Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 210517 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 117 AM EDT TUE OCT 21 2014 .SYNOPSIS... LOW PRESSURE WILL PASS OFF THE MID ATLANTIC COAST ON TUESDAY NIGHT. THE LOW IS THEN EXPECTED TO MOVE SLOWLY NORTH AND NORTHEASTWARD, REACHING THE WATERS OFF CAPE COD AROUND THURSDAY NIGHT AND ARRIVING IN NOVA SCOTIA ON FRIDAY NIGHT. HIGH PRESSURE IS ANTICIPATED TO BUILD INTO OUR REGION FROM THE SOUTHWEST FOR FRIDAY INTO SATURDAY. A COLD FRONT IS EXPECTED TO ARRIVE SATURDAY NIGHT WITH ANOTHER AREA OF HIGH PRESSURE FOLLOWING FOR SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... AN UPPER-LEVEL TROUGH WILL CONTINUE TO AMPLIFY INTO THE NORTHEAST OVERNIGHT. THE WATER VAPOR IMAGERY SHOWS A WELL DEFINED AND COMPACT SHORT WAVE MOVING ACROSS SOUTHWESTERN PENNSYLVANIA. THIS FEATURE WILL CONTINUE TO GRADUALLY SHIFT EASTWARD. OUT AHEAD OF IT, SOME WAA AND THETA-E ADVECTION IS COMBINING WITH SOME SHORT WAVE ENERGY WELL OUT AHEAD OF THE MAIN FEATURE. THIS ALONG WITH JUST ENOUGH LOWER LEVEL CONVERGENCE IS RESULTING IN SOME SHOWERS ACROSS THE WESTERN ZONES AND DOWN INTO VIRGINIA. THIS ACTIVITY IS GRADUALLY SHIFTING EASTWARD, HOWEVER INTO AN INITIALLY DRIER AIRMASS. SOME BRIEF HEAVIER SHOWERS THOUGH WILL SLIDE ACROSS THE FAR WESTERN ZONES THROUGH ABOUT 08Z. OVERALL, THE QPF IS EXPECTED TO BE LIGHT. WE CONTINUE SLIGHT CHC TO LOW CHC POPS FOR SOME SHOWERS MAINLY ACROSS THE WESTERN HALF OF THE CWA. THE HOURLY GRIDS WERE ADJUSTED BASED ON THE LATEST OBSERVATIONS, AND THEN THE LAMP/LAV GUIDANCE WAS BLENDED IN FOR THE TEMPERATURES AND DEW POINTS THROUGH EARLY THIS MORNING. && .SHORT TERM /TUESDAY/... A FILLING SURFACE LOW PRESSURE SYSTEM TO OUR NORTHWEST SLIDES FURTHER SOUTH LATE TOMORROW MORNING AND BECOMES MORE BROAD. THERE WILL LIKELY BE A DRY SLOT SETTING UP ACROSS THE CENTRAL PORTION OF OUR CWA, THOUGH THE EXACT PLACEMENT IS STILL SUSPECT. A BETTER DEFINED AND STRONGER COASTAL LOW FORMS OFF THE DELMARVA LATE IN THE DAY AND MOVES TOWARDS THE NORTHEAST...LOTS OF JET DYNAMICS INVOLVED. CHANCES FOR SHOWERS INCREASES TO LIKELY DURING THE DAY MAINLY ACROSS OUR WESTERN AND NORTHERN ZONES, THOUGH STILL NOT ENTIRELY SOLD ON A COMPLETELY DRY DAY ELSEWHERE SO WE CONTINUE THE CHANCE POPS. NOT LOOKING AT A COMPLETE WASHOUT TOMORROW WITH WIDELY SCATTERED SHOWERS THE MOST PROBABLE. WE KEEP THUNDER OUT OF THE FORECAST, EVEN WITH STEEPER MID-LEVEL LAPSE RATES FORMING, AS THE BETTER DYNAMICS OFFSHORE COULD ROB INLAND AREAS OF ALL THE LUSTER. TEMPERATURES WILL CONTINUE TO CLIMB WITH THE MODIFYING AIR MASS AND SOUTHERLY AHEAD OF THE LOW PRESSURE SYSTEM. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... A UPPER LEVEL JET EXTENDED FROM WESTERN HUDSON BAY, ACROSS WESTERN ONTARIO TO THE WESTERN PART OF THE GREAT LAKES REGION THIS AFTERNOON. A MID LEVEL LOW IS FORECAST TO DEVELOP IN THE LIFT UNDER ITS LEFT FRONT QUADRANT TONIGHT OVER THE LAKE HURON VICINITY. THE MID LEVEL LOW IS EXPECTED TO BE LOCATED OVER EASTERN WEST VIRGINIA ON TUESDAY EVENING AND IT SHOULD PASS OFF THE DELMARVA COAST ON WEDNESDAY MORNING. THE FEATURE IS THEN ANTICIPATED TO MEANDER OFF OUR COAST FROM WEDNESDAY AFTERNOON INTO THURSDAY EVENING BEFORE LIFTING NORTHEASTWARD AND REACHING THE WATERS OFF CAPE COD ON FRIDAY MORNING. A SURFACE LOW IS FORECAST TO FOLLOW