Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 180910 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 510 AM EDT SAT APR 18 2015 .SYNOPSIS...
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LOW PRESSURE WILL QUICKLY MOVE ACROSS NEW ENGLAND THIS AFTERNOON, PULLING A DRY COLD FRONT ACROSS OUR AREA THIS EVENING. HIGH PRESSURE WILL THEN BUILD IN SATURDAY NIGHT INTO SUNDAY BEFORE SHIFTING OFFSHORE. LOW PRESSURE WILL MOVE FROM THE GREAT LAKES TO NEAR HUDSON BAY MONDAY AND TUESDAY THEN STALL. AN ASSOCIATED WARM FRONT WILL LIFT NORTHWARD INTO PORTIONS OF OUR REGION DURING MONDAY, FOLLOWED BY A COLD FRONT MONDAY NIGHT. THE NEXT COLD FRONT ARRIVES WEDNESDAY NIGHT WITH POTENTIALLY ANOTHER COLD FRONT MOVING THROUGH THURSDAY NIGHT INTO FRIDAY.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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PATCHY SHALLOW FOG DEVELOPED IN PARTS OF OUR REGION DURING THE NIGHT. IT SHOULD DISSIPATE RATHER QUICKLY AFTER DAYBREAK. HIGH PRESSURE CENTERED OVER THE OHIO RIVER VALLEY EARLY THIS MORNING WILL SLIDE EASTWARD TODAY. MEANWHILE, A ROBUST MID LEVEL SHORT WAVE TROUGH IS FORECAST TO MOVE FROM EASTERN ONTARIO AND SOUTHWESTERN QUEBEC, ACROSS NORTHEASTERN NEW YORK AND NEW ENGLAND DURING THE AFTERNOON AND EVENING HOURS. THE SHORT WAVE IS EXPECTED TO PUSH A COLD FRONT TOWARD OUR REGION LATE IN THE DAY. WE ARE ANTICIPATING A SUNNY DAY WITH SOME WISPS OF CIRRUS OVERHEAD. A DEVELOPING WESTERLY SURFACE FLOW WILL DRAW WARM AIR INTO OUR REGION. MAXIMUM TEMPERATURES ARE FORECAST TO BE AROUND 80 DEGREES. READINGS ARE EXPECTED TO GET NO HIGHER THAN THE LOWER AND MIDDLE 70S IN THE ELEVATED TERRAIN AND NO HIGHER THAN THE 60S ALONG THE IMMEDIATE COAST. PHILADELPHIA`S LAST 80 PLUS DEGREE DAY WAS ON SEPTEMBER 28 WHEN THE TEMPERATURE ROSE TO 86 DEGREES.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
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A COLD FRONT IS EXPECTED TO BEGIN MOVING INTO THE NORTHERN PART OF OUR FORECAST AREA THIS EVENING. IT SHOULD REACH THE LEHIGH VALLEY AND THE INTERSTATE 78 CORRIDOR IN NEW JERSEY ABOUT 800 PM. THE BOUNDARY WILL CONTINUE TO PUSH SOUTHWARD, REACHING PHILADELPHIA AROUND 1000 PM AND CAPE MAY SHORTLY AFTER MIDNIGHT. THERE WILL BE LITTLE MOISTURE ASSOCIATED WITH THE COLD FRONT AND THE SKY SHOULD REMAIN MOSTLY CLEAR. THE WIND IS FORECAST TO SHIFT FROM THE WEST TO THE NORTH WITH THE FRONTAL PASSAGE. THE WIND IS THEN ANTICIPATED TO VEER TOWARD THE NORTHEAST LATE TONIGHT. TEMPERATURES ARE EXPECTED TO DROP TO AROUND 40 DEGREES IN THE ELEVATED TERRAIN UP NORTH AND INTO THE MIDDLE 40S TO LOWER 50S RANGE ELSEWHERE.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/...
