Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 280801 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 401 AM EDT SAT MAR 28 2015 .SYNOPSIS... A HIGH PRESSURE SYSTEM OVER THE GREAT LAKES WILL SINK SOUTHEAST AND REACH THE SOUTHEAST COAST SUNDAY. A COLD FRONT ASSOCIATED WITH A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE REGION ON MONDAY. THIS WILL BE FOLLOWED QUICKLY BY AN ALBERTA CLIPPER TYPE LOW PRESSURE SYSTEM PASSING NEAR OR THROUGH THE AREA LATE ON TUESDAY. A HIGH PRESSURE SYSTEM SHOULD THEN BUILD INTO THE REGION FOR WEDNESDAY. A COLD FRONT IS PREDICTED TO REACH THE WESTERN GREAT LAKES ON THURSDAY MORNING AND APPROACH THE FORECAST AREA ON FRIDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE SYNOPTIC SETUP IS COMPRISED OF A STRONG UPPER-LEVEL TROUGH ACROSS THE EAST. THE WATER VAPOR IMAGERY SHOWS THIS FEATURE WELL, WITH A STRONG SHORT WAVE ROUNDING THE BASE OF THE TROUGH AND MOVING OFF THE COASTS OF GEORGIA AND SOUTH CAROLINA. AT THE SURFACE, HIGH PRESSURE WILL BE BUILDING INTO THE CENTRAL GREAT LAKES AND OHIO VALLEY DURING THE COURSE OF THE DAY. MEANWHILE, LOW PRESSURE WILL CONTINUE TO DEVELOP WELL TO OUR EAST. AS THE UPPER-LEVEL TROUGH AXIS SETTLES OVERHEAD THIS AFTERNOON, A RATHER COLD AIRMASS FOR THIS TIME OF THE YEAR WILL ARRIVE. THIS WILL OCCUR AS STRONG CAA IS PRESENT. THE COMBINATION OF THIS CAA AND A TIGHTENING PRESSURE GRADIENT WILL RESULT IN BREEZY CONDITIONS, ESPECIALLY LATER THIS MORNING AND THROUGH THE AFTERNOON AS THE DEPTH OF THE MIXING LAYER INCREASES. THE FORECAST SOUNDINGS INDICATE ABOUT 30 MPH WINDS SHOULD OCCUR ACROSS THE AREA. SOME ENERGY SLIDING OFFSHORE WITHIN THE SOUTHWESTERLY FLOW ALOFT AHEAD OF THE TROUGH IS MAINTAINING SOME LIGHT PRECIPITATION VERY CLOSE TO THE COAST. THIS APPEARS TO BE MOSTLY MID LEVEL MOISTURE. OTHERWISE, SOME FLURRIES OR SNOW SHOWERS ARE ACROSS MAINLY CENTRAL PENNSYLVANIA. THE ARRIVAL OF A STRONG SHORT WAVE WITHIN THE TROUGH AXIS IS FORECAST TO ARRIVE BY LATE AFTERNOON. IT APPEARS THAT A SURFACE TROUGH WILL ALSO SETTLE SOUTHWARD ACROSS OUR AREA THIS AFTERNOON. WHILE THE AIRMASS WILL BE UNDERGOING A DRYING TREND, THERE IS ENOUGH MOISTURE FORECAST TO BE PRESENT IN THE LOWER LEVELS. THE COMBINATION OF COLD AIR ALOFT, SOME BOUNDARY LAYER HEATING AND WITH SOME LIFT FROM THE SHORT WAVE AND SURFACE TROUGH THERE SHOULD BE SOME SNOW OR RAIN SHOWERS. SOME OF THIS MAY INITIALLY NOT REACH THE GROUND AS THE LOWEST LEVELS DRY SOME MORE. THERE DOES NOT APPEAR TO BE MUCH IN THE WAY OF INSTABILITY, THEREFORE A CONVECTIVE CONTRIBUTION LOOKS LOW. THERE ARE SOME HINTS IN SOME OF THE HIGH RESOLUTION GUIDANCE THAT SOME NARROW BANDING OR WRAPAROUND