Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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168 FXUS61 KPHI 290917 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 517 AM EDT SUN MAY 29 2016 .SYNOPSIS... High pressure will continue to push further off the Middle Atlantic coast through tonight. Tropical Storm Bonnie will move along the southeastern United States coast over the next several days. Moisture from this system will move northward and into our area today and Monday. High pressure will build towards the region Tuesday, remaining to our north through Thursday. A cold front will move through the area over the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Early this morning...patchy dense fog has formed where it rained ydy along and north of I-80. otherwise, any patchy fog elsewhere should be shallower and less dense and all of this dissipates between 6 and 7 am. Today...Issuing SPS at about 530 am for heat hazard n of I-78. Still very warm but with lower dewpoints into midday, not quite as uncomfortable...however, high dewpoints will be returning from south to north during the mid and late afternoon hours with morning southwest winds of 5 to 15 mph turning more southerly. It will be a mostly sunny morning with increasing cirrus during the afternoon. Then a wall of water via cloud cover (PWAT rising from .5" now over the Delmarva to 2" by 00z this evening) starts advancing nwd through the Delmarva late afternoon with showers, some heavy with possible FLS nuisance flooding, possibly also a thunderstorm. Was conservative on the northward advance. May need to update timing in the 630 AM ESTF. Max temps...again well above normal...ranging from 7F above normal south to as much as 16F above normal north where lower 90s expected again in NNJ and ne PA. Otherwise mid to upper 80s Delmarva...PHL 88, to around 90-93F along and north of I-78 (Lehigh Valley ewd through WRI-MMU). NAM BL temps have been increasing on recent cycles. These max temps for the fourth consecutive day are significantly above all other avbl MOS guidance/blends/bc adjusts (except some ecmwf localized guidance). The heat index will again rise to between 90-95F I-78 north and will SPS at 530 AM. This also should mean a 4th consec day of 90F at KABE and KWRI and a possible official heat wave (see definition in CLI section) for KRDG which is on the margin for 90F. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... Deep layer moisture, PWAT up to 2 inches, in part from Tropical Storm Bonnie is forecast to move across the area with widespread showers and isolated T-storms. General lift is aided as represented by the rrq of an upper level 80 kt 250MB jet core...over southern Ontario. A sfc boundary will focus the heaviest rain, in the light northerly flow along a forming sfc wind shift. A 30 kt 700mb speed max may initially focus heaviest rain near Chesapeake Bay-E Pa Sunday evening, then it appears the 850 southerly inflow will shift the axis of excessive rain potential somewhere just to the east of I95 by Monday morning. Potential exists for a couple of narrow swaths of 3-4" rains by 12z Monday...more details possible late today. no flash flood watch attm but am concerned about the I95 corridor in the 03z-12z time frame. Mild nighttime mins...10 to 15F above normal. Light southerly wind with a shift to northerly near a developing sfc convergence zone around or just east of I-95 late tonight. Will probably post daily record rainfalls as believed appropriate in the CLI section by 5 am. && .LONG TERM /MONDAY THROUGH SATURDAY/... Moisture from Tropical Storm Bonnie will push northward and we will continue to see showers and some thunderstorms on Monday. PWATS remain high, around 2 inches in some areas, so expect some of the showers to be fairly heavy, especially during Monday morning. Memorial Day continues to look like a washout across the region. The pops will start to drop from northwest to southeast but it looks like we will continue to see some showers continuing into Monday evening. Rain will linger longest over our southeastern areas, likely ending by late Monday night. With heavy rain possible, we will need to monitor the flash flooding potential. As mentioned before, the PWATS are 1.5 to just over 2 inches across the region. Some heavy showers and thunderstorms could drop one to two inches of rain with locally higher amounts possible. We will continue to mention the flash flood threat in the HWO. The guidance shows some pretty decent differences in how the remnants of Bonnie are handled. The GFS is a bit dryer and keeps the low to the south of the area and eventually dissipates it near the Carolina coast. The ECMWF keeps the low spinning over the Carolina coast with a gradual push to the northeast, moving it up the Mid- Atlantic coast through the week. The ECMWF solution would keep us in a cloudier set up and a wetter pattern with the chance for the remnant moisture to make its way into the region for Tuesday through Friday, with the best chances across our south and east zones. With the uncertainty of where and when Bonnie will track north/northeast, we have upped the cloud cover through the week and introduced some slight chance/low chance pops. Again, the best chances will remain across southern New Jersey and the Delmarva. A low pressure system will arrive from the west and drag a cold front through the region over the weekend. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 12z...Generally VFR. Light south wind. Today after 12z...VFR with a south-southwest wind gusty to 15 kt midday. Then MVFR or IFR conds in showers/iso tstms spread north through the Delmarva into southern NJ and the Philadelphia late this afternoon-evening. Please see the TAFS for more timing details. No thunder in the TAF since uncertain where best chance of thunder and whether much if any thunder occurs at night in tropical pwat. Tonight...MVFR to IFR conditions in low clouds, fog, and heavy showers, maybe isolated tstms. Sustained winds mostly under 10 kt with a convergence zone of south wind along the coast while a light north wind should develop near I-95 late at night. OUTLOOK... Monday...MVFR to IFR conditions in rain, fog, and thunderstorms affect the terminals. Conditions may drop below IFR at times due to heavy rain. Light winds early will become south to southwest around 10 knots or less. Higher gusts possible in showers and thunderstorms. Tuesday through Thursday...Mainly VFR conditions expected. Westerly winds on Tuesday will become more easterly on Wednesday and Thursday. Winds will generally be around 10 knots or less with gusts up to 15 knots. && .MARINE...