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THE SYNOPTIC SETUP IS COMPRISED OF A CLOSED LOW THAT EJECTS ACROSS THE PLAINS INTO SUNDAY. THIS FEATURE BUILDS RIDGING DOWNSTREAM, WHICH RESULTS IN DRY WEATHER FOR MUCH OF SUNDAY. AN AIR MASS CHANGE THOUGH WILL TAKE PLACE FOR SUNDAY AS HIGH PRESSURE BUILDS DOWN FROM THE NORTH. THE INITIAL CLOSED LOW LOOKS TO GET ABSORBED INTO A LARGE SCALE TROUGH FROM THE MIDWEST AS IT UNDERGOES AMPLIFICATION EASTWARD THROUGH EARLY NEXT WEEK. THIS SHOULD THEN RESULT IN ANOTHER CLOSED LOW ACROSS THE GREAT LAKES REGION TUESDAY THROUGH THURSDAY, BEFORE SHIFTING CLOSER TO NEW ENGLAND FRIDAY. THE MAIN PRECIPITATION EVENT LOOKS TO OCCUR MONDAY ALTHOUGH SOME QUICKER ARRIVAL TIME WITH SOME OF THE GUIDANCE WILL RESULT IN RAIN DEVELOPING SOONER. GIVEN THE SURGE OF MOISTURE, THE RAIN COULD BE HEAVY AT TIMES. THE PATTERN THEREAFTER RESULTS IN CYCLONIC FLOW ACROSS THE EAST ALONG WITH COOLING AND A SERIES OF COLD FRONTS. WE USED A MODEL BLEND FOR SUNDAY INTO TUESDAY, THEN BLENDED IN THE 00Z WPC GUIDANCE. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR SUNDAY...HIGH PRESSURE BUILDING DOWN FROM THE NORTH TO START SUNDAY THEN IT WILL SHIFT OFFSHORE DURING THE COURSE OF THE DAY. THIS WILL ALLOW FOR THE WIND TO BE ONSHORE ALONG WITH A COOLER AIR MASS. THE CLOUDS INCREASE MAINLY LATE SUNDAY AS THE NEXT SYSTEM BEGINS TO APPROACH FROM THE SOUTHWEST. A STRENGTHENING LOW- LEVEL JET AND WAA WILL HELP PUSH A WARM FRONT TOWARD OUR AREA OVERNIGHT SUNDAY. THE STRENGTH OF THE LOW-LEVEL JET MOVING IN MAY ALLOW FOR STRONGER ASCENT TO ARRIVE SOONER /DEEPER ISENTROPIC LIFT OVER THE DEPARTING SURFACE HIGH/, THEREFORE WE INCREASED THE POPS QUICKER BY A FEW HOURS. SOME OF THE RAIN MAY BECOME HEAVY AT TIMES TOWARD DAYBREAK MONDAY. FOR MONDAY AND TUESDAY...AS ENERGY EJECTS EASTWARD FROM A CLOSED LOW AND ALSO FROM THE MIDWEST, LOW PRESSURE ORGANIZES OVER THE GREAT LAKES BEFORE SHIFTING NORTHWARD TOWARD HUDSON BAY. A ROBUST LOW- LEVEL JET AT LEAST DURING THE MORNING COMBINED WITH WAA, DEEP MOISTURE ADVECTION AND LARGE SCALE ASCENT WILL RESULT IN AN AREA OF RAIN. THERE ARE SOME HINTS OF SOME ELEVATED INSTABILITY WITHIN THIS, HOWEVER HELD OFF WITH A THUNDER MENTION AS THE INITIAL DEEP SATURATION TENDS TO NOT BE CONDUCIVE FOR THUNDER. AN AREA OF PW AIR OF NEAR 1.5 INCHES IS FORECAST TO SURGE ACROSS THE CWA, THEREFORE THE RAIN COULD BE HEAVY AT TIMES ESPECIALLY IN THE MORNING. OTHER THAN SOME TYPICAL PONDING OF WATER ON THE ROADWAYS AND POOR DRAINAGE FLOODING DURING HEAVIER RAIN, NO OTHER FLOODING IS ANTICIPATED ATTM. THE WARM SECTOR MAY GET INTO OUR SOUTHERN AREAS AND PERHAPS TO ABOUT THE PHILADELPHIA METRO, AND THEREFORE KEPT A MENTION OF SOME THUNDER MONDAY AFTERNOON AND EARLY EVENING BUT DID EXPAND THIS NORTHWARD A BIT. THE INSTABILITY LOOKS WEAK ENOUGH TO KEEP THE INTENSITY OF ANY THUNDERSTORM ON THE LOWER SIDE, HOWEVER ISOLATED STRONG WIND GUSTS AND SMALL HAIL CANNOT BE RULED OUT IF THE WARM SECTOR CAN GET FARTHER NORTH /ENOUGH HEATING OCCURS/. THE STEADIEST RAIN SHOULD TAPER OFF TO SHOWERS DURING THE LATE MORNING AND EARLY AFTERNOON FROM SOUTHWEST TO NORTHEAST AS A WEAK SURFACE LOW SHIFTS NORTHEAST NEAR A TRIPLE POINT. A ROBUST LOW-LEVEL JET SLIDING ACROSS THE AREA MONDAY MORNING