MAY DEVELOP IN THE VICINITY OF NORTHEASTERN NEW JERSEY LATER THIS AFTERNOON AND EVEN DOWN INTO THE DELMARVA. OVERALL THOUGH, ANY PRECIPITATION SHOULD BE ON THE LIGHTER SIDE. WE WILL CONTINUE TO CARRY SLIGHT TO LOW CHC POPS AS THE EXACT PLACEMENT OF ANYTHING ORGANIZED IS OF LOWER CONFIDENCE ATTM. AS FOR THE HIGH TEMPERATURES, WE USED A NAM/GFS MOS AND ECMWF BLEND OVERALL WITH SOME TWEAKS. WE SHOULD MAINTAIN A DECENT AMOUNT OF CLOUD COVER ACROSS THE AREA FOR MUCH OF THE DAY, AND THIS COMBINED WITH THE STRONG CAA WILL RESULT IN A COLD LATE MARCH DAY. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... AN UPPER-LEVEL TROUGH AXIS IS FORECAST TO SWING ACROSS OUR AREA DURING TONIGHT. THERE IS QUITE A BIT OF SHORT WAVE ENERGY STRETCHED OUT WITHIN IT AS IT SHIFTS ACROSS THE REGION, HOWEVER THE AIRMASS IS FORECAST TO UNDERGO FURTHER DRYING. THE TAILEND OF THIS THOUGH MAY RESULT IN A FEW NARROW STREAMERS OF SNOW SHOWERS ALTHOUGH IT IS DIFFICULT TO PINPOINT EXACTLY WHERE THIS OCCURS IF IT WERE TO HAPPEN. SOME OF THE HIGH RESOLUTION GUIDANCE SUGGESTS THAT OUR SOUTHERN ZONES MAY GET A NARROW BAND OR TWO OF SNOW SHOWERS TO START THE EVENING, AS STRONGER PVA MOVES THROUGH. OVERALL, THIS WOULD BE RATHER LOCALIZED AND GIVEN THE DRYING NOT SURE IF IT ACTUALLY MATERIALIZES INTO MUCH. OTHERWISE, HIGH PRESSURE CONTINUES TO BUILD EASTWARD FROM THE OHIO VALLEY HOWEVER ITS CENTER REMAINS TO OUR WEST. THIS ALLOWS A TIGHT PRESSURE GRADIENT TO REMAIN OVER THE REGION. WHILE THE MIXING SHOULD DECREASE SOME THROUGH THE EVENING, A BREEZE IS EXPECTED TO BE MAINTAINED THROUGH THE NIGHT WITH THE MOST GUSTINESS OCCURRING IN THE EVENING. AS FOR THE LOW TEMPERATURES, A VERY COLD NIGHT IS EXPECTED WITH TEMPERATURES DROPPING DOWN INTO THE 20S AND TEENS. THE WIND MAY HOLD THESE UP SOME, HOWEVER IT WILL ALSO RESULT IN RATHER COLD WIND CHILL VALUES. OVERALL, WE USED A MOS BLEND. && .LONG TERM /SUNDAY THROUGH FRIDAY/... AN ACTIVE LONG TERM WITH A COUPLE OF PCPN SHOTS POSSIBLE. THE WRF-NMMB INITIALIZATION AT 500MB LOOKED BETTER THAN THE GFS, BOTH MODELS WERE ABOUT THE SAME AT 850MB AND 925MB WITH ANY ERRORS ON THE COLD SIDE BY ABOUT 1C. THE DP/DT WITH THE MODELS OVER THE PAST 24 HOURS WAS SHOWING A DEEPER EAST COAST TROF. BASED ON THIS MOVING FORWARD WE WERE SLOWER WITH THE EVOLUTION OF EVENTS. AN AIR MASS MODIFICATION WITH DECREASING WINDS IS PREDICTED FOR SUNDAY. GIVEN THE COLD START, CHANCES ARE THAT THE MAX TEMPS WILL OCCUR LATER IN THE AFTERNOON THAN USUAL. GIVEN FULL SUN AND A DOWNSLOPING WIND, WE WENT FULL ADIABATIC WITH MAX TEMPS CLOSE TO END OF THE AFTERNOON SOUNDING SUGGESTED MAX TEMPS. THE WEAKER OF THE NEXT TWO SYSTEMS WILL APPROACH