Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 011850 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 150 PM EST SUN FEB 1 2015 .SYNOPSIS... LOW PRESSURE IN THE MID MISSISSIPPI VALLEY WILL MOVE EASTWARD INTO THE OHIO VALLEY LATE TODAY INTO TONIGHT, THEN TRACK ACROSS OUR REGION ON MONDAY. HIGH PRESSURE WILL BUILD INTO THE REGION TUESDAY. LOW PRESSURE WILL THEN TRACK FROM THE OHIO VALLEY INTO NEW ENGLAND ON WEDNESDAY, WITH A COLD FRONT MOVING THROUGH OUR REGION WEDNESDAY NIGHT. HIGH PRESSURE SHOULD THEN ARRIVE FOR THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A COLD FRONT IS DRAPED FROM INTERIOR NEW ENGLAND SOUTHWESTWARD TO WESTERN PENNSYLVANIA, THEN TO LOWER PRESSURE IN THE MID-MISSISSIPPI VALLEY. THE WATER VAPOR IMAGERY SHOWS A WELL DEFINED SHORT WAVE DIGGING ACROSS THE CENTRAL PLAINS AND THE MID-MISSISSIPPI VALLEY. THIS FEATURE DOES LOOK MORE AMPLIFIED, WHICH SHOULD RESULT IN A DOWNSTREAM NORTHWARD STORM TRACK OF THE SURFACE LOW. IT IS THIS FEATURE THAT HAS BEEN VARYING SOME AND HAVING AN IMPACT ON THE STORM TRACK AND RELATED THERMAL PROFILES ACROSS MUCH OF OUR REGION THE LAST SEVERAL DAYS. IT DOES APPEAR THAT A WARMER SOLUTION WILL OCCUR, HOWEVER NO CHANGES ARE BEING MADE ATTM TO THE PRECIPITATION TYPE EVOLUTION IN OUR FORECAST OR THE ADVISORIES/WARNINGS. THE 12Z NAM WOULD SUGGEST THAT PHILADELPHIA IS MAINLY JUST RAIN AS THE BOUNDARY LAYER WARMS ENOUGH. WE WILL AWAIT ADDITIONAL MODEL GUIDANCE BEFORE MAKING CHANGES, HOWEVER THE WSW PRODUCT WAS RESENT TO MAKE SOME ADJUSTMENTS TO THE GROUPINGS AND ADD SOME MORE INFORMATION. OTHERWISE, WAA ALOFT AND THE BACKING FLOW IS RESULTING IN CLOUDS ACROSS THE AREA. THESE ARE ANTICIPATED TO THICKEN AND LOWER, ALTHOUGH THERE ARE SOME THIN AREAS SO FAR THIS MORNING. THE LIGHT SOUTHERLY FLOW AND WAA IS ALLOWING THE TEMPERATURES TO RESPOND. THE DEW POINTS ARE ALSO EXPECTED TO INCREASE SOME BY LATE IN THE DAY ESPECIALLY SOUTH AND EAST OF PHILADELPHIA AS THE LOW-LEVEL MOISTURE TRANSPORT BEGINS TO BECOME BETTER DEFINED. THE HOURLY GRIDS WERE ADJUSTED BASED ON THE LATEST OBSERVATIONS, AND THEN THE LAMP/LAV GUIDANCE WAS USED TO ASSIST. THERE HAS BEEN A FEW SNOW SHOWERS OR FLURRIES ACROSS SOUTHEASTERN PENNSYLVANIA WITH SOME INITIAL UPGLIDE, HOWEVER THE BULK OF THE PRECIPITATION IS EXPECTED TO ARRIVE LATE THIS AFTERNOON AND BEYOND. THE 12Z STERLING, VA RAOB SHOWS RATHER DRY AIR BELOW 850 MB. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... THOUGH SOME PRECIP MAY MOVE IN THROUGH THE DAY TODAY, THE MAIN PERIOD OF WHEN OUR REGION WILL BE AFFECTED BY THIS SYSTEM WILL BE STARTING THIS EVENING AS THE CENTER OF THE SURFACE LOW LIFTS FROM SOUTHERN INDIANA INTO WESTERN PA BY MONDAY MORNING. FIRST A FEW NOTES ABOUT THE SYNOPTIC PATTERN. THE MAIN UPPER LEVEL TROUGH ASSOCIATED WITH THIS SYSTEM IS SLIDING EAST OVER THE HIGH PLAINS NOW, THE BASE OF THE TROUGH EARLIER BECAME A CUTOFF LOW OVER THE BAJA PENINSULA. WITHOUT A STRONG UPPER LEVEL JET ON THE BACK SIDE OF THE TROUGH, AND WITH THE WINDOW OF OPPORTUNITY FOR ANY LEE SIDE CYCLOGENESIS QUICKLY CLOSING AS IT MOVES FURTHER AWAY FROM THE ROCKIES, THIS SHOULD BE A RATHER PROGRESSIVE SYSTEM. THE GFS HOWEVER, SHOWS THE LOW INTENSIFYING AND DEEPENING OVER THE NEXT 24 HOURS, MUCH MORE SO THAN ANY OF THE OTHER DETERMINISTIC MODELS. THIS AS A RESULT, AFFECTS THE TIMING OF THE WARM FRONT TONIGHT, AND THUS DOES AFFECT TIMING OF PRECIP TRANSITIONS. AS WITH THE PREVIOUS SHIFT, AM CONCERNED THAT THIS IS TOO FAST IN SCOURING OUT THE COLD AIR IN THE BOUNDARY LAYER THAT IS ALREADY IN PLACE. SO WITH THAT IN MIND, THE FORECAST FAVORS A SLIGHTLY COLDER SOLUTION WHICH SHOWS THE PRECIP AS MOSTLY SN (WITH THE EXCEPTION OF CENTRAL AND SOUTHERN DELMARVA AND FAR SE NJ. THROUGH 06Z, SHOULD SEE A BAND OF SLEET AND FREEZING RAIN MIX DEVELOP OVER THE I95 CORRIDOR. THIS BAND OF MIXED PRECIP IS EXPECTED TO SLOWLY MOVE NORTH AFTER MIDNIGHT AS THE WARMER AIR MOVES IN FROM THE SOUTH. SNOW AND ICE AMOUNTS DID NOT CHANGE TOO MUCH FROM THE PREVIOUS FORECAST. STILL LOOKS LIKE THE HIGHEST SNOW AMOUNTS WILL BE OVER THE POCONOS AND FAR NW NJ WHICH WILL LIKELY SEE ONLY A SMALL WINDOW OF MIXED PRECIPITATION EARLY MONDAY MORNING. HAVE CHANGED THE WINTER STORM WATCH TO A WARNING, WITH THE EXCEPTION OF WESTERN CHESTER WHICH IS IN A WINTER WEATHER ADVISORY ALONG WITH FAR NORTHERN DELMARVA, FAR SE PA, AND MUCH OF CENTRAL AND SOUTHERN NJ. && .LONG TERM /MONDAY THROUGH SATURDAY/... MONDAY THROUGH MONDAY NIGHT: * WINTER STORM CONTINUES FOR AT LEAST THE NORTHERN HALF OF THE REGION* A FRONTAL BOUNDARY WILL BE STALLED FROM WEST TO EAST ACROSS THE REGION AS LOW PRESSURE RIDES ALONG THE BOUNDARY. PLENTY OF MOISTURE AND UPPER LEVEL WARM AIR WILL CONTINUE TO BE DRAWN NORTH AND RUNG OUT ALONG THE FRONTAL BOUNDARY. THIS MAY LEAD TO POTENTIALLY MODERATE TO HEAVY PERIODS OF PRECIPITATION MONDAY MORNING. THE RAIN/ WINTRY MIX LINE WILL SLOWLY MOVE NORTH FROM THE NORTHERN SUBURBS OF PHILADELPHIA TOWARD THE LEHIGH VALLEY AND CENTRAL NJ FROM 12-15Z. A SECONDARY LOW MAY FORM OFFSHORE AS WELL DURING THE MORNING WHICH COULD ALLOW COLD AIR TO ADVECT IN AT THE SURFACE DURING THE LATE MORNING AND AFTERNOON, NON-DIURNAL TEMPERATURE TREND. MAV AND MET BOTH APPEAR TO WARM MONDAY AFTERNOON BUT THE ECMWF TWO METER TEMPERATURES LOOK TO COLD. THE CAA WOULD STOP THE NORTHWARD