SHOULD ALLOW FOR AN INCREASE IN THE SURFACE WINDS SUNDAY NIGHT AND MONDAY MORNING, WITH THE STRONGEST GUSTS CLOSER TO THE COAST DUE TO AN INITIAL ONSHORE FLOW. LOW PRESSURE AND A COLD/OCCLUDING FRONT SHOULD BE EXITING TO OUR EAST TUESDAY MORNING, WITH ANY SHOWERS ENDING. A DEVELOPING CLOSED LOW THOUGH IS FORECAST TO BE AROUND THE GREAT LAKES WITH CYCLONIC FLOW RESULTING. A FEW SHOWERS MAY PERSIST TUESDAY MAINLY ACROSS THE NORTHERN ZONES. FOR WEDNESDAY THROUGH FRIDAY...A CLOSED LOW IS FORECAST TO BE IN PLACE FROM THE GREAT LAKES TO EVENTUALLY NEW ENGLAND. THIS WILL RESULT IN CYCLONIC FLOW ACROSS OUR AREA, ALTHOUGH IT IS NOT REAL CERTAIN HOW SHORT WAVE ENERGY WITHIN THE FLOW RESULTS IN SOME STRONGER FORCING AS THE MAIN SYSTEM STARTS TO SHIFT TO NEW ENGLAND WITH TIME. THESE SHORT WAVES SHOULD SEND A COUPLE OF COLD FRONTS OUR WAY, WITH ONE GENERALLY ON WEDNESDAY AND ANOTHER PROBABLY THURSDAY NIGHT INTO FRIDAY. THERE MAY BE ENOUGH LIFT WITHIN THE CYCLONIC FLOW COMBINED WITH DAYTIME HEATING TO PROMOTE A FEW SHOWERS MAINLY ACROSS THE NORTH. OVERALL, WE FAVORED THE WPC GUIDANCE/CONTINUITY DURING THIS TIME FRAME WHICH ALSO ADVERTISES COOLER TEMPERATURES.
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&& .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY, AND SURROUNDING AREAS. PATCHY FOG AT SOME OF OUR TAF SITES WILL PERSIST UNTIL ABOUT 1200Z OR 1300Z. WE HAVE INCLUDED ITS MENTION AT KRDG, KABE, KMIV AND KACY. IT APPEARS AS THOUGH THE FOG IS RATHER SHALLOW BUT IT IS HAVING AN IMPACT ON THE VISIBILITY VALUES REPORTED BY THE ASOS UNITS. OTHERWISE, VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD WITH A MOSTLY CLEAR SKY. A LIGHT AND VARIABLE WIND EARLY THIS MORNING SHOULD SETTLE INTO THE NORTH TO WEST QUADRANT AT 6 KNOTS OR LESS FOR THE MID TO LATE MORNING HOURS. THE WIND IS FORECAST TO BECOME WESTERLY FOR THE AFTERNOON AT SPEEDS AROUND 6 TO 12 KNOTS. GUSTS NEAR 20 KNOTS ARE POSSIBLE AT OUR NORTHERN TAF SITES, KRDG, KABE AND KTTN. A COLD FRONT IS EXPECTED TO DROP THROUGH OUR REGION FROM NORTH TO SOUTH EARLY TONIGHT AND THE WIND DIRECTION IS FORECAST TO SHIFT TO THE NORTH. OUTLOOK... SUNDAY...VFR INTO THE EVENING WITH INCREASING CLOUDINESS. THE CONDITIONS THEN LOWER TO MVFR/IFR AT NIGHT AS RAIN DEVELOPS FROM SOUTHWEST TO NORTHEAST. EAST-SOUTHEAST WINDS 10-15 KNOTS, WITH SOME GUSTS TO ABOUT 20 KNOTS ESPECIALLY CLOSER TO THE COAST AND AT NIGHT. LOW-LEVEL WIND SHEAR MAY START TO DEVELOP AT NIGHT IN ADVANCE OF A WARM FRONT AND AS A ROBUST LOW-LEVEL JET MOVES IN. MONDAY...MVFR/IFR WITH PERIODS OF RAIN IN THE MORNING TAPERING TO SOME SHOWERS, THEN SOME IMPROVEMENT MAY OCCUR IN THE AFTERNOON. THERE IS A CHANCE FOR SOME THUNDERSTORMS IN THE AFTERNOON AND EARLY EVENING, ESPECIALLY FROM ABOUT THE KPHL METRO TO SOUTH AND EAST. LOW- LEVEL WIND SHEAR MAINLY IN THE MORNING. EAST OR SOUTHEAST WINDS AROUND 10 KNOTS, BECOMING WEST-SOUTHWEST. TUESDAY...MVFR POSSIBLE EARLY, OTHERWISE VFR. A FEW SHOWERS REMAIN POSSIBLE MAINLY FROM KTTN TO KABE NORTHWARD. WESTERLY WINDS MAINLY 10 KNOTS OR LESS. WEDNESDAY...MAINLY VFR. SOME AFTERNOON SHOWERS ARE POSSIBLE, MAINLY FROM KPHL AND TO THE NORTH AND WEST. WESTERLY WINDS GENERALLY 10 KNOTS OR LESS.
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&& .MARINE...
