Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 122326 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 626 PM EST FRI FEB 12 2016 .SYNOPSIS... AN ARCTIC FRONT WILL CROSS THE AREA TONIGHT. HIGH PRESSURE WILL BUILD ACROSS THE AREA LATER THIS WEEKEND AND THEN MOVE EAST SUNDAY NIGHT. LOW PRESSURE WILL DEEPEN ACROSS THE LOWER MISSISSIPPI VALLEY MONDAY AND THEN MOVE ALONG THE APPALACHIANS TUESDAY AND THEN NORTH INTO CANADA WEDNESDAY. MORE HIGH PRESSURE WILL BUILD IN FOR THE END OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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TONIGHT...SHALLOW MOIST ADVECTION ON S-SW FLOW PRIOR TO THE CFP. LATEST RADAR IMAGERY SHOWED SOME ENHANCED ECHOES...SNOW SHOWERS...ACRS SERN PA,NRN DE, SRN DE. HAVE INCREASED POPS A BIT ERLY, THOUGH MOST OF THE ECHOES LIKELY NOT REACHING THE GROUND. SW WIND MAY GUST 15 MPH EARLY TONIGHT. THEN A WIND SHIFT TO NORTHWEST AND GUSTY 20-30 MPH BY DAWN SATURDAY....POSSIBLE ISOLATED GUSTS 40-45 MPH AT SUNRISE PER ARRIVING STRONG CAA AND PRES RISES.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... WIND CHILL ADVY AND WIND ADVY POSTED IN ADDITION TO PRIOR WIND CHILL WARNING. SPS FROM YDY NO LONGER NEEDED. DEEPENING BOUNDARY LAYER MOMENTUM TRANSFER IS FEATURED ASSOCIATED WITH THE ONCOMING ARCTIC AIRMASS INVASION. LARGE LOW LVL LAPSE RATES AND BTV SNOW SQUALL PARAMETER INDICATING A POSSIBILITY OF FLURRIES OR SQUALLS BUT WILL THE SFC TT/TD SPREAD EXCEED 25F AND MAKE THOSE SQUALLS JUST VIRGA? SEEMS LIKE BEST CHC FOR A SQUALL WOULD BE THE MORNING AND IN THE REGION S OF THE PA TURNPIKE. AM THINKING OF GUSTS 50 MPH IN THE POCONOS AND ALSO SCATTERED 50 MPH GUSTS DEVELOPING IN THE KRDG-KPHL-KILG KACY AND NORTH SIDE OF DE BAY SLOT FOR THE AFTN. WIND ADVY ISSUED. NOT SURE HOW MANY NOTICED BUT THE NAM AND OP ECMWF HAVE BEEN A LITTLE CONSERVATIVE ON WIND. JUST LOOKS LIKE TOO DEEP A MIXED LAYER TO AVOID CONNECTING A FEW EDDIES OF 50 KT GUSTS DOWN FROM 6000 TO 7000 FT ALOFT. THE INVERSION SINKS TO NEAR 850 MB LATE IN THE DAY SATURDAY. STRONGEST WINDS ASIDE FROM THE INITIAL BURST NEAR 11-12Z, MAY BE LATE AFTN AND EVENING. FOR NOW WANTED TO LIMIT ADVY ONLY TO THE DAY AND IF ITS GUSTING 40 KT AT 3 PM SATURDAY, THEN SUSPECT IT CAN GUST 40-45 KT THROUGH 10 PM. CONFIDENCE ON VERIFICATION IS AVERAGE. THIS COULD BE OVERDONE BUT HAVE SEEN REPEATEDLY THE POCS WIND MATCH THE OVERWATER WIND NEAR 44065, AND NW FLOW STRONGEST GUSTS NEAR A RDG-PHL LINE. ALSO ADDED MD E SHORE ALONG THE STILL WARM CHES BAY AND DELAWARE ALONG THE BAY FROM WILMINGTON TO LEWES WHERE I THINK SOME HEFTY GUSTS COULD ADD TO THE CHILL. OTHERWISE WIDESPREAD GUSTS 40 MPH SATURDAY WITH PARTLY TO MOSTLY SUNNY SKIES .. TENDING TO CLEAR LATE DAY. WINDS WERE DERIVED FROM THE GFS, THE TEMPS FROM THE NAM MOS BLENDED WITH THE 2M TEMPS OF THE 12Z GFS/NAM. HRRX INDICATED NEAR 0 AT KMPO AT 17Z SATURDAY...WITHOUT A WIND CHILL. CANT SEE IT MORE THAN 17F AT PHL AT 18Z SAT...MAYBE EVEN A DEGREE OR 2 COLDER?. