Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 030932 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 532 AM EDT TUE MAY 3 2016 .SYNOPSIS... BROAD LOW PRESSURE CENTERED OVER DELAWARE THIS MORNING WILL RELOCATE ALONG THE MID ATLANTIC COAST LATER TODAY. A PIECE OF THE LOW MAY MOVE NORTHEAST TOWARD CAPE COD LATE WEDNESDAY WHILE THE PRIMARY LOW PRESSURE SYSTEM DEVELOPS OFF THE NEW JERSEY COAST LATER THIS WEEK. THE LOW MOVES OUT TO SEA SATURDAY WITH A WEAK COLD FRONTAL PASSAGE FOLLOWING SUNDAY MORNING. HIGH PRESSURE SHOULD BECOME DOMINANT HERE EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AN UPPER-LEVEL TROUGH REMAINS WELL TO OUR WEST TODAY. THIS RESULTS IN THE MAINTENANCE OF SOUTHWESTERLY FLOW ALOFT. A SHORT WAVE EMBEDDED IN THE FLOW IS FORECAST TO TRANSLATE TO OUR NORTHEAST THIS MORNING, TAKING MUCH OF THE FORCING FOR ASCENT WITH IT. AS A RESULT, SHOWERS, OR A PERIOD OF RAIN, WILL MOSTLY TAPER OFF BY LATER THIS MORNING FROM WEST TO EAST. SOME HIGH RESOLUTION GUIDANCE INDICATES THAT THERE MAY BE TWO AREAS OF MORE CONCENTRATED SHOWERS EARLY TODAY, ONE ACROSS THE WESTERN ZONES AND THE OTHER NEAR THE COAST. THE RADAR TRENDS SO FAR EARLY THIS MORNING APPEARS TO BE RESEMBLING THIS, THEREFORE POPS WERE ADJUSTED. A WEAK SURFACE LOW HOWEVER REMAINS VERY NEAR THE AREA, KEEPING A FRONTAL ZONE MAINLY TO OUR SOUTH. THIS WILL ENHANCE A LOW-LEVEL NORTHEASTERLY FLOW KEEPING A MARINE INFLUENCE GOING. OUR AREA REMAINS IN THE RIGHT REAR QUADRANT OF A 250 MB JET DURING MUCH OF TODAY, THEREFORE SOME ADDITIONAL SHOWERS CANNOT BE RULED OUT THIS AFTERNOON AS WELL. SOME THUNDER THIS AFTERNOON COULD BE CLOSE TO OUR FAR SOUTHERN ZONES, HOWEVER THIS LOOKS TO BE MAINLY REMOVED FROM OUR AREA. THEREFORE DID NOT ADD IN THUNDER ATTM. THE PRESENCE OF A LOW-LEVEL NORTHEAST FLOW OFF THE COOL OCEAN WILL KEEP LOWER CLOUDS IN PLACE. THE FORECAST SOUNDINGS HOWEVER INDICATE THAT DRYING ALOFT OCCURS THIS AFTERNOON. WHILE THERE IS AN INVERSION IN PLACE, SOME BREAKS IN THE CLOUDS ARE POSSIBLE. GIVEN A RATHER MOIST LOW-LEVEL PROFILE IN THE SOUNDINGS, OPTED TO KEEP TEMPERATURES ON THE COOLER SIDE AND WE USED A MOS/CONTINUITY BLEND FOR THE HIGH TEMPERATURES. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... THE AFOREMENTIONED UPPER-LEVEL TROUGH IS FORECAST TO SHARPEN SOME TO OUR WEST DURING THE COURSE OF TONIGHT. THERE DOES NOT APPEAR TO BE A MORE FOCUSED SHORT WAVE WITHIN THE SOUTHWESTERLY FLOW ALOFT UNTIL TOWARD MORNING. THE 250 MB JET IS FORECAST TO MOVE RIGHT OVER OUR AREA TONIGHT, REMOVING THE REGION FROM THE MORE FAVORABLE AREA OF LIFT. AS A RESULT, WE KEPT POPS IN THE SLIGHT CHC TO LOW CHC RANGE AS SOME SHOWERS CANNOT BE RULED OUT. THE IDEA OF LOW CLOUDS CONTINUES ACROSS THE AREA GIVEN THE MARINE INFLUENCE, AND THEREFORE SOME DRIZZLE IS POSSIBLE AS THE FORECAST SOUNDINGS INDICATE SOME MID LEVEL DRYING IN PLACE. WHILE SOME FOG MAY BE AROUND IT IS NOT ANTICIPATED TO BE SIGNIFICANT AS THE STRATUS MAY LIMIT THE ACTUAL DEVELOPMENT OVERALL. THEREFORE, OPTED TO NOT INCLUDE FOG ATTM BUT THIS WILL BE REVISITED LATER. AS FOR THE LOW TEMPERATURES, WE USED A MOS BLEND OVERALL. TEMPERATURES SHOULD NOT FALL A LOT GIVEN THE CLOUD COVER AND DEW POINTS GENERALLY REMAINING UP DUE TO NEAR LOW-LEVEL SATURATION. && .