22 2014 .SYNOPSIS... A COLD FRONT WILL CROSS THE AREA THIS EVENING. HIGH PRESSURE WILL THEN BUILD IN BEHIND THE FRONT FOR WEDNESDAY AND THURSDAY. THE HIGH COMBINED WITH LOW PRESSURE EAST OF NEW ENGLAND WILL RESULT IN GUSTY NORTHWEST WINDS ON WEDNESDAY AND THURSDAY. ANOTHER AREA OF LOW PRESSURE WILL MOVE TO THE NORTH AND BRING A WEAK FRONT THROUGH THE REGION LATE FRIDAY INTO EARLY SATURDAY, FOLLOWED BY MORE HIGH PRESSURE AND FAIR WEATHER FOR SUNDAY. ANOTHER STORM SYSTEM APPROACHES SLOWLY FROM THE SOUTHWEST AND BEGINS TO AFFECT OUR REGION LATER MONDAY INTO TUESDAY. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 930PM UPDATE...INITIAL LINE OF SHOWERS AND STORMS HAS MOSTLY FALLEN APART. THERE ARE STILL TWO AREAS OF SHOWERS, ONE ALONG THE CHESAPEAKE BAY, AND ANOTHER NORTH OF THE POCONOS THAT MAY HAVE A CHANCE TO MOVE INTO THE REGION A BIT LATER AS THE MAIN FRONT ARRIVES. BASED ON OBS, IT LOOKS LIKE THE SHOWERS AND STORMS OUT RAN THE COLD FRONT, SO THE MAIN COLD FRONT REMAINS JUST OUTSIDE OF OUR CWA AT THIS TIME. ADJUSTED POPS TO ACCOUNT FOR THE LATEST TRENDS, BUT OTHERWISE NO MAJOR CHANGES TO THE FORECAST. PREVIOUS NEAR TERM DISCUSSION...THROUGH LATE-DAY, A COLD FRONT WILL CONTINUE TO SLOWLY PROGRESS EASTWARD, EVENTUALLY CROSSING OUR FORECAST AREA BY LATE EVENING. MODEL GUIDANCE AND ACTUAL OBSERVATIONS TO OUR WEST CONTINUE TO SHOW LIMITED MOISTURE WITH THIS FRONTAL PASSAGE, AND MOST AREAS WILL ONLY SEE A TENTH TO PERHAPS TWO TENTHS OF AN INCH OF RAIN FROM SHOWERS AS THE FRONT PASSES THROUGH THE REGION. THERE IS ALSO LIMITED INSTABILITY THROUGH LATE-DAY AND THIS EVENING, BUT WE DID KEEP SLIGHT CHANCE/ISOLATED THUNDER IN THE FORECAST BASED ON FORECAST CAPES OFF THE GFS/NAM AND ECMWF. WINDS WILL CONTINUE TO BE OUT OF THE SOUTHWEST EARLY, THEN BECOMING MORE WESTERLY FOLLOWING THE FRONTAL PASSAGE. WE QUICKLY DECREASE POPS AFTER ABOUT 01Z FROM WEST TO EAST ACROSS THE FORECAST AREA AS THE FRONT ADVANCES TOWARD THE COAST AND OFFSHORE. THROUGH THE OVERNIGHT HOURS THEN, COOLER AND DRIER AIR WILL BEGIN TO OVERSPREAD THE REGION ON GUSTY NORTHWEST WINDS. IN FACT, THROUGH THE EARLY MORNING HOURS, NORTHWEST WINDS GUSTING BETWEEN 20 TO 25 MPH ARE ANTICIPATED. FOR TEMPERATURES, WE MOSTLY TOOK A MET/MAV GUIDANCE BLEND WITH SOME LOCAL ADJUSTMENTS AND EXPECT LOWS TO BE MAINLY IN THE 40S ACROSS THE REGION. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... A WINDY AND DRY DAY IS EXPECTED ON WEDNESDAY AS STRENGTHENING LOW PRESSURE LINGERS TO OUR NORTH OVER THE NEW ENGLAND STATES AND HIGH PRESSURE ACROSS THE GREAT LAKES AND MIDWEST GRADUALLY BUILDS EASTWARD THROUGH THE DAY. WITH THE STRONG PRESSURE GRADIENT BETWEEN THESE TWO SYSTEMS, GUSTY NORTHWEST WINDS WILL BE FELT ACROSS OUR FORECAST AREA THROUGH THE DAY, WITH GUSTS INTO THE 30 TO 35 MPH RANGE. WITH A MID-LEVEL TROUGH PASSING OVERHEAD, A COUPLE OF ISOLATED SHOWERS OVER THE HIGHER TERRAIN OF OUR FAR NORTHWEST ZONES CANNOT BE RULED OUT, BUT OTHERWISE, DRY CONDITIONS AND SOME SUNSHINE ARE EXPECTED. DAYTIME TEMPERATURES ARE EXPECTED TO BE AROUND 10 TO 15 DEGREES COOLER THAN TUESDAY, WITH 850/925MB TEMPS SUPPORTING HIGHS REACHING MOSTLY IN THE UPPER 50S TO LOWER 60S FOR MUCH OF THE REGION. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... HIGH PRESSURE WILL BE BUILDING OUT OF THE GREAT LAKES REGION TOWARD OUR AREA AT THE BEGINNING OF THIS TIME PERIOD WHILE A STRONG LOW PRESSURE SYSTEM NEAR MAINE MOVES SLOWLY AWAY. THE PRESSURE GRADIENT BETWEEN THE TWO SYSTEM WILL RESULT IN STRONG WINDS OVER AREA FOR WEDNESDAY NIGHT INTO THURSDAY. SIGNIFICANT FIRE WEATHER THREAT POSSIBLE ON THURSDAY WITH THE COMBINED AFFECT OF THE STRONG WINDS AND DAYTIME RELATIVE HUMIDITIES DROPPING BELOW 25 PERCENT FOR THE AREA. FOR WEDNESDAY NIGHT INTO FRIDAY...USED A MET/MAV BLEND FOR TEMPERATURES. NEXT STORM SYSTEM PASSING BY TO OUR NORTH LATE FRIDAY INTO EARLY SATURDAY BRINGS ANOTHER FRONT THROUGH THE REGION. USED WPC SURFACE FRONT FORECAST FOR PRECIPITATION/WIND TIMING. END RESULT WAS VERY LITTLE CHANGE FROM WHAT WAS PREVIOUSLY IN THE GRIDS. FOR FRIDAY NIGHT INTO TUESDAY...USED WPC EXTENDED RANGE GUIDANCE AS FIRST GUESS FOR GRIDS. ONLY MINOR MODIFICATIONS MADE TO THAT DATA SET. NEXT STORM SYSTEM TO AFFECT THE REGION WILL BE LATER MONDAY INTO TUESDAY. THIS IS A SLOW MOVING SYSTEM PER WPC MAPS AND DISCUSSION. TRIMMED BACK PRECIPITATION START TIME IN PREVIOUS FORECAST TO LATER ON MONDAY. ADDITIONAL ADJUSTMENTS MAY BE NEEDED DOWN THE ROAD AS SLOW MOVING SYSTEMS TEND TO BE EVER SLOWER THAN INITIALLY FORECAST. REVIEWING THE FORECAST TEMPERATURES FOR THIS TIME PERIOD... OVERALL VERY CLOSE TO SEASONAL NORMS. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. EVENING UPDATE...THE THUNDERSTORM THREAT IS GENERALLY OVER FOR MOST TERMINALS. THERE IS A SMALL THREAT THAT MVFR CEILINGS WILL DEVELOP BEHIND THE COLD FRONT THAT WILL MOVE THROUGH THE REGION SHORTLY, BUT IT IS TOO SMALL OF A THREAT TO MENTION IN THE TAFS NOW. PREVIOUS AVIATION DISCUSSION...MAINLY VFR CONDITIONS WILL CONTINUE LATE-DAY AND THIS EVENING; ALTHOUGH, A BRIEF REDUCTION TO MVFR IS POSSIBLE IN RAIN SHOWERS, MAINLY DUE TO REDUCED VISIBILITIES. WHILE ISOLATED TSTMS CANNOT BE RULED OUT, WE HAVE LOW CONFIDENCE IN THUNDER FOR THE TAF SITES...SO THIS WAS NOT INCLUDED IN THE TAFS. WINDS WILL TURN FROM THE SOUTHWEST TO WEST WITH THE FRONTAL PASSAGE THIS EVENING AND BECOME GUSTY AND OUT OF THE NORTHWEST DURING THE OVERNIGHT HOURS. GUSTS TO BETWEEN 20 TO 25 KNOTS CAN BE EXPECTED DURING THE OVERNIGHT