Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 190658 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 258 AM EDT TUE MAY 19 2015 .SYNOPSIS... A COLD FRONT IS FORECAST TO APPROACH FROM THE WEST TODAY, THEN PASS THROUGH OUR REGION EARLY TONIGHT. HIGH PRESSURE IS EXPECTED TO FOLLOW FOR WEDNESDAY INTO THURSDAY. WEAK LOW PRESSURE IS ANTICIPATED TO PASS OFF THE NORTH CAROLINA COAST ON THURSDAY NIGHT BEFORE MOVING OUT TO SEA. ANOTHER COLD FRONT IS FORECAST TO ARRIVE ON FRIDAY AFTERNOON WITH HIGH PRESSURE EXPECTED IN ITS WAKE FOR SATURDAY AND SUNDAY. A WARM FRONT MAY THEN APPROACH FROM THE SOUTHWEST FOR SUNDAY NIGHT AND MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AN UPPER-LEVEL RIDGE WILL CONTINUE TO SHIFT TO OUR EAST EARLY THIS MORNING. THIS WILL TAKE SURFACE HIGH PRESSURE EAST AS WELL, WHICH WILL RESULT IN A LESSENING OF THE MARINE INFLUENCE WITH TIME. BEFORE THIS HAPPENS THOUGH, STRATUS ALONG WITH SOME FOG REMAINS ACROSS THE CWA. THIS IS EXPECTED TO LIFT AND THIN OUT AS THE MORNING AND EARLY AFTERNOON WEARS ON, PLUS AS OUR WINDS VEER FROM ONSHORE TO SOUTHWEST AND WEST BY LATE AFTERNOON. THERE APPEARS TO BE SOME WEAK ISENTROPIC UPGLIDE OVER THE THE MARINE LAYER AND THIS IS PRODUCING SOME SHOWERS. THE CONVECTIVE CLUSTER ACROSS THE DELMARVA CONTINUES TO GRADUALLY WEAKEN AS IT PROGRESSES INTO LESS LINGERING INSTABILITY AND BECOMES MORE ELEVATED WITH A NORTHEASTERN EXTENT. THIS ACTIVITY SHOULD WANE THROUGH THE MORNING, WITH SOME ADDITIONAL SHOWERS EXPECTED FROM THE WEST AHEAD OF A COLD FRONT. THE MAIN SURFACE LOW AND DYNAMICS ARE LIFTING WELL TO OUR NORTH, HOWEVER THE BACKDOOR FRONT SHOULD EITHER LIFT NORTHWARD AS A WEAK WARM FRONT OR DISSIPATE AS THE LOW-LEVEL FLOW VEERS. AS THE FLOW INCREASES SOME ALOFT THROUGH THE DAY WITH AN INCOMING UPPER-LEVEL TROUGH, SOME INCREASE IN SHEAR AND PERHAPS SOME HELP BY EITHER A DIFFERENTIAL HEATING BOUNDARY OR ESPECIALLY A PRE-FRONTAL TROUGH SHOULD BE ENOUGH TO PRODUCE AT LEAST ISOLATED OR SCATTERED CONVECTION THROUGH THE AFTERNOON /AIDED BY SOME GRADUAL COOLING ALOFT/. OUR AREA THOUGH LOOKS TO BE ON THE SOUTHERN EDGE OF THE STRONGER FLOW ALOFT, WHICH PLACES OUR NORTHERN AREAS IN A BIT BETTER SETUP FOR A GUSTY THUNDERSTORM. THE FORECAST SOUNDINGS SHOW ONCE THE STRATUS BREAKS, ENOUGH HEATING OCCURS TO BOOST THE INSTABILITY HOWEVER THE AIRMASS ESPECIALLY IN THE MID TO UPPER LEVELS ARE FORECAST TO BE DRYING QUITE A BIT THIS AFTERNOON. THE DRYING MAY LIMIT OVERALL ORGANIZATION, HOWEVER IF SOME STRONG ENOUGH CONVECTIVE CORES CAN DEVELOP THEN LOCALLY GUSTY WINDS /ENHANCED BY A POSSIBLE LOW-LEVEL INVERTED-V SIGNATURE DEVELOPING BY LATE AFTERNOON/ CAN OCCUR. AS FOR THE HIGH TEMPERATURES, WE USED MOSTLY AN EVEN BLEND OF THE GFS/NAM MOS. WE OPTED NOT TO GO ABOVE GUIDANCE OVERALL GIVEN THE EXPECTATION OF STRATUS TO BE AROUND FOR AWHILE THIS MORNING. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... AN UPPER-LEVEL TROUGH IS FORECAST TO START SHARPENING UP ACROSS SOUTHEASTERN CANADA AND INTO THE NORTHEAST LATER TONIGHT. THIS WILL DRIVE A COLD FRONT OFFSHORE THIS EVENING AND ANY LINGERING CONVECTION WILL EITHER DISSIPATE OR MOVE OUT TO SEA. AS A RESULT, KEPT A MENTION IN FOR A TIME IN THE EVENING BUT QUICKLY TAPER THE POPS DOWN FROM WEST TO EAST. FOLLOWING THE COLD FRONTAL PASSAGE, CAA BEGINS TO OVERTAKE THE AREA THROUGH THE NIGHT. THE PRESSURE GRADIENT SHOULD TIGHTEN SOME THROUGH THE NIGHT AS LOW PRESSURE TRACKS NORTH OF MAINE AND HIGH PRESSURE BUILDS INTO THE OHIO VALLEY. THIS ALONG WITH SOME CAA SHOULD PROMOTE SOME MIXING THROUGH THE NIGHT AND THEREFORE AT LEAST SOME WIND AT THE SURFACE. THE AIRMASS IS DRYING QUITE A BIT THEREFORE OTHER THAN SOME STRATOCUMULUS ACROSS THE NORTHWEST ZONES, MOST AREAS SHOULD HAVE A CLEAR OR MOSTLY CLEAR SKY. AS FOR THE LOW TEMPERATURES, WE USED A NAM/GFS MOS BLEND WITH SOME TWEAKS. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... HIGH PRESSURE IS EXPECTED TO FOLLOW THE COLD FRONT FOR WEDNESDAY INTO THURSDAY AND IT SHOULD BRING DRY WEATHER CONDITIONS AND BELOW NORMAL TEMPERATURES. READINGS MAY FALL INTO THE UPPER 30S IN PARTS OF THE POCONO REGION AND NORTHWESTERN NEW JERSEY EARLY ON THURSDAY MORNING. IT COULD BE CLOSE FOR LOCALIZED FROST. THE MODEL GUIDANCE DIFFERS A BIT IN THE HANDLING OF THE WEAK LOW THAT IS EXPECTED TO PASS OFF THE NORTH CAROLINA COAST ON THURSDAY NIGHT. IT APPEARS AS THOUGH MID LEVEL CLOUDS WILL OVERSPREAD MUCH OF OUR REGION ON THURSDAY WITH STRATOCUMULUS REACHING OUR SOUTHERN COUNTIES FOR LATE THURSDAY INTO THURSDAY NIGHT. WE ARE NOT PARTICULARLY CONFIDENT IN THE NORTHWARD EXTEND OF THE RAINFALL ASSOCIATED WITH THE SYSTEM. WE WILL SIMPLY FORECAST LOW CHANCE PROBABILITIES OF RAIN FOR OUR FAR SOUTHERN COUNTIES. A MID LEVEL SHORT WAVE TROUGH IS FORECAST TO APPROACH FROM THE WEST ON THURSDAY NIGHT AND IT SHOULD PASS OVERHEAD ON FRIDAY MORNING. A SURFACE COLD FRONT IS ANTICIPATED TO FOLLOW ON FRIDAY AFTERNOON. THE SYSTEM WILL NOT HAVE MUCH MOISTURE ASSOCIATED WITH IT, SO WE WILL NOT