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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CONFIDENCE IN ANY DETAILS OF THIS FORECAST FROM WEDNESDAY THROUGH EARLY NEXT WEEK IS AVERAGE TO BELOW AVERAGE. A VERTICALLY DEEP CLOSED LOW WILL FORM ALONG THE MID ATLANTIC COAST LATER THIS WEEK THEN WEAKEN EASTWARD THIS COMING WEEKEND IN RESPONSE TO INTERACTION WITH A CLOSED LOW SHORT WAVE OVER HUDSON BAY. CALENDAR DAY AVERAGE TEMPS: ABOUT 5 DEGREES BELOW NORMAL WED-FRI, NEAR NORMAL SAT-MON. CONSIDERABLE CLOUDINESS WILL DOMINATE WEDNESDAY THROUGH AT LEAST FRIDAY EVENING WITH SEVERAL PERIODS OF SHOWERS AFFECTING THE REGION. SHOWER/RAIN GENERATION IS BLAMED IN PART ON INSTABILITY AS THE COLD POOL EVOLVES OVERHEAD WITH THE 500MB TEMP AT PHL -14C THIS MORNING COOLING TO -23C FRIDAY, AND SOME OF IT ATLANTIC INFLOW AS THE 850-700MB LOW MAY HUG THE MID ATLANTIC COAST WITH DEEP MOISTURE JUST TO THE LEFT OF THE TRACK. MUCH OF THE TIME FROM WEDNESDAY THROUGH FRIDAY NIGHT MAY BE RAINFREE BUT TIMING THE PERIODIC LULLS IN RAINFALL WAS NOT CONFIDENTLY ASSESSED THIS MORNING. IF IT CLEARS A BIT FOR A FEW HOURS AT NIGHT, THEN FOG COULD DEVELOP. OVERALL, DAYTIME TEMPERATURES WILL BE COOLER THAN NORMAL AND NIGHTTIME MINS NEAR NORMAL (NARROW DIURNALS DUE TO MOISTURE) NEXT WEEKEND INTO EARLY NEXT WEEK...IT SHOULD BRIGHTEN AND WARM UP TO NEAR NORMAL AS THE LOW PRESSURE SYSTEM HEADS EAST. A WEAK COLD FRONT COULD BRING A FEW SHOWERS WITH ITS PASSAGE SUNDAY MORNING BUT AT THIS TIME ANY RAIN OCCURRENCE DOES NOT LOOK TO BE AS PROLONGED AS WHAT MAY OCCUR LATER THIS WORK WEEK.
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&& .AVIATION /09Z TUESDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THROUGH TODAY...VARYING CEILING HEIGHTS EARLY ARE EXPECTED TO SETTLE INTO THE IFR RANGE THIS MORNING. AN IMPROVEMENT THIS AFTERNOON TO MVFR IS ANTICIPATED, HOWEVER CONFIDENCE IS ON THE LOWER SIDE. SHOWERS MOST NUMEROUS THIS MORNING, THEN LESS COVERAGE DURING THE AFTERNOON. EAST TO NORTHEAST WINDS MAINLY 10 KNOTS OR LESS. TONIGHT...MVFR TO IFR CEILINGS WITH A CONTINUED ONSHORE FLOW. A COUPLE OF SHOWERS OR SOME DRIZZLE POSSIBLE, WITH LOCAL MVFR VISIBILITY AT TIMES. NORTHEAST WINDS 3-6 KNOTS OVERALL. OUTLOOK... WEDNESDAY THROUGH FRIDAY...VARYING BETWEEN VFR CIGS AND MVFR CONDITIONS WITH THE POTENTIAL FOR RAIN SHOWERS DURING THE PERIOD. CONDITIONS MAY DROP TO IFR AT TIMES IN THE RAIN SHOWERS. IN A GENERAL A NORTHEAST WIND, WHICH MAY BECOME GUSTY 15 TO 20 KT AT TIMES, ESPECIALLY FRIDAY. SATURDAY...MAINLY VFR.
