Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 201232 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 832 AM EDT WED AUG 20 2014 .SYNOPSIS...
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LOW PRESSURE IN GREAT LAKES REGION WILL WEAKEN AS IT MOVES TO NEAR LAKE ONTARIO THURSDAY. A SECOND AREA OF LOW PRESSURE WILL DEVELOP NEAR THE CHESAPEAKE BAY THURSDAY NIGHT. HIGH PRESSURE IN EASTERN CANADA WILL BUILD DOWN ALONG THE EAST COAST LATER THIS WEEKEND INTO NEXT WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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MIXED CLOUDS AND SUN PROBABLY FAVORING MORE SUN. ANOTHER NICE DAY. A COMPLEX OF SHOWERS AND STORMS IN WPA/WVA ASSOCIATED WITH A MID- LVL SHORTWAVE TROUGH OUT AHEAD OF THE GREAT LAKES LOW SHOULD WEAKEN AS IT MOVES EASTWARD INTO AN INCREASINGLY STABLE AIRMASS THAT RESIDES EAST OF THE OH VLY. THIS IMPULSE IS FORECAST TO REACH CENTRAL PA BY MIDDAY AND EASTERN PA BETWEEN 18Z-00Z. THERE IS A POTENTIAL FOR ISOLATED SHOWERS TO DEVELOP AHEAD OF THE SHORTWAVE TROUGH DURING THE MID TO LATE AFTERNOON JUST OF OUR CWA. NO CHANGE IN AREAL COVERAGE FROM THE 330AM/630AM FCST.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
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HIGH PRESSURE WILL RETREAT OFF THE EASTERN SEABOARD TONIGHT AS THE ABOVE MENTIONED SHORTWAVE TROUGH MOVES INTO THE AREA FROM THE WEST. EXPECT SHOWERS AND PERHAPS A FEW THUNDERSTORMS WEST OF THE APPALACHIAN RIDGE. FORECAST IS CONSERVATIVE IN REGARDS TO HOW FAR EAST SHOWERS AND STORMS WERE MENTIONED AS MODELS GENERALLY SHOW CONVECTION DECAYING AS IT MOVES EASTWARD INTO A MORE STABLE AIRMASS OVER NJ/DE. CLOUDS COVER, WHICH WILL INCREASES ACROSS THE ENTIRE AREA WITH THE APPROACH OF THE TROUGH, WILL LIMIT RADIATIONAL COOLING TONIGHT. OFFICIAL MIN TEMP FORECAST SLIGHTLY WARMER THAN MOS GUIDANCE.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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THE LONG TERM FORECAST STARTS OFF WITH RAIN CHANCES, BEFORE A DRYING OUT PERIOD SETS IN ACROSS THE AREA. ON THURSDAY, THE AREA OF LOW PRESSURE AND ASSOCIATED FRONTAL BOUNDARY TO OUR NORTHWEST WILL WEAKEN AS IT MOVES SE OUT OF THE GREAT LAKES AND INTO UPSTATE NEW YORK. HOWEVER, THE MID/UPPER-LEVEL LOW WILL SWING THROUGH THE NORTHEAST AND MID-ATLANTIC THROUGH THURSDAY AND THURSDAY NIGHT. THIS WILL ALLOW FOR SHOWERS, AND WITH A FAIR AMOUNT OF INSTABILITY, SCATTERED THUNDERSTORMS TO DEVELOP AND MOVE INTO THE AREA. THERE IS NOT MUCH SHEAR OR MUCH OF A WIND FIELD, SO WE DO NOT EXPECT SEVERE WEATHER AT THIS TIME. PW VALUES ARE GENERALLY FORECAST AROUND 1.5-1.75 INCHES, SO SOME SHOWERS/STORMS COULD PRODUCE A PERIOD OF MODERATE TO HEAVY RAINFALL. ISOLATED SMALL HAIL NOT IMPOSSIBLE AS TT NEAR 50 IN AREA OF MAX INSTABILITY