392 FXUS61 KPHI 151456 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 956 AM EST TUE JAN 15 2013 .SYNOPSIS... WEAK LOW PRESSURE OVER NORTH CAROLINA EARLY THIS MORNING WILL MOVE NORTHEAST OFF THE MID ATLANTIC COAST LATER THIS MORNING. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT LATER TODAY INTO TONIGHT BEFORE MOVING EAST OF THE AREA. LOW PRESSURE DEVELOPING OVER THE WESTERN CAROLINAS LATE THIS EVENING WILL PASS JUST EAST OF THE AREA WEDNESDAY AFTERNOON. A COLD FRONT WILL CROSS THE REGION THURSDAY... WITH HIGH PRESSURE FOLLOWING FOR THE END OF THE WEEK INTO THE EARLY WEEKEND. AN ARCTIC COLD WILL CROSS THE AREA LATE THIS WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A COOL, DAMP DAY REMAINS IN STORE ACROSS THE AREA TODAY AS MOISTURE STREAMS NORTHEASTWARD ACROSS THE AREA IN THE SOUTHWEST FLOW ALOFT. CLOUDS ARE EXPECTED TO REMAIN IN PLACE ACROSS THE ENTIRE AREA, WHICH COMBINED WITH A NORTH-NORTHEAST ELY FLOW AT THE SURFACE WILL PREVENT TEMPERATURES FROM RISING MUCH DURING THE DAY. IN FACT, TEMPERATURES WILL LIKELY REMAIN MOSTLY STEADY THROUGH THE DAY, THEN SLOWLY DROP LATER TODAY. THE ONLY PLACES THAT MIGHT RISE A FEW DEGREES DURING THE DAY IS THE EXTREME NORTHERN AREAS WHERE A FEW HOURS OF PARTIAL SUNLIGHT MIGHT HELP TEMPERATURES RISE SLIGHTLY, BUT THIS SHOULD BE BRIEF AS FULL CLOUD COVER FILLS BACK IN. PERIODS OF LIGHT RAIN WILL CONTINUE FOR SOUTHERN NEW JERSEY AND CENTRAL/SOUTHERN DELMARVA THROUGH THE DAY AS WELL. AREAS FARTHER NORTH SHOULD REMAIN PRECIPITATION FREE UNTIL LATER THIS AFTERNOON INTO THIS EVENING. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... THE SECOND WAVE OF LOW PRESSURE WILL NEAR THE REGION LATER THIS EVENING FROM THE SOUTHWEST. THIS IS A VERY FAST MOVING AND DYNAMIC EVENT AND A WINTER WEATHER ADVISORY WAS RAISED FROM LATE THIS EVENING THROUGH LATE WEDNESDAY MORNING FOR AREAS NORTH AND WEST OF PHL. BASED ON THE FORECAST POSITION OF THE BAROCLINIC ZONE, THIS SYSTEM WILL BE CLOSE ENOUGH TO THE CWA TO PRODUCE A MULTIFACETED P-TYPE EVENT. AS HAS BEEN THE CASE FOR JUST ABOUT THE ENTIRE WINTER AREAS SOUTH AND EAST OF PHL WILL REMAIN ALL RAIN WHILE AREAS NORTH AND WEST OF THE CITY WILL SEE A CHANGE OVER TO MORE OF A FROZEN PRECIPITATION AFTER MIDNIGHT. AS WAS STATED LAST NIGHT, DUE TO THE PROGRESSIVE NATURE OF BOTH WAVES WITH THE STRONGER WINDS IN THE DENDRITIC GROWTH ZONE, EVEN WITH SLIGHTLY HIGHER PWATS, WE WONT SEE TREMENDOUS SNOW GROWTH KEEPING TOTALS DOWN. STILL HAVE