116 FXUS61 KPHI 160520 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1220 AM EST SAT FEB 16 2013 .SYNOPSIS... LOW PRESSURE ALONG A COLD FRONT FROM SOUTHEASTERN NEW YORK STATE TO SOUTHERN VIRGINIA WILL MOVE OFF THE COAST EARLY SATURDAY MORNING. A NEW LOW PRESSURE SYSTEM WILL FORM ALONG THIS FRONT EAST OF NORTH CAROLINA SATURDAY AFTERNOON...INTENSIFYING AS IT PASSES EAST OF CAPE COD ON SUNDAY AS A LARGE AND STRONG GALE. HIGH PRESSURE IS FORECAST TO FOLLOW FOR MONDAY INTO EARLY TUESDAY. THEN A COLD FRONT FROM THE GREAT LAKES SHOULD MOVE THROUGH THE NORTHEAST LATER ON TUESDAY. A LARGE HIGH PRESSURE SYSTEM FROM CENTRAL CANADA SHOULD THEN BEGIN SLOWLY BUILD INTO THE AREA LATER ON WEDNESDAY THROUGH THURSDAY. A WARM FRONT MAY LIFT NORTH TOWARD THE AREA EARLY FRIDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... A DECENT BAND, POST-FRONTAL, DEVELOPED WITH SOME ENHANCEMENT DUE TO AN UPPER-LEVEL JET OVERHEAD. THIS ALSO LOOKED TO BE DRIVEN BY DEEPER LIFT WITHIN A COOLING AIRMASS, ALLOWING FOR MUCH IMPROVED SNOW GROWTH. THE BAND HAS WEAKENED SOME AND IS SLIDING EAST- NORTHEASTWARD. THE BACK EDGE IS MOVING INTO THE FAR WESTERN ZONES, THEREFORE THE ADVISORY THAT WAS PREVIOUSLY ISSUED FOR SOME OF THE NORTHWESTERN COUNTIES CAN PROBABLY BE CANCELLED EARLY. WE HAVE RECEIVED SOME REPORTS OF UP TO 2 INCHES OF SNOW THUS FAR ESPECIALLY IN THE HIGHER ELEVATIONS OF THE WEST/NORTHWEST ZONES. THE CHANGEOVER TO ALL SNOW IS GETTING CLOSER TO TRENTON, PHILADELPHIA AND WILMINGTON, HOWEVER THE LESSENING OF THE PRECIPITATION BAND COULD RESULT IN MORE RAIN OR RAIN/SNOW MIX. TEMPERATURES ACROSS THE WESTERN AREAS HAVE DROPPED TO NEAR FREEZING, THEREFORE UNTREATED SURFACES /ESPECIALLY BRIDGES AND OVERPASSES/ CAN BE SLIPPERY. THE HOURLY GRIDS WERE ADJUSTED USING THE 05Z OBS AND ALSO SOME OF THE LAMP/LAV GUIDANCE. THIS INCLUDED COLDER READINGS ACROSS THE WESTERN HALF OF THE CWA THUS FAR. WE WILL ALSO BE ADJUSTING THE POPS ESPECIALLY BASED ON RADAR DATA AND SOME NEW MODEL GUIDANCE. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/... THE FIRST IMPULSE SHOULD CLEAR US EARLY IN THE SHORT TERM. THEN, IF ONE WANTS A SNOWIER FORECAST, ONE FALLS INTO THE CANADIAN/GFS CAMP. OUR FORECAST THROUGH THE SHORT TERM LEANS AWAY FROM THIS AND TOWARD A ECMWF/NAM KIND OF SOLUTION, ALTHOUGH WE DO INCORPORATE SOME OF THE FORMER BECAUSE OF THE UNCERTAINTY. THE GFS AND CANADIAN ARE DEVELOPING MORE OF A NEGATIVE TILT WITH A STRONGER SECOND IMPULSE AT H5, AND THAT HAS THEM DEEPER AND FURTHER EAST WITH THE ASSOCIATED LOW PRESSURE SYSTEM (THE MAIN ONE WITH THIS MAJOR TROUGH AXIS). ALTHOUGH OUR QPF IS ON THE