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No marine headlines are anticipated through tonight although dense fog may become a marine hazard toward dawn Monday on the Atlantic waters where ssts are near 60F and the dewpoints should be rising above the SST Monday morning. OUTLOOK... Monday...Sub-SCA conditions are expected on the area waters. Fog is possible in the early morning and again overnight. Waves may start to build in response to Tropical Storm Bonnie but we expect them to remain below 5 feet at this time. However, confidence is not high that we will see much affect until Bonnie moves north of the Carolinas. Tuesday through Thursday...Sub-SCA conditions are expected on the area waters. RIP CURRENTS: Posted a low risk today. This may need an upgrade this afternoon dependent on whether a stronger southerly wind develops than now indicated. We are moving into the high tide cycle this afternoon so that appears favorable for reducing the frequency and coverage of rip current formation. relatively cold water temperatures along the north and central NJ coast probably also minimizes risk taking. However, it will be quite warm by noon with large beach crowds anticipated. Swimming within the watchful eyes of life guards ensures a safe and fun beach experience. This mornings LBI beach report is posted.
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&& .HYDROLOGY... There is potential for heavy rain and localized flooding from tonight through Monday. This is due to an influx of tropical moisture from Tropical Storm Bonnie. PWATs are forecast to be near 2 inches, well above normal, especially for late May. Depending on how the heavier showers and t-storms set up, isolated locations could easily receive 4 inches or more of rainfall. This may result in localized flooding. The potential for heavy rain was added to the forecast. For now please use a combination of the WPC and MARFC qpf fcsts. as it stands now...general 1-2" is expected across the forecast area with isolated 4+, mainly between 21z today and 21z Monday. && .CLIMATE... Daily record rainfalls that have a chance of exceedance, if heavy showers can persist for 1 to 2 hours. Note, splitting amounts between two days lowers the chance of occurrence. We wont look at monthly rankings until sometime Monday (if time) but there is a good chance a couple of locations will increase to a top 10 ranking for the month of May. Today KGED 1.62 in 1990 por 1948 Monday ACY 3.07 1984 por 1874 PHL 1.74 1908 por 1872 ILG 1.10 1983 por 1894 ABE 1.68 1968 por 1922 TTN 1.62 1912 por 1865 GED 2.04 1984 por 1948 RDG 2.92 1904 por 1869 (highly unlikely to approach a record daily rainfall) MPO 1.86 1990 POR 1901 Record max temps today appear less vulnerable today than yesterday with only Mount Poconos 89F in 1911 being threatened. Right now we KMPO projected for 87F. You probably saw the near records yesterday at KMPO (-1), KABE (-1), KRDG (-2). Daytime max temp guidance continues to be significantly under forecast across PA/NJ for the past 3 days, especially by Super and National blends. We are better off in these sunny non-marine influenced summerlike regimes using the latest operational guidance as a starting point and modifying this upward by adding 4F to the 18z ECMWF 2m temps. The GFS 2m temperature fcsts have also been biased low, in part because of too much low lvl moisture. Also a note about heat waves: here in the northeast USA, we tend to stay close to the AMS glossary of Meteorology definition of a heat wave and as follows: In 1900, A.T Burrows more rigidly defined a `hot wave` as a spell of three or more days on each of which the maximum shade temperature reaches or exceeds 90F. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Meola Near Term...Drag Short Term...Drag Long Term...Meola Aviation...Drag/Meola Marine...Drag/Meola 517A Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.