Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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950 FXUS61 KPHI 152056 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 356 PM EST Fri Dec 15 2017 .SYNOPSIS... Surface low pressure, well off Delmarva, will track northeast into the open Atlantic this evening. High pressure, centered over the southeastern United States, will nose into the region early on Saturday. This will be short-lived as a cold front, coming in from the north, will move into or through the area on Saturday night and Sunday. This front will then stall before lifting northward as a warm front Sunday night and Monday. A cold front will progress through the region around the middle of next week. Another system may affect the area near the close of next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... The forecast appears to be in good shape overall with this ongoing snow event. Radar trends show that the focus of mesoscale banding is shifting east toward the NJ Turnpike and Garden State Parkway in southern and central NJ, which matches up well with our snowfall forecast. This is where the greatest impacts for the evening commute will occur with locally higher snowfall rates of 1" per hour and poor visibility making travel on congested roadways difficult. Storm total snowfall accumulations still appear to be in the 1-3" range for areas covered by the Winter Weather Advisory with locally higher amounts near 4" possible across southern and east-central portions of NJ. The threat of freezing rain appears to be winding down late this afternoon across eastern MD and southern DE as precipitation changes over to snow with better dynamical cooling. The back edge of the snow is already progressing quickly eastward toward Reading and Mount Pocono as we approach 4 PM. Expect snow to taper off across the I-95 corridor by 6 or 7 PM and coastal areas by about 8 PM. A cold night is in store with temperatures dipping into the teens across eastern PA and northern NJ and 20s elsewhere. Any untreated roads and sidewalks will remain slippery tonight even after the snow ends. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Shortwave energy rotating around the based of the large scale trough is forecast to move across the Great Lakes and Northeast states on Saturday. At the surface, a weak area of low pressure will pass to our north but a northwest flow behind this disturbance will help steer a cold front southward into the I-80 corridor by the late afternoon. Even with the deepest, more organized synoptic lift staying to our north, models show a ribbon of low-level convergence/frontogenetical lift near the front that could support some snow shower activity across the I-80 and I-78 corridor during the mid to late afternoon. We are currently only expecting minor accumulations. Elsewhere, expect clouds to increase as the day progresses. Forecast high temperatures range from the lower 30s across the I-80 corridor to the lower 40s in Delmarva and coastal NJ. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Overview...The period starts with a deepening surface low off Delmarva. This low will track to the northeast overnight into the open Atlantic. Surface high pressure, centered across the deep south, will push up into the Mid-Atlantic by daybreak Saturday. This high won`t hang around long. A cold front, coming in from the north, will move into or through the forecast area Saturday night into Sunday. This front will back up as a warm front Sunday night into Monday. Another cold front will push through the region in the Tuesday/Wednesday timeframe. Surface high pressure is expected on Thursday. This will elide to a warm front later on Thursday into Friday and a cold front very late in the period. Both of these fronts are associated with low pressure moving across the eastern Great Lakes. Temperatures...For reference, normals for KPHL are around 30 and in the middle 40s. Sunday will be slightly below normal. Monday and Tuesday will be above normal with some mid-50s possible across portions of the coastal plain. Wednesday looks to be about normal with Thursday slightly below. Friday will rebound once again with above normal temperatures. Once again, portions of the coastal plain could see temperatures top out in the middle 50s. Precipitation...Small PoPs have been inserted late Sunday and maintained into Sunday night. This associated with the warm front in the vicinity. Small PoPs will continue into Monday and through Tuesday night. Wednesday and Thursday will be PoP free behind the mid-week cold front. Some chance PoPs will be inserted into the grids on Friday. Winds...Fairly benign through the period. Moist noticeable winds will be right ahead and behind the cold front Tuesday and Wednesday. Impacts...While the forecast will see a roller coaster week with temperatures and multiple chances of precipitation, none are expected to create widespread hazardous weather at this time. && .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Into this evening...IFR and MVFR in snow. Light and variable wind. Tonight...Improving to VFR. Ceilings lifting to 4000 to 5000 feet. Light and variable wind. Saturday...VFR. Mostly clear in the morning, then increasing clouds. Southwest wind 5 to 10 knots. Outlook... Saturday night...Generally VFR with light and variable winds. Medium confidence. Sunday...Generally VFR. Light northeast winds to start the day and southeast to finish. Increasing clouds and a small chance of precipitation later in the day. Medium confidence. Sunday night and Monday...Generally VFR, though brief sub-VFR conditions are possible with light rain or snow, especially north of PHL. Light winds generally transitioning from southeast to southwest during the period. Low confidence. Monday night and Tuesday: Sub-VFR conditions possible, with scattered showers during the period, especially on Tuesday. Winds primarily southwest at 5 to 15 kts. Medium confidence. Tuesday night and Wednesday...Generally VFR. Decreasing clouds and showers on Tuesday night. No precipitation expected on Wednesday. Winds west or northwest 10 to 20 mph. Medium confidence. && .MARINE... N-NE winds are currently light but are expected increase this evening and become NWly as low pressure intensifies while tracking to our east. Opted for a SCA instead of a GLW for tonight and Friday with winds generally in the 25-30 kt range. However, a brief ramp up in winds are expected late tonight when pressure rises behind the offshore low are greatest. An isolated gust to near gale force at our offshore buoys is certainly a possibility. Outlook... Saturday night: Residual advisory-level northwest winds in the evening will diminish overnight. Gale force gusts during the evening can`t be ruled out. Seas below criteria. Sunday and Sunday night: Sub small craft advisory conditions. No headlines anticipated. There may be some light rain in the afternoon and overnight with potential for some visibility restrictions. Monday and Monday night: Sub small craft advisory conditions. No headlines anticipated. Scattered showers, at times, could create visibility restrictions. Tuesday: Southwest winds increasing to near advisory levels by afternoon with seas also building. A chance of showers and visibility restrictions. Tuesday night and Wednesday...Small craft advisory conditions expected due to northwest winds behind the front and building seas. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Winter Weather Advisory until 9 PM EST this evening for PAZ070- 071. Winter Weather Advisory until 7 PM EST this evening for PAZ102- 104-106. NJ...Winter Weather Advisory until 9 PM EST this evening for NJZ012>027. DE...Winter Weather Advisory until 9 PM EST this evening for DEZ001>003. MD...Winter Weather Advisory until 9 PM EST this evening for MDZ008- 012-015-019-020. MARINE...Small Craft Advisory from 7 PM this evening to 1 AM EST Sunday for ANZ452>455. Small Craft Advisory from 11 PM this evening to 1 AM EST Sunday for ANZ450-451. Small Craft Advisory from 1 AM to 6 PM EST Saturday for ANZ430- 431. && $$ Synopsis...Kruzdlo Near Term...Klein Short Term...Klein Long Term...Kruzdlo Aviation...Iovino/Klein/Kruzdlo Marine...Klein/Kruzdlo is the U.S. government's official web portal to all federal, state and local government web resources and services.