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... THE HEART OF THE ARCTIC AIR MASS WILL BE ACROSS THE AREA SATURDAY NIGHT AND INTO SUNDAY. DANGEROUSLY COLD TEMPERATURES AND WIND CHILL READINGS WILL BE ACROSS THE ENTIRE FORECAST AREA. NO PRECIPITATION IS EXPECTED. WINDS WILL DIMINISH THROUGH THE DAY SUNDAY. LOW TEMPERATURES SAT NIGHT AROUND -10 ACROSS THE FAR NORTH AND CLOSER TO 5 DEGREES ACROSS THE METRO PHILLY AREAS AND OVER THE DELMARVA. HIGH TEMPS SUNDAY IN THE TEENS MOST AREAS...BUT SINGLE DIGITS OVER THE SRN POCONOS. WIND CHILL READINGS -20 TO -32 FAR NORTH AND -5 TO -10 OVER THE DELMARVA. THE NEXT STORM SYSTEM WILL DEEPEN ACROSS THE SOUTH MONDAY AND MOVE UP THE INLAND EAST COAST TUESDAY/WEDNESDAY. THE TRACK OF THE SYSTEM THAT SEEMS TO BE COMING INTO BETTER AGREEMENT AMONGST THE OP MODELS FAVOR A LOW TRACK ACROSS THE CENTRAL/WESTERN PART OF OUR AREA. THIS WILL ALLOW A DECENT FLOW OF WARMER AIR TO OVERSPREAD THE REGION. THE PRECIPITATION WILL BEGIN ACROSS THE AREA MONDAY AS SNOW...BUT WILL CHANGE TO RAIN LATER MON NIGHT AND REMAIN MOSTLY RAIN TUESDAY. THE QPF COULD BE UP TO 2 INCHES OF RAIN IN MANY AREAS. THERE IS ALSO SOME CHC FOR AN ACCUMULATING SNOW MONDAY ACROSS (MOST LIKELY) ERN/NERN PA BEFORE THE CHANGE TO RAIN. EARLIEST PREDICTIONS FOR SNOW ACCUMS WOULD BE AROUND 1-3 INCHES AT THIS POINT. THE DETAILS WILL BE TUNED UP AS THE WEEKEND PROGRESSES. THE STORM MOVES UP INTO CANADA WEDNESDAY AND WILL BE FOLLOWED BY HIGH PRESSURE AND DRIER COOLER AIR FOR THE MIDDLE OF NEXT WEEK. && .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDS WILL CONTINUE. HOWEVER, BASED ON LATEST RADAR SHOWING SOME ENHANCED ECHOES, HAVE MOVED UP THE TIMING OF THE SHSN. MUCH OF ACTIVITY IS NOT REACHING THE GROUND, BUT AS CLOSE AS KPNE IS REPORTING SOME -SN. SO FAR THE SHSN HAS BEEN LIGHT ENOUGH TO BE VFR. HOWEVER, SOME MVFR CAN NOT BE RULED OUT, AND WILL CONTINUE TO INCLUDE IN THE FCSTS. SATURDAY...THE BIGGEST ISSUE AFFECTING AVIATION TRAVEL ON SATURDAY WILL BE THE WINDS. BEHIND THE AFOREMENTIONED COLD FRONT, THE WINDS WILL QUICKLY TURN TO THE WEST THEN NORTHWEST AND BECOME VERY GUSTY. SUSTAINED WINDS WILL BE AROUND 15-20 KNOTS BY 12-15Z AND INCREASE INTO THE AFTERNOON. WIND GUSTS FROM 25 KNOTS EARLY WILL INCREASE TO NEAR 40 KNOTS BY THE AFTERNOON. OUTLOOK... SATURDAY NIGHT AND SUNDAY...VFR CONDITIONS EXPECTED. NORTHWEST WINDS 10 TO 25 KNOTS WITH GUSTS 30-35 KNOTS EARLY, DIMINISHING SOME OVERNIGHT INTO SUNDAY. GUSTS STILL 20-25 KNOTS OVERNIGHT INTO EARLY SUNDAY. MONDAY-MONDAY NIGHT...DEGRADING CONDITIONS WITH MVFR/IFR LIKELY THROUGH THE DAY MONDAY INTO MONDAY NIGHT. SNOW POSSIBLY BEGINNING MONDAY FOR MANY AREAS, POSSIBLY MIXING WITH RAIN AT TIMES FOR SOME AREAS. TUESDAY-TUESDAY NIGHT...WIDESPREAD MVFR/IFR CONDITIONS. WINDY. WEDNESDAY...IMPROVING CONDITIONS. WINDY.