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&& .MARINE...
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A WEAK LOW PRESSURE SYSTEM OVER THE AREA TODAY INTO TONIGHT WILL KEEP AN ONSHORE FLOW IN PLACE. WHILE THIS MAY SOME INCREASE FOR A TIME ESPECIALLY LATER TODAY AND TONIGHT ACROSS THE NORTHERN ATLANTIC COASTAL WATERS, IT SHOULD REMAIN BELOW 25 KNOTS. SINCE THE FLOW IS FORECAST TO BE WEAK ENOUGH, SEAS ARE ANTICIPATED TO BE 4 FEET OR LESS. THEREFORE, THE CONDITIONS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH TONIGHT. OUTLOOK... WEDNESDAY THROUGH THURSDAY...WAVE HEIGHTS ON OUR OCEAN WATERS MAY BUILD AROUND 5 FEET IN THE NORTHEASTERLY FLOW. THURSDAY NIGHT AND FRIDAY...SCA PROBABLE IN RESPONSE TO LOW PRESSURE ORGANIZING OFF THE NJ COAST. ATLANTIC SEAS WERE CAPPED AT 6 FEET, 1-2 FT BELOW GUIDANCE, DUE TO LOW CONFIDENCE REGARDING THE WIND FIELDS ASSOCIATED WITH THE MID ATLANTIC COASTAL LOW. SATURDAY...NO MARINE HEADLINES ANTICIPATED AT THIS TIME.
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&& .HYDROLOGY...
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WE WILL APPRECIATE ANY UNUSUAL FLOODING REPORT FROM MARYLANDS EASTERN SHORE AND CENTRAL-SOUTHERN DELAWARE LAST NIGHT, AS WELL AS ANY DAMAGING WIND OR LARGE HAIL REPORTS. YOU SAW THE 50 KT AT BRANDYWINE IN OUR LSR.
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&& .TIDES/COASTAL FLOODING...
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A LONG DURATION NORTHEASTERLY FETCH IS EXPECTED TO DEVELOP OFF OUR MID ATLANTIC COAST WEDNESDAY THROUGH FRIDAY. ASTRONOMICAL TIDES WILL BE ON THE INCREASE AS WE APPROACH THE NEW MOON ON FRIDAY. AS A RESULT, THERE COULD BE SOME MINOR TIDAL FLOODING AROUND THE TIMES OF HIGH TIDE (6-7 PM EDT) ON WEDNESDAY EVENING, THURSDAY EVENING AND MORE LIKELY FRIDAY EVENING (WITHIN 1 HOUR OF THE HIGH TIDE NEAR 8PM), PENDING MODELS CONTINUING TO FOCUS LOW PRESSURE DEVELOPMENT SOUTH OF LONG ISLAND LATER THIS WEEK. THE FRIDAY EVENING HIGH TIDE CYCLE WILL ONLY NEED A SURGE OF .7 FEET TO RAISE THE WATER LEVEL TO MINOR THRESHOLD. THERE IS EVEN A SLIGHT CHANCE OF REACHING A MODERATE THRESHOLD FRIDAY EVENING BUT WE CANT SAY THIS WITH CONFIDENCE SINCE ITS ALL DEPENDENT ON THE POSITION AND STRENGTH OF THE LOW FORMING ALONG THE MID ATLANTIC COAST. AS A SIDE NOTE: IT IS OUR UNDERSTANDING THAT EVENTUALLY WE WILL BEGIN REFERENCING COASTAL FLOODING WITH RESPECT TO MHHW WHICH WILL EQUATE TO INUNDATION DEPTH WITH RESPECT TO NORMALLY DRY GROUND. THERE WILL LIKELY BE TRAINING REFERENCES DURING THE TRANSITION.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG 531 NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...DRAG 531 AVIATION...DRAG/GORSE MARINE...DRAG/GORSE HYDROLOGY...531 TIDES/COASTAL FLOODING...531

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