Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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274 FXUS61 KPHI 040943 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 443 AM EST Sun Dec 4 2016 .SYNOPSIS...
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High pressure over the region today will progress offshore tonight. A weak disturbance will pass through the area tonight into early Monday. High pressure builds back into the Mid-Atlantic states Monday afternoon and night. An area of low pressure over the Gulf of Mexico tracks northeastward and toward the region Tuesday. This low is forecast to pass to our south Tuesday afternoon and evening and then move off the Mid-Atlantic coast late Tuesday night and Wednesday. A strong cold front likely moves through our area Thursday as another area of low pressure tracks across the Northeast states. This low will strengthen over the Canadian Maritimes Friday and Saturday while high pressure builds in from the central U.S.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Low clouds are stubbornly hanging on this morning over the forecast area in spite of model RH forecasts which indicates clouds should be breaking up or dissipating. Anyway, the cloud cover is keeping temps a few degrees above the forecast overnight mins in most areas. Winds have diminished and become more northerly as the center of surface high pressure approaches from the west. For today, high pressure will continue to move across the area with light NW to N winds continuing. The low clouds should tend to break up during the morning but by afternoon high-level cirrus will be spreading in from the SW ahead of the next approaching shortwave trof. Afternoon max temps are forecast to be a few degrees cooler than yesterday across the area.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
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A fast moving shortwave trof and associated surface pres trof will cross the area tonight. Winds become southerly with some decent low- level warm advection and upward VV ahead of the trof. Some increased moisture should be available as clouds are streaming NE from the NW GulfMex already. Our forecast area should see a quick shot of fairly light precip between midnight and dawn on Monday. Based on the forecast temperature and moisture profiles, it looks like p-type will be mostly snow in the Poconos and NW NJ, a mix of rain and snow N/W of PHL and north-central NJ, and mostly rain elsewhere. Some snow accumulation, up to around and inch, is possible where the precip remains mostly snow.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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A northern-stream shortwave disturbance and associated surface trough is forecast to quickly swing through the region early Monday morning. Models have trended toward a more progressive system, which would equate to a faster ending time of precipitation Monday morning. This trend is good news for the Monday morning commute in northeastern PA and northwestern NJ as any snowfall accumulations after sunrise should be minor. We may still see up to an additional half inch of snowfall in the higher elevations along and north of I- 80 before it all ends later that morning. High pressure briefly builds into the region Monday afternoon and night. Expect skies to clear from southwest to northeast during the afternoon. High temperatures Monday afternoon range from the upper 30s in the Poconos to the lower 50s from Philadelphia and points south/east. A favorable radiational cooling pattern will initially be in place Monday night with a break in clouds and calm winds underneath the high. High clouds will start to overspread the area from the southwest late tomorrow night as low pressure approaches from the Gulf Coast states; which may curb cooling across the south. Low temperatures near or slightly below freezing are forecast for all of northeastern PA/northwestern NJ, and rural locations west of the Phila metro in southeast PA and in the NJ Pine Barrens. Low pressure lifts northeastward toward the Ohio Valley on Tuesday. Models are in good agreement with a secondary low developing on the lee side of the southern Appalachians Tuesday morning. This secondary coastal low will then track up the Southeast coastline Tuesday, passing to our south by Tuesday evening and offshore later Tuesday night. Precipitation from this system will likely reach the Delmarva by the morning rush, then spread farther north through the day. Thermal profiles look warm enough for the ptype to be rain for most of the region. However, precip at the onset may briefly start out as snow or a rain/snow mix west of the Fall Line. Precip in these northwestern zones should transition to liquid during the afternoon as a warm nose aloft becomes established. Some of the model guidance shows surface temperatures hovering in the mid 30s in our coldest spots north of I-80 (southern Poconos in PA, Sussex County in NJ). There is an outside chance of freezing rain if temperatures in these coldest spots wind up being only a few degrees lower than forecast. It will be important to monitor trends/biases in wet-bulb temperatures for this event. Kept snow/ice accumulations out of the forecast for Tuesday and Tuesday night due to low confidence. By Wednesday morning, the southern low will have moved offshore and will be east of the area. However, we may still be under the influence of a surface trough associated with this low through the day Wedensday into Wednesday night. As a couple of short wave/vorticity impulses slide across the area, we could continue to have low clouds and precipitation affect the area. By early Thursday, the low pressure across southern Canada and the low offshore weaken. They then combine to our north during the day Thursday into Thursday night, before strengthening and slowly lifting northward Friday into Saturday. A strong west to northwest flow will develop across the area. With steep lapse rates across the northern portions of the area and enhanced low- mid level moisture forecast to remain, especially across the northern portions of the area and farther north, we could continue to see snow or rain showers Thursday through Friday, and possibly continue into Saturday. One thing for sure for the end of the week, regardless of precipitation, is it will get cold and windy for the latter portion of Thursday, but especially Friday and Saturday. Wind chills will likely get into the single digits to lower teens for many areas overnight each morning Thursday night through Saturday morning when the temperatures are the lowest.
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&& .AVIATION /10Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions should continue at all the TAF site through today and this evening. The low cloud cover with ceilings 4000 to 5000 ft has been very persistent but some breaks should appear as the day wears on. Winds today will be NW 10 kt or less as a ridge of high pressure moves over the area. Ceilings will begin to lower this evening ahead of low pressure moving in from the west. MVFR conditions are expected to develop overnight in light rain and fog. A mix of rain and snow is likely at ABE and RDG so visibility may be further reduced there. OUTLOOK... Monday...Precip, mainly RA, ends by mid morning. RA may mix with SN at northern terminals (RDG/ABE/TTN). MVFR or IFR around daybreak will improve to VFR from SW to NE during the morning and early afternoon. Monday night...VFR. Tuesday-Wednesday...Conditions lowering to MVFR/IFR during the morning with periods of rain/fog/drizzle likely. Snow also possible for northern areas. Winds likely become gusty 15-20 knots out of the northwest late in the day. Wednesday night...Steady rain likely ends during the evening, but lower clouds may linger into the night. Gusty northwest winds 20-25 knots possible. Thursday...Generally VFR, but scattered showers are possible during the day which may temporarily lower conditions. Gusty northwest winds 25-30 knots.
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&& .MARINE...
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Sub SCA conditions are expected through today and tonight. NW winds should remain a bit gusty for a while today but will diminish by this evening as a ridge of high pressure moves overhead. Seas will gradually subside along with the wind. Winds overnight will become light and variable, however visibility may be reduces in areas of rain and fog after midnight. Monday and Monday night...Winds and seas below SCA criteria. Tuesday-Wednesday...Onshore flow strengthens on Tuesday. SCA may be needed for winds by Tuesday afternoon. SCA for winds and seas likely Tuesday night and Wednesday. Winds may reach gale force for a period late in the day Tuesday, particularly across the coastal waters of DE and southern NJ as well as the lower DE Bay. Wednesday night...Winds likely drop below advisory levels, but seas could remain above 5 feet. Thursday and Thursday night...Northwest winds increase behind a cold front. A SCA will likely be needed.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...None.
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&& $$ Synopsis...Klein Near Term...AMC Short Term...AMC Long Term...Klein/Robertson Aviation...AMC/Klein/Robertson Marine...AMC/Klein/Robertson

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