Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 231940 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 340 PM EDT Tue May 23 2017 .SYNOPSIS...
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A couple of areas of low pressure will pass to our south this evening then east of our area overnight into Wednesday as they combine and move along a frontal boundary. As an area of low pressure moves into the Ohio Valley Wednesday night into Thursday, an occluded front and warm front will lift toward our region. A triple point low will develop and take over as the dominant low as it moves across our area Thursday night. This low will move away from the area Friday, with a weak frontal boundary or surface trough crossing the area during the day. Weak high pressure may briefly move across the area Friday night into early Saturday. Another frontal system is expected to affect the area Saturday night into Sunday, followed by another on Monday and Tuesday.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... An email briefing with a coastal flood graphic will post by 315 PM this afternoon. It highlights tidal inundation flood potential for the Wed-Thu evening high tide cycles on the Atlantic coasts of DE and NJ. The next briefing of either a full scale package or email will post around 3 PM Wednesday, incorporating not only the minor to possibly moderate coastal flood threat and associated products but also a possible QLCS event for se PA/ the Delmarva/s NJ late Thursday. Isolated showers may be drying into sprinkles as this is written near and sw of PHL. Otherwise sprinkles are departing se DE. Tonight: Low pressure off the mid Atlantic coast will continue to slide northeast, with showers along the coasts but chancey for e PA/nNJ late tonight. northeast wind. This forecast was based on a 50 50 blend of the 12z/23 GFS/NAM. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... Wednesday...scattered leftover showers possible in the morning but it should dry out and be a decent afternoon everywhere. Northeast wind becomes southeast in the afternoon. This forecast was based on a 50 50 blend of the 12z/23 GFS/NAM. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
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An unsettled weather pattern continues for much of the extended forecast with several periods of rain possible. On Wednesday night, an area of low pressure will be lifting through the Ohio Valley and toward the southern Great Lakes region. Meanwhile, an occluded front and warm front will be lifting toward our area. A triple point low is forecast to develop to our southwest overnight, which will likely slow down the northward progression of the frontal boundaries. This will lead to an area of rainfall overrunning the frontal boundary and lifting across out area overnight Wednesday into Thursday morning. As the short wave/vorticity impulse that helps create this area of rainfall lifts north of the area, this area of rainfall will move north as well early in the day. Then the question for the afternoon becomes how far north the warm front progresses as the triple point low approaches from the west. Another period of rainfall is expected during the afternoon and evening, but depending on how far north the front lifts, there could be a chance of thunderstorms to develop later in the day for a portion of the area. The best chance for this to happen would be for portions of Delaware and the eastern shore of Maryland, as well as far southern New Jersey. The rest of the area would likely be stable enough to prevent thunderstorms, and just receive rain. By Thursday night, the triple point low will begin moving across the area, pulling the occluded frontal system across the area as well. This will lead to continuing scattered showers during the night Thursday. On Friday, the low will continue to move to our northeast and offshore of New England. A weak frontal boundary or surface trough New England is forecast to move across the area during the day. This could lead to another chance of scattered showers during the afternoon. Friday night through most of Saturday is expected to be dry as weak high pressure quickly moves across the area. However, a warm front will begin approaching the area from the south late in the day and into the overnight hours as an area of low pressure lifts into the Great Lakes region. As the low continues to lift through the Great Lakes region Sunday, the warm front may lift across the area before a triple point low forms and moves across the area as well. The exact timing of these features is still a little uncertain, but Saturday night through Sunday looks like there should be several periods of showers, and possible thunderstorms if enough instability builds on Sunday. The low pressure system that moves across the Great Lakes over the weekend is forecast to remain nearly stationary across south-central Canada Monday into Tuesday. This may send a couple of frontal boundaries across the area Monday and Tuesday, leading to additional showers or thunderstorms early next week.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through tonight...VFR lowering CIGS with potential MVFR Conds in showers KACY/KMIV late at night while any period of showers elsewhere should not lower conditions to MVFR. Northeast wind, may gust 20 kt ACY. Wednesday...VFR cigs inn the morning and then sct-bkn aoa 4000 ft in the aftn. MVFR/IFR conditions possible early in the day, mainly at KMIV/KACY. northeast wind become southeast in the afternoon. max gusts 15 kt. Outlook... Wednesday night-Thursday...Conditions lowering to IFR overnight and continuing into Thursday as periods of rain affect the area late Wednesday night into Thursday. Improvement to VFR possible for southern areas later in the day. Thursday night...MVFR to IFR conditions possible with low clouds and fog/drizzle possible. Friday-Friday night...Improving to VFR during the day and into the night, scattered showers possible during the daytime. Gusty northwest winds 20-25 knots. Saturday...Generally VFR. Showers moving into the area later in the day, which will lead to lowering ceilings. Saturday night-Sunday...MVFR to IFR conditions possible with periods of low clouds and rain. Thunderstorms possible Sunday. An improvement to VFR possible Sunday outside of showers/thunderstorms.
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&& .MARINE...
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SCA continues DE Atlc waters late tonight and now extended through the day tomorrow. SCA added for the NJ waters, primarily there for hazardous 5 ft seas. There is a chance the guidance might be a foot too high but I had to issue since our fcst is for 4 to 6 ft. Outlook... Wednesday night-Friday...Small Craft Advisory conditions possible. Varies between wind and waves criteria each period. Friday night-Sunday...Conditions expected to remain below advisory levels.
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&& .TIDES/COASTAL FLOODING... CFW for minor coastal flooding issued for the Wednesday evening high tide cycle. A CF Watch may be needed for the Thursday evening high tide cycle for Monmouth/Ocean and Middlesex counties but that wont be issued, if at all, until sometime Wednesday. This afternoons issuance is also appended to a blast email for Em`s including an image with a followup Wednesday around or shortly after 3 Pm. Some of the highest astronomical tides of the year are occuring late this week. The new moon cycle on Thursday, combined with a possible prolonged easterly flow, we will probably see some of our coastal sites exceed minor tidal flooding levels during the Wednesday and Thursday evening tide cycles. There is also a small chance that we could reach moderate levels in a few spots. && .CLIMATE... ACY is #6 wettest May on record with its 6.07. The record there for May is 8.80 set in 1948....POR back to 1874. Monthly avg temps should end up within .7 degrees of where they are now, possibly edging on the warmer side of the current departures as seen in our climate data ending the 22nd. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...Coastal Flood Advisory from 6 PM Wednesday to midnight EDT Wednesday night for NJZ012>014-020>027. DE...Coastal Flood Advisory from 6 PM Wednesday to midnight EDT Wednesday night for DEZ002>004. MD...None. MARINE...Small Craft Advisory from noon to 4 PM EDT Wednesday for ANZ450>453. Small Craft Advisory from midnight tonight to 4 PM EDT Wednesday for ANZ454-455.
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&& $$ Synopsis...Robertson Near Term...Drag Short Term...Drag Long Term...Robertson Aviation...Drag/Robertson Marine...Drag/Robertson Tides/Coastal Flooding... Climate...

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