Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KPHI 250138 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 938 PM EDT Mon Apr 24 2017 .SYNOPSIS... Low pressure over the Southeast States will slowly lift north along the Atlantic Seaboard tonight through Tuesday night, then track east on Wednesday. High pressure builds along the coast on Thursday. A cold front approaches on Friday, but may become stationary north of our area into the weekend as high pressure becomes entrenched over the western Atlantic Ocean. A warm front lifts north through the area for early next week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
-- Changed Discussion --
An upper air analysis early this evening shows a closed low centered over South Carolina and Georgia, and a narrow ridge axis is over our region. There are areas of 850 mb warm air advection to the east and north of the closed low. The main short wave energy is still to our south, and therefore mostly just isentropic lift is occurring in our area given the uptick in warm air advection aloft. As we go through the overnight hours, the low-level warm air advection is forecast to increase as a southeasterly low-level jet of nearly 50 knots approaches from offshore. This should continue to support waves of showers through the overnight, although coverage may be less. Some elevated instability has been noted across the far southern zones this evening, however it appears that any lightning remains to our south and/or offshore. The PoPs were lowered some as the coverage looks a bit less, however some showers are expected through the night. The majority of the showers have been on the lighter side thus far. The dry low-level air up across the north is gradually eroding as dew points have increased some, however there is still a pocket of lower dew points remaining around the Philadelphia metro area. The hourly temperature, dew point and wind grids were adjusted based on the latest observations, then the LAMP/LAV guidance was blended in for the next few hours. Temperatures should be more uniform across the area given the northeasterly flow off the cooler ocean along with some showers. Low temperatures were lowered some across the southern zones with this update as current temperatures are very near previous forecast lows.
-- End Changed Discussion --
&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Closed mid-level low lifting northward along the eastern seaboard will entrain some tropical moisture as it does so. There is model disagreement between the NAM/GFS, with most of the international models supporting the wetter NAM solution. This brings a strong easterly 850 hPa jet of 50 to 60 knots across the region, which will lead to heavy downpours. Stability indices also decrease, as a plume of steep mid-level lapse rates promotes elevated instability. As a result, we have inserted thunder into the forecast across much of the area. Precip amounts of 1-2 inches are expected, especially southeast of the NJ Turnpike/I-95, with resulting urban and poor drainage flooding the biggest concern. High temperatures will be in the 50s over PA and NJ, with low to mid 60s in Delmarva. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... By Tuesday evening, low pressure should be centered just over the Delmarva Peninsula. Swaths of moderate to locally heavy rain will continue to track northeast along the coast through Tuesday evening, gradually tapering off from southwest to northeast as the low slowly tracks along the NJ coast. Wednesday afternoon, the surface low will be just east of the region, moving into NYC and western Long Island. Although the bulk of the rainfall will be tapering off, the upper level low will be just to the west of the surface low. This will keep at least some showers in the region through Wednesday, but for now, will keep PoPs capped at chance through the morning, diminishing to slight chance as the afternoon progresses. Upper level ridging will build into western NY/PA Wednesday night as weak high pressure builds towards the East Coast. With an abundance of moisture over the area due to the rainfall, patchy fog is possible Wednesday night as skies clear out and winds become nearly calm. That ridge builds east on Thursday, and although there will be an onshore component to the winds, temperatures will rise into the 70s for much of the area, and possibly into the lower 80s over the Delmarva. Right along the coasts, however, highs should stay in the 60s. For the end of this week and into the start of the new week, Bermuda high pressure looks to become entrenched over the western Atlantic waters. There is a cold front that will approach on Friday, but the strength of the offshore