OUR AREA ON MONDAY NIGHT. THERE WILL BE DECENT MID LEVEL QVEC CONVERGENCE, BUT THE PREDICTED ISENTROPIC LIFT AND FGEN FORCING ARE MORE MUTED. THE JET IS NOT IN A BAD POSITION. GIVEN THE OVERALL DRYNESS OF THE INITIAL AIR MASS, MODELS ARE NOT PREDICTING MUCH PCPN. BECAUSE OF THE DPVA AND THE MID LEVEL QVEC CONVERGENCE, PCPN SHOULD BE FALLING FROM A MID CLOUD DECK. NOT SURE IF IT WILL MAKE IT TO THE GROUND, BUT FOR NOW WE WENT HIGHER THAN STAT GUIDANCE BECAUSE OF THE FORCING. WHILE A LLJ WILL BE WARMING THE SUB CLOUD LAYER AND MIGHT BE ABLE TO OFFSET EVAPORATIONAL COOLING EFFECTS, SNOW AS A PTYPE IS A POSSIBILITY IN THE NORTHERN PART OF OUR CWA. BECAUSE QPF AMOUNTS ARE LOW, ANY ACCUMS ARE EXPECTED TO BE LESS THAN AN INCH. MIN TEMPS WILL LIKELY OCCUR EARLIER IN THE NIGHT AND RISE TOWARD MORNING. USUALLY THE CASE WITH THESE WEAK SYSTEMS, ANY PCPN OCCURS IN THE WAA PHASE WITH LITTLE IF ANY WITH THE CFP ITSELF. MODELS ARE PRETTY CLOSE ON THAT DURING THE DAY ON MONDAY. WITH THE LAGGING STRONGER CAA, THE DOWNSLOPING WINDS SHOULD MORE THAN COMPENSATE FOR COOLING ALOFT. A STAT GUIDANCE COMBO LOOKS DECENT FOR MAX TEMPERATURES. IT WILL BECOME WINDIER WIND PEAK GUSTS LIKELY REACHING AT LEAST 20 TO 30 MPH. THE RIDGING FROM THE NEXT HIGH PRESSURE SYSTEM PASSES OVER OUR FORECAST AREA ON MONDAY NIGHT. BUT WE MAY REMAIN IN A BIT OF A GRADIENT AND DID NOT BOTTOM MIN TEMPERATURES. AT LEAST ON PAPER TODAY, THE NEXT ALBERTA TYPE LOW PRESSURE SYSTEM LOOKS MORE ROBUST. A MUCH BETTER PREDICTED COUPLET OF MID LEVEL FGEN AND QVEC FORCING IN OUR AREA. THIS CAN BE SEEN WITH IN THE QPF FIELD BY ITSELF. THERE ARE TRACK DIFFERENCES WITH DIFFERENCES IN OPINION AS TO THE GREATER IMPACT. FOR NOW WE HAVE COMPROMISED BETWEEN THE DATASETS, THUS ONSET OF UPPED PCPN CHANCES IS TUESDAY AFTERNOON AND CONTINUING INTO TUESDAY NIGHT. WHILE THE BOUNDARY LAYER WILL GET WARMED ON TUESDAY, IT IS STILL COLD ALOFT AND A CHANGE TO SNOW, ESPECIALLY OVER THE HIGHER TERRAIN NORTH WOULD BE THE LOGICAL OUTCOME FOR SUCH A SCENARIO. THIS ONE COULD BE SNOWIER. BECAUSE OF DIFFERENCES WITH THE TRACK AND THE INHERENT UNCERTAINTY OF TIMING, THERE EXISTS THE POTENTIAL FOR SOME BIG ERRORS WITH MAX TEMPS ON TUE. WE ARE TOWARD THE HIGHER END OF THE GUIDANCE SPECTRUM. WEAKER HIGH PRESSURE SYSTEM TO FOLLOW ON WEDNESDAY WHICH MEANS LITTLE IF ANY DROP IN MAXIMUM TEMPERATURES. THE REST OF THE LONG TERM WE SHIED AWAY FROM THE FASTER GFS CFP TIMING. THUS OUR MAX TEMPS THURSDAY ARE HIGHER THAN ITS STAT GUIDANCE. WE ALSO PUSHED BACK THE ONSET OF SHOWER CHANCES CLOSER TO THE ECMWF`S TIMING AND PERSISTED IT THROUGH FRIDAY. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY, AND SURROUNDING AREAS. TODAY...VFR WITH CEILINGS MAINLY AROUND 5000 FEET. NORTH TO NORTHWEST WINDS INCREASING TO AROUND 15 KNOTS WITH GUSTS TO AROUND 25 KNOTS BY MIDDAY. A FEW SNOW OR RAIN SHOWERS ARE POSSIBLE, HOWEVER WITH LOW CONFIDENCE ON ANY ORGANIZATION A MENTION WAS NOT INCLUDED AT THIS TIME. TONIGHT...VFR CEILINGS GENERALLY SCATTERING OUT. NORTHWEST WINDS 10- 15 KNOTS WITH GUSTS TO AROUND 20 KNOTS. OUTLOOK... SUNDAY...VFR. GUSTY NORTHWEST WINDS WILL BE DECREASING. SUNDAY NIGHT AND MONDAY...SOME LOWER MVFR CIGS AND VSBYS IN SCATTERED RAIN, HIGHER TERRAIN SNOW, SHOWERS. THERE IS A CHANCE FOR LLWS AT SOUTHERN AIRPORTS. NORTHWEST WINDS ON MONDAY SHOULD GUST TO AROUND 25 KNOTS. MONDAY NIGHT...VFR. TUESDAY AND TUESDAY NIGHT...POTENTIAL MVFR OR IFR RESTRICTIONS IN RAIN AND POSSIBLY SNOW AT HIGHER TERRAIN AIRPORTS. WEDNESDAY...VFR OR BECOMING VFR AS THE DAY PROGRESSES. && .MARINE... THE CAA WILL INCREASE THROUGH THE DAY AS THE PRESSURE GRADIENT TIGHTENS BETWEEN LOW PRESSURE ORGANIZING WELL OFFSHORE AND HIGH PRESSURE BUILDING INTO THE OHIO VALLEY. THIS WILL RESULT IN NORTH TO NORTHWEST WINDS INCREASING TO SMALL CRAFT ADVISORY LEVELS. THE FORECAST SOUNDINGS INDICATE THAT THE MIXING DEPTH WILL INCREASE INTO TONIGHT WITH GUSTS UP TO 30 KNOTS. THIS WILL CONTINUE TONIGHT AS WELL. THE UPTICK IN THE WINDS WILL ALLOW THE SEAS TO BUILD SOME ONCE AGAIN, ALTHOUGH GIVEN THE OFFSHORE COMPONENT THE HIGHER SETS WILL BE NEAR THE MOUTH OF DELAWARE BAY AND ALSO FARTHER OFFSHORE. AS A RESULT, THE SMALL CRAFTS ADVISORY REMAINS IN EFFECT. OUTLOOK... SUNDAY...THE SMALL CRAFT ADVISORY WAS EXTENDED INTO SUNDAY MORNING. WINDS AND SEAS SHOULD BE BELOW SCA CRITERIA BY THE AFTERNOON AS THE GRADIENT RELAXES. SUNDAY NIGHT AND MONDAY...ANOTHER ROUND OF SCA CONDITIONS IS POSSIBLE IN THE INCREASING SW FLOW PRECEDING THE NEXT CFP. WHILE AIR TEMPERATURES WILL BE WARMING MONDAY, MIXING NEAR COASTAL AREAS COULD KEEP SCA CONDITIONS PERSISTING EVEN AFTER THE CFP. MONDAY NIGHT...SUB SCA CONDITIONS OUTLOOKED TO RETURN AS THE PRESSURE GRADIENT WEAKENS AGAIN. TUESDAY THROUGH WEDNESDAY...PRIMARILY SUB SMALL CRAFT ADVISORY CONDITIONS ARE OUTLOOKED. THE ONE CAVEAT IS THAT WITH A CLIPPER LOW PRESSURE SYSTEM PASSING THROUGH OR NEAR OUR COASTAL WATERS, WE WILL HAVE TO MONITOR A STRONGER OVERALL LOW THAT MIGHT INCREASE BOTH WINDS AND SEAS INTO SMALL CRAFT ADVISORY CRITERIA. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT SUNDAY FOR ANZ430-431- 450>455. && $$ SYNOPSIS...GAINES/GIGI NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...GIGI AVIATION...GAINES/GIGI/GORSE MARINE...GAINES/GIGI/GORSE

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