Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 040612 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 112 AM EST WED MAR 4 2015 .SYNOPSIS... A WARM FRONT WILL LIFT THROUGH THE AREA OVERNIGHT...FOLLOWED BY A ARCTIC COLD FRONT DURING THE DAY WEDNESDAY. THE FRONT WILL PUSH TO OUR SOUTH INTO THURSDAY WHILE LOW PRESSURE DEVELOPS AND MOVES ALONG THE BOUNDARY. HIGH PRESSURE WILL RETURN TO THE MID ATLANTIC REGION FOR FRIDAY AND FRIDAY NIGHT. A FRONTAL PASSAGE IS EXPECTED SATURDAY INTO SATURDAY NIGHT...FOLLOWED BY HIGH PRESSURE AGAIN SUNDAY INTO SUNDAY NIGHT. ANOTHER FRONTAL PASSAGE IS EXPECTED MONDAY INTO MONDAY NIGHT. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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THE WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR BERKS COUNTY, UPPER BUCKS COUNTY, SOMERSET COUNTY AND POINTS NORTH. THE ADVISORY HAS BEEN DISCONTINUED SOUTH OF THAT LINE WHERE TEMPERATURES ARE ABOVE FREEZING, MAINLY IN THE MIDDLE AND UPPER 30S. WE CONTINUE TO EXPECT PATCHY LIGHT RAIN AND DRIZZLE OVERNIGHT THROUGHOUT OUR FORECAST AREA. SOME OF THE LIGHT RAIN AND DRIZZLE WILL CONTINUE TO FREEZE UPON CONTACT WITH THE GROUND IN THE ADVISORY AREA WHERE MANY LOCATIONS WILL REMAIN AT OR BELOW 32 DEGREES THROUGH THE BALANCE OF THE NIGHT.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/...
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WINTER WEATHER ADVISORY CONTINUES INTO THE FIRST PART OF WEDNESDAY MORNING FOR THE POCONO`S AND FAR NORTHWEST NJ, WHERE POCKETS OF SUB-FREEZING TEMPS AND FREEZING RAIN WILL PERSIST. OTHERWISE, WEDNESDAY WILL BE A RELATIVELY QUIET PERIOD IN BETWEEN TWO WINTER EVENTS. A COLD FRONT WILL APPROACH FROM THE NORTHWEST IN THE MORNING AND SLOWLY SAG SOUTHEASTWARD THROUGHOUT THE DAY. EXPECT PERIOD OF RAIN THROUGHOUT THE DAY FOR MUCH OF THE AREA. THE COVERAGE OF RAIN WILL BE HIGHEST NEAR THIS FRONTAL BOUNDARY. QPF AMOUNTS WILL BE LIGHT- LESS THAN A HALF INCH. LEANED TOWARD THE COOLER MET GUIDANCE FOR TEMPS GIVEN THE PERSISTENT CLOUDS AND PRECIP OVER THE AREA, AS WELL AS THE END TO THE WAA REGIME WITH WINDS VEERING OUT OF THE SOUTH AND SOUTHWEST. HIGHS WEDNESDAY RANGE FROM THE MID 30S IN THE POCONO`S TO THE UPPER 40S IN SOUTHERN DE. 18Z/3 NAM THERMAL PROFILE SUGGEST SLEET AND OR SNOW COULD BEGIN MIXING WITH ANY RAIN FALLING NEAR SUNSET FROM KRDG TO KABE NORTHWESTWARD.
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&& .LONG TERM /TONIGHT THROUGH TUESDAY/...
