000 FXUS61 KPHI 182346 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 646 PM EST TUE NOV 18 2008 .SYNOPSIS... LOW PRESSURE WILL EAST OF THE NEW JERSEY COAST WILL INTENSIFY AS IT MOVES NORTHEAST AWAY FROM THE REGION OVERNIGHT. HIGH PRESSURE WILL BUILD IN FROM THE SOUTHWEST FOR WEDNESDAY. AN AREA OF LOW PRESSURE MOVING THROUGH THE GREAT LAKES IS FORECAST TO PASS OVER OR NEAR OUR REGION ON THURSDAY. ITS DRIVING UPPER AIR DISTURBANCE WILL THEN MOVE THROUGH THE AREA ON FRIDAY. HIGH PRESSURE IS THEN ANTICIPATED TO BUILD IN FROM THE WEST FOR THE UPCOMING WEEKEND. A COLD FRONT IS THEN FORECAST TO MOVE THROUGH THE NORTHEAST AROUND MONDAY NIGHT. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... BOTH THE GFS AND WRF-NMM CONTINUE TO INITIALIZE QUITE WELL WITH VERY LITTLE DIFFERENCE FROM EACH OTHER OR REALITY. THEY BOTH ARE VERY SIMILAR THROUGH THURSDAY DAY WITH DIFFERENCES FOR FRIDAY. LATEST PMDHMD SUGGESTS THE LATEST CAN GGEM AS A COMPROMISE BETWEEN THE DIFFERENCES WHICH MOVES TOWARD THE WRF-NMM SOLUTION FOR FRIDAY DAY. GETTING BACK TO TONIGHT...WITH THE LOW PRESSURE SYSTEM FAR ENOUGH OFFSHORE AND WITHOUT ITS NORLUN BRETHREN CLOSER TO THE NJ COAST, WINDS HAVE STAYED SLIGHTLY LOWER THAN FCST. THE TIGHTEST GRADIENT IS EXPECTED TO OCCUR THIS EVENING BEFORE IT WEAKENS OVERNIGHT. VERY PRETTY MOSAIC ON VSB SATL IMAGERY OF CUMULUS CLOUDS BECAUSE OF THE CLOSED LOW ALOFT. WHERE CHESAPEAKE BAY FAILED YDA (SEE BELOW), ITS DOING OK TODAY WITH A BAY EFFECT PLUME. SO FAR MOST OF THE OBSERVED SNOW HAS BEEN FLURRIES, WE HAVE SEEN ONLY TWO REPORTS OF HEAVIER SNOW: AT MPO AND EAST NANTMEAL IN CHESTER CTY PA. WITH THE CLOSED LOW SLOW TO MOVE OFF AND AN ADIABATIC LAPSE RATE FCST TO CONTINUE THRU ABT 7 PM, WE WILL CARRY THE CHC OF FLURRIES (AND SHSN FARTHER N) INTO THIS EVENING AND CONTINUING FLURRIES OVERNIGHT FAR FAR NW. ONLY SO-CALLED PLUS SIDE FOR TONIGHT WITH THE WIND REMAINING BRISK, TEMPS SHOULD NOT TANK AND THE LOWER ETA MOS LOOKS TOO COLD. ON THE NEGATIVE SIDE, THE GRADIENT WILL PRODUCE WIND CHILL FACTORS BY WEDNESDAY MORNING WILL BE IN THE SINGLE NUMBERS AND TEENS. DRESS WARMLY. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY/... ON WEDNESDAY THE UPPER TROUGH SHIFTS TO THE EAST ALLOWING WEAK RIDGING TO DEVELOP ALOFT AS SFC HIGH PRESSURE TRIES TO BUILD IN FROM THE SOUTHWEST. EXCEPT FOR SOME SNOW FLURRIES WHICH ARE POSSIBLE MAINLY IN THE POCONOS, WE WILL KEEP THE FORECAST DRY. NO HURRY TO WARM WEDNESDAY AS THE AIR MASS WILL BE QUITE COLD IN THE MORNING. MOS GUIDANCE LOOKS REASONABLE. WEAK ALBERTA TYPE LOW PRESSURE SYSTEM FORECAST TO REACH AS FAR EAST AS NW PA BY SUNRISE ON THURSDAY. FORECAST MODELS ARE PRETTY SIMILAR IN HAVING A FAIRLY ROBUST ISENTROPIC LIFT/WAA PATTERN IN THE OHIO VALLEY FALL APART AT THE SEAMS AS IT APPROACHES AND PASSES OVER THE APPALACHIANS AT NIGHT. THE FCST ISENTROPIC LIFT AND QVEC CONVERGENCE IS STRONGER S THAN N ACROSS OUR CWA, BUT THE FCST MOISTURE IS DEEPER NORTH. IN THIS BALANCING ACT ITS OFTEN THE NORTH THAT WINS BECAUSE OF THE HIGHER TERRAIN. WE WILL SEE IN FUTURE MODEL RUNS IF THE FOLLOWING TENDENCY CONTINUES. THUS WITH WAA INDUCED PCPN (OR IN THIS CASE WHICH