LIGHTER SIDE BECAUSE WE FAVOR A LESS VIGOROUS SOLUTION AT OUR LATITUDE, ALL MODEL SOUNDINGS SAY THAT ALL AREAS WOULD SEE SNOW EITHER FROM THE START OF OR ONLY A FEW HOURS INTO THE SHORT TERM. WE HAVE THEREFORE ADJUSTED MAX TEMPERATURES DOWNWARD. OUR QPF AND SNOW VALUES IN THE LATTER PART OF THE SHORT TERM AND THE FIRST PART OF THE LONG TERM COMBINED WOULD BRING OUR EASTERN ZONES INTO ADVISORY TERRITORY. GIVEN THE UNCERTAINTY, WE HAVE DECIDED NOT TO ISSUE ONE AT THIS TIME. WE DO NOTE THAT IF OUR FORECAST WERE CORRECT FROM THE NEAR TERM THROUGH THE EARLY PART OF THE LONG TERM, THEN WE WOULD SEE LOWER END ADVISORY SNOW AMOUNTS OVER A FAIR AMOUNT OF THE FORECAST AREA. HOWEVER, THIS WOULD HAPPEN OVER A PERIOD OF AT LEAST 24 HOURS, SOME OF WHICH WOULD BE FREE OF SIGNIFICANT PRECIPITATION. && .LONG TERM /TONIGHT THROUGH FRIDAY/... MODELS CONTINUE TO DIFFER ON HOW MUCH SNOW MIGHT FALL LATER SATURDAY AND SATURDAY NIGHT. THE LATEST RUN OF THE GFS INDICATES A SLIGHTLY MORE WESTERN TRACK WHILE THE LATEST ECMWF INDICATES A MORE EASTERLY TRACK. AS A RESULT...NO DRASTIC CHANGE HAS BEEN MADE TO THE FORECAST AT THIS POINT IN TIME. BASICALLY AN ADVISORY TO SUB-ADVISORY EVENT FOR THE CWA, WITH THE HIGHEST AMOUNTS CLOSEST TO THE COASTAL AREAS...WITH LESSER AMOUNTS FURTHER INLAND. WHATEVER SNOW DOES FALL, THE BULK OF IT SHOULD BE OVER BY 6 AM SUNDAY. SLIGHT POPS WERE ADDED TO THE WEATHER GRIDS FOR SUNDAY DUE TO THE PROXIMITY OF THE MID-LEVEL TROUGH, BUT NOTHING SIGNIFICANT IS EXPECTED DURING THIS TIME PERIOD. A BLUSTERY DAY IS EXPECTED IN THE CWA ON SUNDAY DUE TO THE PRESSURE GRADIENT FROM THE EXITING STORM. WITH HIGH TEMPERATURES IN THE MID 20S IN THE NORTH AND LOW TO MID 30S SOUTH...IT WILL FEEL LIKE WINTER AGAIN. WHETHER OR NOT WIND ADVISORIES WILL BE NECESSARY WILL DEPEND ON HOW FAR EAST THE STORM TRACK HAPPENS TO BE. MONDAY SHOULD BE A LESS WINDIER DAY WITH SUNNY SKIES. TEMPERATURES THOUGH SHOULD STILL BE ABOUT 5 TO 10 DEGREES COLDER THAN AVERAGE. AS THE HIGH SLIDES OFF THE COAST EARLY TUESDAY...A WARM FRONT WILL LIFT NORTH ALLOWING TEMPERATURES TO RISE INTO THE MID TO UPPER 40S IN MOST PLACES. PRECIPITATION COULD START OUT AS SNOW...BUT SHOULD CHANGE OVER TO RAIN AS THE DAY WEAR ON. A COLD FRONT ASSOCIATED WITH A LOW PRESSURE SYSTEM MOVING THROUGH THE GREAT LAKES REGION WILL PASS THROUGH THE CWA TUESDAY EVENING/NIGHT...WHICH WILL BRING BACK COLDER TEMPERATURES AND CHANGE ANY LINGERING RAIN TO SNOW...ESPECIALLY IN THE NORTH. THEN BASICALLY BENIGN WEATHER UNTIL THE NEXT SYSTEM APPROACHES FROM THE WEST ON FRIDAY. PRECIP WITH THAT EVENT LOOKS LIKE IT WILL BE MAINLY RAIN IN THE SOUTH WITH A LEAST A MIXTURE IN THE NORTH. && .