high should be enough to keep the front from making too much eastern headway. Southwest flow develops ahead of this front, and this will allow a very warm and humid airmass to spread into the Mid- Atlantic and Northeast. With H8 temps between 14C-16C, highs on Friday will climb into the low to mid 80s for most of the area, although the Poconos will top off in the mid 70s, and coastal NJ/DE will remain in the 70s due to the sea breeze. That frontal boundary will make a slow eastward progression over the weekend as the high remains over the western Atlantic waters. Conditions remain warm and humid into the weekend with highs generally in the 70s and 80s. Although the main system will remain to the west, several weak upper level shortwaves will spin off ahead of the front, and with a warm and humid airmass in place, there should be enough instability to touch off some showers and thunderstorms over the weekend and into the new week. For now, will keep PoPs capped at slight chance/chance. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR conditions lower to MVFR/IFR late this evening and especially overnight. Some showers will move through, with the intensity mostly on the lighter side. Northeasterly winds in the 5- 15 knot range overall, with local gusts at times to around 20 knots especially closer to the coast. Tuesday...IFR conditions, with LIFR at times, due to low clouds and periods of rain. Some of the rain can be heavy at times, allowing for times of even lower visibility. Northeast to east winds around 15 knots with gusts to around 25 knots. The highest winds are expected to from about PHL south and east. OUTLOOK... Tuesday night...IFR and lower conditions in rain. E-NE winds 10-15 KT with gusts up to 25 KT, diminishing towards daybreak. Wednesday...Lingering showers through Wednesday afternoon with MVFR/IFR conditions. Improvement expected late. NE winds become N at 5-10 KT. Wednesday night through Thursday morning...IFR and lower conditions possible in fog/stratus. Thursday afternoon...VFR. SE winds 5-10 KT. Friday through Saturday...VFR. SW winds 5-10 KT.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
A Gale Warning is in effect for all the coastal waters expect upper Delaware Bay where a SCA remains in effect. The Gale Warning is from 10Z to 22Z Tuesday, and the SCA is through 10Z Wednesday. The strongest east winds are expected from late morning into the afternoon on Tuesday. Seas will build and range from 2 to 4 feet on Delaware Bay and 7 to 10 feet on the ocean. OUTLOOK... Tuesday night through Wednesday...Gale force winds will diminish to 25-30 KT Tuesday evening, and then winds diminish to less than 20 KT by daybreak Wednesday. However, seas on the ocean will remain elevated at 7-10 KT, gradually diminishing to 4-6 FT by late Wednesday. Wednesday night through Friday...Lingering 3-5 ft seas on the ocean. Saturday...Sub-SCA conditions.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING...
-- Changed Discussion --
The cumulative effects of the onshore flow into Tuesday night and the approaching new moon will likely result in minor coastal flooding. The minor flooding is anticipated along the New Jersey shore, at the Delaware beaches and along Delaware Bay and on the far lower part of the Delaware River around Tuesday evening`s high tide. The minor flooding should affect the back bays and the estuaries, as well. We have issued a Coastal Flood Advisory for those areas for Tuesday evening. The surge on top of the base astronomical tides is expected to be a foot to a foot and a half at that time. It appears as though the tidal Delaware River above the Commodore Barry Bridge area may just reach the minor flooding threshold. However, the impacts should not be widespread enough there to warrant a Coastal Flood Advisory. We are not anticipating any coastal flooding along the upper eastern shore of Chesapeake Bay.
-- End Changed Discussion --
&& .PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None. NJ...Coastal Flood Advisory from 6 PM Tuesday to midnight EDT Tuesday night for NJZ012>014-020>027. Coastal Flood Advisory from 9 PM Tuesday to 1 AM EDT Wednesday for NJZ016. DE...Coastal Flood Advisory from 6 PM Tuesday to midnight EDT Tuesday night for DEZ002>004. Coastal Flood Advisory from 9 PM Tuesday to 1 AM EDT Wednesday for DEZ001. MD...None. MARINE...Gale Warning from 6 AM to 6 PM EDT Tuesday for ANZ431-450>455. Small Craft Advisory until 6 AM EDT Wednesday for ANZ430.
-- End Changed Discussion --
&& $$ Synopsis...MPS Near Term...Gorse Short Term...Franck Long Term...MPS Aviation...Franck/Gorse/MPS Marine...Franck/MPS Tides/Coastal Flooding...Iovino

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.