MIGHT BE SNIRGA) OFTEN RUNS AT THE FAST END IF NOT FASTER THAN GUIDANCE, WE KEPT MENTION OF FLURRIES AFTER MIDNIGHT NW OF THE I95 CORRIDOR. MINS MIGHT NOT BE LOW ENOUGH IN THE SOUTHERN ZONES IF CLOUDS DO NOT INCREASE OR OCCUR. UP N CONFIDENCE IS HIGHER WITH US USING A DATASET BLEND. WITH THE FCST WAA GONE AND THE SFC BOUNDARY WEAKENING, THE FCST MODELS CONT TO NOT GENERATE MUCH PCPN ACROSS OUR CWA DURING THE DAY ON THURSDAY. THERE HAS BEEN PRETTY GOOD MODEL CONSISTENCY ABOUT THIS SCENARIO. THERE ARE STILL SOME CHANNELIZED VORT MAXES FORECAST TO MOVE THROUGH. SO WE HAVE KEPT LOW CHC POPS IN...AROUND AND TO THE N OF THIS FEATURE. THERE IS SOME AIR MASS RECOVERY PRECEDING THE BOUNDARY RELATIVELY SPEAKING. GUIDANCE MAX TEMPS THOUGH AWAY FROM DELMARVA WHERE THERE SHOULD BE MORE SUN LOOK TOO HIGH. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... THE LONG WAVE TROF HAS YET TO MOVE THROUGH OUR CWA COME THURSDAY NIGHT AND THERE ARE MODEL DIFFERENCES AS TO HOW MUCH OF A HANG BACK BOUNDARY THERE WILL BE ACROSS OUR CWA FOR FRIDAY. THE CAN GGEM AND WRF-NMM HAVE MORE THAN THE GFS, ECMWF OR UKMET. FARTHER UP IN THE ATMOSPHERE MODEL GUIDANCE HAS BEEN WORKING ITS WAY BACK TO A SHARPER TROF AS THE ECMWF HAS HAD FOR A COUPLE OF DAYS. ANOTHER SHORT WAVE IS FORECAST TO MOVE THRU OUR CWA LATE THURSDAY NIGHT. WE WILL NEED GREATER INSTABILITY AND THUS WE JUST KEPT FLURRIES IN AGAIN MAINLY NW OF THE I95 CORRIDOR. ON FRIDAY THE MODELS ARE FORECASTING US TO COME CLOSER TO A WINDEX TYPE DAY THAN TODAY. THE GFS DOES NOT HAVE THE SFC BOUNDARY BUT HAS ARCTIC THICKNESSES MOVING IN. THE WRF-NMM HAS THE BOUNDARY, BUT DOES NOT HAVE A TIGHT LI GRADIENT. OVERALL ITS FCST LLVL THICKNESSES ARE HIGHER. OVERALL THERE ARE MORE POSITIVES THAN NEGATIVE RIGHT NOW. THUS WE HAVE BUMPED UP POPS INTO CHANCE. PTYPE SHOULD MAINLY BE SNOW. THE WRF-NMM SOLUTION MIGHT MAKE IT WARM ENUF (WITH LIGHT INTENSITY ALSO) FOR POSSIBLY SOME RAIN SOUTH AND THIS ASPECT OF THE FCST WILL BE IMPROVED AS WE GET CLOSER. HIGH PRESSURE THEN MOVES EASTWARD FOR THE WEEKEND WHICH IS TRENDING DRY. WE KEPT A LOW CHC POP FAR NORTH SUNDAY NIGHT FOR THE POSSIBILITY OF SOME WAA INDUCED PCPN WITH THE APPROACHING WARM FRONT. OTHERWISE THE BEST PCPN CHANCE THRUT OUR CWA WOULD BE WITH THE CFP ON OR ABOUT MONDAY NIGHT. AIR MASS WILL START MODIFYING AND TEMPS SHOULD GET CLOSER TO NORMAL EARLY NEXT WEEK AND SHOULD DROP BELOW NORMAL AGAIN TOWARD THANKSGIVING. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. AN INTENSIFYING LOW PRESSURE SYSTEM WELL EAST OF OUR AREA WILL CONTINUE TO MOVE NORTHEASTWARD TONIGHT AND FARTHER AWAY FROM OUR REGION. THE COMBINATION OF THIS INTENSIFYING STORM, HIGH PRESSURE SLOWLY BUILDING TOWARD OUR AREA FROM THE WEST, AND COLDER AIR INFILTRATING THE REGION, WILL ALLOW A BRISK WIND TO HOLD UP FOR MOST. THE FLY IN THE OINTMENT THOUGH IS THAT SOME AREAS HAVE EXPERIENCED A DIMINISHING OF THE WIND SO FAR FOLLOWING A SECONDARY FRONTAL BOUNDARY. MUCH DRIER AIR IS ARRIVING BEHIND THIS FEATURE. FORECAST SOUNDINGS ALONG WITH SOME ACARS SOUNDINGS INDICATE 20 TO 25 KNOTS OF WIND AT ABOUT 800 FEET. IT IS JUST A MATTER OF HOW MUCH CAN THIS MIX DOWN