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Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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715 FXUS61 KPHI 140140 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 940 PM EDT Sat Jul 13 2024 .SYNOPSIS... High pressure returns late tonight and persists through Tuesday night. A cold front approaches from the northwest on Wednesday before crossing our area during Wednesday night. High pressure then builds back in from the west to end the week. && .NEAR TERM /THROUGH SUNDAY/... As of 935 PM, a few isolated showers even thunder are across central Pennsylvania. These are slowly sliding east-southeastward and toward some lower instability. The water vapor imagery shows a subtle shortwave near West Virginia toward southwest Pennsylvania and this may be assisting in the aformentioned isolated convection. Cannot rule out a few isolated cells making it to the Poconos to perhaps adjacent areas of the Lehigh Valley, therefore included a slight chance PoP (15-20 percent) into the overnight. Otherwise, coastal web cams show little fog along much of the New Jersey Shore although some haze is visible with some marine fog onto the beach in Cape May. The fog should become more widespread overnight especially along the coast given light southerly flow with high dew point air moving over the cooler nearshore waters. The Delaware Beaches has some spots of thicker fog however it looks localized at this point. May need a Dense Fog Advisory for the coastal areas, however held off for now. Otherwise, high pressure builds in from the west tonight. Abundant low level moisture will remain in place, and it looks like we will have a similar set up to last week when we had several days in a row for marine fog encroaching on the coast. For Sunday, zonal flow aloft and very light flow in the low levels. With moisture still in place, we`ll have another chance for isolated or scattered showers/storms. Think the coverage will be limited as we will lack a focus for surface convergence. Additionally, some model soundings are depicting a mid level inversion which would limit instability. As for the heat, no significant changes at this time with the temperatures and heat index values. Although by strictest heat index criteria, we are forecasting to barely get to heat advisory criteria, this is the start of a multi-day excessive heat risk, combined with relatively warm lows Sunday morning means little in the way of relief. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... Early in the new week will feature excessive heat and humidity, increasing with each passing day through Tuesday or Wednesday. Bermuda high pressure and broad low pressure across the Great Lakes will funnel heat and humidity northward across the East Coast and into the Mid-Atlantic. Quasi-zonal flow will exist aloft, though with a trough and jet feature approaching gradually with each day. Meanwhile, MCS remnants from upstream across the Midwest will stream into the area Monday and Tuesday, yielding potential for convection each day. The convection should generally be favored during the afternoon and evening time frame, mainly near and northwest of I-95 where diurnal instability is greater. SPC does not have our area outlooked for any day, however we`ll need to monitor the potential for severe thunderstorms. Any severe threat (and greater coverage thunderstorm threat) will be dictated by upstream convection, so predictability in our area remains low at this time. On Wednesday, a cold front associated with the trough will begin approaching the area. A prefrontal trough may develop on the leeward side of the mountains as well. This combined with greater synoptic forcing and greater shear should result in greater coverage of thunderstorms, and could lead to an increase threat for severe thunderstorms Wednesday afternoon and evening as well. But again, details remain a bit unclear on this threat at the moment. Nevertheless, we`ve included the greatest PoPs for the week on Wednesday. As far as the heat and humidity go, it`s indeed going to be another excessively hot and humid stretch of days. Temperatures Monday will be a bit hotter than Sunday with highs mainly in the mid to upper 90s outside of the higher terrain and away from the coast. However, dewpoints should mix out a bit more, so resulting heat indices will be similar to Monday across the board, generally in the upper 90s to low 100s. Therefore, the Heat Advisory was extended through Monday night (replacing the Excessive Heat Watch for that time frame). Low temperatures will be quite warm as well, mainly in the low to mid 70s Sunday night and Monday night, which will not offer much relief from the heat. By Tuesday, temperatures increase even more along with lower chances for convection. Tuesday is shaping up to be the hottest and most oppressively humid day of the heatwave, with highs largely in the upper 90s to near 100 degrees in some spots. Dewpoints remaining in the low 70s will support heat indices ranging from near 105-110 degrees across much of the area. Lows Tuesday night will likely be the warmest of the heatwave, ranging from the mid 70s to near 80 degrees. Wednesday remains a bit more uncertain with