ADVANCE OF THE CHANGEOVER TO RAIN BY MID MORNING. A WARM NOSE MAY MAKE ALL THE WAY INTO THE POCONOS AROUND SUNRISE MONDAY IF THE 00Z GFS SOUNDING IS TO VERIFY, SO HAVE ADDED SLEET INTO THE EQUATION HERE. THE PRECIPITATION TYPE FORECAST IS MAINLY DERIVED FROM THE 00Z NAM. THE 00Z GFS LOOKED TO HAVE TO INTENSE OF A LOW PRESSURE SYSTEM WHICH IN TURN ALLOWS FOR MORE WARM AIR ADVECTION. THE ECMWF IS STILL ON THE COOLER END OF THE SPECTRUM WITH THE NAM IN BETWEEN THESE SOLUTIONS. THE SREF AND WPC QPF FORECAST WAS USED AS WELL WITH GOOD MODEL AGREEMENT ON QPF IN THIS PERIOD. THIS RESULTS IN ADDITIONAL SNOW AND ICE ACCUMULATIONS FOR NORTHERN PARTS OF THE CWA IN THIS PERIOD. ALSO, SOUNDINGS INDICATE THE POTENTIAL FOR SOME 30 MPH NORTHWEST WIND GUSTS MONDAY EVENING AS WELL. TUESDAY AND WEDNESDAY: BEHIND THE SYSTEM, A PRETTY POTENT BLAST OF COLD COMES INTO THE REGION BY TUESDAY. 925 AND 850 MB BOTH WILL BE WELL BELOW -10C COUPLED WITH STRONG NORTHWESTERLY WINDS. THIS QUICKLY MODIFIES BY WEDNESDAY AS HIGH PRESSURE MOVES OFFSHORE COUPLED WITH A RETURN TO SOUTHERLY WINDS. STAYED CLOSE TO THE ENSEMBLE GUIDANCE ON TEMPERATURES BOTH DAYS. A SHORTWAVE AND ASSOCIATED WEAK LOW PRESSURE WILL LIKELY TRACK NORTHWEST OF OUR REGION WEDNESDAY AND HAVE INCLUDED A CHANCE FOR SOME LIGHT SNOW IN THE POCONOS AND NW NJ. WEDNESDAY NIGHT THROUGH FRIDAY NIGHT: A COLD FRONTAL BOUNDARY WILL APPROACH THE REGION WEDNESDAY NIGHT AND MOVE THROUGH THE AREA ON THURSDAY. ENOUGH FORCING LOOKS TO TO BE PRESENT FOR A BAND OF LIGHT SNOW, PERHAPS A RAIN/SNOW MIX ACROSS THE DELMARVA ON AND BEHIND THE COLD FRONT. MAINTAINED LOW CHANCE POPS CENTERED ON THURSDAY. DEPENDING ON THE FRONTAL TIMING A NON-DIURNAL TEMPERATURE TREND COULD OCCUR. OF CONTINUED UNCERTAINTY IS THE POTENTIAL FOR A LOW PRESSURE IN THE GULF OF MEXICO TO RIDE NORTHEAST ALONG THE FRONT. THE UKMET AND CMC HAVE BEEN PERSISTENT IN THIS POSSIBILITY FOR A FEW MODEL CYCLES NOW. THE 00Z ECMWF APPEARS TO HAVE TRENDED LESS PROGRESSIVE THAN IN PREVIOUS RUNS AS WELL. WITH THAT SAID, WILL CONTINUE SLIGHT TO LOW CHANCE POPS FOR SNOW THURSDAY NIGHT. TEMPERATURES REMAIN CLOSE TO A CONSENSUS OF THE WPC ENSEMBLE GUIDANCE AND THAT OF THE MODELED TWO METER TEMPERATURES IN MOST PARTS OF THIS PERIOD. THE 00Z GFS WAS STRONGER WITH A COLD BLAST ON FRIDAY, FOR NOW, DID NOT INCORPORATE THE TEMPERATURES FROM THIS RUN ON FRIDAY. SATURDAY AND SATURDAY NIGHT: MODERATING TREND, CLIPPER SYSTEM BY SATURDAY NIGHT CAN NOT BE RULED OUT. FOR NOW WENT DRY. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THIS AFTERNOON - TONIGHT...VFR TO START BEFORE DROPPING TO MVFR/IFR AS LIGHT SNOW MOVES IN FROM THE WEST-SOUTHWEST LATER THIS EVENING. THE SNOWIEST TERMINALS WILL BE RDG/ABE WHILE THE I-95 TERMINALS SEE SOME SNOW, WITH A QUICK TRANSITION TO FREEZING RAIN TO RAIN...MIV/ACY SHOULD BE QUICK SNOW TO RAIN...MINIMAL MIXING EXPECTED. WINDS WILL OUT OF THE WEST EARLY AND BACKING TOWARDS THE SOUTH-SOUTHEAST LATE TONIGHT. MONDAY...IFR TRENDING TO MVFR LATE IN THE CYCLE. RDG/ABE WILL BE THE LAST TERMINALS TO CHANGE OVER TO ALL RAIN BY LATER MONDAY MORNING. WINDS BECOME LIGHTER AS THE CENTER OF THE LOW PRESSURE PASSING BY. MODERATE TO HEAVY RAIN MAY OCCUR LATE MORNING INTO THE EARLY AFTERNOON. STRONGER WEST-NORTHWEST WINDS KICK IN BEHIND THE SYSTEM WITH STRONG GUSTS EXPECTED LATE IN THE CYCLE. A CHANGEOVER BACK TO SOME SNOW SHOWERS IS POSSIBLE LATE AFTERNOON, IF ANY MOISTURE REMAINS. OUTLOOK... MONDAY NIGHT: IMPROVING CONDITIONS TO VFR. NORTHWEST WIND GUSTS 20-30 KNOTS. TUESDAY AND WEDNESDAY: VFR. INCREASE IN CLOUDS TUESDAY NIGHT. NORTHWEST WINDS SHIFTING TO SOUTHWEST UNDER 10 KNOTS. && .MARINE... WINDS AND SEAS WILL REMAIN BELOW SCA CRITERIA FOR MUCH OF THE DAY TODAY. BEGINNING TONIGHT, WINDS WILL INCREASE AND COULD REACH GUSTS TO 25KT AFTER MIDNIGHT. OUTLOOK... MONDAY THROUGH TUESDAY: SCA SEAS THROUGH TUESDAY MORNING. NORTHWEST WINDS INCREASING MONDAY WITH SOME GALE GUSTS LIKELY FROM 23Z MONDAY THROUGH 11Z TUESDAY. GALE WATCH IN EFFECT. PERIOD OF SCA NW WIND GUSTS TUESDAY MORNING FOLLOWING THE NW GALE WIND GUSTS. MEDIUM TO HIGH CONFIDENCE IN GALE GUSTS. TUESDAY NIGHT THROUGH WEDNESDAY: SUB SCA SEAS AND WINDS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 1 PM EST MONDAY FOR PAZ060>062-103-105. WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST MONDAY FOR PAZ070-071. WINTER STORM WARNING FROM 7 PM THIS EVENING TO 4 PM EST MONDAY FOR PAZ054-055. WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST MONDAY FOR PAZ101-102-104-106. NJ...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 1 PM EST MONDAY FOR NJZ007>010-012. WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST MONDAY FOR NJZ016>022-025>027. WINTER STORM WARNING FROM 7 PM THIS EVENING TO 4 PM EST MONDAY FOR NJZ001. WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST MONDAY FOR NJZ013>015. DE...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST MONDAY FOR DEZ001. MD...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST MONDAY FOR MDZ008-012. MARINE...GALE WATCH FROM MONDAY EVENING THROUGH LATE MONDAY NIGHT FOR ANZ430-431-450>455. && $$ SYNOPSIS...GAINES/GORSE NEAR TERM...GORSE SHORT TERM...JOHNSON LONG TERM...GAINES AVIATION...GAINES/HEAVENER MARINE...GAINES/JOHNSON

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