Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 200119 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 919 PM EDT Thu Apr 19 2018 .SYNOPSIS... Low pressure will move further offshore and into the Canadian Maritimes tonight. High pressure will build in from the west through Friday and remain in the area through the weekend before sliding offshore on Monday. Low pressure developing over the southeastern United States will move up the Mid Atlantic coast, affecting our area through the mid week period. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Low pressure will continue to move into the Canadian Maritimes tonight, while high pressure moves into the Great Lakes region. This will keep our are under a tight pressure gradient and steady northwest flow overnight. A steady NW cyclonic flow continues around the departing upper low. Clouds are breaking up across SE PA and parts of NJ this evening. The clouds will hang on the longest N/W where some showers (rain or snow) will continue into the early overnight. Few changes were made to the pop/weather grids, since things appear to be working out fairly well. Some minor adjustments to temperatures and winds were made however. Temperatures fall well below normal again tonight. Portions of eastern Pennsylvania and northeastern Maryland where the growing season has started have the potential for overnight/Friday morning lows to fall to freezing or lower. Therefore we have issued a Freeze Warning for these areas. Elsewhere across other portions where the growing season has started, we do not expect temperatures to fall to freezing or lower at this time except a few isolated spots; such as some sheltered areas in the Pine Barrens. Farther north across northeast Pennsylvania and northern New Jersey, temperatures are expected to fall to freezing or lower, but their growing season was pushed back a couple of more days. We do not expect much frost to develop overnight, although temperatures will likely be low enough that it would form on other days. However, we expect there to remain a breeze overnight around 5- 10 mph and it may be too dry for frost to form. So no Frost Advisory was issued at this time. We are expecting a steady NW winds overnight with some gustiness at times, perhaps up to 20 mph. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Low pressure will continue to linger near the Canadian Maritimes on Friday, while high pressure over the Great Lakes tries to build eastward. The high will not make it into the area through the daytime hours, so this will keep a steady northwest flow across the area through the day. While there could be some cloud cover develop during the day Friday, we do not expect any precipitation as there will be dry air in place as evident from PW values near a quarter to a third of an inch. Winds will continue to be gusty out of the northwest with gusts 20 to 25 mph, with occasional gusts up to 30 mph at times possible. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Friday night through Monday...High pressure will be building into the region Friday night and overspreading the area through the weekend. The high remains across the region through Sunday before sliding offshore Monday afternoon/evening. Friday night will be the start of a nice weekend across the region. Skies will clear and winds will become light which will promote good radiational cooling. Temperatures are expected to drop down into the 30s across much of the region, falling below freezing across the Lehigh Valley, southern Poconos, and northwest New Jersey. Some near freezing temperatures will be possible in parts of Berks, Chester, upper Montgomery, and upper Bucks counties, as well as parts of north central New Jersey. With the high in control, we should see some nice weather across the region, lasting through the weekend. Dry and warming conditions are expected. Winds will be fairly light through this period and we should see plenty of sunshine. Highs on Saturday will be in the upper 40s across the higher elevations of the southern Poconos and northwest New Jersey and into the mid to upper 50s across the rest of the region. Areas along the coast will remain slightly cooler and in the low to mid 50s. Sunday will be fairly similar to Saturday but the air mass will modify a bit and we should maximum temperatures a few degrees warmer than on Saturday. Tuesday through Thursday...A low pressure system will move across the Mississippi Valley and into the southeastern United States early next week. As the low pushes towards the coast, it starts to move northward towards the Mid-Atlantic states. While the models agree that there is some form of a coastal low develops and impacts our area, there are marked timing and phasing differences that lead to a low confidence forecast at this time. The system will bear watching as it will have good moisture associated with it and the potential for some heavy rain will exist. Strong onshore flow could also bring some coastal flooding concerns and will also need to be monitored. Still a long way out and plenty of time to see how the models come together on this system over the coming week. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR most areas, few lower CIGS/VSBYS in snow showers near KMPO. Clouds diminishing over most areas overnight. NW winds with gusts could remain through the night for many locations, although the speeds will diminish some. Friday...VFR conditions are expected on Friday, with scattered clouds possibly developing around 4,000-5,000 feet during the day. Winds will remain gusty out of the northwest, with gusts reaching 20- 25 knots. Outlook... Friday night...VFR conditions expected. Northwest winds around 5 to 20 knots...gradually decreasing overnight. High confidence. Saturday...VFR conditions expected. Northwest winds around 10 knots. High confidence. Sunday...VFR conditions expected. Light winds. High confidence. Monday...VFR conditions expected. Light winds becoming northeast to east around 5 to 10 knots...becoming southeast by Monday afternoon/evening. Moderate confidence. Tuesday...Mainly VFR conditions expected. East to southeast winds around 10 to 15 knots. Increasing cloudiness through the day. Moderate confidence. && .MARINE... Gale Warning remains in effect for the Delaware Bay and the southern New Jersey and Delaware Atlantic coastal waters for the overnight hours. Wind guts around 35 knots are occurring this evening and will remain into the overnight. A Small Craft Advisory remain in effect for the northern and central New Jersey coastal waters. Once the Gale Warning ends Friday morning, it will likely need to be replaced with a Small Craft Advisory. Winds will likely diminish during the afternoon hours Friday, so the expiration time was left at noon. Outlook... Friday night through Monday....Sub-advisory conditions are expected on the the area waters. Tuesday...Seas will increase through Tuesday in advance of an approaching coastal low pressure system. Winds will increase later Tuesday. A Small Craft Advisory will likely be needed towards Tuesday afternoon/evening. && .FIRE WEATHER... Minimum RH values on Friday are forecast to be in the low 30s, with most places 35-40 percent. With the rainfall and clouds today, fuels likely did not dry out much. Even though it will be quite windy Friday, with the relatively moderate RH values and non critical fuels expected, we do not anticipate enhanced fire weather concerns Friday. If the RH values drop, we may coordinate with our state partners to discuss the need for any enhanced statements. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Freeze Warning from 2 AM to 8 AM EDT Friday for PAZ060-101>103. NJ...None. DE...None. MD...Freeze Warning from 2 AM to 8 AM EDT Friday for MDZ008. MARINE...Small Craft Advisory until noon EDT Friday for ANZ450>452. Gale Warning until 8 AM EDT Friday for ANZ430-431-453>455. && $$ Synopsis...Meola Near Term...Robertson/PO Short Term...Robertson Long Term...Meola Aviation...Robertson/Meola/PO Marine...Robertson/Meola/PO Fire Weather...Robertson is the U.S. government's official web portal to all federal, state and local government web resources and services.