Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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375 FXUS61 KPHI 292331 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 731 PM EDT SUN MAY 29 2016 .SYNOPSIS... Tropical moisture will continue to track northward across our area tonight through Monday. A cold front will then cross the area Tuesday followed by high pressure for the middle of the week. A cold front, attached to low pressure moving across eastern Canada, will slide across the Mid Atlantic region early next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... An upper air analysis showed a ridge axis over the area and it extends into Southeastern Canada. An upper-level jet was positioned from Southeastern Canada to the Lower Ohio Valley. Meanwhile at the surface, a cold front was draped from the Great Lakes to the Tennessee Valley. A plume of tropical moisture continues to surge northward, which is tied to Tropical Depression Bonnie that is located near coastal South Carolina. The forecast challenge is the extent of showers and the intensity. The ongoing showers lifting northward from the Delmarva, southwestern New Jersey into southeastern Pennsylvania appear to be tied to the leading edge of the deeper moisture surge. This moisture surge initially was feeding off of a pocket of instability across the Delmarva however this decreased northward due earlier to lower surface dew points. The dew points are on the rise though from south to north as this initial moisture surge arrives. The PW values are forecast to rise to about 2 inches through the night and the forecast soundings show deep moisture along with high freezing levels. This would indicate that showers and especially stronger embedded cells can be efficient rainfall producers due to warm rain processes. This however may temper the thunder chance. The model guidance overall shows our area becoming better positioned into the right entrance region of a 250 MB jet overnight. This is when better forcing should then arrive and a band of heavy showers could nearly train across some areas. The idea of locally heavy rain remains, although the guidance has been battling where this actually occurs. Given the south to southeast inflow, near and west of I-95 may end up being the areas that get the heaviest rain through the night before it starts to shift eastward. There remains some meager instability in the forecast soundings therefore some thunder can occur, however we did tone down the mention given the rather moist soundings. The temperature and dew point grids were adjusted using the latest obs, then the lamp/lav guidance was blended in. Significant adjustments were needed earlier to capture the much lower dew points across portions of the central to northern areas and increasing values across the south. The pops were adjusted based on radar trends and then with some assistance by the HRRR model. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... With the slower timing, it now appears that there will be more precip on Monday, than earlier fcst. Periods of rain now look to continue for a good portion of the day, especially for srn and ern areas. Nrn and wrn areas cud see precip end durg the aftn, with srn and ern sections most likely holding onto rain thru at least sunset. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... The remaining showers from the back edge of the system affecting the area during the short term will be moving offshore Monday evening. Pops will then decrease below slight chc by dawn Tuesday. Except for some fog overnight...fair weather is expected. Low temperatures will be in the low to mid 60s. High pressure will build in from the north Tuesday and remain into Wednesday night. Dry weather is expected much of the time with above normal temperatures in most areas. Highs both days will be in the low/mid 80s in most areas with some 70s for highs along the shore and the higher elevations well to the north. A few scattered showers may creep into the Delmarva areas later Wed as the edge of moisture associated with what will be left of Tropical Depression Bonnie will be moving south/east of the area. The pops across srn Delaware at these times will only be 20-25 pct at most. The tropical moisture and an advancing h5 trough will be setting up across our area towards the end of next week. This will bring some unsettled conditions with typical late spring/early summer showers/tstms to the area. Pops will be mostly in the chc range for now with details yet to be specific with regards to timing and locations. Temperatures during this period will be close to normal. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR ceilings lowering to MVFR through 06z from south to north, then lowering to IFR overall. This timing will especially be determined on the extent of the showers and intensity. The visibility will lower to MVFR and IFR at times especially during heavier showers. Some thunder should occur through the night, however the areal coverage looks low and therefore it was not included in the TAFs. Southerly winds less than 10 knots, becoming light and variable at some terminals. Monday...MVFR/IFR conditions in the morning along with times of heavy showers and some thunder, then the main area of showers shift toward the coast in the afternoon. The lower conditions last the longest at KACY to KMIV, with possible improvement in the afternoon to VFR at KABE and KRDG. South to southwest winds mostly in the 5-10 knot range. OUTLOOK... Monday night...Showers end from w to E, VFR conditions return. Patchy fog possible late however. Tue-Wed night...Mostly VFR. Few showers psbl far South Wed. Thu- Fri...Mostly vfr but lower conditions psbl in sct showers/tstms. && .MARINE... Wind may gust in the 15 to 20 kt range overnight before decreasing to around 10 kts Monday aftn. Seas are expected to increase and could reach nr 5 ft on the srn waters. Due to confidence being lower than average, wind below criteria and ww possibly being overdone, will not issue sca attm. There is some lcl dense fog in the nr shore waters. If the rain does not improve the visibilities then a dense fog advisory for a portion of the marine area may be needed. OUTLOOK... Sub-sca conditions expected most of the period. Seas on the ocean may reach close to 5 ft Thu night...but low confid in this attm. Sct tstms with higher winds/seas possible Fri. && .HYDROLOGY... Locally heavy rain is expected through the night and Monday which may result in localized flooding. This is due to an influx of tropical moisture from Tropical Depression Bonnie, which increases the PWATs to near 2 inches. Depending on where the heavier showers and some t-storms set up, isolated locations may possibly see 3 inches of rain. While the threat of localized flooding is there, the areal extent is more uncertain and therefore we held off on a flash flood watch at this time. && .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 a single day record event occurrence. There is a good chance several long term climate sites will increase to a top 10 ranking for the month of May in our CWA. PHL ACY AND ILG only need an inch of rain these last 3 days of the month to rank as a top 10 wettest month of May. 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 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse/O`Hara Near Term...Gorse Short Term...Nierenberg Long Term...O`Hara Aviation...Gorse/O`Hara Marine...Nierenberg/O`Hara Hydrology... Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.