THE MID LEVEL LOW CLOSELY DURING THE PERIOD. WE ARE EXPECTING THE POTENTIAL FOR RAIN FROM TUESDAY NIGHT THROUGH THURSDAY MORNING. THE POSSIBILITY OF MODERATE TO HEAVY RAINFALL SHOULD BE MOSTLY ON THE EAST SIDE OF THE DEVELOPING MID LEVEL LOW. AS A RESULT, WE ARE NOT ANTICIPATING MUCH MODERATE TO HEAVY RAINFALL IN OUR REGION. THE ONLY EXCEPTION IS IN OUR COASTAL AREAS FROM TUESDAY NIGHT INTO WEDNESDAY WHERE RAINFALL AMOUNTS MAY APPROACH AN INCH AT SOME LOCATIONS. ALSO, MARGINAL INSTABILITY IN THAT AREA MAY TRANSLATE INTO ISOLATED LIGHTNING AND THUNDER. REGARDLESS, THE EXPECTED RAINFALL TOTALS SHOULD NOT RESULT IN ANY FLOODING PROBLEMS. AS THE LOW BEGINS TO PULL AWAY TO OUR NORTHEAST ON THURSDAY NIGHT, THE POTENTIAL FOR RAIN SHOWERS SHOULD END GRADUALLY IN OUR AREA. A COUPLE OF REINFORCING MID LEVEL SHORT WAVES SHOULD DROP OVER OUR REGION FROM THE NORTHWEST IN THE CYCLONIC FLOW AROUND THE DEPARTING MID LEVEL LOW OVER THE COMING WEEKEND. THE SHORT WAVES ARE NOT EXPECTED TO HAVE MUCH MOISTURE ASSOCIATED WITH THEM. THEREFORE, WE ARE NOT ANTICIPATING ANY PRECIPITATION AT THAT TIME. A MID LEVEL RIDGE FROM THE WEST SHOULD BUILD TOWARD OUR REGION FOR SUNDAY AND MONDAY. DAYTIME HIGHS ARE FORECAST TO BE A BIT BELOW NORMAL WITH THE RAIN ON WEDNESDAY AND THURSDAY. READINGS SHOULD RETURN TO NEAR NORMAL FOR THE PERIOD FROM FRIDAY THROUGH MONDAY. && .AVIATION /05Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OVERNIGHT...VFR OVERALL. LIGHT SOUTHERLY WINDS. SOME SHOWERS WILL GENERALLY BE NORTH AND WEST OF KPHL, WITH A BRIEF HEAVIER SHOWER AT KRDG AND KABE THROUGH ABOUT 08Z. WHILE SOME MVFR FOG CANNOT BE RULED OUT, MAINLY AT KRDG AND KABE, CONFIDENCE IS ON THE LOW SIDE GIVEN THE CLOUD COVER AND SHOWERS AND THEREFORE IT WAS NOT INCLUDED AT THIS TIME. TUESDAY...MOSTLY VFR. WEAK LOW PRESSURE SYSTEM NEARS FROM THE WEST-NORTHWEST. WINDS START OFF LIGHT OUT OF THE SOUTH, MAYBE SOUTHEAST, AND VEER TOWARDS THE WEST-NORTHWEST. SOME SHOWERS ARE EXPECTED TO BE AROUND, HOWEVER THERE IS SOME LOWER CONFIDENCE ON THE COVERAGE AND ACTUAL TIMING. OUTLOOK... TUESDAY NIGHT THROUGH THURSDAY...CONDITIONS VARYING BETWEEN VFR AND MVFR IN PERIODS OF RAIN. THURSDAY NIGHT...MAINLY VFR WITH A CHANCE OF SHOWERS. FRIDAY THROUGH SATURDAY...MAINLY VFR. && .MARINE... OVERNIGHT...SUB-SCA CONDITIONS EXPECTED OVERALL. SOUTHERLY WINDS IN THE 10-20 KNOT RANGE OVERALL, WITH THE GREATEST MIXING OUT TOWARDS 20NM. THIS IS WHERE SEAS INCREASED TO 5 FEET EARLIER, HOWEVER THESE HAVE SUBSIDED A LITTLE. SINCE THIS APPEARS TO BE TOWARD THE OUTER EDGE OF THE COASTAL WATERS, NO SMALL CRAFT ADVISORY ATTM. SEAS REMAIN MAINLY AT 4 FEET OR LESS. TUESDAY...SUB-SCA CONDITIONS. WINDS BACK TOWARDS THE SOUTH- SOUTHWEST TOMORROW AFTERNOON AND BEGIN TO DECREASE AS WEAK LOW PRESSURE MOVES IN OVERHEAD. SEAS REMAIN 2 TO 3 FEET. OUTLOOK... TUESDAY NIGHT...NO MARINE HEADLINES ARE ANTICIPATED. WEDNESDAY...NORTHERLY WIND GUSTS OF 25 TO 30 KNOTS ARE POSSIBLE. WEDNESDAY NIGHT THROUGH FRIDAY NIGHT...NORTHWESTERLY WIND GUSTS OF 25 TO 30 KNOTS ARE POSSIBLE. SATURDAY...NO MARINE HEADLINES ARE ANTICIPATED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...IOVINO NEAR TERM...GORSE SHORT TERM...HEAVENER LONG TERM...IOVINO AVIATION...GORSE/IOVINO/HEAVENER MARINE...GORSE/IOVINO/HEAVENER

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