Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 270135 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 935 PM EDT SAT JUL 26 2014 .SYNOPSIS... A WARM FRONT WILL LIFT NORTHWARD TOWARD THE AREA TONIGHT, BEFORE LIFTING ACROSS THE AREA ON SUNDAY AS AN AREA OF LOW PRESSURE MOVES INTO SOUTHEASTERN CANADA. ANOTHER LOW PRESSURE SYSTEM WILL LIFT INTO NEW ENGLAND MONDAY, PULLING A COLD FRONT ACROSS THE AREA. HIGH PRESSURE WILL RETURN TO THE EAST COAST FOR THE MIDDLE AND END OF THE UPCOMING WEEK. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... SEVERAL SHORTWAVES MOVING THROUGH THE WNW UPPER FLOW WILL BRING ROUNDS OF SHOWERS/TSTMS TO WRN/CNTRL PA DOWN INTO MD OVERNIGHT. THE PCPN MAY BRUSH THE ERN SHORE COUNTIES LATE TONIGHT. A FEW OF THE MODELS ARE SHOWING MORE PCPN DEVELOPING TOWARDS DAWN AND MOVING ACROSS ERN PA/NJ. POPS HAVE ONLY BEEN SLIGHTLY ADJUSTED THIS EVENING. THE TREND TOWARD HIGHER POPS SUN MORNING WAS KEPT IN FROM BEFORE. FEW IF ANY CHANGES WERE MADE TO TEMPS/DEW POINTS OR WINDS FOR THE UPDATE. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... SLIGHT RISK FOR SEVERE THUNDERSTORMS CONTINUES FOR SUNDAY AS OUR RUN OF DRY WEEKEND WEATHER REALLY TAKES A HIT. NOW COMES THE FORECAST PROBLEMS OF SHORT WAVE STRENGTH AND THEIR EFFECT ON THE SENSIBLE WEATHER. HERE OUR CONFIDENCE IS LESS THAN AVERAGE BASED ON THIS MORNING`S OUTCOME. THE NEXT SHORT WAVE IS INITIATING AN MCS IN EASTERN NEBRASKA AS WE TYPE. THIS IS THE ONE THAT THE GFS TAKES TO THE NTH DEGREE ON SUNDAY MORNING AND MAKES FOLLOWING ITS MASS FIELDS FOR THE REST OF SUNDAY IMPOSSIBLE. THE GENERAL IDEA APPEARS CORRECT. BUT DOES THIS SHORT WAVE ARRIVE TOO SOON BEFORE INSTABILITY CAN INCREASE ADEQUATELY FOR SEVERE AND STABILIZE US "SOMEWHAT"? DOES THE CONVECTION MUDDY THE CONVECTIVE WATERS FOR THE REAL DEAL COMING OUT OF EASTERN CANADA? DOES THE PREDECESSOR SHORT WAVE LINGER TOO LONG DURING THE EARLY MORNING? THE FCST BULK SHEAR IS WELL WITHIN RANGE OF SEVERE AT 30-40KTS. THE QUESTION BECOMES ABOUT AIR MASS RECOVERY OR PURITY AROUND THESE SHORT WAVES. WE DONT HAVE THE ANSWER YET. THE SUNNIER SUNDAY IS, THE TRULY STRONGER THE CONVECTION WILL BECOME. REGARDLESS, A MORE THAN ADEQUATE WIND FIELD IS IN PLACE (ANOMALOUSLY STRONG FOR LATE JULY) AND WE WILL CONTINUE THE ENHANCED WORDING IN THE ZONES/GRIDS STARTING DURING THE AFTERNOON. CAN GGEM AND UKMET TIMING WOULD GIVE OUR CWA A HIGHER CHANCE FOR SEVERE. GFS/ECMWF TIMING AT LEAST THRU THE DAYTIME HOURS WOULD BE LESS. POPS WERE LEFT AS LIKELY WITH AN INCREASE FROM SOUTHWEST TO NORTHEAST AS THE AFTERNOON AND EARLY EVENING PROGRESS. DONT WANT TO FORGO THE HEAVY RAIN THREAT, BUT WITH A FASTER OVERALL WIND FIELD WOULD HAVE TO SEE TRAINING TO HAVE ANY FLASH FLOOD THREAT. BECAUSE OF UNCERTAINTY AS TO CLOUD COVER AND A DOWNWARD TREND TO THE GFS THERMAL FIELDS, WE TENDED TO LEAN TOWARD THE LOWER GFS MOS FOR MAX TEMPS. PRETTY CLOSE TO CONTINUITY. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... A WET START TO THE LONG TERM, FOLLOWED BY A PROLONGED DRY PERIOD. ON SUNDAY NIGHT, WE EXPECT AN INITIAL SURFACE TROUGH TO MOVE ACROSS THE AREA DURING THE EVENING AND PUSH OFFSHORE OVERNIGHT AS AN AREA OF SURFACE LOW PRESSURE MOVES THROUGH PENNSYLVANIAN INTO NEW YORK. MEANWHILE, SEVERAL SHORT WAVE/VORTICITY IMPULSES WILL SLIDE ACROSS THE AREA WITHIN THE SOUTHWEST FLOW ALOFT AS THE MID-LEVEL LOW MOVES OUT OF THE GREAT LAKES AND INTO WESTERN PENNSYLVANIA. THIS WILL KEEP A HIGH LIKELIHOOD OF SHOWERS AND THUNDERSTORMS ACROSS THE AREA. PW VALUES ARE FORECAST TO BE CLOSE TO 1.5-1.75 INCHES EARLY IN THE NIGHT, SO A PERIOD OF HEAVY