067 FXUS61 KPHI 121803 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 203 PM EDT Fri Apr 12 2019 .SYNOPSIS... A warm front will lift across the area today, before a cold front moves across the area tonight into Saturday morning. This front will stall near the area Saturday, before lifting northward as a warm front Saturday night. This warm front will lift across the area Sunday as an area of low pressure moves across the Midwest region. As this low moves into the northeastern states Sunday night into Monday, a second warm front may lift across the area Sunday night, before a cold front moves across the east coast early Monday. A warm front will develop to our west on Tuesday, before moving into the Mid Atlantic region by Tuesday night and stalling near the area through the middle of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 915 AM Update...Warm front about to push north through the area and behind it some partial clearing has been occuring so we reduced cloud cover slightly for today. Overall, still expecting a partly to mostly cloudy day across the area but there will be periods of at least partial sunshine, especially near and south of the Mason-Dixon line. Previous Discussion...Seems as if some drier air got hung up along and north of the Fall Line, as there is a pocket of lower dewpoints, generally in the 20s, in the Lehigh Valley, southern Poconos, and northern New Jersey. As a result, the fog and stratus has not quite developed up north just yet. Low level moisture continues to lift into the region from the south, so there may still be some low stratus/light rain/drizzle. For areas to the south, some low stratus still possible this morning. Otherwise, surface high pressure centered about 100 miles south and east of Nantucket Island will continue to drift east into the western Atlantic today. Meanwhile, low pressure over the Midwest will lift to the northeast and will be over Lake Superior by late afternoon/early evening. Out ahead of that low, a warm front currently extends from the Ohio Valley, across the Appalachians, and just south of the Delmarva Peninsula. That front will lift north throughout the day, likely not clearing the southern Poconos until late afternoon/early evening. A trailing cold front behind the low will move through the Great Lakes and Ohio Valley late in the day, and a pre-frontal trough develops out ahead of that front, and moves through western Pennsylvania and western New York, and will be into central Pennsylvania and central New York by late afternoon. In terms of sensible weather today, as the warm front lifts north, skies partially clear out over far southern zones. The clearing skies and warming of the low levels of the atmosphere should help allow that warm front to push north. Quite warm and fairly humid with surface dewpoints rising into the 50s throughout. Highs generally in the 60s across much of the region, and in the lower 70s along the I-95 corridor from Trenton to Philadelphia, and across Delmarva. Along the coasts, temperatures will be slightly cooler, generally in the low 60s, due to southerly winds and ocean temps in the 40s. With that warm and humid airmass overrunning the colder ocean waters, patchy fog will develop along the coasts throughout the day. A tightening pressure gradient will result in southerly winds 15-20 mph with gusts to 25 mph. Showers ahead of the pre-frontal trough may begin to move into far western zones late in the afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... Showers and scattered thunderstorms develop this evening as a pre- frontal trough moves through the region. Meanwhile, low pressure passes north of the region, and a trailing cold front will slowly work its way through the region late in the overnight hours. The risk for thunderstorms will come to an end after midnight as the atmosphere stabilizes, but showers, possibly producing heavy rainfall, will continue through the early morning hours of Saturday. PWATs will be around 1.5-1.75 inches, and there may be localized poor drainage flooding. With abundant low level moisture in place, patchy fog likely to develop as well. Lows tonight generally in the 50s. && .LONG TERM /SATURDAY THROUGH FRIDAY/... The highlight of the long term forecast will be the strong storm system expected to affect the east coast Sunday night into Monday morning. The cold front that will be moving across the area tonight will likely stall near the area during the day Saturday. Showers will continue to push southward through the day, but eastern New Jersey and central/southern Delaware and Maryland will keep a chance of showers through the day Saturday. This front is expected to lift back northward as a warm front overnight Saturday as an area of low pressure moves across the Midwest region, and continue to slowly lift across the area during the day Sunday. This may be a slow process with how fast this front lifts across the area, but with increasing moisture and lift associate with several short waves riding over the frontal boundary, there will be a chance of showers Saturday night through Sunday. As mentioned before, the main concern with the forecast is overnight Sunday into Monday morning. As the low pressure moves into the