Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 221549 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1149 AM EDT WED MAY 22 2013 .SYNOPSIS... HIGH PRESSURE WILL REMAIN ANCHORED OFF THE SOUTHEASTERN UNITED STATES COAST THROUGH THURSDAY. LOW PRESSURE WILL APPROACH FROM THE WEST, TRACKING TO OUR NORTH, AND WILL THEN DRAG A COLD FRONT THROUGH OUR REGION LATE THURSDAY INTO FRIDAY. HIGH PRESSURE WILL THEN BUILD INTO THE REGION FOR THE HOLIDAY WEEKEND AND LAST INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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SOME CONVECTION RAPIDLY DEVELOPED LATE THIS MORNING ACROSS NORTHEASTERN PENNSYLVANIA. THESE SEEM TO HAVE INITIATED NEAR THE WARM FRONT WITH PERHAPS SOME HELP FROM DIFFERENTIAL HEATING AND LIFT UP AND OVER THE FRONT. THERE IS PLENTY OF INSTABILITY WITH EVEN SOME INCREASE IN SHEAR AS ONE CROSSES THE WARM FRONT, THEREFORE PERHAPS SOME HAIL WITH THEM. THE CONVECTIVE COVERAGE HOWEVER LOOKS LOW WITH MORE ORGANIZATION TO OUR NORTH. SOME ADJUSTMENTS IN POPS WERE MADE, BUT OVERALL NO MAJOR CHANGES. OTHERWISE, A RATHER SOUPY AIRMASS ACROSS THE REGION. THE 12Z STERLING, VIRGINIA RAOB SHOWED A PRONOUNCED LOW-LEVEL INVERSION WHICH HAS HELPED TO MAINTAIN THE WEALTH OF STRATUS. THE STRATUS IS NOW LIFTING SOME AND ERODING FROM THE WEST, AND THIS SHOULD CONTINUE TOWARD THE EAST THROUGH THE AFTERNOON. HOW QUICKLY THIS OCCURS WILL HAVE AN AFFECT ON OUR HIGH TEMPERATURES, HOWEVER THE 12Z RAOB SHOWS ONCE WE BREAK OUT INTO THE SUNSHINE TEMPERATURES WILL BE RATHER TOASTY. WE THEN LOOK TO THE CONVECTIVE POTENTIAL ESPECIALLY THIS AFTERNOON. THE MODEL GUIDANCE OVERALL SEEMS TO BE KEYING IN ON OUR NORTHWEST ZONES WHERE THESE AREAS WILL BE CLOSER TO THE BETTER LARGE SCALE FORCING AS A FRONTAL BOUNDARY AND SURFACE LOW ARE DRAPED ACROSS THE GREAT LAKES. A FRONT SITTING VERY CLOSE TO OUR NORTHEAST ZONES SHOULD LIFT NORTHWARD THROUGH THE AFTERNOON. WE ARE NOT ANTICIPATING THIS TO BACK SOUTHWESTWARD. THERE IS PLENTY OF INSTABILITY TO BE IN PLACE TODAY OWING TO THE HIGHER DEW POINTS. HOWEVER, THE LACK OF FOCUSED FORCING MAY KEEP THE CONVECTIVE COVERAGE ON THE LOW SIDE. AFTER THE INITIAL CONVECTION NEAR MIDDAY IN NORTHEAST PENNSYLVANIA, THE ENTITY TO WATCH IS AN INCOMING SHORT WAVE LATER THIS AFTERNOON THAT COULD TEAM UP WITH A LEE SIDE TROUGH, INITIATING CONVECTION TO OUR WEST. THE EASTERN AND SOUTHERN ZONES MAY NOT HAVE ANY CONVECTION THROUGH THE DAY, UNLESS SOMETHING IS ABLE TO FORM WITH SOME LOW-LEVEL CONVERGENCE NEAR THE SOUTHEASTERN NEW JERSEY COAST. THE STRONGER WESTERLY FLOW ALOFT IS FARTHER NORTH AND MOSTLY FROM THE GREAT LAKES REGION AND ACROSS NEW YORK STATE. SOME OF THE HIGH RESOLUTION MODELS INDICATE CONVECTION DEVELOPING THIS AFTERNOON ACROSS CENTRAL PENNSYLVANIA THEN TRACKING NORTHEASTWARD. THIS INITIATION COULD BE ENHANCED SOME BY THE TERRAIN AND A LEE SIDE TROUGH AS A SHORT WAVE APPROACHES, AND IF THIS CONVECTION ARRIVES IT COULD CONTAIN LOCALLY STRONG WINDS AND HAIL MOSTLY ACROSS OUR FAR NORTHWESTERN ZONES