Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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814 FXUS61 KPHI 290731 CCA AFDPHI Area Forecast Discussion...CORRECTED National Weather Service Mount Holly NJ 331 AM EDT SUN MAY 29 2016 .SYNOPSIS...
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High pressure will continue to push further off the Middle Atlantic coast 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.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1230 AM ESTF: little change to the overnight forecast grids. Temps and dewpoints are following the guidance from 24 hours ago...tending to run cooler than 24 hours ago as a wedge of very dry aloft slides nwd over our fcst area. fair skies with a light south wind. Patchy dense fog possible along and N of I-80 where ydy afternoons heavy rains have left a moist near sfc layer. Today...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 starts advancing nwd through the delmarva late afternoon with showers, some heavy and possibly a thunderstorm. More details on timing will be attempted in the 330 am AFD. Max temps...again well above normal...10-15F...ranging from the mid to upper 80s Delmarva...PHL 88, to around 90-91F along and north of I-78 (Lehigh Valley ewd through WRI-MMU). NAM BL temps have been increasing on recent cycles. && .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 an upper level 250MB jet...rrq of the 90kt core over southern Ontario. A sfc boundary will focus the heaviest rain, usually found in the lift region just 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, 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 swat5hs of 1-3" rains by 12z Monday...more details possible at 330 am but more likely delayed til the Sunday afternoon-evening assessments. Mild nighttime mins...well above normal. Light southerly wind with a wshift to north near a developing sfc convergence zone around or just east of I-95 late at night. Will probably post daily record rainfalls as believed appropriate in the CLI section by 5 am Sunday. && .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 /08Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 12z...Generally VFR. small chc MVFR vsby toward 10z KRDG/KABE. 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 during the afternoon. Please see the TAFS for more timing details. Tonight...MVFR to IFR conditions in low clouds, fog, and heavy showers/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... No marine headlines are anticipated through tonight although fog may become a marine hazard toward dawn Monday on the atlantic waters. 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. && .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, some locations could receive 2 inches or more of rainfall. This may result in localized flooding. The potential for heavy rain was added to the forecast. && .CLIMATE... Once our overnight assessment is completed, we`ll post around 5 AM, any daily record rainfall considered for exceeding. This will also impact monthly totals, probably pushing some of our locations into a top ten wettest month of May. 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 op guidance as a starting point and modifying this upward by adding 4F to the 18z ECMWF 2m temps. The GFS 2m temp fcsts have also been biased low, think in part to 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 Hydrology... Climate...

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