Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 210734 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 334 AM EDT THU AUG 21 2014 .SYNOPSIS... THE REGION WILL SEE AN ACTIVE WEATHER PATTERN FOR THE NEXT TWO DAYS AS ONE AREA OF HIGH PRESSURE REMAINS OVER THE DEEP SOUTH, WHILE ANOTHER IS SITUATED OVER THE HUDSON BAY. THE CANADIAN HIGH WILL EVENTUALLY BUILD SOUTH OVER THE REGION BY LATE THIS WEEKEND AND REMAIN THE THE MAIN WEATHER FEATURE FOR THE MID ATLANTIC THROUGH MID WEEK NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THERE ARE A COUPLE OF AREAS OF ISOLATED/SCATTERED SHOWERS AROUND THE AREA EARLY THIS MORNING, ALL ASSOCIATED WITH A FEW INDIVIDUAL VORTICITY IMPULSES MOVING THROUGH THE CYCLONIC FLOW ALOFT. THE FIRST IS EXITING OUR AREA TO THE NORTHEAST, AND WILL BRING WITH IT IT`S AREA OF SHOWERS. THE OTHERS ARE LOCATED ACROSS CENTRAL AND WESTERN PENNSYLVANIA. THE HRRR AND RUC HAVE THESE DRIFTING EASTWARD AND MOSTLY DRYING OUT OR LIFTING TO OUR NORTH BEFORE THEY GET HERE. AFTER THESE SHOWERS EARLY THIS MORNING, WE SHOULD GET A PERIOD FROM MID/LATE MORNING INTO THE EARLY AFTERNOON WHERE WE SHOULD BE MOSTLY SHOWER FREE. HOWEVER, AS WE MOVE INTO THE MID TO LATE AFTERNOON, WE EXPECT SHOWERS TO BEGIN TO INCREASE TO OUR WEST AND MOVE INTO OUR AREA. THESE WILL BE ASSOCIATED WITH ANOTHER SHORT WAVE/VORTICITY IMPULSE THAT WILL BE MOVING INTO OUR AREA AS THE MID/UPPER LOW SLOWLY DRIFTS EASTWARD. AT THE SURFACE, AN AREA OF LOW PRESSURE REMAINS ACROSS THE EASTERN GREAT LAKES, WHILE A WEAKENING FRONTAL BOUNDARY EXTENDS SOUTH OF THE LOW. ANOTHER FRONTAL BOUNDARY REMAINS SNAKED FROM WESTERN PENNSYLVANIA SOUTHWARD THROUGH VIRGINIA AND NORTH CAROLINA. NONE OF THESE FEATURES ARE EXPECTED TO MOVE INTO THE AREA TODAY AS THE LOW IS EXPECTED TO REMAIN TO OUR NORTH AND THE FRONTAL BOUNDARY TO OUR SOUTH IS EXPECTED TO REMAIN STATIONARY THROUGH THE DAY. THERE REMAINS SOME INSTABILITY FORECAST TODAY, ALTHOUGH THERE IS NOT MUCH SHEAR OR MUCH OF A WIND FIELD, SO WE DO NOT EXPECT SEVERE WEATHER AT THIS TIME. IF THERE ARE ANY THUNDERSTORMS LATER TODAY, AND IF THEY GROW TALL ENOUGH, SOME GUSTY WINDS COULD BE POSSIBLE AND WITH THE WETBULB AS LOW AS IT IS, SOME SMALL HAIL CANNOT BE RULED OUT. PW VALUES ARE GENERALLY FORECAST AROUND 1.5-1.75 INCHES, SO SOME SHOWERS/STORMS COULD PRODUCE A PERIOD MODERATE TO HEAVY RAINFALL. FOR HIGHS, USED A BLEND OF MAV/MET MOS, MOSGUIDE, AND MIXED 925 MB TEMPS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... WE EXPECT SHOWERS AND POSSIBLY THUNDERSTORMS TO BE ONGOING AT THE START OF THE SHORT TERM PERIOD AS THE VORTICITY IMPULSE WILL BE MOVING THROUGH THE AREA AS THE MID/UPPER LOW CONTINUES TO DRIFT EASTWARD INTO NEW ENGLAND. ALSO, A SECOND AREA OF SURFACE LOW PRESSURE IS FORECAST TO DEVELOP NEAR THE CHESAPEAKE BAY ALONG THE STATIONARY BOUNDARY TO OUR SOUTH AS IT TRIES TO LIFT NORTHWARD INTO OUR SOUTHERN AREAS. THIS MAY KEEP A FOCUS FOR PRECIPITATION OVERNIGHT ACROSS OUR SOUTHERN AREAS WHERE SHOWERS MAY LAST INTO THE EARLY MORNING HOURS OF FRIDAY. AS THE ENERGY FROM THE VORTICITY IMPULSE MOVES AWAY FROM THE AREA, SHOWERS SHOULD MOSTLY END BY DAYBREAK. FOR LOWS, USED A BLEND OF MAV/MET MOS AND MOSGUIDE. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... FRIDAY THROUGH SATURDAY...THE REGION REMAINS UNDER NORTHWEST FLOW AS THE STOUT RIDGE REMAINS OVER THE MISSISSIPPI VALLEY, AND THE OTHER HIGH REMAINS OVER EASTERN CANADA. WITH THE NORTHWEST FLOW, EXPECT A FEW EMBEDDED SHORT WAVE TROUGHS TO BRING CHANCES FOR THUNDERSTORMS THROUGH THIS PERIOD. HOWEVER, THE TIMING OF THE INDIVIDUAL SHORT WAVE TROUGHS REMAINS UNCERTAIN. SUNDAY THROUGH THURSDAY...THE HIGH OVER EASTERN CANADA BUILDS SOUTH. WITH THE ASSOCIATED COLD AIR ADVECTION, COULD SEE HIGHS ESPECIALLY EARLY IN THE WEEKEND 5 TO 10 DEGREES BELOW NORMAL. BY TUESDAY HOWEVER, THE HIGH STARTS TO SHIFT OFF SHORE, LEAVING THE REGION UNDER SOUTHERLY FLOW AND LEADING TO A MODEST WARMING TREND. HOWEVER, ALSO TOWARDS THE END OF THIS FORECAST PERIOD THE GFS AND ECMWF SOLUTIONS DIFFER GREATLY ON THE TIMING OF AN UPPER LEVEL TROUGH AND ASSOCIATED SURFACE COLD FRONT THAT WILL BE PROPAGATING EAST ON THE HEALS OF THE HIGH. STILL, BOTH SOLUTIONS SHOW THESE FEATURES JUST BEYOND THE SEVEN DAY FORECAST. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OVERALL, WE EXPECT MOSTLY VFR CONDITIONS FOR THE TAF SITES TODAY, ALTHOUGH THERE IS THE POTENTIAL FOR LOWER CONDITIONS LATER TODAY INTO THIS EVENING. A PERIOD OF MVFR CIG AND/OR VSBY IS POSSIBLE EARLY THIS MORNING MAINLY FOR ABE/RDG/MIV, BUT THIS SHOULD RETURN TO VFR BY MID-MORNING. WE EXPECT SCATTERED SHOWERS, AND POSSIBLY THUNDERSTORMS, TO DEVELOP TO OUR WEST TROUGH THE DAY AND MOVE INTO OUR AREA LATER THIS AFTERNOON INTO THIS EVENING AS A DISTURBANCE ALOFT MOVES THROUGH THE AREA. CONFIDENCE IN THUNDERSTORM ACTIVITY OCCURRENCE AND TIMING IS LOW, SO THEY WERE NOT INCLUDED IN THE TAFS AT THIS TIME. THERE IS THE POTENTIAL FOR SOME MODERATE TO HEAVY SHOWERS, SO WE HAVE INCLUDED MODERATE SHOWERS WITH MVFR CONDITIONS LATER TODAY INTO THIS EVENING. ONE MODEL GIVES US VFR THROUGH THE PERIOD, WHILE THE OTHER BRINGS EVERYONE TO IFR. NOT CONFIDENT ON IFR, BUT THINK WE COULD GET SOME LOWER CONDITIONS TEMPORARILY WITH THE HEAVIER SHOWERS. WINDS TODAY SHOULD BE MOSTLY SOUTH TO SOUTHEAST AROUND 5 TO 10 KNOTS. OUTLOOK... FRIDAY AND SATURDAY...MOSTLY VFR. ISOLATED TO SCATTERED TSRA ARE POSSIBLE ACROSS THE REGION. UNDER ANY TSRA MVFR CEILINGS AND BRIEF IFR VISIBILITIES WILL BE POSSIBLE. SUNDAY THROUGH MONDAY...GENERALLY VFR. && .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED TODAY WITH SEAS 2-3 FEET OR LESS AND SOUTHEAST WINDS 5 TO 10 KNOTS. OUTLOOK... FRIDAY...CONDITIONS EXPECTED TO STAY BELOW SMALL CRAFT ADVISORY CRITERIA. SATURDAY...OCCASIONAL GUSTS NEAR 25 KT AND WAVE HEIGHTS APPROACHING 5 FT ARE POSSIBLE ESPECIALLY SATURDAY AFTERNOON THROUGH SATURDAY NIGHT. SUNDAY AND MONDAY...WAVE HEIGHTS AND WINDS SLOWLY FALLING BELOW SMALL CRAFT ADVISORY CRITERIA SUNDAY MORNING AND SHOULD REMAIN BELOW CRITERIA THROUGH MONDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...JOHNSON NEAR TERM...ROBERTSON SHORT TERM...ROBERTSON LONG TERM...JOHNSON AVIATION...JOHNSON/ROBERTSON MARINE...JOHNSON/ROBERTSON

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