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OVERNIGHT...A PERIOD OF MVFR/IFR CEILINGS FROM WEST TO EAST AT MOST TERMINALS, THEN THE CEILINGS SHOULD TREND TOWARD VFR. A BAND OF RAIN MIXING WITH AND CHANGING TO SNOW SHOULD CONTINUE TO LIFT NORTHEASTWARD AND WEAKEN. THIS WILL END THE SNOW AT KABE AND KRDG GENERALLY BY 07Z. THERE SHOULD BE SOME SNOW MIX IN OR BRIEFLY ALL SNOW FROM KTTN TO THE KPHL METRO AND KILG. LESSER RAIN/SNOW AT KMIV AND KACY. VISIBILITIES WILL VARY FROM VFR/MVFR TO IFR WITH THE LOWEST OCCURRING DURING ALL SNOW. NORTHWEST WINDS GENERALLY NEAR 10 KNOTS. SATURDAY...VFR/MVFR CEILINGS AS ANY PRECIPITATION ENDS, HOWEVER THERE COULD BE SOME SNOW FOR A TIME NEAR KMIV AND KACY AS LOW PRESSURE TRACKS TO OUR EAST. NORTH-NORTHWEST WINDS GENERALLY 10-15 KNOTS. SOME LOWER CONFIDENCE ON HOW FAR INLAND ANY SNOW GETS FROM THE STRENGTHENING STORM OFFSHORE, THEREFORE WENT WITH A TEMPO GROUP AT KMIV AND KACY FOR NOW. SATURDAY NIGHT...ALL THE TERMINALS VFR OR IMPROVING TO VFR. NORTHWEST WINDS 10-15 KNOTS WITH GUSTS TO 20 KNOTS. OUTLOOK... SUNDAY...MAINLY VFR AND BLUSTERY. POSSIBLE MVFR SNOW SHWRS NORTH. NORTHWEST WINDS GUSTING 25 TO 30 KNOTS. CONFIDENCE MODERATE. MONDAY AND MONDAY NIGHT...MAINLY VFR. CONFIDENCE HIGH. TUESDAY...LOWERING TO MVFR OR IFR IN MIXED PRECIPITATION IN THE MORNING. CHANCE OF LLWS. CONFIDENCE IS MODERATE. TUESDAY NIGHT...IMPROVING TO VFR. WEDNESDAY...MAINLY VFR. && .MARINE... SUB-ADVISORY CONDITIONS ARE FORECAST INTO SATURDAY, BUT THEN WILL APPROACH OR REACH ADVISORY CONDITIONS LATE IN THE DAY ON GOOD COLD AIR ADVECTION AND A NORTHWEST FLOW. SEAS SHOULD BUILD TO ADVISORY CONDITIONS BY LATE SATURDAY AFTERNOON. OUTLOOK... THE DEVELOPING AND DEEPENING OFFSHORE LOW OFF NORTH CAROLINA WILL CONTINUE SCA CONDITIONS OVER MARINE AREA (OCEAN AND DELAWARE BAY) WIDESPREAD SCA CONDITIONS THROUGH THE REMAIN PORTION OF THE WEEKEND. DEPENDING ON THE PATH OF THIS STORM...GALES ARE EVEN POSSIBLE SATURDAY NIGHT INTO SUNDAY ON THE OCEAN AND LOWER DELAWARE BAY. THIS SITUATION WILL BE RE- EXAMINED WITH LATER MODEL RUNS. A SOUTHWEST FLOW BEHIND AN ADVANCING WARM FRONT IS EXPECTED TO SCA BACK TO THE FORECAST WATERS ON TUESDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...WINTER WEATHER ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR PAZ055. NJ...WINTER WEATHER ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR NJZ001-007-008. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG/MIKETTA NEAR TERM...GORSE SHORT TERM...DELISI LONG TERM...MIKETTA AVIATION...GORSE/MIKETTA MARINE...DELISI/DRAG/MIKETTA