Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 221955 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 355 PM EDT WED APR 22 2015 .SYNOPSIS...
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A COLD FRONT WILL PASS EAST OF THE MID ATLANTIC THIS EVENING, FOLLOWED BY A WEAKER, SECONDARY COLD FRONT CROSSING THE AREA DURING THURSDAY. HIGH PRESSURE WILL BRIEFLY BUILD OVER THE REGION FRIDAY INTO EARLY SATURDAY. LOW PRESSURE IS THEN FORECAST TO PASS BY TO OUR SOUTH FROM SATURDAY NIGHT INTO SUNDAY, TRACKING FROM AROUND THE TENNESSEE VALLEY TO OFF THE CAROLINA COAST. MORE HIGH PRESSURE MAY INFLUENCE OUR AREA LATE SUNDAY AND INTO EARLY NEXT WEEK, BEFORE THE NEXT STRONG LOW PRESSURE SYSTEM APPROACHES OUR REGION FROM THE SOUTH.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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COLD FRONT IS CURRENTLY SLIDING THROUGH THE REGION AND SHOULD BE MOVING OFF SHORE BY 6 OR 7 PM THIS EVENING. GIVEN THE DRY AIR ALREADY IN PLACE, THE WINDOW OF OPPORTUNITY FOR PRECIPITATION WILL CLOSE RAPIDLY AS THE FRONT PULLS AWAY FROM THE REGION. THE ONE POSSIBLE EXCEPTION TO THIS IS IN THE POCONOS WHERE TERRAIN ENHANCED LIFT MAY HELP PRECIP TO LINGER FOR MUCH OF THE EVENING. THE OTHER CONCERN TONIGHT WILL BE COLD AND FROST. FOR LOCATIONS GENERALLY ALONG AND NW OF THE FALL LINE, LOWS WILL LIKELY BE IN THE MID 30S OR LOWER. HOWEVER, FOR MANY OF THESE LOCATIONS WINDS WILL STAY NEAR OR ABOVE 10KT AND SKIES WILL BE VERY SLOWLY TO CLEAR. THEREFORE, HAVE ONLY MENTIONED PATCHY FROST FOR BERKS AND WESTERN CHESTER UP THROUGH THE LEHIGH VALLEY, BUT WILL HOLD OFF ON A FROST ADVISORY AT THIS TIME. AS FOR FREEZE WARNINGS, EVEN SLIGHTLY UNDERCUTTING GUIDANCE, THE ONLY PLACES THAT LOOK TO DROP BELOW FREEZING ARE IN THE POCONOS WHERE THE GROWING SEASON HAS NOT STARTED YET.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
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A SECONDARY, WEAK COLD FRONT IS EXPECTED TO CROSS THE REGION MID DAY TOMORROW. HOWEVER, EXPECT LITTLE IMPACT ASIDE FROM KEEPING WINDS GUSTY THROUGH THE DAY. WITH THE CONTINUED VERY DRY CONDITIONS, THERE WILL BE SOME FIRE WEATHER CONCERNS, SEE THE FIRE WEATHER SECTION BELOW. IN THE WAKE OF BOTH THE FRONT TODAY AND THE FRONT TOMORROW, HIGHS WILL BE CONSIDERABLY LOWER THAN WHAT WE SAW TODAY. HIGHS ARE GENERALLY EXPECTED IN THE 40S AND 50S, AROUND 10 TO 15 DEGREES BELOW NORMAL.
