Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 201122 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 622 AM EST Mon Nov 20 2017 .SYNOPSIS... High pressure over the southern Mississippi River Valley will build east, then move off the Mid-Atlantic coast tonight. A cold front will approach Tuesday night and pass through the area on Wednesday. At the same time, low pressure over the southeast portion of the country will approach the Mid- Atlantic and move out to sea. High pressure will build through the area by the end of the work week. A cold front is expected to pass through on Saturday, with high pressure gradually building east early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 630 am update: I added some flurries to areas generally north of I-80 for the next couple of hours based on the stubborn remains of a lake-effect band in this general vicinity early this morning. Made some adjustments to sky cover, though I am worried the grids are overly optimistic early this morning for the northern CWA. A more pessimistic forecast may be required should current satellite trends continue. Impressive vort max moving through the region at this time with deep northwesterly flow very effectively streaming sufficient moisture from the Great Lakes southeastward into northern portions of the CWA the past few hours. Several snow showers have developed in this regime, with even some bursts of moderate snow and brief, gusty winds with some of them given the favorably deep low-level thermodynamic profiles and strong winds aloft. The snow showers are now on the wane, mainly confined to northern New Jersey as of 2:30 am. Another streamer is moving into the southern Poconos, so a couple more hours of occasional snow showers are expected. However, as the lift diminishes thanks to the departing wave, should see snow showers mainly confined to areas farther north/west of the CWA by daybreak. As such, I have no PoPs in the forecast after 8 am. Surface high pressure should progress eastward to the Carolinas this afternoon, with midlevel flow becoming somewhat more zonal upstream of the vort max. A fairly strong north-south pressure gradient will exist today as a strong surface low meanders in the Maritime Provinces. Thus, another breezy day should be expected, albeit far less windy than yesterday. Clouds have been stubborn to dissipate in the northern/western CWA as the low levels are dry enough (and mixing strong enough) to maintain a scattered to broken deck around 4000-6000 feet. However, as deep-layer descent increases today, there should be noticeably clearer skies than yesterday. Temperatures will be below average as cold air advection continues this morning before winding down later today. Expect highs around 5 to 10 degrees below seasonal averages. There is very good agreement among the statistical guidance, so used a blend for max temperatures. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... The surface high will progress offshore to our south tonight, and midlevel flow will become more southwesterly as a vort max digs southeastward into the Upper Midwest by 12Z Tuesday. Low-level warm- air advection should be in full swing by the overnight hours, and this will prevent much of a fall in temperatures, despite the lighter winds and mostly clear skies expected. Once again, statistical guidance is in good agreement regarding temperatures, so a blend was used for lows. Generally expecting readings around average. Temperatures may actually flatline relatively early in the night as warm-air advection increases via increasingly more favorable low-level trajectories. && .LONG TERM /TUESDAY THROUGH SUNDAY/... High pressure over the Mid-Atlantic is expected to move off the Mid- Atlantic coast on Tuesday. Return flow sets up, and highs on Tuesday will be about 3-5 degrees above normal, topping off in the 40s in the Poconos, otherwise in the low to mid 50s north and west of I-95, and near 60s in the Delmarva and southern NJ. S to SW winds increase Tuesday afternoon to 15-20 mph with gusts up to 30 mph. Low pressure is expected to develop over the Gulf Coast on Tuesday, move off the Southeast U.S. coast Tuesday night, then approach the mid-Atlantic coast before moving out to sea on Wednesday. A cold front will pass through the region Wednesday afternoon. Based on latest model guidance, will continue a swath of likely PoPs across southern DE and southeast NJ, and chance PoPs for most areas south and east of the Fall Line. Cooler temps will move into the Poconos Wednesday afternoon, but stronger CAA will not get underway until Wednesday night. Chilly high pressure builds through the region Thanksgiving Day with temperatures 6-8 degrees below normal. Highs top off in the mid and upper 30s in the Poconos, otherwise in the low to mid 40s. High pressure reestablishes itself over the area Friday with highs a few degrees warmer than Thursday. Low pressure passing well north of the region will drag a cold front through the region on Saturday, and then low pressure remains over eastern Canada through next weekend even as surface high pressure begins building in from the west. Unsettled weather possible. && .AVIATION /11Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR with west winds increasing to 10 to 15 kts with gusts to 25 kts. Confidence above average. Tonight...VFR with west winds decreasing quickly after sunset and likely becoming southwesterly with time. Speeds generally below 10 kts. Confidence above average. Outlook... Tuesday...VFR. SW winds 15-20 KT with gusts up to 25 KT Tuesday afternoon. Tuesday night and Wednesday...Mainly VFR. Rain possible south and east of I-95 Tuesday night through Wednesday morning with MVFR or lower conditions. SW winds 5-10 KT become NW Wednesday afternoon and increase to 10-20 KT. Wednesday night and Thursday...VFR. NW winds gradually diminishing. A storm system is currently expected to remain offshore. Forecast confidence: Medium to High. Friday...VFR. NW winds 5-10 KT. Saturday...VFR early...then MVFR or lower conditions possible in rain showers later in the day. SW winds 10-15 KT. && .MARINE... 630 am update: Lower Delaware Bay wind gusts are currently borderline gale, which has not been well forecast by the guidance early this morning. The trend will be downward this morning, so kept everything as is for now. Nevertheless, if there is another uptick in wind gusts early this morning, may need to issue a marine weather statement for a couple of hours. Gale warning was dropped, as gusts above 34 kts have not been observed in the past couple of hours. Trend with the winds will be downward today, but small craft advisory conditions will continue through the morning for Delaware Bay and the Delaware coastal waters and through much of the day off the New Jersey coast. There will likely be a brief lull in winds off the New Jersey coast late this afternoon and this evening before southwest winds pick up again overnight. For this reason, kept the small craft advisory going through Monday night. Outlook... Tuesday and Tuesday night...Brief lull in SCA conditions through Tuesday morning. Otherwise, 25-30 KT wind gusts, primarily on the ocean waters, may possibly over Lower DE Bay Tuesday afternoon. Wednesday...Lull in SCA conditions possible Wednesday morning. Otherwise, winds shift to the NW and increase to 15-20 KT with 25-30 KT gusts. Thursday through Saturday...Sub-SCA conditions expected. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EST Tuesday for ANZ450>453. Small Craft Advisory until 1 PM EST this afternoon for ANZ430- 431-454-455. && $$ Synopsis...Miketta Near Term...CMS Short Term...CMS Long Term...Miketta Aviation...CMS/Miketta Marine...CMS/Miketta is the U.S. government's official web portal to all federal, state and local government web resources and services.