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S/WV ENERGY ROUNDING THE BASE OF A MID-LEVEL TROUGH SITUATED OVER GREAT LAKES WILL GRADUALLY VEER LARGE SCALE FLOW TO THE SOUTHWEST OVER THE MID-ATLANTIC. THIS WILL SLOW THE ADVANCE OF AN ARCTIC FRONT MOVING THROUGH THE AREA ON WEDNESDAY AND IT WILL BRIEFLY BECOME STATIONARY TO OUR SOUTH ON THURSDAY. MEANWHILE...CLOSED MID-LEVEL LOW EJECTS NEWD OUT OF BAJA CALIFORNIA...ACCOMPANIED BY SEVERAL SOUTHERN STREAM S/WV DISTURBANCES THAT WILL LEAD TO LOW PRES DEVELOPMENT ALONG THE NOW STATIONARY FRONT TO OUR SOUTH. THIS WILL PROMOTE A ROBUST OVERRUNNING REGIME OVER THE MID-ATL... FED BY BAJA/GMEX MOISTURE AND SUPPORTED BY THE LF QUADRANT OF A VIGOROUS 250 HPA JET. THE OPERATIONAL MODELS AND THEIR RESPECTIVE ENSEMBLES HAVE SIGNALED THIS SCENARIO FOR OVER A WEEK NOW...AND FINALLY APPEAR MUCH CLOSER TO A CONSENSUS ON THE LOW-LEVEL THERMAL PROFILE...BUT DIFFERENCES REMAIN IN THEIR DEPICTION OF THE QPF BULLSEYE AND AMOUNTS. AT THIS TIME...WE FAVOR THE NAM/ECMWF QPF...AND FEEL THE GFS IS OVERDONE. THIS WOULD PLACE THE MAX QPF BULLSEYE IN THE 00Z WED THRU 00Z THU TIME FRAME ALONG THE I-95 CORRIDOR. AS COLDER AIR WORKS IN FROM THE NORTHWEST...WE EXPECT RAIN TO GRADUALLY CHANGE TO SNOW FROM NORTH TO SOUTH WED NIGHT. KEEP IN MIND THERE IS STILL SOME DISAGREEMENT ON HOW QUICKLY THE LOW-LEVEL THERMAL PROFILE COOLS...AS SLPR FIELDS INDICATE THE REGION IS IN A SADDLE...WHICH IS SUPPORTIVE OF A SLOW COLD FROPA. ATTM...WE EXPECT THE RAIN TO CHANGEOVER TO SNOW IN THE NORTHWEST AROUND 00Z...AND PERHAPS AS LATE AS 09Z IN THE LOWER DELMARVA. AS FAR AS PTYPE AND AMOUNTS...WE`RE EXPECTING 6 TO 8 INCHES OF SNOW IN THE I-95 CORRIDOR WITH 4 TO 6 INCHES NORTH AND SOUTH OF THIS AREA. IF A MORE ROBUST WARM NOSE WORKS IN ALOFT...AS SUGGESTED BY THE NAM...THERE WOULD BE MORE SLEET WHICH WOULD CUT DOWN ON THE SNOWFALL AMOUNTS. ON THE OTHER HAND...ALTHOUGH OMEGA IN THE DENDRITIC SNOW GROWTH ZONE IS NOT ROBUST...FGEN IS INDICATED IN THE MID-LEVELS AND THIS COULD BOOST SNOWFALL TOTALS. FINALLY...IT IS QUESTIONABLE HOW MUCH DRY AIR AND/OR DOWNSLOPING DUE A NORTHERLY SURFACE FLOW WILL CUT DOWN ON QPF ACROSS THE NORTHERN PART OF THE CWA. FURTHER TO THE SOUTH OVER THE DELMARVA...SNOWFALL TOTALS COULD BE LOWER DUE TO A WARMER THERMAL PROFILE...IMPLYING A LONGER TRANSITION FROM RAIN TO SNOW. WITH THIS PACKAGE WE HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM WED NIGHT THRU THU EVE...WITH THE GREATEST UNCERTAINTY IN MEETING SNOWFALL CRITERIA NORTH OF THE I-78 CORRIDOR AND OVER FAR SOUTHEAST NJ AND THE SOUTHERN DELMARVA. WE EXPECT THE THURSDAY MORNING RUSH HOUR TO BE PARTICULARLY IMPACTED...ESPECIALLY IN THE I-95 CORRIDOR...WHERE SNOW COULD FALL MODERATE AT TIMES. SNOW IS EXPECTED TO END THURSDAY EVENING...AS THE MID-LEVEL TROUGH APPROACHES FROM THE WEST...AND PUSHES THE SYSTEM OFFSHORE. MUCH COLDER AIR WILL FILTER IN THU NIGHT WITH MIN TEMPS AROUND 20 DEGREES BELOW NORMAL. OTHERWISE...GENERALLY FAIR WEATHER IS EXPECTED THRU THE WEEKEND... WITH A WEAK COLD FRONTAL PASSAGE LIKELY LATER SAT OR EARLY SUNDAY. THE FRONT HAS LIMITED MOISTURE ATTM...SO THE FORECAST IS KEPT DRY. TEMPS MAY ACTUAL APPROACH SEASONABLE LEVELS ON SUNDAY. EARLY NEXT WEEK...THERE IS A LOT OF UNCERTAINTY WITH REGARD TO THE EVOLUTION OF BOTH NORTHERN AND SOUTHERN STREAM ENERGY...AND THE DEGREE OF PHASING THAT TAKES PLACE BETWEEN THE TWO OVER THE ERN CONUS. FOR NOW WE KEPT THIS PART OF THE FORECAST DRY AS WELL.