HOURS, WITH GUSTS IN THE 30 KNOT RANGE DURING THE DAYTIME WEDNESDAY. OTHERWISE, VFR AND DRY CONDITIONS ARE EXPECTED THROUGH THE DAYTIME WEDNESDAY. OUTLOOK... WED NIGHT THROUGH THU...VFR CONDS WITH NW WINDS IN THE 20 TO 30 KT RANGE. HIGH CONFIDENCE. FRI THROUGH SAT...MAINLY VFR BUT LOCALLY MVFR IN SCATTERED SHOWERS FRI NIGHT INTO EARLY SAT. MDT CONFIDENCE. SUN...VFR CONDITIONS. MODERATE CONFIDENCE. && .MARINE... WITH THE AFTERNOON PACKAGE, WE DECIDED TO UPGRADE THE GALE WATCH TO A GALE WARNING FOR OUR ATLANTIC COASTAL WATERS, BEGINNING AT 12Z WEDNESDAY AND LASTING INTO THE DAYTIME THURSDAY. WIND GUSTS AND SEAS WILL BEGIN TO INCREASE INTO SCA TERRITORY DURING THE OVERNIGHT HOURS FOLLOWING A COLD FRONTAL PASSAGE. DURING THE DAYTIME WEDNESDAY AND INTO THURSDAY GALE FORCE WIND GUSTS AROUND 35 KNOTS PLUS ARE EXPECTED. FOR DELAWARE BAY, WE MAINTAIN THE SMALL CRAFT ADVISORY AND EXTENDED IT INTO THE DAYTIME THURSDAY. WIND GUSTS FOR THE BAY SHOULD PRIMARILY TOP OUT AROUND 30 KNOTS DURING WEDNESDAY. OUTLOOK... WED NIGHT THROUGH THU...GALE FORCE GUSTS LIKELY ON THE OCEAN WITH GUSTS AROUND 35 KT AND POSSIBLY HIGHER. A GALE WARNING HAS NOW BEEN ISSUED. WIND SUBSIDING LATER THU. FRI THROUGH SUN...NO MARINE HEADLINES ARE ANTICIPATED AT THIS TIME, THOUGH WE COULD APPROACH SCA WIND BY SAT NIGHT. && .FIRE WEATHER... A FIRE WEATHER WATCH HAS BEEN ISSUED FOR WEDNESDAY. NORTHWEST WINDS WITH GUSTS OVER 30 MPH WILL BE WELL OVER FIRE WEATHER CRITERIA. RH VALUES MAY STAY ABOVE 30 PERCENT ON WEDNESDAY BUT FUEL MOISTURE VALUES WILL ALSO BE A PROBLEM AS RAINFALL TONIGHT IS EXPECTED TO BE LIGHT. BOTTOM-LINE IS THAT THERE IS ENOUGH OF A RISK BASED ON THE WINDS AND FUEL MOISTURE TO JUSTIFY A WATCH FOR WEDNESDAY. PROBLEMS ARE LIKELY TO CONTINUE INTO THURSDAY. THOUGH WINDS GUSTS MAY BE A LITTLE LOWER, RH VALUES WILL DROP BELOW 20% IN MANY LOCATIONS THURSDAY AFTERNOON AND FUEL MOISTURE LEVELS WILL CONTINUE TO BE A PROBLEM. MONITOR THE FORECAST AS FIRE WEATHER HEADLINES MAY BE REQUIRED ON THURSDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING FOR PAZ054-055-060>062-070-071-101>106. NJ...FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING FOR NJZ001-007>010-012>027. DE...FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING FOR DEZ001>004. MD...FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING FOR MDZ008-012-015-019-020. MARINE...GALE WARNING FROM 8 AM WEDNESDAY TO NOON EDT THURSDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL NOON EDT THURSDAY FOR ANZ430-431. && $$ SYNOPSIS...SZATKOWSKI NEAR TERM...JOHNSON/KLINE SHORT TERM...KLINE LONG TERM...SZATKOWSKI AVIATION...SZATKOWSKI/JOHNSON/KLINE MARINE...SZATKOWSKI/KLINE FIRE WEATHER...

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