THROUGH THE OVERNIGHT. THE LATEST THINKING IS THAT WINDS WILL HOLD UP IN THE 10 TO 15 KNOT RANGE ON AVERAGE, WITH SOME OCCASIONAL GUSTS FOR AWHILE. AS MUCH DRIER AIR CONTINUES TO POUR INTO THE AREA, THE CLOUDS HAVE TRENDED TO THIN OUT QUITE A BIT WITH THE EARLIER SNOW SHOWERS AND FLURRIES RAPIDLY DIMINISHED. THE OVERALL WIND FLOW LOOKS TO NORTHERLY TO ALLOW FOR ADDITIONAL LAKE EFFECT STREAMERS TO MAKE IT THIS FAR SOUTH, THEREFORE WE WILL CARRY NO PRECIPITATION AND JUST SOME LINGERING STRATOCUMULUS WITHIN THIS COLD FLOW OF AIR. OUTLOOK... A LARGE AREA OF HIGH PRESSURE FROM THE MIDWEST TO THE SOUTHERN PLAINS TONIGHT WILL SLIDE TOWARD OUR AREA ON WEDNESDAY. THIS FEATURE MAY TEND TO GET SHOVED TO OUR SOUTH AS A QUICK MOVING CLIPPER SYSTEM DIVES SOUTHEASTWARD ACROSS THE GREAT LAKES. THE INFLUENCE OF THE HIGH WILL ALLOW FOR LIGHTER WINDS WITH TIME, HOWEVER OVERALL STILL IN THE 10 TO 15 KNOT RANGE FOR MOST OF WEDNESDAY. FORECAST SOUNDINGS INDICATE STILL SOME GUST POTENTIAL, ESPECIALLY THE FIRST HALF OF THE DAY, HOWEVER WE OPTED TO LEAVE THIS OUT FOR NOW. THE PRESSURE GRADIENT IS EXPECTED TO GREATLY RELAX IN THE AFTERNOON AND ESPECIALLY DURING THE EVENING HOURS. WE THEN TURN TO A CLIPPER SYSTEM TO OUR NORTHWEST. THIS SYSTEM LOOKS TO WEAKEN AS IT CROSSES THE LOWER GREAT LAKES WEDNESDAY NIGHT AND THURSDAY. WE ARE ANTICIPATING AN INCREASE IN MAINLY MID TO HIGH LEVEL CLOUDINESS LATER IN THE DAY WEDNESDAY, WITH MOST OF THE INCREASE ARRIVING WEDNESDAY NIGHT INTO THURSDAY. SOME SNOW SHOWERS OR FLURRIES CANNOT BE RULED OUT THURSDAY WITH THIS WEAKENING SYSTEM. ANOTHER SHOT OF COLD AIR MOVES IN FRIDAY WITH PERHAPS A FEW SNOW SHOWERS AND FLURRIES. ANY SNOW SHOWERS WILL REDUCE THE CEILINGS AND VISIBILITIES FOR A BRIEF TIME. HIGH PRESSURE THEN GRADUALLY SETTLES IN FOR SATURDAY AND SUNDAY. && .MARINE... WE HAVE BEEN GETTING GALE FORCE WIND GUSTS ON DELAWARE BAY, HOWEVER THE WINDS HAVE BEEN SLOW TO INCREASE ON THE OCEAN. SOME OBSERVATIONS FOR THE OCEAN ZONES ARE INDICATING A GRADUAL INCREASE NOW, AND THE 18Z NAM AND GFS FORECAST SOUNDINGS DO INDICATE SOME GALE FORCE WINDS TONIGHT. IT MAY WIND UP BEING A MARGINAL EVENT, HOWEVER FOR NOW WE WILL MAINTAIN THE GALE WARNINGS. AS THE UPPER TROF PUSHES THROUGH AND HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST, THE PRESSURE GRADIENT BETWEEN THE DEVELOPING LOW PRESSURE IN THE ATLANTIC AND THE HIGH IS EXPECTED TO INCREASE. BUOY 44009 HAS 7 FOOT SEAS AND CONDITIONS WILL BE HAZARDOUS, EVEN IF MARGINAL GALE WINDS MATERIALIZE. SMALL CRAFT ADVISORY CONDITIONS WILL LIKELY FOLLOW THE GALE WARNING, AND THEN AS HIGH PRESSURE BUILDS INTO THE AREA LATER WEDNESDAY AND WEDNESDAY NIGHT, THE WIND AND SEAS WILL SUBSIDE. THE NEXT WEAK CLIPPER SYSTEM FOR THURSDAY AND FRIDAY APPEARS TO HAVE LITTLE AFFECT ON WINDS OR SEAS AND WITH HIGH PRESSURE EXPECTED FOR THE WEEKEND, A MORE TRANQUIL PERIOD IS EXPECTED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...GALE WARNING UNTIL 10 AM EST WEDNESDAY FOR ANZ430-431-450>455. && $$ SYNOPSIS...GIGI NEAR TERM...GIGI SHORT TERM...GIGI LONG TERM...GIGI AVIATION...GORSE MARINE...NIERENBERG/GORSE
NWS PHI Office Area Forecast Discussion