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OVERNIGHT...MVFR VARIABLE IFR CONDS IN -RA AND -DZ CHANGING WITH LIGHT SOUTHEAST TO SOUTH SURFACE WINDS BUT LLWS WITH STRONG WINDS NEAR THE INVERSION AROUND 2000 FT. PLS SEE TAFS FOR DETAILS. WEDNESDAY...MVFR OR IFR CONDS IN INTERMITTENT RAIN/DRIZZLE/FOG. POTENTIAL FOR A PERIOD OF LIFR FOG IN THE FRONTAL BOUNDARY DURING THE MORNING AS WARM AIR TEMPORARILY LAYS CLOSE TO THE NEAR FREEZING SNOW AND ICE SURFACES. SLEET/SNOW SHOULD BEGIN MIXING WITH ANY ON GOING RAIN VCNTY KABE AND KRDG AROUND 23Z. OUTLOOK... WED NIGHT AND THURSDAY...RAIN WILL GRADUALLY CHANGEOVER TO SLEET... THEN SNOW ACROSS THE TERMINALS FROM NORTH TO SOUTH. THE CHANGEOVER IS EXPECTED TO OCCUR AT ABE AND RDG BETWEEN AROUND 23Z/4-01Z/5...AT TTN, PNE, PHL, AND ILG AROUND 03Z/5...AND MIV AND ACY AROUND 06Z/5. THERE IS STILL SOME UNCERTAINTY AS TO WHAT TIME THE CHANGE TAKES PLACE. EXPECT MVFR CONDITIONS WITH IFR POSSIBLE IN SNOW AND LOW CEILINGS...PARTICULARLY AT TTN, PNE, PHL, AND ILG. THURSDAY NIGHT AND FRIDAY...SNOW WILL GRADUALLY END FROM WEST TO EAST ACROSS THE TERMINALS THU EVENING. EXPECT MVFR/IFR CONDITIONS TO IMPROVE TO VFR BY THURSDAY NIGHT AND REMAIN VFR THRU FRIDAY. SATURDAY AND SUNDAY...MVFR POSSIBLE IN LOW CLOUDS AND SHRA/SNSH WITH THE PASSAGE OF A COLD FRONT LATE SAT INTO EARLY SUNDAY... OTHERWISE VFR CONDITIONS EXPECTED.
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&& .MARINE...
