Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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876 FXUS61 KPHI 131617 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1217 PM EDT Tue Aug 13 2024 .SYNOPSIS... High pressure will gradually build closer to our area through tonight, then slide over our area Wednesday and Thursday before shifting to our east. Low pressure and an associated warm and cold front are forecast to arrive over the weekend, with the cold front shifting offshore during Monday. && .NEAR TERM /THROUGH TONIGHT/... 12:15PM...No major changes to the forecast at this time; quiet conditions persist across the region. Tranquil weather conditions with below normal temperatures continuing today and through tonight. Troughing aloft remains just offshore with weak subsidence in place across the entire region. At the surface, expansive high pressure will be centered across the Great Lakes, extending its reach toward the East Coast. The pressure gradient will be a bit lighter today than it was Monday, and this should favor sea and bay breezes developing into the afternoon. Elsewhere, north to northwest winds near 5-10 mph can be expected. 850 mb temperatures will be a degree or two cooler today than Monday, so high temperatures should also be a couple degrees cooler in the upper 70s to low 80s. The drier air aloft and subsidence should help mix out the dewpoints quite well into the mid 50s this afternoon. This will translate to an usually pleasant mid August day across the area. Can`t entirely rule out a shower popping up over the higher terrain or on a sea breeze, but thinking subsidence and limited diurnal instability will preclude any mention of this in the forecast. We should see pretty extensive fair weather cumulus development this afternoon though. The column starts moistening up a bit into tonight, and with us still on the fringes of the surface high, radiational cooling won`t be quite as good tonight. Nevertheless, low temperatures will still be below normal in the mid 50s to low 60s (mid 60s for the coasts and urban corridor). && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... While the axis of an upper-level trough is forecast to be positioned to our east Wednesday, we continue to be under cyclonic flow aloft. Some shortwave energy sliding southward across our area will team up with daytime heating to result in cumulus development. The model forecast soundings overall show dry air below cloud base and also drier air in the mid levels, however instability increases through the afternoon. While the shear is low, a couple of showers or a thunderstorm cannot be ruled out across parts of the area Wednesday afternoon to early evening. The coverage looks to be low and therefore maintained some slight chance PoPs (15-20 percent) for parts of the region. Outside of any spotty rain, the dew points should lower some during peak heating given plenty of drier air within the boundary layer (blended in the CONSAll guidance for dew points to better reflect the mixing down especially during peak heating). High temperatures are forecast to be near average. Any showers dissipate in the evening with lingering cumulus flattening and then dissipating as well. As we go through Thursday, it looks similar to Wednesday although we start to lose some of the influence of the upper- level trough. Some additional shortwave energy sliding southward on the western side of the departing trough may touch off a shower or thunderstorm during the afternoon before the mid level flow starts to become less cyclonic. Some warming aloft however may temper some of the cumulus development and therefore any showers, however kept a slight chance PoP (15-20 percent) for parts of the area during the afternoon. A sea breeze each day may also try to focus a few afternoon showers. The dew points during peak heating may lower a bit again given enough dry air within the boundary layer. && .LONG TERM /FRIDAY THROUGH MONDAY/... Summary...An increase is shower chances associated with a slow arriving system. Synoptic Overview...An upper-level trough is forecast to amplify into the East from the Great Lakes region during the weekend, then remain in place early next week. At the surface, low pressure across the Great Lakes Friday tracks to our north with a warm front lifting north across our area Saturday. A cold front then crosses our area late Sunday and Monday. For Friday...Weak high pressure initially across our area shifts east and offshore at night. This is in response to a weak mid level ridge that arrives ahead of the next system. An increase in warm air advection and the approach of a warm front may provide enough lift and forcing for ascent for some showers to develop or arrive from the west and southwest. This looks to be mostly late in the afternoon and especially at night, therefore the PoPs reflect this current thinking. The dew points are forecast to increase some, although not to very humid levels. For Saturday through Monday...A more unsettled pattern is forecast as an upper-level trough gradually settles into the East. While there still remains some uncertainty especially with the timing, the overall theme is for increasing chances for showers and some thunder. As of now, surface low pressure tracks across the Great Lakes region and then to our north over the weekend. A warm front lifts into or just north of our area during Saturday, then a trailing cold front works its way across our area during Monday. This entire process could be slower especially if the parent upper- level trough becomes closed which some guidance/ensembles suggest. A more humid air mass is forecast to get pulled up ahead of the cold front, and with increased warm advection for a time temperatures will warm some outside of any more organized showers/thunder. The intensity of thunder at this time is uncertain as this will depend on the timing of the forcing, extent of the showers and cloud cover and magnitude of the instability. The PoPs are mainly in the 30-60 percent range, but do decrease during Monday based on the cold front shifting east as of now. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR with SCT cumulus developing by 18Z. North to northwest winds 5-10 kts. High confidence in prevailing conditions. Tonight...Prevailing VFR conditions expected. Winds diminishing to 5 kts or less, favoring a north to northwesterly direction. High confidence. Outlook... Wednesday through Friday...VFR overall, however a few showers or a thunderstorm possible mostly Friday night. Saturday...Times of sub-VFR conditions possible with the chance of showers and some thunderstorms. && .MARINE... Conditions are forecast to remain below advisory conditions through tonight. Winds 10-15 kts from the north to northwest this morning (land breeze) shifting southerly this afternoon (sea breeze), then back to a land breeze again tonight. Seas 1-2 feet. Fair weather. Outlook... Wednesday through Friday...The conditions are anticipated to be below Small Craft Advisory criteria. Saturday...Small Craft Advisory conditions possible on the Atlantic coastal waters as southerly winds increase and seas build. Rip Currents... For Today...Northerly winds around 5-10 mph in the morning, will become south-southeast in the afternoon. Breaking waves around 1-2 feet with a 7-8 second period. Have maintained a LOW risk for the development of dangerous rip currents at the Jersey Shore and the Delaware Beaches. For Wednesday...Similar wind and breaking wave conditions are expected with an 8-9 second period. For this reason, have opted to continue with a LOW risk for rip currents for both the Jersey Shore and the Delaware Beaches. For specific beach forecasts, visit weather.gov/beach/phi && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...Gorse NEAR TERM...Staarmann/Wunderlin SHORT TERM...Gorse LONG TERM...Gorse AVIATION...Gorse/Staarmann MARINE...Gorse/Staarmann