A SHOT AT SEEING UPWARDS OF 2-4 INCHES FROM BERKS COUNTY NORTHEAST THROUGH MORRIS COUNTY. MODELS ARE SHOWING A DECENT AMOUNT OF MID-LEVEL FRONTOGENETIC FORCING TAKING PLACE AROUND THE 06-12Z TIMEFRAME TONIGHT WHICH SHOULD BE ENOUGH TO GET A BAND OR TWO GOING...PLACEMENT STILL NEEDS TO BE REFINED. THERE IS STILL A WARM NOSE ALOFT, ABOVE 800MB, WHICH COULD PROVIDE A LITTLE MORE MIXTURE OF SLEET INTO AREAS WHERE WE ARE FORECASTING SNOW...NORTH AND WEST OF THE METRO AREA. IF WE WERE TO LOSE THE BETTER VERTICAL MOTIONS FASTER THAN WHAT IS CURRENTLY THOUGHT, THE ENTIRE COLUMN WOULD CONTAIN ALL LIQUID AND LIGHT FREEZING RAIN BECOMES MORE LIKELY. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... THE EARLY PART OF THIS PERIOD LOOKS TO BE THE MOST INTERESTING... WITH LINGERING PRECIPITATION TYPE FORECAST ISSUES. THE STRONG MID LEVEL FLOW BEHIND THE SYSTEM THAT PRODUCES THE PRECIPITATION WEDNESDAY PROBABLY KEEPS LOW PRESSURE SUPPRESSED FOR THURSDAY NIGHT INTO FRIDAY MORNING. MID RANGE MODELS SUGGEST THAT IT MAY NOT BE UNTIL SUNDAY OR EVEN MONDAY BEFORE THE MUCH COLDER AIR ARRIVES IN THE FORECAST AREA. THE BEST VERTICAL VELOCITIES ASSOCIATED WITH THE EXITING MID LEVEL FRONTOGENETIC FORCING BAND SHOULD CROSS THE SOUTHERN POCONOS AND NORTHWEST NEW JERSEY BETWEEN 1200 AND 1500 UTC WEDNESDAY. IN THIS BAND...THERE SHOULD STILL BE ENOUGH ICE IN THE COLUMN FOR SNOWFLAKE PRODUCTION. THE BANDING ALLOW FOR SOME ADDITIONAL LIGHT SNOW ACCUMULATIONS IN THE ABOVEMENTIONED AREAS. FURTHER SOUTHEAST IN NORTHWEST NEW JERSEY AND THE UPPER LEHIGH VALLEY...SURFACE TEMPERATURES COULD STILL BE NEAR THE FREEZING MARK...AS LOW LEVEL WARMING WILL BE TOUGH TO COME BY EARLY. WITH THE ABILITY TO PRODUCE SNOWFLAKES GONE WITH THE BEST VERTICAL VELOCITIES...LIGHT FREEZING RAIN AND FREEZING DRIZZLE IS EXPECTED. ELSEWHERE...SURFACE TEMPERATURES WILL BE WARM ENOUGH FOR MAINLY. SHORT TERM MODELS CONTINUE TO POINT TO A SECONDARY BAND OF MID LEVEL FRONTOGENETIC FORCING STRETCHING FROM NORTHEAST MARYLAND ACROSS SOUTHERN NEW JERSEY. THE BAND COINCIDES WITH THE BEST THETA E RIDGING...AND PRECIPITABLE WATER VALUES NEAR 1.25 INCHES. THE COMBINATION COULD RESULT IN A BAND OF HEAVY RAIN WEDNESDAY MORNING IN THE AREAS MENTIONED ABOVE. AT THIS POINT...THE BAND LOOKS TO BE TRANSITORY ENOUGH TO KEEP THE THREAT OF MORE THAN NUISANCE FLOODING LOW. THE BEST LIFT EXITS THE COAST BY 1800 UTC OR SO. SHORT TERM MODELS SHOW LOW AND MID LEVEL DRYING RAPIDLY EXPANDING EAST DURING