LATER THIS AFTERNOON. THE PW VALUES ARE A LITTLE OVER AN INCH TODAY, THEREFORE ANY STORM THAT IS ABLE TO DEVELOP WILL BE CAPABLE OF PRODUCING LOCALLY HEAVY RAIN. OUR CONFIDENCE IN THE CONVECTIVE COVERAGE AND STRENGTH IS ON THE LOWER SIDE, HOWEVER A MENTION IS IN THE HAZARDOUS WEATHER OUTLOOK FOR MAINLY THE NORTHWESTERN ZONES. THE HOURLY GRIDS WERE ADJUSTED WITH SOME OF THE LAMP/LAV GUIDANCE TO ASSIST. LITTLE IN THE WAY OF CHANGES WERE MADE ATTM TO THE HIGH TEMPERATURES AWAY FROM THE IMMEDIATE COAST.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... A COUPLE OF ROUNDS OF SHOWERS/THUNDERSTORMS LOOK POSSIBLE OVERNIGHT WEDNESDAY INTO THURSDAY MORNING. THE FIRST ROUND LOOKS TO BE EARLY IN THE EVENING ASSOCIATED WITH SHORT WAVE/VORT MAX MOVING THROUGH LATE IN THE DAY AND INTO EARLY EVENING. WE MAY THEN GET A BREAK FOR A PORTION OF THE OVERNIGHT, FOLLOWED BY ANOTHER POSSIBLE CHANCE OF PRECIPITATION CLOSER TO SUNRISE THURSDAY. THIS WOULD BE ASSOCIATED WITH A SECOND SHORT WAVE/VORT MAX MOVING THROUGH. WITH DEWPOINTS REMAINING ELEVATED ACROSS THE AREA, OVERNIGHT LOWS WILL REMAIN HIGH. GENERALLY TEMPERATURES ARE EXPECTED TO ONLY DROP INTO THE MID-UPPER 60S. && .LONG TERM /THURSDAY THROUGH TUESDAY/... WITH HIGH PRESSURE SITTING TO OUR SOUTHEAST, WE WILL CONTINUE TO SEE A SOUTH TO SOUTHWESTERLY FLOW WHICH WILL CONTINUE TO ADVECT WARM AND MOIST AIR TO OUR AREA. THIS WILL KEEP OUR TEMPERATURES AT OR ABOVE NORMAL FOR THURSDAY. A LOW PRESSURE SYSTEM WILL APPROACH FROM THE WEST ON THURSDAY, WITH THE CENTER PASSING OFF JUST TO OUR NORTH. THE ATTACHED COLD FRONT IS FORECAST TO MOVE THROUGH OUR AREA THURSDAY INTO FRIDAY, MOST LIKELY LATER IN THE DAY THURSDAY INTO EARLY FRIDAY. THE LATEST MODEL GUIDANCE CONTINUES TO SLOW DOWN THE FRONTAL PASSAGE AND ALSO STARTS TO DEVELOP A MID LEVEL FEATURE ALONG THE MID-ATLANTIC COAST. WITH PRECIPITABLE WATER VALUES AROUND 1.5 INCHES, ANY SLOWING OF THE FRONTAL PASSAGE MAY END UP CONTRIBUTING TO FLOODING AS HEAVY RAIN WILL BE POSSIBLE. THIS WILL NEED TO BE MONITORED, ESPECIALLY FOR THE AREAS WITH LOWER FFG VALUES, MAINLY ACROSS CENTRAL AND NORTHERN NEW JERSEY. SHOWERS AND THUNDERSTORMS MAY DEVELOP AHEAD OF THE FRONT ON THURSDAY AS SURFACE HEATING AND SOME WEAK INSTABILITY WILL BE IN PLACE. WHILE THE SEVERE THREAT DOES NOT LOOK TO BE ALL THAT GREAT AT THIS TIME, THERE IS A CHANCE THAT SOME STORMS MAY BECOME STRONG AND SPC HAS HIGHLIGHTED OUR AREA IN THEIR DAY 2 OUTLOOK WITH A SEE TEXT. THE FRONT PUSHES THROUGH AND OFFSHORE ON FRIDAY MORNING. SOME LINGERING SHOWERS MAY CONTINUE THROUGH FRIDAY MORNING BUT OVERALL THE AREAS SHOULD DRY OUT BY FRIDAY AFTERNOON. COOLER AIR WILL BE PUSHED INTO THE REGION ON A NORTHWEST FLOW AND TEMPERATURES WILL FALL BELOW NORMAL FOR FRIDAY. HIGHS WILL GENERALLY BE IN THE UPPER 60S TO LOWER 70S. CANADIAN HIGH PRESSURE WILL BUILD INTO THE REGION BEHIND THE FRONT, BRINGING IN SOME COOLER AND DRIER AIR FOR THE HOLIDAY WEEKEND AND INTO EARLY NEXT WEEK. THE MODELS HINT AT A SHORTWAVE MOVING THROUGH THE MID LEVELS ON SATURDAY AND ANOTHER ONE ON SUNDAY. THE AIRMASS LOOKS TO BE TOO DRY FOR ANYTHING TO MAKE IT TO THE SURFACE AND WE HAVE KEPT THE HOLIDAY WEEKEND AND EARLY NEXT WEEK DRY. TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE EARLY PART OF THE WEEK WITH HIGHS IN THE UPPER 60S TO LOWER 70S ACROSS THE REGION. TEMPERATURES WILL GRADUALLY START TO WARM TOWARD THE MIDWEEK TIME FRAME. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF TODAY...CEILINGS CONTINUE TO IMPROVE TO MVFR, THEN TO VFR DURING THE AFTERNOON. THE REDUCED LOCAL VISIBILITIES DUE TO HAZE/FOG ARE EXPECTED TO IMPROVE BY MID AFTERNOON. THERE IS THE CHANCE OF A FEW SHOWERS/THUNDERSTORMS THIS AFTERNOON, WITH THE GREATEST POTENTIAL TO BE NEAR KABE AND KRDG. A MENTION WAS NOT INCLUDED DUE TO A LOW POTENTIAL AT THIS TIME. LIGHT SOUTHWEST WINDS INCREASING TO 10-15 KNOTS, WITH PERHAPS A LITTLE GUSTINESS AT TIMES DURING THE AFTERNOON IF ENOUGH MIXING CAN OCCUR. TONIGHT...VFR, THEN IFR/MVFR CEILINGS AND VISIBILITIES ARE FORECAST TO DEVELOP LATE. THERE COULD BE A SHOWER OR THUNDERSTORM ESPECIALLY IN THE EVENING NORTH AND WEST OF KPHL, THEN ANOTHER CHANCE TOWARD DAYBREAK. SOUTHWEST WINDS GENERALLY UNDER 10 KNOTS. OUTLOOK... THURSDAY AND THURSDAY NIGHT...MAINLY VFR. MVFR, POSSIBLY IFR, CONDITIONS POSSIBLE IN ANY SHOWERS AND THUNDERSTORMS OR HEAVY RAIN. FRIDAY...MAINLY VFR WITH A CHANCE OF SHOWERS MAINLY IN THE MORNING. NORTHWEST WINDS 10 TO 15 KNOTS. SATURDAY AND SUNDAY...VFR. NORTHWEST WINDS 15 TO 20 KNOTS.
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&& .MARINE...
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MAINLY A SOUTH-SOUTHWEST FLOW WILL REMAIN ACROSS THE WATERS TODAY AND TONIGHT. THE GRADIENT MAY TIGHTEN SOME LATE TODAY INTO TONIGHT, AND WINDS MAY GUST CLOSE TO 25 KNOTS. WAVEWATCH HAS BEEN RUNNING A LITTLE HIGH, BUT EVEN IF WE KNOCK A FOOT OFF OF THE SEAS, 5 FOOT SEAS COULD START LATE TODAY INTO THIS EVENING. THEREFORE A SMALL CRAFT ADVISORY HAS BEEN ISSUED STARTING LATE THIS AFTERNOON AND CONTINUING INTO AT LEAST TONIGHT. OUTLOOK... HIGH PRESSURE ANCHORED OFF THE SOUTHEASTERN UNITED STATES COAST WILL CONTINUE TO BRING A TO SOUTHWEST FLOW THROUGH THURSDAY ON THE AREA WATERS. SMALL CRAFT CONDITIONS ARE EXPECTED TO CONTINUE ON THURSDAY. THE COLD FRONT WILL CROSS THE AREA WATERS LATE THURSDAY INTO FRIDAY. THE PRESSURE GRADIENT WILL TIGHTEN AS THE FRONT DEPARTS TO THE EAST AND HIGH PRESSURE STARTS TO BUILD DOWN FROM CANADA. THIS MAY CAUSE WINDS TO GUST UP AROUND 25 KNOTS, ESPECIALLY ON SATURDAY. SEAS WILL LIKELY REMAIN AT OR ABOVE 5 FEET INTO THE EARLY PART OF THE WEEKEND. BOTH WINDS AND SEAS ARE EXPECTED TO SUBSIDE BY LATE SATURDAY AND THEN REMAIN BELOW ADVISORY CRITERIA THROUGH THE REST OF THE HOLIDAY WEEKEND.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 6 PM EDT THURSDAY FOR ANZ450>455. && $$ SYNOPSIS...GORSE/MEOLA NEAR TERM...GORSE SHORT TERM...ROBERTSON LONG TERM...MEOLA AVIATION...GORSE/MEOLA MARINE...ROBERTSON/MEOLA

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