Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 271350 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ Issued by National Weather Service BALTIMORE MD/WASHINGTON DC 950 AM EDT Thu Apr 27 2017 .SYNOPSIS... A cold front will move across the area tonight into Friday morning. A backdoor cold front will move across the area Saturday into Saturday night. This front will remain to our south on Sunday, then return as a warm front on Sunday night. Another cold front is expected on Monday night, with a secondary front or surface trough Tuesday. Another cold front is possible Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Low continues to spin away from the region this morning, with mid/upper level ridging moving overhead ahead of the next system ejecting through the Great Lakes that will affect the region tonight. Lingering low level moisture and low level southeasterly flow has led to the continuation of low clouds from the Philadelphia metro area northeastward and along the shorelines. There is also still some lingering fog in the Poconos this morning. Gradual improvement is expected through the morning hours and into the afternoon, especially across SE PA, central and southern NJ, and DE, with mostly sunny skies already being observed SW of the Philly metro as of 930 am. NE PA and Northern NJ will be the toughest to get sunshine. Highs today in the 70s for most locations, within a few degrees plus/minus of 80F for Philly SW-ward, and stuck in the 60s along the immediate shoreline with continued SE flow.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... The main story tonight will be the cold front expected to move through the region. With the center of the associated surface low (in Central Canada) slowly propagating north, the front is not expected to progress east very quickly. Expect that most precipitation ahead of and with the front will be showers. However, model soundings do show elevated instability, thus have kept mention of thunderstorms overnight. Given persistent cloud cover overnight, and a late arrival of the cold front, do not expect temperatures to drop off much overnight, with lows generally in the upper 50s and lower 60s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The cold front that affects the area Thursday moves offshore Friday morning and any showers will dissipate and/or move offshore through the morning as well. The remainder of Friday will remain dry as weak high pressure briefly affects the area. By Friday night, another frontal boundary is forecast to begin approaching the area from the north as it crosses Pennsylvania and New York. The front is not expected to move into the area until later Saturday, then sink to our south Saturday night. Saturday`s high temperatures will be highly dependent on how fast the front moves through the area. If it waits until the late afternoon/evening, temperatures will be able to warm quite significantly. However, if the front moves through quicker, high temperatures may not be as high as currently forecast. This would be more likely across portions of northeast Pennsylvania and northern New Jersey where the front may cross sooner. A couple of short wave/vorticity impulses are forecast to move across the area Friday night through Saturday night, so there will be a chance for isolated/scattered showers. The front will stall to our south during the day Sunday, which should allow Sunday to be mostly dry, but an isolated shower can not be ruled out. Being the front is a back-door front coming from the north, it will bring cooler conditions on Sunday. Sunday`s highs are forecast to be markedly cooler than Saturday. 15 degrees cooler for many areas. The front will not stay to our south very long as it is expected to lift back northward as a warm front Sunday night/Monday morning. As the front lifts across the area, there will be a chance of showers Sunday night into Monday morning. There could also be some showers and thunderstorms developing during the day Monday ahead of an approaching cold front. However, the best chance for showers and thunderstorms Monday night as a cold front approaches from the west. Being we should enter into the warm sector during the day, we should warm quite nicely, and in turn some instability should build ahead of the front. Therefore there will be a chance of thunderstorms Monday afternoon and Monday night. The front will move offshore by Tuesday morning, but a secondary surface trough may move across the area during the day Tuesday. With a short wave/vorticity moving across the area during the day, there could be some isolated showers across northeastern Pennsylvania and northern New Jersey. Another front may move across the are Wednesday of next week which could bring another chance of showers. The GFS and Canadian continue developing an area of low pressure along the front to our southeast which could move across our area later in the week. However, the ECMWF no longer has this feature. This is still pretty far out, but there will be a chance of showers in the forecast for the end of next week. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. The Sterling office will be updating TAFS after 1230Z today since the Mount Holly office will be off line for a computer upgrade into this afternoon. Today...Generally MVFR conds in st/fog will gradually improve to VFR sct-bkn aoa 3500 ft after 15z. winds mainly southeast to south and may gust 15-20 kt at times during mid afternoon. Tonight...After 03Z, low clouds may move back in over the region. In addition, showers and isolated thunderstorms may approach from the west. There is low confidence though on if individual TAF sites will be affected and the timing. Southerly winds tonight shift west late after frontal passage. OUTLOOK... Friday...VFR conditions expected. Friday night...VFR early. Patchy fog and low CIGS may develop overnight. Saturday...Becoming VFR during the morning, then a chance of showers during the afternoon. Conditions may temporarily be reduced with any showers. Gusty westerly winds 15-20 knots. Saturday night-Sunday night...Low clouds and fog may develop overnight Saturday and continue into Sunday night leading to reduced conditions. Small chance of showers and thunderstorms. Conditions may temporarily be reduced with any showers. Monday...Low conditions in the morning, becoming VFR during the day. A chance of showers thunderstorms during the day, with more likely showers and thunderstorms overnight. Lower conditions possible during the day with any showers or storms, more likely lower conditions overnight. Gusty southwest winds around 25 knots.
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&& .MARINE... Elevated seas are expected to continue today and tonight on the Atlantic Coastal waters, generally ranging from 5 to 6 feet. A few gusts near or above 20 kt are possible this evening. OUTLOOK... Friday...Winds expected to remain below advisory levels, but seas may remain elevated to advisory levels. Friday night-Sunday night...Seas may approach 5 feet at times, and winds may gust near 20 knots, but conditions expected to remain below advisory levels. Monday...Winds likely to gust 25-30 knots, and seas likely to exceed 5 feet as well leading to Small Craft Advisory conditions. && .TIDES/COASTAL FLOODING... Though some of the guidance is depicting minor coastal flooding with the evening high tides today and tomorrow, we are not expecting any coastal flooding as astronomical tides will start to decrease, and by tonight, winds will be shifting to off shore. && .CLIMATE... Presuming our forecast temps these last 5 days of April are accurate, we are assured of a top 3 warmest April on record in much of our forecast area. Sunday is the critical day for determining record or not. (will recheck this projection around 430 PM) Below: April projected within the top April avg temps, the normal for April and the period of record (POR). PHL normal 54.0 POR 1874 59.4 1994 59.2 2017? 58.5 1921 58.4 2010 57.9 1941 ABE normal 49.9 POR 1922 56.6 projecting record 56.4 1941 54.7 1994 ACY normal 51.7 POR 1874 57.2 projecting record 56.3 2010 56.1 2011 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Friday for ANZ450>455. && $$ Synopsis...Robertson Near Term...Muccilli Short Term...Johnson Long Term...Robertson Aviation...Drag/Johnson/Robertson 803 Marine...Johnson/Robertson Tides/Coastal Flooding...PHI Climate...803

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