Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 250131 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 931 PM EDT TUE MAY 24 2016 .SYNOPSIS... Low pressure near Cape Cod will track northeast overnight into Wednesday. At the same time, high pressure will shift from the Ohio Valley to the Eastern Seaboard. A frontal boundary is forecast to settle across the Northeast and northern Mid-Atlantic Thursday through Monday. High pressure is expected on Tuesday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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An area of low pressure was analyzed near Nantucket at 00Z this evening. This vertically-stacked will continue to weaken tonight as it moves northeastward into the Gulf of Maine. Meanwhile, a surface trough was located over central NJ and southeastern PA and marked by a windshift from the west ahead of the boundary to east-northeast behind it. Forcing for ascent for isolated showers and thunderstorms was provided by low-level convergence along the boundary and DPVA ahead of a mid-level shortwave trough rounding the backside of the upper low. Convection has waned over the last hours with the loss of daytime heating and as the shortwave tough near the mouth of the Delaware Bay moves offshore. The last of the shower activity was near Atlantic City at 9 PM. Otherwise, the rest of tonight is shaping up to by dry. The back (western) edge of the mid-level clouds located was over the Delaware Valley as of 9 PM and should progress eastward toward the coast late this evening. Clear skies and light winds are expected overnight, allowing temperatures to drop faster overnight under these increasingly favorable radiational cooling conditions. Fog potential will be low tonight since drier air was advected into the area earlier today. However, Patchy fog may develop across central and northern portions of New Jersey and eastern Pennsylvania where higher dewpoints reside behind the aforementioned sea-breeze front.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... The big story tomorrow will be a dramatic warming trend as the ridge axis slides closer to our region. Have gone slightly above the highest guidance for max temps tomorrow given that the models have recently had a cold bias. With large 1000-500mb thickness increases and mostly clear skies, there are several factors promoting a warming trend and only one factor - a sea breeze, if it develops - that could temper the highs. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Overview...the period will be dominated by an east coast ridge and west coast trof aloft and a weak surface front that is forecast to meander across the Northeast and northern Mid-Atlantic through Monday. The front could sag as far south as northern PA and NJ from time to time and help to trigger showers and thunderstorms as well affect temps with a stronger onshore flow on the northern side of it. A washout is not anticipated, but with the front in place combined with afternoon instability, some locales will get wet. Temps...Normals for PHL through the period are in the mid 70s and mid 50s. With 925 temperatures rising at or above 18 degrees C through Sunday (we`re about 13 degrees C this afternoon), an extended period of above normal temps can be expected. On Monday and Tuesday, a slightly cooler synoptic airmass is forecast to arrive. An onshore flow could also help to lower temps. Temps are going to be the warmest across the interior, with highs about 10 degrees above normal through Sunday, cooling Monday and Tuesday. Along the coastal plain, temps will rise into the mid to upper 70s through Saturday. Sunday is expected to be cooler closer to the ocean as a more onshore gradient develops. Right along the beaches and boardwalk, a chilly seabreeze can be expected each afternoon through Saturday with water temps still in the 50s and the interior forecast to be in the 80s. Sunday through Tuesday, beach temps should be cooler altogether with a more persistent onshore flow. Keep an eye on the surface front to our north. If the surface high building across Quebec is stronger than expected, the front could sag further south and cool temps to levels that are lower than what`s forecast. The further south one goes along the NJ coast and along the DE beaches, confidence is higher that the front will be a non- issue. Precipitation...with the front just to our north or in our vicinity, combined with climbing dewpoints (up to the mid 60s) and instability, afternoon showers and thunderstorms could pop any day across the interior through Saturday. A washout is not expected. We`re talking about isolated to scattered POPS common in a summertime regime. Precip chances spread to the coast on Sunday and Monday. Winds...mainly from the south or southwest through Saturday and less than 15 mph. Winds could turn more easterly on Sunday, more likely on Monday and Tuesday. With ocean temps in the 50s and the I95 forecast to be in the mid 80s, a seabreeze will no doubt develop and push inland. So during the afternoon hours through Saturday, winds are forecast to become more southeast to east. Hazards...The probability for widespread hazardous weather is low through the period. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR expected tonight as earlier showers dissipate/move offshore. Light winds 5-10 kt this evening will be under 5 kt by the overnight. Winds shifted from W to E-NE at TTN, PNE and ABE this evening as a backdoor cold front/sea-breeze front moved inland. Expect this surface boundary to decelerate while progressing farther inland at night as the sea-breeze circulation dissipated but it should reach PHL by 02Z or 03Z. W-NW winds will increase to around 10 kt by late morning Wednesday with gusts to around 15 kt during the afternoon. Outlook... Wednesday night...VFR. West to southwest winds up to 10 knots. Thursday through Sunday...VFR overall, however brief times of MVFR/IFR conditions are possible each afternoon and evening due to a few showers and thunderstorms, especially across the I95 terminals westward. South to southwest winds 15 knots or less. A seabreeze front in expected to track westward through the afternoon hours, so a turn to the southeast should result where the seabreeze front crosses.
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&& .MARINE...
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Light and variable winds tonight across the coastal waters off central NJ. Farther south, southwesterly winds will generally be 10-15 kt. West to southwest winds 5-15 kt are expected Wednesday. Seas will generally be in the 2-3 ft range tonight and Wednesday. Outlook... Wednesday night through Sunday...A ridge aloft over the area combined with high pressure at the surface to our south and east will allow for mainly a prolonged southerly flow across our area, potentially through Saturday night. Winds could back more onshore on Sunday. Conditions are expected to be below Small Craft Advisory criteria through the period. Seabreeze circulations are expected to develop each day, so an increase in winds can be expected along with a bit of chop across the nearshore waters during the afternoon hours.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Kruzdlo Near Term...Klein Short Term...Johnson Long Term...Kruzdlo Aviation...Klein/Kruzdlo Marine...Klein/Kruzdlo

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