THE AFTERNOON. ITS NOT CLEAR WHETHER THE LOW LEVEL DRYING WILL BE ENOUGH TO CRACK THE INVERSION...SO THE DRYING COULD BE OVERDONE. IN ANY EVENT...IMPROVING CONDITIONS ARE EXPECTED FROM WEST TO EAST DURING THE AFTERNOON. HIGHS WERE BASED MAINLY ON THE WARMER GFS MOS NUMBERS...AND THESE NUMBERS WERE BLEND WITH THE PREVIOUS FORECAST. THE INVERSION BREAKS WEDNESDAY EVENING...AND THAT ALLOWS THE LOW LEVEL MOISTURE TO BE SCOURED FOR GOOD. BOUNDARY LAYER WINDS SHOULD STAY UP LONG ENOUGH TO PRECLUDE MUCH IN THE WAY OF RADIATIONAL COOLING. IN FACT...THE GRADIENT FLOW COULD RESULT IN GUSTINESS IN THE HIGHER TERRAIN...AS MODEL SOUNDINGS SHOW 25 TO 30 KNOTS OF WIND AT THE TOP OF THE INVERSION. BECAUSE OF THE MIXING...LOWS SHOULD END UP CLOSE TO THE MOS BLEND. A SHORT WAVE IN THE FAST MID LEVEL FLOW PUSHES A COLD FRONT THROUGH THE AREA THURSDAY AFTERNOON. THE COLUMN IS DRY...SO ONLY THE HIGHER TERRAIN SEES ANY SIGNIFICANT SNOW SHOWER ACTIVITY...AS UPSLOPE AND MOISTURE FROM THE LAKES COMBINE. ELSEWHERE...FLURRIES ARE POSSIBLE FOR NORTH CENTRAL NEW JERSEY AND THE LEHIGH VALLEY...AND HAVE BEEN INCLUDED IN THE FORECAST. FURTHER SOUTH...THE COLUMN LOOKS TOO DRY EVEN FOR FLURRIES. THE BEST COLD AIR ADVECTION TAKES PLACE IN THE MORNING. THIS ALLOWS CONVECTIVE TEMPERATURES TO BE REACHED EARLY ENOUGH IN THE DAY FOR A STRATOCUMULUS SHEET FOR AREAS NORTH AND WEST OF INTERSTATE 95. DESPITE THE CLOUDS AND COLD AIR ADVECTION...MOS GUIDANCE SHOW LITTLE SPREAD FOR THURSDAY FOR HIGHS...AND THE BLEND IS ACCEPTED. A CLOSED LOW IN THE MID LEVEL FLOW OVER TEXAS ON WEDNESDAY SHOULD BE SHUNTED TO THE SOUTH OF THE AREA THURSDAY NIGHT. THE 0000 UTC NAM SHOWS PRECIPITATION ASSOCIATED WITH A SURFACE WAVE FORCED ON THE LOW LEVEL BAROCLINIC REACHING THE SOUTHERN HALF OF THE AREA. THE AMOUNT OF WESTERLY FLOW IN THE MID LEVELS WOULD SUGGEST THAT PRECIPITATION THIS FAR NORTH IN THAT TYPE OF FLOW IS UNLIKELY. ALL OTHER 0000 UTC GUIDANCE (AS WELL AS THE LATEST SREF) KEEP THE MEASURABLE PRECIPITATION SOUTH OF THE AREA LATE THURSDAY INTO THURSDAY NIGHT. GIVEN THE AMOUNT OF WESTERLY FLOW IN THE MID LEVELS...THAT LOOKS MORE CORRECT. WE WILL HAVE TO WATCH FOR A WEAK SHORT WAVE IN THE FLOW THAT COULD BACK THE FLOW JUST ENOUGH TO ALLOW SOUTHERN AREAS TO BE BRUSHED WITH PRECIPITATION. THIS SEEMS UNLIKELY RIGHT NOW...BUT TRENDS WILL NEED TO BE MONITORED. IN ANY EVENT...THE PRECIPITATION SHIELD WITH THE WAVE THURSDAY NIGHT SHOULD BE GONE FRIDAY MORNING. THE MID LEVEL