Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 310125 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 925 PM EDT WED JUL 30 2014 .SYNOPSIS... SEVERAL WEAK SURFACE TROUGHS WILL MOVE INTO THE AREA THROUGH THURSDAY, BEFORE HIGH PRESSURE OVER THE WESTERN ATLANTIC PUSHES AN OFFSHORE WARM FRONT NORTHWESTWARD ACROSS THE EAST COAST THIS WEEKEND. SEVERAL DISTURBANCES WILL MOVE NORTHEAST ALONG THIS BOUNDARY THROUGH THE WEEKEND. ANOTHER COLD FRONT WILL THEN MOVE ACROSS THE AREA LATE TUESDAY INTO WEDNESDAY. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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AN UPPER-LEVEL TROUGH CONTINUES TO INFLUENCE OUR WEATHER. A SERIES OF DISTURBANCES ROTATING AROUND THE MAIN UPPER-LEVEL TROUGH ARE PRODUCING CONVECTION TO OUR WEST. THE CURRENT ACTIVITY IS TIED TO A WELL DEFINED SHORT WAVE FROM NEAR LAKE ONTARIO TO WESTERN PENNSYLVANIA /VIA WATER VAPOR IMAGERY/. ITS FORCING IN COMBINATION WITH SOME DEEPER MOISTURE WITHIN AN AREA OF LINGERING INSTABILITY IS MAINTAINING SOME CONVECTION. THIS SHORT WAVE WILL CONTINUE TO LIFT TO THE EAST AND NORTHEAST THROUGH THE NIGHT, HOWEVER THE CONVECTION IS WEAKENING. THEREFORE, HELD ONTO SOME SLIGHT CHC/LOW CHC POPS ACROSS THE NORTHWESTERN ZONES THROUGH ABOUT MIDNIGHT FOR THE POTENTIAL OF A FEW SHOWERS. THE INSTABILITY IS WANING AND BASED ON THE DOWNWARD TREND IN REFLECTIVITY AND LIGHTNING TO OUR WEST, THE THUNDER WAS REMOVED. THE MODEL GUIDANCE OVERALL DOES NOT SHOW MUCH INSTABILITY HOLDING ON THROUGH THE NIGHT. IT IS POSSIBLE THAT AN AREA OF SOMEWHAT STEEPER MID LEVEL LAPSE RATES OVERSPREADS A PORTION OF THE REGION OVERNIGHT TO KEEP A FEW SHOWERS GOING AS THE SOUTHERN PORTION OF THE SHORT WAVE SLIDES BY. OVERALL, THE PRECIPITATION CHCS WERE KEPT ON THE LOW SIDE OVERNIGHT AND MAINLY CONFINED TO THE NORTH AND WEST OF PHILADELPHIA. THE HOURLY GRIDS WERE TWEAKED BASED ON THE LATEST OBSERVATIONS, THEN THE LAMP/LAV GUIDANCE WAS BLENDED IN. THE CLOUD COVER WAS ADJUSTED DOWNWARD QUITE A BIT TO START BASED ON SATELLITE DATA, HOWEVER SOME INCREASE WAS THEN MAINTAINED FROM WEST TO EAST AS AT LEAST SOME CLOUD DEBRIS SHOULD ARRIVE. NO MAJOR CHANGES WERE MADE TO THE LOW TEMPERATURES ATTM.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... STRONGER SHORTWAVE INTERACTION WITH INCREASING COLUMN MOISTURE AND BETTER, NOT GREAT, INSTABILITY SHOULD LEAD TO WIDELY SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. MAX TEMPERATURES SHOULD BE A DEGREE OR 2 BELOW NORMAL WITH AMPLE CLOUD COVER AND SCATTERED OR ISOLATED AFTERNOON SHOWER ACTIVITY. 50 50 BLEND OF THE 12Z/30 NAM/GFS MOS. CONFIDENCE BELOW AVERAGE ON WHERE THE GREATEST CHC OF A SHOWER OR ISOLATED TSTM SHOULD OCCUR THURSDAY THOUGH AM FAVORING I78 NORTHWARD. EVEN THE TIMING IS LESS THAN CERTAIN. THERE COULD BE SOME DYING SHOWERS IN E PA AND NNJ AT 8AM THEN NEWLY DEVELOPING SHOWERS/ISOLATED TSTMS DURING MID AFTN IN E PA. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... A WET WEEKEND AHEAD AS PERIODS OF SHOWERS AND THUNDERSTORMS ARE LIKELY FOR THE END OF THE WEEK, THROUGH THE WEEKEND, INTO EARLY NEXT WEEK. THE BROAD MID/UPPER TROUGH WILL REMAIN ACROSS THE EASTERN HALF OF THE COUNTRY INTO THE WEEKEND. HOWEVER, AS THE CLOSED LOW BEGINS TO LIFT INTO EASTERN CANADA THIS WEEKEND INTO EARLY NEXT WEEK, THE TROUGH WILL BEGIN TO FLATTEN OUT. WITH THE TROUGH REMAINING IN PLACE THROUGH THIS WEEKEND, THE EAST COAST WILL REMAIN UNDER SOUTHWEST FLOW ALOFT. SEVERAL SHORT WAVE/VORTICITY IMPULSES WILL TRAVERSE THE AREA WITHIN THE SOUTHWEST FLOW FRIDAY, SATURDAY, AND SUNDAY. AT THE SAME TIME, HIGH PRESSURE OVER THE WESTERN ATLANTIC WILL BEGIN TO BUILD WESTWARD, AND PUSH A FRONTAL BOUNDARY BACK TOWARD THE EAST COAST. WHILE THE FRONT WILL BE DRAPED NEAR THE EAST COAST, SEVERAL WEAK SURFACE WAVES WILL MOVE ALONG THE BOUNDARY AT THE SAME TIME AS THE SHORT WAVE/VORT MAXES ALOFT. THIS WILL HELP LEAD TO SEVERAL PERIODS OF ENHANCED PRECIPITATION PROBABILITIES THROUGH THE WEEKEND. BY MONDAY, THE MID/UPPER TROUGH FLATTENS OUT AND THE FRONTAL BOUNDARY MAY BEGIN PUSHING BACK FURTHER OFFSHORE. HOWEVER, THERE WILL STILL BE ENOUGH MOISTURE AROUND AND WE MAY BE CLOSE ENOUGH TO THE FRONT THAT SOME SHOWER/THUNDERSTORM ACTIVITY REMAINS POSSIBLE. ANOTHER COLD FRONT IS FORECAST TO MOVE ACROSS THE AREA LATE TUESDAY INTO TUESDAY NIGHT. THERE IS NOT ANY STRONG SHORT WAVE/VORTICITY IMPULSES CURRENTLY FORECAST, SO PRECIPITATION CHANCES ARE SMALL AT THIS TIME WITH THE APPROACH AND PASSAGE OF THE FRONTAL BOUNDARY. BEHIND THIS FRONT, HIGH PRESSURE SHOULD BUILD IN AND LEAD TO DRIER WEATHER FOR WEDNESDAY. WITH CLOUD COVER AND RAINFALL EXPECTED OVER THE WEEKEND, THE HIGHS SATURDAY AND SUNDAY ARE FORECAST TO BE SEVERAL DEGREES ABOVE NORMAL. HOWEVER, WE RETURN TO ABOVE NORMAL TEMPERATURES EARLY NEXT WEEK AS WE SHOULD BEGIN TO SEE MORE SUNSHINE. && .AVIATION /02Z THURSDAY THROUGH MONDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF TONIGHT...VFR, WITH SOME BASES AT OR ABOVE 5,000 FEET MOVING IN. THERE COULD BE A FEW SHOWERS NORTH AND WEST OF KPHL. SOUTH-SOUTHWEST WINDS AROUND 5 KNOTS, BECOMING LIGHT AND VARIABLE OR LOCALLY CALM. THURSDAY...MOSTLY VFR CEILINGS DEVELOPING WITH ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS POSSIBLE. LOCAL SUB-VFR CONDITIONS IN SHOWER/THUNDER ACTIVITY, MAINLY ACROSS EASTERN PENNSYLVANIA AND NORTHERN NEW JERSEY. SOUTHWESTERLY WINDS GENERALLY AROUND 10 KNOTS. OUTLOOK... THURSDAY NIGHT-FRIDAY...MOSTLY VFR. SHOWERS AND THUNDERSTORMS POSSIBLE, ESPECIALLY FRIDAY WHICH COULD TEMPORARILY REDUCED CIGS AND VSBYS. FRIDAY NIGHT-MONDAY...SHOWERS AND THUNDERSTORMS POSSIBLE PERIODICALLY THROUGH THE WEEKEND INTO EARLY NEXT WEEK. REDUCED CIGS AND/OR VSBYS POSSIBLE OVER THE WEEKEND, ESPECIALLY SATURDAY THROUGH SUNDAY.
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&& .MARINE... ANNOUNCEMENT: WE BEGAN A NEW EXPERIMENTAL MARINE OBSERVATION PROGRAM THAT ANY MARINER CAN EASILY USE TO COMMUNICATE WITH THE NWS HERE IN MOUNT HOLLY... PROVIDED YOU HAVE INTERNET ACCESS. THIS CAN HELP US FINE TUNE OUR FORECASTS...ESPECIALLY IF THE FORECAST IS NOT REFLECTING THE REALITY AT YOUR MARINE LOCATION. FORECAST: WINDS AND SEAS TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH THURSDAY WITH WINDS STAYING BELOW 15 KT AND SEAS BETWEEN 1 AND 3 FEET. SOUTHERLY WINDS WITH A SLIGHT ONSHORE COMPONENT EACH AFTERNOON AND A MORE WESTERLY COMPONENT LATE AT NIGHT. OUTLOOK... THURSDAY NIGHT-MONDAY...SUB-SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED THROUGH EARLY NEXT WEEK. HOWEVER, WIND MAY PERIODICALLY GUST AROUND 20 KNOTS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...ROBERTSON NEAR TERM...GORSE SHORT TERM...DRAG LONG TERM...ROBERTSON AVIATION...DRAG/GORSE/ROBERTSON MARINE...DRAG/ROBERTSON

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