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&& .MARINE... LULL IN THE WIND AND SEAS WILL END SHORTLY AFTER MIDNIGHT. GALES AND FREEZING SPRAY WARNINGS-ADVISORIES POSTED. THE HEAVIEST FREEZING SPRAY WILL BE MIDNIGHT TO 7 AM ALONG THE SHORE WHERE SSTS NOW DOWN TO ABOUT 35-36F AND USED 35 FOR THE ZY THRESHOLD. ISOLATED 50 KT GUSTS POSSIBLE SATURDAY IN FUNNELED NW WIND DOWN DE BAY. OUTLOOK... SATURDAY-SATURDAY NIGHT...GALE WARNING CONTINUES WITH STRONG NORTHWEST FLOW ACROSS THE AREA. FREEZING SPRAY ADVISORY REMAINS IN EFFECT AS VERY COLD AIR AND STRONG WINDS WILL LEAD TO AT LEAST MODERATE FREEZING SPRAY. SUNDAY-SUNDAY NIGHT...GALE WARNING AND FREEZING SPRAY ADVISORY CONTINUE INTO SUNDAY MORNING. HOWEVER, WINDS WILL DIMINISH THROUGH THE DAY AND SUNDAY NIGHT AS HIGH PRESSURE BUILDS INTO THE AREA. MONDAY...SUB-SCA CONDITIONS. MONDAY NIGHT-WEDNESDAY...SMALL CRAFT ADVISORY CONDITIONS LIKELY...GALES POSSIBLE AS STRONG LOW PRESSURE MOVES UP THE EAST COAST. && .HYDROLOGY... BEFORE EVERYONE HEADS INTO THE WEEKEND, I WANTED TO BRING NEXT WEEK`S STORM INTO LIGHT AND MENTION THAT THERE IS A POTENTIAL FOR FLOODING ACROSS THE HSA. THERE`S STILL A LOT THAT NEEDS TO UNFOLD, BUT THE 5-DAY WPC QPF OF 1.50 TO 2.50 INCHES OF LIQUID COMBINED WITH ANOTHER 0.25 TO 0.50 INCH OF SWE ON THE GROUND WOULD VERY LIKELY CAUSE NUISANCE LOW-LYING FLOODING AND POSSIBLY SOME MINOR TO MODERATE RIVER FLOODING (RIVERS ASSOCIATED WITH OUR FORECAST POINTS). THIS ASSUMES MOST, IF NOT ALL, THE PRECIPITATION FALLS AS RAIN. THE UNCERTAINTY THIS AFTERNOON IS LARGE. YESTERDAY AT THIS TIME, THE PRECIPITATION WAS HEAVIEST TUESDAY AND TUESDAY NIGHT. NOW IT`S LATE MONDAY NIGHT INTO TUESDAY. BESIDES TIMING, TRACK IS QUITE DIFFERENT BETWEEN THE GFS AND EURO WITH THE EURO BEING FURTHER WEST AND MORE LIQUIDY. TRACK WILL PLAY A ROLE IN TEMPS AND NOT ONLY AFFECT WHAT TYPE OF PRECIPITATION FALLS, BUT ALSO AFFECT WHAT REMAINING SWE MELTS. THERE`S ABOUT 0.25 TO 0.50 SCATTERED ACROSS THE AREA. I CAN SAY WE ARE IN A BETTER SPOT THAN ON THE 3RD AND 4TH WHEN THERE WAS IN EXCESS OF 2.00 OF SWE ALONG THE I-78 CORRIDOR. AS AN FYI, ONE OF THE MAIN REASONS WE DIDN`T SEE THE FLOODING, THAT MODELS SUGGESTED, ON THE 3RD AND 4TH WAS BECAUSE ALL THE SWE DID NOT RAPIDLY COME OUT OF THE SNOWPACK. SNOWMELT CAN BE A TOUGH NUT TO CRACK. WHILE THE LACK OF SWE IS LOOKING BETTER ACROSS THE HSA, NOT ALL THE RIVERS HAVE RECEDED BACK TO WHERE THEY WERE PRIOR TO THE 3RD. SO RIVERS WILL START HIGHER AND THE COLD