Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KPHI 011828 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 228 PM EDT Sat Oct 1 2016 .SYNOPSIS...
-- Changed Discussion --
Persistent low pressure sitting to our west will finally start to lift northeast through Sunday as it weakens. By Monday, the low will be over New England, and the associated cold front will slide through our region. A surface high will build and stay north our our region through much of the remainder of the work week.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
A closed low, which has been stuck in the upper Ohio Valley, is forecast to slowly move into the eastern Great Lakes region tonight. Meanwhile, high pressure at the surface up across northern New England to the Canadian Maritimes has been locked in, however this feature will gradually weaken and shift eastward tonight. This will continue with an onshore flow tonight, however it has weakened. There remains a pronounced low-level inversion with easterly flow below it which then veers to southerly above it. This is locking in the low clouds across the area and at times has produced some drizzle. There is a weak surface low tracking northward, especially just offshore, however there is an area of diffluent flow aloft between it and the closed low. This along with just enough lift up and over the marine layer is result in some showers lifting northward this afternoon. These are anticipated to continue to gradually lift north and northwestward through this evening. Some instability to our south, near and south of a frontal zone, could result in a few thunderstorms, however we are anticipating these to weaken as they encounter the deeper marine layer. Otherwise, some additional drizzle cannot be ruled out through the night. We kept some POPs in through the night due to the chance of at least some additional showers. Given the wealth of low-level moisture in place combined with a lessening wind field should yield to some fog development. It is not all that clear if this becomes dense given the stratus that is in place. The fog should be more widespread in the higher terrain, however widespread dense fog is not currently expected mainly due to the expected stratus deck to be maintained. As for the low temperatures, we used a blend of mostly continuity and MOS. The hourly temperature and dew point grids were adjusted based on the latest obs, then the LAMP/LAV guidance was blended into this evening.
-- End Changed Discussion --
&& .SHORT TERM /SUNDAY/...
-- Changed Discussion --
The pesky closed low is forecast to slowly shift northeastward from the eastern Great Lakes during the course of Sunday. As additional short wave energy continues to move around this closed low, some showers should be around during the day. The day however should start out with some fog and/or drizzle. The flow should start to transition during Sunday, therefore allowing some possible drying working in from the south. As this occurs, the cloud bases should lift some especially across the southern areas with perhaps even some breaks of sunshine during the afternoon. If this occurs, afternoon temperatures are expected to be warmer especially as the onshore flow lessens a bit more. Overall, some improvement is expected but we did not rush in the partial clearing. High temperatures were a blend of MOS and continuity with some local tweaks made, which resulted in some lowering of the highs for many areas.
-- End Changed Discussion --
&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
-- Changed Discussion --
Monday...low pressure may dig southeast, sliding offshore. In its wake, an upper level short wave ridge builds in. Tuesday through Thursday...through this period, a surface high will remain north of our region, with the upper level ridge slowly sliding east through the period. Low level on shore flow is expected, but expect little precip through the period as subsidence associated with the ridge should continue through the period. More likely, we will just see persistent cloud cover for much of the period. Friday through Saturday...forecast through this period is very uncertain thanks to uncertainty with the evolution of Hurricane Matthew. For now have stayed close to the previous forecast and an average of guidance through this period. However we will continue to monitor the forecast track over the next several days. Please see latest NHC advisories for the latest information on Hurricane Matthew.
-- End Changed Discussion --
&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of This Afternoon...Ceilings mainly ranging between 500-1000 feet. Some showers around will locally reduce the visibility to MVFR, although some drizzle especially at ACY will lower the visibility. Northeast winds mostly around 10 knots. Tonight...IFR/LIFR ceilings as low clouds persist. Some showers or drizzle around with even some fog developing, which will all reduce the visibility at times. As of now, widespread fog below 1SM is not anticipated given the stratus in place. Northeast winds becoming mainly 5 knots or less. Sunday...IFR/LIFR conditions to start should improve to MVFR during the afternoon. If enough drying is able to work in during the afternoon, ceilings could rise to VFR especially south and east of PHL. Northeast to east winds 4-8 knots. Outlook... Monday through Tuesday...mostly VFR conditions expected. Small chance of showers with MVFR conditions Tuesday. Wednesday...conditions lowering to IFR for Delaware Valley Sites (KPHL, KILG, KTTN, KPNE) and Coastal Plains (KMIV and KACY) as onshore flow results in low stratus clouds.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
The onshore flow is weakening as high pressure to the north is tending to shift a bit farther from our area, allowing the pressure gradient to relax. As a result, the Small Craft Advisory for the Lower Delaware Bay will be cancelled before 4 PM. The advisory continues through 06z tonight for the Atlantic coastal waters zones as seas remain in the 4-7 foot range, although these gradually subsiding. The conditions are then expected to be below advisory criteria on Sunday. The sensible weather features some showers and/or drizzle with perhaps some fog at times. Outlook... Monday...winds and seas should stay below SCA criteria. Tuesday and Wednesday...Winds and seas are expected to build through the day Tuesday, and SCA conditions could develop as early as mid day Tuesday.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING...
-- Changed Discussion --
The high tide tonight looks to fall short of advisory criteria as it is the lower tide. Despite the departures holding up some, the flow has weakened along with the seas, therefore the next high tide on Sunday should also fall short of advisory criteria.
-- End Changed Discussion --
&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 2 AM EDT Sunday for ANZ450>455. Small Craft Advisory until 4 PM EDT this afternoon for ANZ431. && $$ Synopsis...Johnson Near Term...Gorse Short Term...Gorse Long Term...Johnson Aviation...Gorse/Johnson Marine...Gorse/Johnson Tides/Coastal Flooding...Gorse

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.