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HIGH PRESSURE IS FORECAST TO INFLUENCE THE COASTAL WATERS OF NEW JERSEY AND DELAWARE FOR TODAY. A COLD FRONT FROM THE NORTH IS EXPECTED TO PASS THROUGH THE REGION TONIGHT. THE WIND SHOULD BE LIGHT AND VARIABLE FOR TODAY AS WARM AIR FROM THE WEST RIDES OVER THE COLD WATER. THE WIND DIRECTION SHOULD SETTLE INTO THE NORTH AND NORTHEAST TONIGHT AFTER THE COLD FRONT PASSES. SPEEDS ARE ANTICIPATED TO PICK UP TO AROUND 15 KNOTS AT THAT TIME WITH WAVES ON OUR OCEAN WATERS BUILDING TO 3 TO 4 FEET. OUTLOOK... SUNDAY...A STRENGTHENING LOW-LEVEL JET ARRIVES AT NIGHT, THEREFORE A NORTHEAST WIND WILL SHIFT TO EASTERLY AT NIGHT AND INCREASE. THIS MAY BE STRONG ENOUGH FOR GUSTS TO AROUND 25 KNOTS LATER AT NIGHT. THE ONSHORE FLOW WILL ALSO START TO BUILD THE SEAS. MONDAY AND TUESDAY...WINDS WILL INCREASE AS A RESULT OF A STRENGTHENING LOW-LEVEL JET MOVING THROUGH MOSTLY MONDAY MORNING. WHILE THE STABILITY NEAR THE SURFACE SHOULD KEEP MUCH OF THE WIND ABOVE THE GROUND, IT DOES APPEAR THERE WILL BE A PERIOD OF TIME WHERE THE ONSHORE FLOW GUSTS TO AROUND 30 KNOTS MONDAY BEFORE SHIFTING TO THE SOUTH AND DIMINISHING SOME. AS A FRONTAL SYSTEM MOVES IN THE FLOW IS EXPECTED TO TURN MORE SOUTHERLY LATER MONDAY THEN WESTERLY INTO TUESDAY. SEAS WILL BUILD TO AND ABOVE 5 FEET ON THE OCEAN AND MAY BE SLOW TO SUBSIDE ON TUESDAY. A SMALL CRAFT ADVISORY LOOKS TO BE NEEDED. WEDNESDAY...THE CONDITIONS ARE EXPECTED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA.
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&& .FIRE WEATHER...
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WE HAVE UPGRADED THE FIRE WEATHER WATCH TO A RED FLAG WARNING FOR THE COUNTIES OF BERKS, UPPER MONTGOMERY, BUCKS, MERCER, INLAND MONMOUTH AND POINTS NORTHWARD. IT IS IN EFFECT FROM 300 PM UNTIL 800 PM. RELATIVE HUMIDITY VALUES ARE FORECAST TO DROP INTO THE 20 TO 25 PERCENT RANGE THERE THIS AFTERNOON AND FINE FUELS WILL CONTINUE TO DRY. AS A COLD FRONT APPROACHES FROM THE NORTH, A WESTERLY WIND IS ANTICIPATED TO GUST INTO THE 20 TO 25 MPH RANGE INCREASING THE THREAT FOR WILDFIRE SPREAD. THE RELATIVE HUMIDITY LEVELS ARE FORECAST TO DROP INTO THE 20 TO 30 PERCENT RANGE IN SOUTHEASTERN PENNSYLVANIA, EXTREME NORTHEASTERN MARYLAND, NORTHERN DELAWARE AND SOUTHERN NEW JERSEY AND FINE FUELS WILL CONTINUE TO DRY THERE, AS WELL. HOWEVER, WIND SPEEDS ARE EXPECTED TO BE LOWER THAN THOSE IN AREAS TO THE NORTH, LIMITING THE POTENTIAL FOR WILDFIRE SPREAD AND THE NEED FOR A RED FLAG WARNING. RELATIVE HUMIDITY LEVELS SHOULD BE HIGHER AND WIND SPEEDS LOWER IN CENTRAL AND SOUTHERN DELAWARE AND IN THE ADJACENT COUNTIES OF NORTHEASTERN MARYLAND THAN AT LOCATIONS TO THE NORTH. AS A RESULT, THERE ARE NO SIGNIFICANT FIRE WEATHER CONCERNS FOR TODAY IN THOSE AREAS.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...RED FLAG WARNING FROM 3 PM THIS AFTERNOON TO 8 PM EDT THIS EVENING FOR PAZ054-055-060>062-103-105-106. NJ...RED FLAG WARNING FROM 3 PM THIS AFTERNOON TO 8 PM EDT THIS EVENING FOR NJZ001-007>010-012-013-015. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE NEAR TERM...IOVINO SHORT TERM...IOVINO LONG TERM...GORSE AVIATION...GORSE/IOVINO MARINE...GORSE/IOVINO FIRE WEATHER...IOVINO

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