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&& .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
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BELOW AVERAGE TEMPERATURES ARE EXPECTED FOR THE REGION INTO THE LONG TERM PERIOD. FOLLOWING THE PASSAGE OF A SECONDARY COLD FRONT ACROSS OUR AREA DURING THE DAYTIME THURSDAY, BRISK WEST-NORTHWEST WINDS WILL CONTINUE INTO THURSDAY NIGHT, DELIVERING A REINFORCING SHOT OF COOL, DRY AIR INTO THE REGION. THIS AIRMASS MAY BE COLD ENOUGH TO WARRANT FROST OR FREEZE RELATED HEADLINES IN PA AND NJ WHERE THE GROWING SEASON HAS STARTED, WHICH WOULD INCLUDE ALL OF OUR NORTHERN CWA EXCEPT FOR THE POCONOS. INTO FRIDAY, DAYTIME TEMPERATURES ARE EXPECTED TO RUN AROUND TEN DEGREES BELOW LATE APRIL AVERAGES AS AN AREA OF HIGH PRESSURE TO OUR WEST GRADUALLY SPREADS INTO THE MID ATLANTIC. THE RATHER BRISK WEST- NORTHWEST FLOW WILL CONTINUE ACROSS THE REGION, WITH WINDS FOR A TIME GUSTING TOWARD 25 TO 30 MPH, ESPECIALLY INTO THE AFTERNOON. BY FRIDAY NIGHT AS HIGH PRESSURE BUILDS OVER THE REGION, WINDS SHOULD BEGIN TO SUBSIDE, BUT MAINLY CLEAR SKIES AND A DRY AIRMASS WILL ALLOW FOR GOOD RADIATIONAL COOLING WITH MORE POTENTIAL FROST/FREEZE CONCERNS, ESPECIALLY IN MORE RURAL LOCATIONS. THE PREVIOUSLY MENTIONED HIGH PRESSURE IS FORECAST TO BE EDGING EAST AND OFFSHORE THROUGH THE COURSE OF SATURDAY AS A LOW PRESSURE SYSTEM ORGANIZES OVER THE CENTRAL PLAINS TO MID-MISSISSIPPI VALLEY REGION. THIS LOW PRESSURE SYSTEM IS THEN PROGGED TO TRACK ACROSS THE TENNESSEE VALLEY TO OFF THE CAROLINA COAST FROM SATURDAY NIGHT INTO SUNDAY. WHILE THIS SYSTEM IS ANTICIPATED TO REMAIN TO OUR SOUTH, SOME LIGHT SHOWERS/RAIN CANNOT BE RULED OUT SATURDAY NIGHT, MAINLY FOR OUR DELMARVA ZONES AND PERHAPS FAR SOUTHERN NEW JERSEY. THIS LOW PRESSURE SYSTEM IS THEN FORECAST TO MOVE OUT TO SEA RATHER QUICKLY THROUGH THE COURSE OF SUNDAY, LEAVING THE DAYTIME SUNDAY FOR OUR AREA WITH QUIET CONDITIONS, SLIGHTLY BELOW AVERAGE TEMPERATURES, AND A LIGHT NORTHWEST FLOW. GOING INTO EARLY NEXT WEEK, MODEL SOLUTIONS TEND TO DIVERGE MORE, LEADING TO MORE UNCERTAINTY IN THE TIMING AND DEVELOPMENT OF THE NEXT POTENTIAL LOW PRESSURE SYSTEM TO AFFECT THE REGION. AN OVERALL MODEL CONSENSUS WOULD INDICATE THAT WEAK HIGH PRESSURE WOULD CONTINUE TO INFLUENCE THE REGION THROUGH MOST OF MONDAY AND TUESDAY, WITH A CONTINUED NORTHWEST FLOW AS A MID/UPPER LOW LINGERS OVER THE NEW ENGLAND STATES. THERE ARE SOME MODEL DIFFERENCES BETWEEN THE ECMWF, GFS, AND OTHERS WITH REGARDS TO THE PLACEMENT OF THIS MID/UPPER LOW, AND THERE MAY BE THE POTENTIAL FOR SOME ISOLATED/SCATTERED SHOWERS INTO OUR REGION, ESPECIALLY FOR OUR NORTHERN CWA. THE MAIN DEVELOPING SYSTEM TO WATCH, THOUGH, WILL BE A STRONGER AREA OF LOW PRESSURE ORGANIZING SOMEWHERE OVER THE SOUTH- CENTRAL UNITED STATES. WITH THIS SYSTEM, THERE ARE EVEN GREATER MODEL DIFFERENCES, WITH THE PREVIOUS RUN OF THE GFS SHOWING STRONG SURFACE LOW PRESSURE OVER THE CENTRAL PLAINS EARLY TUESDAY EVENTUALLY TRACKING TO OFF THE MID ATLANTIC COAST INTO MIDWEEK, WHILE THE ECMWF INDICATES A MORE SOUTHERN TRACK FROM AROUND THE LOWER MISSISSIPPI VALLEY TUESDAY TO OFF THE SOUTHEASTERN SEABOARD INTO WEDNESDAY. THE LATEST 12Z GFS, HOWEVER, IS BEGINNING TO TREND MORE IN THE DIRECTION OF THE ECMWF, WITH MORE OF A SOUTHERN TRACK LOW PRESSURE THAT EVENTUALLY EMERGES MORE OFF THE SOUTHEASTERN SEABOARD BEFORE TRACKING NORTHEAST ALONG THE COAST. WHILE THE GFS MAY BE TRENDING MORE TOWARD THE ECMWF TRACK-WISE, THERE ARE STILL NOTICEABLE TIMING DIFFERENCES AS THIS LOW PRESSURE THEN TRACKS NORTHEAST ALONG THE EAST COAST DURING THE MIDWEEK PERIOD. DESPITE THE RATHER LARGE MODEL DIFFERENCES IN THE TRACK AND TIMING OF THIS SYSTEM, THERE DOES LOOK TO BE AN INCREASING POTENTIAL FOR PRECIP ASSOCIATED WITH THIS SYSTEM INTO OUR REGION BY MIDWEEK, AND WE HAVE OPTED FOR CHANCE POPS AT THIS TIME, ESPECIALLY FROM TUESDAY NIGHT THROUGH WEDNESDAY.