regard to just how hot it will get. The increasing clouds and approaching convection could limit more efficient heating as will be seen on Monday and Tuesday. however, a slower evolution of the system will probably result in hotter temperatures in the mid to upper 90s, and thus heat indices near 105-110 degrees yet again as dewpoints will be a bit higher. A faster solution would yield slightly cooler temperatures, say in the low to mid 90s. Either way, another very hot and humid day regardless of the specific numbers. Therefore, the Excessive Heat Watch was extended through Wednesday. The Watch was also expanded to include Morris and Warren Counties in New Jersey, and all Delmarva zones. The southwesterly flow will likely result in 100-105 degree heat indices near the New Jersey shore and Delaware Beaches as well on Tuesday and Wednesday. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The approaching cold front on Wednesday will begin to make it`s way through our area Wednesday night into Thursday, albeit slowly. Showers and thunderstorms likely lingering into the night, especially near and southeast of I-95. We`ll finally get some relief from the early week excessive heat and humidity by Thursday with cloud cover and lingering convection around, again mainly southeast of I-95. Dewpoints will fall into the 60s with a northerly breeze for a change, with high temperatures in the mid 80s. Dewpoints fall even further into Friday. Lows will be in the 60s. The stalled boundary just south of our area will likely result in some scattered showers or storms late in the week across the southern forecast zones. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR, however some fog on the ocean should spread at least a little inland. Additionally, we could see fog develop in the river valleys. Lowest conditions (LIFR) are likely to be with any marine fog that moves inland, which could get to KACY and KMIV. Otherwise, expect MVFR or IFR visibilities for most TAF sites once the fog develops late. Southerly winds near 5 knots becoming light and variable to locally calm. Low confidence on when the fog will develop and how low the visibilities will be. Sunday...Once the fog dissipates, VFR. A few showers or thunderstorms possible primarily after 16z (could result in brief local MVFR conditions). Given the limited coverage, a mentioned is not included in the TAFs at this time. Winds favoring south to southwest 5-10 knots, but may be more south- southeast at KACY. Low confidence if a thunderstorm will directly impact a TAF site. Outlook... Sunday night and Monday...A chance of some showers and thunderstorms, mainly later Monday. Tuesday...VFR overall. Wednesday and Thursday...Some showers and thunderstorms. && .MARINE... The conditions will stay below Small Craft Advisory criteria through Sunday. As of 935 PM, some fog was evident on the Lewes, DE and Cape May, NJ web cams and given the setup opted to expand the Dense Fog Advisory to include Delaware Bay (until 10 AM Sunday). The Dense Fog Advisory continues through 12 PM Sunday for the New Jersey and Delaware Atlantic coastal waters with additional fog developing overnight. The thicker fog should be more focused closer to the coast. Outlook... Sunday night through Tuesday night...Southerly winds remain near 10- 15 kts with some gusts near 20 kts possible at times. Seas 3-4 feet. Some areas of fog possible at times, which may warrant additional Marine Dense Fog Advisories for the Atlantic coastal waters. Wednesday...Southerly winds increasing closer to 15-20 kts with some gusts near 25 kts possible at times. Seas increasing to 4-5 feet. Small Craft Advisory may ne needed. Showers and thunderstorms likely developing by the evening hours. Areas of fog possible. Rip Currents... For Sunday and Monday, weak flow out of the south/southwest will continue with wave heights only 1 to 3 feet and a 5 to 7 second period, therefore a LOW risk for the development of dangerous rip currents for both the New Jersey Shore and the Delaware Beaches. Fog at times will cause reduced visibility along the shoreline through Sunday afternoon. For specific beach forecasts, visit weather.gov/beach/phi && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Heat Advisory from 10 AM Sunday to 6 AM EDT Tuesday for PAZ060>062-070-071-101>106. Excessive Heat Watch from Tuesday morning through Wednesday evening for PAZ060>062-070-071-101>106. NJ...Heat Advisory from 10 AM Sunday to 6 AM EDT Tuesday for NJZ009- 010-012-013-015>022-027. Excessive Heat Watch from Tuesday morning through Wednesday evening for NJZ007>010-012-013-015>022-027. DE...Heat Advisory from 10 AM Sunday to 6 AM EDT Tuesday for DEZ001. Excessive Heat Watch from Tuesday morning through Wednesday evening for DEZ001. Excessive Heat Watch from Tuesday morning through Wednesday evening for DEZ002>004. MD...Excessive Heat Watch from Tuesday morning through Wednesday evening for MDZ012-015-019-020. MARINE...Dense Fog Advisory until 10 AM EDT Sunday for ANZ430-431. Dense Fog Advisory until noon EDT Sunday for ANZ450>455. && $$ SYNOPSIS...DeSilva/Wunderlin NEAR TERM...Johnson SHORT TERM...Gorse/Staarmann LONG TERM...Staarmann AVIATION...Gorse/Johnson/Staarmann MARINE...Gorse/Hoeflich/Johnson/Staarmann