northeastern states overnight Sunday, a secondary warm front may move across the area, before a cold front follows behind it. As the warm front lifts across the area, PW values increase across the area to 1.50-1.75 inches. Enhanced lift associated with additional short waves/vorticity impulses overriding the warm front will likely lead to a period of moderate to heavy rainfall. There is not a significant amount of instability forecast at this time, however, there could be enough to help lead to areas of convection, which may lead to additional enhancement of heavy rainfall. At least poor drainage flooding is possible with any heavy rainfall. If any thunderstorms do develop, there could also produce some strong/gusty winds as well. The cold front is forecast to make its way into the area around daybreak Monday, then a secondary front/surface trough will likely cross the area during the day Monday. The heavier showers will likely be continuing through the morning hours Monday then move offshore as the initial cold front moves off the coast. As the secondary front/surface trough moves across the area during the day, additional showers will be possible. As the winds turn west to northwesterly, they will become gusty during the afternoon hours, with gusts reaching at least 25-30 mph, with potentially higher peak gusts. These strong winds will likely continue into the evening hours Monday, before relaxing some overnight as the winds aloft weaken. Any showers are expected to be ending by the evening hours, and a dry forecast is expected overnight. Tuesday is expected to continue with gusty winds as a west to northwest flow remains across the area. However, there is some indication that a frontal boundary will develop to our west during the day Tuesday, before sliding toward the Mid Atlantic later Tuesday into Tuesday night. If this happens, there will be a chance of showers starting later Tuesday into Tuesday night. This frontal boundary may stall near the area through Wednesday and Thursday. If this happens, periods of clouds, along with a chance of showers will remain across the area. These showers are not expected to be heavy. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This afternoon...Mainly low VFR with southerly winds 10-15 gusting 20-25 knots. Tonight...Showers developing with conditions lowering to MVFR through the evening and IFR overnight. There will also be some embedded thunder with the best chances of storm occuring near KRDG. There will also be some patchy fog overnight. South winds 10-15 kt with gusts up to 20 kt, becoming southwest around 10 kt late. Saturday...Conditions improving behind a cold front as showers end. Most sites should be VFR by the end of the TAF period with the possible exceptions being KMIV and KACY which should improve to VFR by around mid afternoon. SW winds 5-10 knots. OUTLOOK... Saturday night...MVFR and IFR conditions likely to develop overnight with stratus and fog. Sunday...Conditions may improve some during the day, however, MVFR ceilings may remain through the day. There will also be an increase chance of showers and thunderstorms through the day. Sunday night...Showers and possible thunderstorms expected overnight with will lead to MVFR and IFR conditions. Winds may become gusty at times overnight Sunday with gusts 20-25 knots possible out of the south. Monday...Conditions improve to VFR during the day, however, a chance of showers remains through the day. Winds shift to west- northwest and become gusty 20-30 knots later in the day. Monday night...VFR conditions and gusty winds continue with west to northwest winds gusting to 20-30 knots early, diminishing overnight. Tuesday...VFR conditions continue. Gusty west to northwest winds around 20 knots possible. && .MARINE... Today...A warm front lifts north through the day. South winds 15-20 kt with gusts up to 25 kt this afternoon, and seas build to 5 ft late. Small Craft Advisory in effect for all waters. Tonight...Showers and scattered thunderstorms this evening, then showers through the overnight. VSBY restrictions in fog as well. Although winds diminish late, seas on the ocean remain elevated above 5 feet. SCA ends on DE Bay by daybreak Saturday. OUTLOOK... Saturday...Small Craft Advisory continues on the ocean as seas expected to remain 5-6 feet through the day. Saturday night...Conditions expected to drop below advisory levels. Sunday...Sub Small Craft Advisory levels expected most of the day, however, winds may begin to increase later in the day Sunday. Sunday night...Small Craft Advisory level winds are likely to increase overnight Sunday, while seas build as well. Monday...Small Craft Advisory conditions likely to continue with building seas and gusty winds. Monday night...Winds may increase to gale force for a period overnight Monday, otherwise, Small Craft Advisory conditions continue. Tuesday...Small Craft Advisory conditions possible early Tuesday, before lowering through the day. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ450>455. Small Craft Advisory until 6 AM EDT Saturday for ANZ430-431. && $$ Synopsis...Robertson Near Term...Fitzsimmons/MPS Short Term...MPS Long Term...Robertson Aviation...Robertson/MPS Marine...Fitzsimmons/Robertson/MPS