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. SHOWERS AND STORMS WILL BE MOVING OFF SHORE BY 00Z. AS THEY DO, EXPECT WINDS TO SUBSIDE, ESPECIALLY AFTER SUNSET. ONCE THE SHOWERS AND STORMS MOVE OUT OF THE REGION, EXPECT VFR CONDITIONS FOR THE REMAINDER OF THE TAF PERIOD. WINDS WILL INCREASE AFTER SUNRISE AGAIN TOMORROW MORNING, AND REMAIN BREEZY THROUGH THE DAY. OUTLOOK... THURSDAY NIGHT...VFR CONDITIONS WITH WESTERLY WINDS AVERAGING 10 TO 15 KNOTS THROUGH THE NIGHT. FRIDAY...CONTINUED MAINLY VFR CONDITIONS, WITH GUSTY WEST-NORTHWEST WINDS TO AROUND 25 KNOTS, ESPECIALLY LATE MORNING AND THROUGH THE AFTERNOON. SATURDAY...CONTINUED MAINLY VFR CONDITIONS. SOME SHOWERS AND SUB-VFR ARE POSSIBLE INTO SATURDAY NIGHT, MAINLY SOUTH OF A KILG/KACY LINE. SUNDAY AND MONDAY...MAINLY VFR CONDITIONS ARE EXPECTED.
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&& .MARINE...
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STRONG GUSTS ARE POSSIBLE IN THE VICINITY OF SHOWERS AND THUNDERSTORMS THAT WILL BE MOVING THROUGH FROM NOW THROUGH THE EARLY EVENING HOURS. ONCE SHOWERS AND STORMS MOVE OUT, WIND GUSTS NEAR OR ABOVE 25 KT, AND WAVE HEIGHTS NEAR 5 FT ARE EXPECTED TO CONTINUE ON THE OCEAN WATERS TONIGHT AND TOMORROW. ON THE BAY, SCA CONDITIONS ARE EXPECTED THROUGH THE OVERNIGHT HOURS. HOWEVER, BY TOMORROW, WIND GUSTS SHOULD BE NEAR 20KT. OUTLOOK... THURSDAY NIGHT AND FRIDAY...SCA CONDITIONS WILL LIKELY BE FELT ON THE AREA WATERS, ESPECIALLY DURING THE DAYTIME FRIDAY AS WEST- NORTHWEST WINDS ARE ANTICIPATED TO GUST INTO THE 25 TO 30 KNOT RANGE. SATURDAY AND SUNDAY...SUB-ADVISORY CONDITIONS ARE EXPECTED. MONDAY...CONTINUED SUB-SCA CONDITIONS; ALTHOUGH, SOME WIND GUSTS TO AROUND 20 KNOTS PLUS ARE POSSIBLE.
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&& .FIRE WEATHER...
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VERY DRY AND GUSTY CONDITIONS ARE EXPECTED DURING THE DAY TOMORROW. AT THIS POINT, EXPECT MINIMUM RELATIVE HUMIDITY VALUES TO BE RIGHT AT OR JUST ABOVE 30 PERCENT. SO FIRE WEATHER CONDITIONS WILL BE MARGINAL. HOWEVER, RAIN AMOUNTS TODAY HAVE BEEN VERY LIGHT, GENERALLY ONLY A FEW HUNDREDTHS OF AN INCH. SO FUELS ARE EXPECTED TO DRY OUT QUICKLY TOMORROW, AND WHILE WE MAY NOT QUITE REACH RED FLAG CRITERIA TOMORROW, THIS COULD SET THE STAGE FOR WORSE CONDITIONS ON FRIDAY. CONDITIONS MAY BE ENHANCED ON FRIDAY FOR THE POTENTIAL OF WILDFIRE SPREAD ACROSS THE REGION. FRIDAY`S RELATIVE HUMIDITY VALUES ARE PROGGED TO DROP POSSIBLY BELOW 30 PERCENT IN SOME AREAS FOR A TIME FROM LATE FRIDAY MORNING AND THROUGH THE AFTERNOON TO EARLY EVENING. IN ADDITION, SUSTAINED WEST-NORTHWEST WINDS BETWEEN 15 TO 20 MPH ARE FORECAST DURING THIS TIMEFRAME, WITH GUSTS REACHING BETWEEN 25 TO 30 MPH AT TIMES. WE WILL CONTINUE TO MONITOR THE LATEST GUIDANCE AND COORDINATE WITH OUR FIRE WEATHER PARTNERS IF ANY ADDITIONAL PRODUCTS BECOME NECESSARY.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY 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/KLINE

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