Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 151627 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1227 PM EDT Sat Jul 15 2017 .SYNOPSIS... Weak low pressure passes through the Delmarva and southern New Jersey early this morning, and this will pull a cold front through the region later this morning. That front will become nearly stationary over the Mid-Atlantic as high pressure builds in from the west. The high works its way east through the weekend, and moves offshore Sunday night. Weak areas of low pressure will develop along the stalled boundary and pass through the region Monday and Tuesday. High pressure builds across the region on Wednesday. Several cold fronts then approach from the west Thursday and Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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An upper trough and sfc front are crossing srn NJ and Delmarva early this afternoon. Scattered showers have developed ahead of the feature. There is enough low level instability and rotation to produce waterspouts across the Chesapeake Bay. A recent waterspout near Kent Island prompted a tornado warning across this region. A slow improvement from N/W to S/E is still expected this afternoon as the drier air behind the front advects into the area. High temps were not changed attm, but a few adjustments in the hourly grids were made. Overall, high temperatures will end up at or slightly above normal. The higher temps S/E will be realized later in the day then N/W.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... An upper-level trough remains in place across the Northeast and northern Mid Atlantic, with even some amplification over the Great Lakes as the next stronger short wave digs east- southeastward. Meanwhile, surface high pressure gradually extends more to the east into our area. While some upstream high-level moisture might translate into some cirrus into our region through the night, overall we are anticipating a clear to partly cloudy sky. Given lower dew points and light winds, temperatures are expected to be noticeably cooler compared to the last few mornings. Low temperatures are mainly a blend of MOS and continuity, although did tweak these down a bit for some local areas. && .LONG TERM /SUNDAY THROUGH FRIDAY/... High pressure builds across the region on Sunday. Plenty of sunshine on tap with warm and mild conditions. Highs top off in the mid and upper 80s throughout the region with relatively comfortable humidity levels as surface dewpoints will be in the low to mid 60s. The pattern then changes as high pressure moves offshore Sunday night. Return flow sets up behind the departing high, and humidity levels build back up as dewpoints climb into the mid and upper 60s, and possibly into the lower 70s across NE MD and DE. During this time, H5 trough with several shortwaves rotating around the base of the trough will move east, with the trough digging from the Ohio Valley and Northeast down into the Southeast. This trough will become nearly stationary along the East Coast Monday and Tuesday, and several weak areas of low pressure will develop on the stationary front along the Mid- Atlantic and pass through the region during the start of the new week. Best chances for precip will be over the Lehigh Valley and Pocono Mountains Monday afternoon as surface low pressure develops on the boundary over the Mid-Atlantic, and then lifts to the north throughout the day and moves offshore Monday night. The upper trough remains along the coast, and another shortwave dives into the base of the trough on Tuesday. Another surface low develops Tuesday afternoon and passes through the region Tuesday night. Surface high pressure builds in from the west on Wednesday, and the upper trough will be slow to depart. As a result, this keeps at least a slight chance/chance for showers/thunderstorms in the forecast on Wednesday. High pressure moves offshore Wednesday night/Thursday morning. From there, several weak cold fronts approach from the west for Thursday and Friday. Each front could touch off at least isolated to scattered showers and thunderstorms. The warmest temps during the week look to occur on Wednesday and Thursday, when a southwest flow ushers a hot and humid airmass into the region with highs in the upper 80s to low 90s and surface dewpoints in the upper 60s to low 70s. Dewpoints may back off a bit on Friday behind one of the weak cold fronts. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...The low conditions are expected to improve to VFR by Midday. A few showers around through about Midday, however given low coverage anticipated these were not included in the TAFs. Light and variable winds, become northwesterly mainly in the 5 to 10 knot range. Tonight...VFR. Northwest winds 5-10 knots early, becoming light and variable at most terminals. OUTLOOK... Sunday through Sunday night...VFR conditions expected. Light and variable winds, becoming SW 5-10 KT. Light and variable winds at night. Monday through Wednesday...Mainly VFR conditions expected. Afternoon showers and thunderstorms with MVFR or lower conditions possible. South to southeast winds around 10 knots. Thursday...VFR conditions expected. SW winds 5-10 KT. && .MARINE... The conditions are expected to remain below Small Craft Advisory criteria today and tonight. A cold front is forecast to shift off the coast this morning then stall offshore and to our south. An easterly surface wind has been continuing across the northern coastal waters, however all areas will see a wind shift to the west and northwest this morning behind the front. The flow looks light enough though where the winds should turn southerly this afternoon and into this evening especially for the New Jersey coastal waters. OUTLOOK... Sunday through Thursday...Sub-SCA conditions expected on the waters. Scattered showers and thunderstorms possible, mainly during the afternoon and early evening hours Monday through Wednesday. Heavy rain, gusty winds, and lightning can accompany those thunderstorms. RIP CURRENTS... A low risk for the formation of dangerous rip currents is anticipated for today into this evening, despite a light enough wind becoming west to northwest then potentially turning back to southerly this afternoon. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...MPS Near Term...PO Short Term...Gorse Long Term...MPS Aviation...Gorse/MPS Marine...Gorse/MPS

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