RAIN IS POSSIBLE. HOWEVER, AS THE NIGHT MOVES ON, THE PW VALUES DROP, SO HEAVY RAIN WILL BECOME LESS LIKELY. ON MONDAY, THIS LOW PRESSURE WILL CONTINUE TO MOVE INTO NEW ENGLAND, EVENTUALLY PULLING A COLD FRONT ACROSS THE AREA AND OFF THE EAST COAST. PW VALUES MAY REBOUND CLOSE TO 1.5 INCHES, BUT OVERALL, IT LOOKS DRIER THAN THE DAY LEADING UP. STILL, WITH THE MID-LEVEL TROUGH SWINGING CLOSE BY OR OVERHEAD, THERE WILL REMAIN THE CHANCE FOR AT LEAST SCATTERED SHOWERS/THUNDERSTORMS, ESPECIALLY UP NORTH CLOSER TO THE CENTER OF THE TROUGH. THERE MAY BE SOME LINGERING SHOWERS MONDAY EVENING AS THE FRONT CONTINUES TO PUSH OFFSHORE AND THE MID-LEVEL TROUGH LIFTS OUT, BUT ANY PRECIPITATION IS EXPECTED TO END BY MIDNIGHT. AFTER THIS WET PERIOD, WE THEN ENTER INTO A DRY PERIOD FOR MUCH OF THE REMAINDER OF THE WEEK. PW VALUES DROP TO AN INCH OR LOWER FOR TUESDAY AND WEDNESDAY, BUT MAY RETURN TO 1-1.25 INCHES FOR THURSDAY AND FRIDAY. HOWEVER, WITH HIGH PRESSURE BUILDING ACROSS THE REGION, AND NO SIGNIFICANT SHORT WAVE/VORTICITY IMPULSES THROUGH MUCH OF THE WEEK, WE ARE NOT EXPECTING ANY PRECIPITATION. IT WOULD NOT BE SURPRISING IF SOME ISOLATED SHOWERS DEVELOPED THURSDAY INTO FRIDAY WITH DAYTIME INSTABILITY, BUT CHANCES ARE LOW ENOUGH AT THIS TIME THAT WE DID NOT INCLUDE THEM FOR THURSDAY AND FRIDAY ONLY HAS A SLIGHT CHANCE AT THIS TIME. AS WE MOVE INTO NEXT WEEKEND, WE GET MORE SOLID RETURN OF MOISTURE ACROSS THE AREA. WE ALSO HAVE A BETTER CHANCE OF VORTICITY IMPULSES AFFECTING OUR AREA WITHIN THE SOUTHWEST FLOW ALOFT AS THE MID-LEVEL TROUGH DEEPENS TO OUR WEST. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. DECIDED TO RETAIN THE MENTION OF SHOWERS AND MVFR CONDITIONS EARLY SUNDAY THAT WERE IN THE PREVIOUS TAFS. CONFID IN THIS IS LOW. MOSTLY SRLY WINDS OVERNIGHT AND VFR CONDITIONS EARLY...THEN SOME MVFR FOG POSSIBLE. FOLLOWING THE PASSAGE OF THE SHOWER THREAT, PREVAILING VFR CONDITIONS ARE PREDICTED TO RETURN TO ALL TERMINALS BY THE MIDDLE OF SUNDAY MORNING. WINDS SHOULD BE SLIGHTLY STRONGER THAN TODAY AND SLIGHTLY MORE FROM THE WEST WITH SPEEDS AVERAGING 10 TO 15 KNOTS. MORE ORGANIZED CONVECTION IS LIKELY EITHER SUNDAY AFTERNOON OR EVENING. WHILE CONFIDENCE IS MODERATE ABOUT OCCURRENCE, IT IS LOWER AS TO TIMING. PLEASE LOOK FOR FURTHER UPDATES IN FUTURE TAFS. OUTLOOK... SUNDAY NIGHT...SHOWERS AND THUNDERSTORMS LIKELY, WHICH COULD REDUCE CIGS/VSBYS TO MVFR OR IFR. MONDAY...A CHANCE OF SHOWERS AND THUNDERSTORMS, WHICH COULD REDUCE CIGS/VSBYS TO MVFR OR IFR...OTHERWISE, VFR EXPECTED. GUSTY SW-W WINDS 20-25 KNOTS. MONDAY NIGHT-THURSDAY...MAINLY VFR. && .MARINE... NO SMALL CRAFT ADVISORY HEADLINES IN MARINE PRODUCTS. THE TREND FOR WAVE WATCH GUIDANCE HAS BEEN DOWNWARD FROM RECENT RUNS THROUGH SUNDAY DAY. THE ATTENDANT FCST LLJ IS WEAKER. COUPLED WITH WARMER AIR OVER COOLER WATER DOES NOT APPEAR LIKELY THAT EITHER WINDS OR SEAS (ON THE OCEAN) WILL MAKE CRITERIA THROUGH THE DAY. THE GREATER CONCERN IS MORE SHORT FUSED IN NATURE WITH SPECIAL MARINE WARNING TYPE STRONG/SEVERE THUNDERSTORMS. OUTLOOK... SUNDAY NIGHT-MONDAY...IT IS POSSIBLE THAT SEAS MAY BUILD CLOSE TO 5 FEET, WHICH MAY REQUIRE A SMALL CRAFT ADVISORY. WINDS MAY INCREASE TO 20-25 KNOTS AS WELL. MONDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS POSSIBLE EARLY MONDAY NIGHT, THEN SUBSIDE AND REMAIN BELOW ADVISORY LEVELS THROUGH THE PERIOD. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...ROBERTSON NEAR TERM...GIGI/O`HARA SHORT TERM...GIGI LONG TERM...ROBERTSON AVIATION...GIGI/ROBERTSON/PO MARINE...GIGI/ROBERTSON

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