IN NJ (NEAR THE DELAWARE RIVER). THURSDAY NIGHT, A SECOND AREA OF SURFACE LOW PRESSURE IS FORECAST TO DEVELOP NEAR THE CHESAPEAKE BAY ALONG THE STATIONARY BOUNDARY TO OUR SOUTH. IT IS POSSIBLE THAT THIS MAY HELP KEEP A FOCUS FOR PRECIPITATION THURSDAY NIGHT, BEFORE IT SAGS TO OUR SOUTH. FOR FRIDAY INTO THE WEEKEND, THE MID/UPPER LOW WILL REMAIN TO OUR NORTHEAST, KEEPING A NORTHWEST FLOW ALOFT ACROSS OUR AREA. MEANWHILE, HIGH PRESSURE WILL BEGIN BUILDING DOWN ACROSS THE EAST COAST FROM EASTERN CANADA. BEFORE THE HIGH TAKES FULL CONTROL OF THE WEATHER, THERE WILL REMAIN A CHANCE OF SCATTERED SHOWERS FRIDAY AND SATURDAY AS THERE MAY BE A FEW SHORT WAVE/VORT MAXES THAT AFFECT THE AREA IN THE NORTHWEST FLOW ALOFT. BY SUNDAY INTO EARLY NEXT WEEK, THE SURFACE HIGH BUILDS FURTHER INTO THE MID-ATLANTIC REGION, WHICH SHOULD BRING DRY WEATHER TO THE AREA. HIGHS ARE EXPECTED TO START OUT CLOSE TO OR SLIGHTLY ABOVE NORMAL THURSDAY INTO FRIDAY, BUT AS THE HIGH BUILDS DOWN OUT OF EASTERN CANADA AND THE NORTHWEST FLOW ALOFT REMAINS ACROSS THE AREA OVER THE WEEKEND, 925/850 MB TEMPS AND THICKNESSES LOWER. THIS WILL ALLOW FOR SLIGHTLY BELOW NORMAL TEMPERATURES OVER THE WEEKEND. AS WE MOVE INTO EARLY NEXT WEEK, WE SHOULD START TO GET MORE OF A RETURN SURFACE FLOW AND RIDGING ALOFT BEGINS TO TAKE PLACE ONCE AGAIN, ALLOWING FOR REBOUNDING TEMPERATURES.
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&& .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...VFR SCT-BKN AOA 5000 FT. LIGHT SE TO S WIND. TONIGHT...VFR CIGS LIKELY. LIGHT SOUTH WIND. PROB30 GROUP FOR SHRA ADDED FOR RDG/ABE EARLY THIS EVE WHEN A DISTURBANCE MOVES THRU. OUTLOOK... THURSDAY-THURSDAY NIGHT...GENERALLY VFR. LIGHT SOUTH WIND. CHANCE OF SHOWERS AND THUNDERSTORMS WHICH MAY LOWER CIGS/VSBYS. FRIDAY-SUNDAY...PERIODS OF LOW END VFR OR MVFR CIGS POSSIBLE WITH A CHANCE OF SHOWERS, ESPECIALLY FRIDAY INTO SATURDAY.
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&& .MARINE...
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NO MARINE RELATED HEADLINES THROUGH THURSDAY. EASTERLY WINDS BETWEEN 5-10 KT THIS MORNING WILL BECOME SOUTHEASTERLY THIS AFTN AS HIPRES MOVES OFFSHORE. LOCALLY HIGHER WINDS TO 15 KT POSSIBLE THIS AFTN AND EVE. OUTLOOK... THURSDAY-FRIDAY NIGHT...SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED. SATURDAY-SUNDAY...SEAS MAY BEGIN TO APPROACH SMALL CRAFT ADVISORY LEVELS AS A LONG FETCH DEVELOPS AROUND HIGH PRESSURE BUILDING IN FROM THE NORTHEAST OUT OF EASTERN CANADA.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...ROBERTSON/DRAG 831 NEAR TERM...DRAG/KLEIN 831 SHORT TERM...DRAG/KLEIN 831 LONG TERM...ROBERTSON/DRAG 831 AVIATION...DRAG/KLEIN/ROBERTSON 831 MARINE...DRAG/KLEIN/ROBERTSON 831

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