FLOW STARTS TO BECOME MORE ZONAL WITH TIME. AT THE SURFACE...HIGH PRESSURE BUILDS INTO THE REGION FOR FRIDAY AND SATURDAY. THE COLUMN BECOMES COLDER WITH TIME...AND EVEN THOUGH FRIDAY WILL FEEL COLDER...TEMPERATURES WILL ACTUALLY BE CLOSE TO NORMAL. THE COLD AIR EXITS AS SOON AS IT ARRIVES...AS THE MID LEVEL HEIGHTS RISE FRIDAY NIGHT AND SATURDAY. AS THE SURFACE HIGH GETS OFFSHORE... THE RETURN FLOW COULD ALLOW HIGHS SATURDAY TO BE 10 DEGREES HIGHER THAN FRIDAY. AT THIS POINT...SATURDAY LOOKS DRY. MID RANGE MODELS ARE STILL WORKING OUT THE DETAILS OF DROPPING THE POLAR VORTEX CLOSE ENOUGH FOR STEEPLY DROPPING HEIGHTS...ALLOWING DELIVERY OF THE COLDEST AIR OF THE SEAS SUNDAY INTO EARLY NEXT WEEK. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. QUASI-STATIONARY FRONTAL BOUNDARY IS JUST TO THE SOUTHEAST OF THE REGION THIS MORNING. THE FIRST OF TWO WAVES IS CURRENTLY MOVING ALONG THIS BOUNDARY AT THIS TIME WHICH PROVIDED THE REGION WITH A DECENT AMOUNT OF RAIN AND MORE LOW-LEVEL MOISTURE. THE TAF SITES ALONG THE DELAWARE RIVER NORTHWARD SHOULD REMAIN VFR FOR MUCH OF THE DAY. THERE ARE SOME LOWER CIGS TRYING TO INCH FARTHER NORTH OUT OF SOUTHERN NEW JERSEY AND DELAWARE/MARYLAND, SO WE WILL NEED TO KEEP AN EYE ON THESE IN CASE MVFR CIGS DO REACH ILG/PHL/PNE. MIV/ACY SHOULD REMAIN NO HIGHER THAN MVFR, WITH PERIODS OF IFR CIGS/VSBYS THROUGH THE REST OF THE DAY WITH PERIODS OF LIGHT RAIN EXPECTED. THE SECOND WAVE IS A LOT MORE DYNAMIC IN TERMS OF PRECIPITATION TYPE ACROSS OUR TERMINALS. STILL LOOKS LIKE BY LATER THIS EVENING THE PRECIPITATION SHIELD WILL BE ENTERING OUR TERMINALS PROVIDING A MIX-BAG OF RAIN/SNOW/SLEET. EXPECT AN ALL RAIN EVENT FROM KPHL SOUTH AND EAST, WITH POSSIBLY MORE MIX OF RAIN/SNOW AT KTTN AND MORE SNOW AT KRDG AND KABE. THE FROZEN PRECIPITATION WOULD ALLOW A SHARP DECREASE IN VSBYS TONIGHT. FOR THE MOST PART WE ARE EXPECTING CONDITIONS TO DROP INTO THE IFR/LIFR RANGE SHORTLY AFTER MIDNIGHT TONIGHT AS HEAVIER PRECIPITATION MAKES ITS WAY INTO THE REGION. OUTLOOK... WEDNESDAY...LIFR/IFR IN THE MORNING WITH WINTRY PRECIPITATION POSSIBLE NORTHWEST OF THE I 95 CORRIDOR. CONDITIONS IMPROVING TO MVFR FROM WEST TO EAST IN THE AFTERNOON. THURSDAY...VFR CONDITIONS ARE EXPECTED. WEST WINDS COULD GUST TO 25 KNOTS...ESPECIALLY IN THE AFTERNOON. FRIDAY...VFR CONDITIONS ARE EXPECTED. SATURDAY...VFR CONDITIONS ARE EXPECTED. && .MARINE... SUB-ADVISORY CONDITIONS ARE EXPECTED ON OUR WATERS TODAY AND TONIGHT. ANOTHER