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SOUTHERLY WINDS WILL INCREASE THIS EVENING. ALTHOUGH STORM-FORCE WINDS WILL BE LOCATED ONLY 1,000 FT AGL AND GALE-FORCE WINDS 200 FT AGL, A STRONG INVERSION WILL NOT BE FAVORABLE FOR THESE WINDS TO MIX DOWN TO THE SURFACE. HOWEVER, THE PRESSURE GRADIENT TIGHTENS ENOUGH FOR SUSTAINED WINDS TO APPROACH SCA CRITERIA TONIGHT. SEAS ARE ALSO FORECAST TO BUILD TO 4-5 FT OVERNIGHT. THEREFORE, A SCA WAS ISSUED FOR THE COASTAL WATERS. THE WINDS TURN MORE WESTERLY ON WEDNESDAY AND DECREASE JUST AHEAD OF A COLD FRONT. DO NOT EXPECT SCA GUSTS. HOWEVER, ELEVATED SEAS NEAR 5 FT MAY LINGER INTO THE MORNING. CONFIDENCE WASN`T HIGH ENOUGH TO EXTEND THE ADVISORY AT THIS POINT. OUTLOOK... WED NIGHT THRU FRIDAY...WINDS AND SEAS WILL LIKELY MEET SCA THRESHOLDS WED NIGHT THRU AT LEAST FRIDAY MORNING. FRIDAY AFTERNOON THRU SUNDAY...WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SCA THRESHOLDS.
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&& .HYDROLOGY...
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PLEASE MONITOR LATEST QPF FCSTS FROM WPC AND MARFC. TUESDAY FORECAST CYCLES CAME IN WETTER FOR WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT, ESPECIALLY SOUTH OF PHILLY. THE GFS, FOR INSTANCE, HAS 0.75 TO ABOUT 1.00 OF LIQUID ACROSS THE DELMARVA AND SOUTHERN NJ, SOUTH OF THE I295 CORRIDOR. WE`RE ONCE AGAIN TAKING NOTICE. A CHANGEOVER TO SLEET OR SNOW ISN`T EXPECTED TO OCCUR UNTIL EARLY THURSDAY MORNING. WHILE THERE ISN`T MUCH OF A SNOWPACK ACROSS THE SOUTHERN HALF OF OUR CWA, THE GROUND IS FROZEN, AND ANY RUNOFF WILL BE VERY EFFICIENT. IF THE 0.75 TO 1.00 MATERIALIZES, WE FEEL NUISANCE POOR DRAINAGE AND LOW LYING FLOODING WILL BE THE MOST LIKELY OUTCOME. MODELED SOLUTIONS SUGGEST WE WOULD NEED ABOUT 2.50 INCHES OF LIQUID, EITHER IN THE FORM OF ALL RAIN OR RAIN AND MELTING SNOW TO HAVE OUR SOUTHERN CREEKS AND STREAMS LEAVE THEIR BANKS. WITH MORE SNOW OR SLEET EXPECTED ACROSS THE NORTHERN HALF OF THE CWA, WE`RE NOT CONCERNED ABOUT FLOODING THERE. WITH THE RAINFALL, THE FLOW ON AREA CREEKS AND STREAMS WILL INCREASE. THIS COULD START TO MOVE ICE, AND IN A WORST CASE SCENARIO, CREATE RESTRICTIONS OR JAMS. CONTINUE TO MONITOR THE FORECAST. KEEP IN MIND THAT SNOWMELT AND THE WARMER TEMPERATURES EXPECTED TOMORROW, BY THEMSELVES, WOULD NOT CAUSE FLOODING. THE AMOUNT OF RAIN THAT WE RECEIVE WILL BE THE DETERMINING FACTOR.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...WINTER WEATHER ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR PAZ060>062-105. WINTER STORM WATCH FROM THIS EVENING THROUGH THURSDAY EVENING FOR PAZ054-055-060>062-101>106. WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR PAZ070-071. WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR PAZ054- 055. NJ...WINTER WEATHER ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR NJZ007>010. WINTER STORM WATCH FROM THIS EVENING THROUGH THURSDAY EVENING FOR NJZ001-007>010-012-015. WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR NJZ021>025. WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR NJZ013-014-016>020-026-027. WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR NJZ001. DE...WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR DEZ002>004. WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR DEZ001. MD...WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR MDZ015-019-020. WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY EVENING FOR MDZ008-012. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR ANZ450>455.
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&& $$ SYNOPSIS...FRANCK NEAR TERM...DRAG/IOVINO/KLEIN SHORT TERM...DRAG/KLEIN LONG TERM...FRANCK AVIATION...DRAG/FRANCK/KLEIN MARINE...DRAG/FRANCK/KLEIN HYDROLOGY...KRUZDLO

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