Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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343 FXUS61 KPHI 301559 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1159 AM EDT Tue Apr 30 2024 .SYNOPSIS... Backdoor front will remain stalled over the region today. A cold front crosses through tonight and may stall over the region through Wednesday. Weak high pressure looks to influence the region Wednesday night through Friday. A cold front approaches this weekend, which may bring some unsettled weather into early next week. && .NEAR TERM /THROUGH TONIGHT/... Following the passage of a backdoor cold front coming in from the northeast last night, actually reaching down past Philadelphia with a push of cool air on northeast winds, we continue to see an area of stubborn low clouds hanging tough. This area extends from north of about an Allentown to Trenton to Lakewood, NJ line near midday on Tuesday. With that, there is an impressive contrast in temperatures. Sunshine and southerly winds will continue to bring temperatures up through the 70s and eventually well into the 80s this afternoon to the south of that boundary, meanwhile it is still in the low 60s around Trenton at the midday hour, with even just upper 50s over much of northern NJ. Expect those clouds will slowly erode northward this afternoon, but some places farther northeast toward Monmouth and Morris Counties may struggle to see much sun today. In addition to temperatures, the other forecast concern today is the potential for showers and thunderstorms. The main round of showers and storms is expected with a weak cold front approaching from the west. The timing for this looks to have trended slightly later, likely 5 PM or later. That being said, can`t rule out some isolated storms developing along the first (backdoor) cold front if we are able to reach the convective temperature. This is a bit of a question as there is likely to be a stout inversion in place around 800 mb for much of the day. All that being said, once showers and storms develop from either of the fronts mentioned above, there is a potential for strong storms with gusty winds. Model soundings show CAPE values near 1000 J/kg in areas well west of the backdoor cold front. That being said, the larger scale forcing will be coming in after peak heating, when instability will be waning. The main hazard with the stronger storms is likely to be gusty winds. In addition to bulk shear values near 30 kt, model soundings show a mid level dry layer that could promote a downburst or two. Instability within the hail growth zone is too low to suggest much of a concern with that. Showers should weaken and decrease in coverage through the overnight hours as the front progresses further east. Depending on how much rain we get, low level stratus could develop over portions of the region late tonight. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... The weak cold front that comes through the region Tuesday night is forecast to stall over the region for Wednesday. This is will likely cause things to remain unsettled Wednesday before weak surface high pressure builds in for the Wednesday night time frame. Weak high pressure is then forecast to hold influence over the region into Friday. However, weak surface high pressure influence may not mean freedom from unsettled conditions. A small upper-level trough just north of the Great Lakes region Wednesday night looks to slide southeastwards with time, remaining just to our north into Thursday night. Some upper-level shortwave energy may continue to plague the region through the short term. Slight chance and chance of PoPs for Wednesday thanks to the stalled front and lingering shortwave energy; PoPs will decrease with time Wednesday. NBM and most model guidance suggests a dry forecast for Wednesday night through Thursday night; no PoP included in the forecast. However, with the upper-level trough movement to our north and possible shortwave energy, a few stray and isolated pop-up showers should not be ruled out. If any showers do manifest Wednesday night onwards, they will not be all that impactful. Temperatures will remain rather warm for this time of year. Looking at mostly 70s across the region for Wednesday with colder temperatures for the coastal areas. More interior and urban areas will likely get into the mid 70s. Temperatures are expected to be warmer Thursday than Wednesday. More interior and urban areas could see high temperatures around 80F Thursday. && .LONG TERM /FRIDAY THROUGH MONDAY/... Ensemble guidance suggests an upper-level ridge axis will be placed over the eastern CONUS Friday. This ridge axis is forecast to move eastward and breakdown with time rather slowly. Eventually, a more zonal pattern looks to take hold around the time frame of Sunday through the rest of the long term; this zonal upper-level pattern being quite slow and stagnant to change. Really the whole upper- level pattern evolution looks rather slow/stagnant and suggests a slow-to-change situation will be in place for most of the long term. At the surface-level, a cold front well to our west Friday looks to march eastward while slowing down, and decaying some, with time. Cold front could look to approach our region for several periods, keeping things unsettled while slowly drawing near. Cold front may not even cross through the region until Sunday or later. Given the upper-level situation, the front may even stall over our region beyond its arrival. Given the descriptions above, expect an unsettled and showery long term. PoPs increasing from the west Friday night into Saturday with slowing frontal approach. Chance PoPS included Saturday through Sunday night. Slight chance PoPs remaining Monday with the front possibly stalling. Temperatures around average look to return for Friday onwards. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Low clouds near TTN and ABE will continue to gradually lift northward as we pass midday. Otherwise farther south, VFR conditions for the bulk of the day. Winds will be NE from ABE to TTN northward, but will tend to swing around to the S or SW at 5-10 kt for the bulk of the afternoon elsewhere. Some showers or a stray thunderstorm may approach RDG/ABE after 21Z. Moderate confidence. Tonight...Showers and a few thunderstorms are expected to progress from west to east. The storms could start as early as 21Z, but more likely near or after 00Z for most of our region. Because of how close this is occuring to sunset, expect the coverage of TSRA to be very limited. Consequently, have only mentioned SHRA in the TAFs for now. Once showers and storms decrease in coverage between 03 and 06Z, we could then see a return of low level stratus with MVFR restrictions, mainly north of PHL toward TTN and ABE. Winds light and variable. Low confidence. Outlook... Wednesday...Mainly VFR, though some sub-VFR conditions could linger in the morning. Wednesday night thru Friday...VFR. Friday night/Saturday...Sub-VFR conditions possible. && .MARINE... Winds and seas are mostly expected to stay below Small Craft Advisory criteria through tonight. However, In the Atlantic Coastal waters of South Jersey and Delaware, seas could briefly build near 5 ft late this afternoon into this evening. Low confidence of this occuring, and even if it does, it should be just barely to criteria. Therefore, decided not to issue an SCA at this time. Outlook... Wednesday through Saturday...No marine headlines anticipated. Showers possible (20-30%) for Wednesday. Showers possible starting Friday night into the weekend. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...Wunderlin NEAR TERM...Johnson SHORT TERM...Dodd/Wunderlin LONG TERM...Wunderlin AVIATION...Dodd/Johnson/Wunderlin MARINE...Dodd/Johnson/Wunderlin