FORECAST ANY RAINFALL. SURFACE HIGH PRESSURE WILL BUILD INTO OUR REGION ON FRIDAY NIGHT AND SATURDAY. THE CENTER OF THE HIGH IS EXPECTED TO PASS OFF THE COAST LATE ON SATURDAY. THE AIR MASS SHOULD BRING OUR FORECAST AREA DRY WEATHER CONDITIONS FOR SATURDAY AND SUNDAY ALONG WITH NEAR NORMAL TEMPERATURES. WARMTH AND MOISTURE WILL LIKELY BE ON THE INCREASE ON THE BACK SIDE OF THE HIGH AS WE GET INTO LATE SUNDAY AND MONDAY. WE ARE ANTICIPATING AN INCREASE IN CLOUD COVER IN THE DEVELOPING ISENTROPIC LIFT. ALSO, WE WILL INDICATE A CHANCE OF SHOWERS AT THAT TIME. && .AVIATION /07Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...IFR/LIFR CEILINGS IMPROVING TO MVFR TOWARD LATE MORNING, THEN VFR DURING THE AFTERNOON AS A COLD FRONT APPROACHES. MOSTLY MVFR FOG AT TIMES IS EXPECTED TO IMPROVE THROUGH THE MORNING. LIGHT EAST TO SOUTHEAST WINDS, TURNING TOWARDS THE SOUTH AND SOUTHWEST AROUND 10 KNOTS IN THE AFTERNOON. SOME SHOWERS AND THUNDERSTORMS /AFTERNOON/ ARE EXPECTED TO OCCUR AHEAD OF THE COLD FRONT, HOWEVER THESE MAY BE MAINLY SCATTERED. LOWER CONFIDENCE ON THE TIMING OF IMPROVEMENT TO MVFR/VFR, AND ALSO SHOWER/THUNDER COVERAGE ESPECIALLY THIS AFTERNOON. TONIGHT...A FEW SHOWERS OR A THUNDERSTORM EARLY, OTHERWISE VFR. WEST TO NORTHWEST WINDS MOSTLY 5-15 KNOTS. OUTLOOK... WEDNESDAY THROUGH SATURDAY...MAINLY VFR. && .MARINE... A LIGHT ONSHORE FLOW TO START TODAY WILL VEER TO SOUTH THEN TO SOUTHWEST AND WEST BY LATE AFTERNOON. A COLD FRONT WILL MOVE THROUGH THIS EVENING WITH CAA DEVELOPING IN ITS WAKE. THE CONDITIONS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA TODAY INTO TONIGHT, HOWEVER THE CAA LATE TONIGHT AND MAINLY TOWARD DAYBREAK WEDNESDAY MAY ALLOW FOR WIND GUSTS TO NEAR 25 KNOTS. THIS LOOKS SHORT IN DURATION THOUGH IF IT WERE TO OCCUR. SOME SHOWERS AND THUNDERSTORMS ARE EXPECTED TODAY INTO TONIGHT AHEAD OF THE COLD FRONT. OUTLOOK... WEDNESDAY...WIND GUSTS MAY APPROACH 25 KNOTS, ESPECIALLY EARLY. WEDNESDAY NIGHT THROUGH SATURDAY...NO MARINE HEADLINES ARE ANTICIPATED. && .FIRE WEATHER... WIND GUSTS MAY BE AROUND 20 MPH FROM THE NORTHWEST ON WEDNESDAY AFTERNOON. RELATIVE HUMIDITY VALUES MAY FALL INTO THE 30 TO 35 PERCENT RANGE AT THAT TIME, ESPECIALLY IN PARTS OF EASTERN PENNSYLVANIA AND NEW JERSEY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE/IOVINO NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...IOVINO AVIATION...GORSE/IOVINO MARINE...GORSE/IOVINO FIRE WEATHER...

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