Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 091447 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1047 AM EDT Sun Aug 9 2020 .SYNOPSIS... High pressure will shift off shore later today. A series of weak lows will bring chances for showers and storms starting Tuesday. A cold front is expected to approach the region Thursday into Friday, but may stall north of our area. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Any lingering fog is dissipating, and skies will be partly to mostly sunny for the rest of the day. A weak mid-level shortwave trough will cross the region this afternoon. The lift associated with this feature is rather weak, and moisture above the boundary layer remains lower than what has been in place the last several days. Any showers or storms will be isolated, so will cap PoPs at slight chance, primarily west of the I-95 corridor. Due to a weak low-level southwesterly flow, conditions will begin to warm up, with highs generally in the mid to upper 80s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... The mid level short wave trough will be slow to exit the region. However, I don`t expect showers and storms to linger much past sunset thanks to limited instability. However, it may help to limit the extent of fog (as compared to what we saw Sunday morning). Although the ground remains saturated in several locations, the lack of subsidence above the boundary layer may help to limit widespread fog and low stratus development. However, with low dew point depressions, patchy fog will be possible, especially in river valleys. && .LONG TERM /MONDAY THROUGH SATURDAY/... Overview: No period looks completely dry in the long term. However, it doesn`t look like we will have widespread chances for showers and storms until at least Thursday or Friday. Details: Monday...A low and mid level trough over the Ohio Valley could bring isolated showers and storms to the western portions of our region Monday afternoon, but most of the convection should stay to our northwest. The warming trend continues with may locations getting back into the lower 90s once again. Tuesday and Wednesday...Two weak troughs ahead of the main cold front (more on that below) could result in showers and storms each afternoon. As mentioned by the previous shift, with abundant low level moisture in place, even weak lift could result in convective initiation. While highs each day should be around highs on Monday, increasing low level moisture will result in heat index values generally in the upper 90s. Thursday through Saturday...There remains poor agreement among guidance and from run to run on the details of how the pattern will evolve at the end of the week. In the mid and upper levels, the low over Central Canada should finally start to progress east. However, at least one operational model shows the main trough digging towards our region, becoming positively tilted and stalling, which seems unlikely with the larger pattern. Other models show that trough staying well to our north with a weak southern stream low pressure system lifting into our region from the mid Mississippi Valley. With so much uncertainty in how the mid and upper level pattern will develop, other details, including timing and how far south the cold front will get before stalling, remain quite uncertain. However, even if the front stalls northwest of our region, it could be close enough to bring the next chance for a widespread rain for our region. A this point, the most likely time period for this looks to be Thursday into Friday. Given the uncertainty, have gone with a blend of guidance and the previous forecast through this period. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Some BKN MVFR CIGs are sliding down the Delaware River, so will TEMPO BKN025 until 16Z at KPHL/KPNE. Not expecting this to persist much beyond noon. Otherwise, VFR for the remainder of the day. Winds mostly light southwesterly, but southerly or even southeasterly winds of 10 to 15 kt are possible behind a sea breeze. The sea breeze is likely to affect KACY, however it is unclear how much further inland it will reach. High confidence on all aspects except the sea breeze. Tonight...Starting VFR. However, another round of fog is possible, reducing conditions to MVFR or even lower, generally after 06Z. Light and variable winds. Moderate confidence on the overall pattern, but low confidence on the details of the fog. Outlook... Monday...Mostly VFR conditions are expected. There is a slight chance for afternoon showers and storms at KABE and KRDG. Southwesterly winds 5 to 15 kt. High confidence. Monday night...Mostly VFR conditions expected, but patchy fog may result in MVFR or even IFR conditions. Light southerly winds. Moderate confidence on most aspects of the forecast, but low confidence on the fog potential. Tuesday through Wednesday night...Mostly VFR conditions expected. There is a chance for showers and thunderstorms, primarily in the afternoon each day which could result in brief MVFR conditions. Southerly winds up to 10 kt. Moderate confidence on most aspects of the forecast, but low confidence on the potential for storms at the TAF sites. Thursday...Starting with VFR conditions. MVFR or even IFR conditions may develop by Thursday afternoon as the chance for showers and thunderstorms increase. Southeasterly winds 10 kt or less. Low confidence.
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&& .MARINE... Winds and seas should stay below Small Craft Advisory criteria through tonight. Patchy fog is possible right along the coast late tonight. Outlook... Sunday night through Thursday...Winds and seas should stay below SCA criteria. Thunderstorms are possible, especially towards the end of the week, which could produce locally higher winds and waves. Rip Currents... There is a low risk for the development of dangerous rip currents on Sunday and Monday. Weather conditions and waves should be similar on both days. No precipitation is anticipated. The wind is expected to favor the southeast and south at 5 to 10 MPH. Breaking waves are forecast to be less than 2 feet with a medium period swell from the southeast. && .EQUIPMENT... The NOAA Weather Radio All-Hazards broadcast from Hibernia Park Pennsylvania (Station WNG-704) remains off the air. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Johnson Near Term...Johnson/MPS Short Term...Johnson Long Term...Johnson Aviation...Johnson/MPS Marine...Johnson Equipment...WFO PHI

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