THIS WEEKEND WILL SURELY GET THE GROUND HARD FOR A VERY EFFICIENT RUNOFF. SO THE TAKE AWAY HEADING INTO THE WEEKEND IS TO UNDERSTAND THAT IF THE MONDAY INTO TUESDAY (OR TUESDAY INTO WEDNESDAY) EVENT IS ALL LIQUID ACROSS THE AREA, LOW-LYING, POOR DRAINAGE FLOODING IS LIKELY AND MINOR TO MODERATE RIVER FLOODING IS POSSIBLE. IF THE PRECIPITATION STARTS OFF AS SNOW OR ICE, THE FLOODING THREAT DECREASES. IF ALL SNOW FALLS, WE`RE POTENTIALLY JUST KICKING THE CAN DOWN THE ROAD FOR FUTURE FLOODING. TIME WILL TELL. && .CLIMATE... NEAR RECORD COLD IS STILL EXPECTED FOR PORTIONS OF OUR AREA SUNDAY MORNING, DESPITE THE MOS GUIDANCE...AND BY FAR THE COLDEST AIR OF THE SEASON SO FAR. BEST CHANCE FOR RECORD EQUALING OR EXCEEDING FOR VALENTINES DAY: KABE, KTTN, KPHL AND KMPO. RECORD LOW MAX`S CAN ONLY OCCUR FOR THIS EVENT ON SUNDAY THE 14TH, IF THEN. THOSE HAVE BEEN ADDED RECENTLY BELOW. SITE 2015-16 COLDEST SO FAR RECORD LOW FEB. 14TH ----RER LOW MAX ---------------------- -------------------- ABE 8 -1 IN 1979 14-1979 ACY 10 -6 IN 1979 13-1979 PHL 12 +2 IN 1979 14-1979 ILG 12 -4 IN 1979 13-1979 RDG 10 -4 IN 1983 TTN 9 0 IN 1916 GED 13 -7 IN 1979 MPO -1 -12 IN 1970 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WIND CHILL ADVISORY FROM 6 PM SATURDAY TO 9 AM EST SUNDAY FOR PAZ060>062-070-071-101>106. WIND ADVISORY FROM 6 AM TO 6 PM EST SATURDAY FOR PAZ054-055- 060-061-070-071-101>106. WIND CHILL WARNING FROM 6 AM SATURDAY TO 1 PM EST SUNDAY FOR PAZ054-055. NJ...WIND CHILL ADVISORY FROM 6 PM SATURDAY TO 9 AM EST SUNDAY FOR NJZ007>010-012>027. WIND ADVISORY FROM 6 AM TO 6 PM EST SATURDAY FOR NJZ001-014- 016>027. WIND CHILL WARNING FROM 6 AM SATURDAY TO 1 PM EST SUNDAY FOR NJZ001. DE...WIND CHILL ADVISORY FROM 6 PM SATURDAY TO 9 AM EST SUNDAY FOR DEZ001-002. WIND ADVISORY FROM 6 AM TO 6 PM EST SATURDAY FOR DEZ001>004. MD...WIND CHILL ADVISORY FROM 6 PM SATURDAY TO 9 AM EST SUNDAY FOR MDZ008-012. WIND ADVISORY FROM 6 AM TO 6 PM EST SATURDAY FOR MDZ008-012- 015-020. MARINE...HEAVY FREEZING SPRAY WARNING FROM MIDNIGHT SATURDAY NIGHT TO 9 AM EST SUNDAY FOR ANZ450>453. GALE WARNING FROM 4 AM SATURDAY TO 10 AM EST SUNDAY FOR ANZ430- 431-450>455. FREEZING SPRAY ADVISORY FROM 4 AM SATURDAY TO 10 AM EST SUNDAY FOR ANZ430-431-454-455. && $$ SYNOPSIS...O`HARA NEAR TERM...DRAG/NIERENBERG SHORT TERM...DRAG LONG TERM...O`HARA AVIATION...DRAG/NIERENBERG/O`HARA MARINE...DRAG/O`HARA HYDROLOGY... CLIMATE...

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