SURFACE WAVE WILL FORM TO OUR SOUTHWEST AND RIDE ALONG THE STALLED FRONTAL BOUNDARY TONIGHT. LOOKS LIKE A DECENT AMOUNT OF RAIN WILL MOVE UP WITH THIS SECOND SYSTEM TONIGHT. STRONGER GUSTS ARE POSSIBLE WITH ITS PASSAGE, THOUGH WE STILL KEEP GUSTS BELOW SCA LEVELS AS THEY SHOULD BE BRIEF IN NATURE. SEAS WILL JUMP UPWARDS OF 4 FEET BY TOMORROW MORNING. OUTLOOK... AS THE SURFACE LOW COMES ASTRIDE OF THE NEW JERSEY COAST WEDNESDAY AFTERNOON...WINDS WILL QUICKLY SHIFT TO THE WEST NORTHWEST. MODEL SOUNDINGS SUGGEST THAT MIXING WILL NOT OCCUR DIRECTLY BEHIND THE FRONT...SO AT THIS POINT IS LOOKS LIKE WINDS REMAIN BELOW SMALL CRAFT LEVELS INTO WEDNESDAY EVENING. SEAS WILL COME UP IN THE EASTERLY SWELL BEHIND THE DEPARTING LOW INT HE AFTERNOON...BUT RIGHT NOW IT LOOKS AS THOUGH SEAS MAY COME UP JUST SHORT OF 5 FEET. IF THE SWELL DOES REACH 5 FEET WEDNESDAY...IT WOULD MOST LIKELY OCCUR ACROSS THE SOUTHERN OCEAN WATERS IN THE LATE AFTERNOON AND EVENING. THE GRADIENT LOOKS AS THOUGH IT WILL SUPPORT SMALL CRAFT WINDS GUSTS WEDNESDAY NIGHT. HOWEVER...MODEL SOUNDINGS ARE SUGGESTING THAT THE 30 TO 40 KNOTS OF WIND AT 925 MB STAY LARGELY ABOVE THE SURFACE... AS THE MIXED LATER REMAINS BELOW 2500 FEET. THE GRADIENT SHOULD SUPPORT SMALL CRAFT WINDS INTO THURSDAY AS WELL...AS MODEL SOUNDINGS SHOW 25 TO 30 KNOTS OF WIND AT THE TOP OF THE INVERSION. IN FACT...THE GRADIENT PROBABLY REMAINS SUPPORTIVE OF SMALL CRAFT WEST TO NORTHWEST WINDS INTO THURSDAY NIGHT AND FRIDAY MORNING. THE LAST PUSH OF THE COLD AIR ADVECTION THURSDAY EVENING COULD RESULT IN WIND GUSTS NEAR 30 KNOTS...ESPECIALLY ACROSS THE NORTHERN OCEAN WATERS. HOWEVER...THE POTENTIAL FOR GALE FORCE WIND GUST THURSDAY EVENING APPEARS TO BE LOW. THE GRADIENT FLOW BACKS OFF ENOUGH FOR WINDS TO DROP BELOW SMALL CRAFT LIMITS FRIDAY AFTERNOON AND FRIDAY NIGHT. THE SOUTHWEST FLOW AHEAD OF THE NEXT COLD FRONT COULD GET CLOSE TO SMALL CRAFT LEVELS SATURDAY AFTERNOON AND EVENING. IN ADDITION...THE INCREASING FETCH COULD ALSO BOOST SEAS CLOSE TO THE 5 FOOT BENCHMARK ON THE OCEAN DURING THE SAME TIME PERIOD. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 11 AM EST WEDNESDAY FOR PAZ054-055-060>062. NJ...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 11 AM EST WEDNESDAY FOR NJZ001-007-008. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...HAYES NEAR TERM...HEAVENER/ROBERTSON SHORT TERM...HEAVENER LONG TERM...HAYES AVIATION...HAYES/HEAVENER/ROBERTSON MARINE...HAYES/HEAVENER