Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 220852 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 352 AM EST Wed Jan 22 2020 .SYNOPSIS... High pressure will build eastward across the Mid Atlantic and northeast states today through Thursday. This high will weaken and retreat to the northeast Friday before a storm system moves across the Mid Atlantic and northeast states late in the week and into the weekend. This low will strengthen as it moves into the Canadian Maritimes early next week while high pressure builds to our southwest, then across the east coast by the middle of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Expansive high pressure over the Ohio and Tennessee Valleys will build east throughout the day, and should be nearly overhead by late afternoon. Clear and cold this morning with temperatures generally in the teens, but winds will be light, so not much in the way of a wind chill. Abundant sunshine on tap today, and with WAA and increasing low level moisture, highs will top off in the 30s to around 40. These temperatures will be right around normal for this time of year. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... High pressure will be over the area tonight. With the center of the high right over New Jersey, winds will be calm and skies will be clear. This will allow for excellent radiational cooling conditions. With a slightly warmer airmass over the region, lows will generally drop into the teens and low 20s, which will be a few degrees warmer than this morning. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Quiet weather continues through the beginning of the long term forecast, then unsettled weather returns for the end of the week into the weekend, then quiet weather is expected to return again early next week. High pressure remains across the Mid Atlantic and northeast states through Thursday, keeping dry, quiet weather in the forecast. Temperatures warm above normal by Thursday as thicknesses increase. Actually, temperatures through the extended period are forecast to be above normal. The high pressure will begin to weaken and retreat to the northeast by Thursday night and Friday. The forecast remains dry through Friday, however, cloud cover will be on the increase in advance of an approaching storm system as a couple of short wave moves across the area. The main story of the long term forecast continues to be the storm system over the weekend. An area of low pressure will be lifting across the Mid-West and into the Great Lakes Friday into Friday night, while lifting a frontal system toward the Mid- Atlantic region. A secondary low is forecast to develop to our southwest across the central Appalachians Friday night near the triple point of the occluding frontal system, then lift to the northeast near our region Saturday, and strengthen and become the main low of the storm system. There continues to be slight timing and placement differences with the development of this secondary low, and this will have an impact on the precipitation type. The GFS continues to be faster and closer to the coast, while the ECMWF is slower and farther inland, although the differences are not as big as last night. What this leads to is the potential for a wintry mix for areas along and north of I-78 starting Friday night and continuing through Saturday into Saturday night. Areas along the I-78 corridor may change over to all rain for a time Saturday, before changing back to snow by Saturday night. Areas farther north, especially along and north of the I-80 corridor will likely remain all snow during the event. Those areas that see all snow may end up with several inches of snow, while areas farther south could see a couple of inches along with some icing. Areas farther south of the I-78 corridor will likely remain all rain until Saturday night into Sunday as the precipitation changes to snow for many areas as colder air wraps around the low as it moves to the northeast. Any precipitation will begin to end later Sunday into Sunday night as the low pulls farther away from the area. High pressure will build to our southwest early next week, while low pressure moves through the Canadian Maritimes. Winds will become gusty due to a tight pressure gradient between the low to our northeast and the high to our southwest, beginning later Saturday, and continuing through Monday. Dry weather will return to the forecast for Monday and continue into Tuesday. As high pressure begins to build toward the east coast Tuesday, winds will begin to diminish as well. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR/SKC. LGT/VRB winds this morning, becoming SW 5-7 kt this afternoon. High confidence. Tonight...VFR/SKC. LGT/VRB winds. High confidence. Outlook... Thursday-Friday...VFR conditions will continue through the period. Winds will be fairly light through the period. -High confidence. Friday night...Conditions begin to lower to MVFR the IFR overnight as precipitation moves into the area. Rain is expected across southeast Pennsylvania, central/southern New Jersey, Delaware, and eastern Maryland. A wintry mix is possible across portions of northeast Pennsylvania and northern New Jersey. Light winds become easterly overnight -Moderate confidence. Saturday-Saturday night...Precipitation continues across the area with IFR conditions in place. Winds shift front easterly, to north, to northwest and become gusty 15-25 knots at times. -Moderate confidence. Sunday...Conditions improve to MVFR then VFR during the day. Wind remain northwest 20-30 knots. -Moderate confidence. && .MARINE... Sub-SCA conditions with high pressure building into the region. Light north winds today, then light and variable winds tonight. Seas 1-3 feet on the ocean and 1-2 feet on DE Bay. OUTLOOK... Wednesday-Thursday...Conditions expected to remain below advisory levels. Thursday night-Friday night...Winds expected to remain below advisory levels, however, seas are expected to build above advisory levels to 5-7 feet. Saturday-Sunday...Seas remain above advisory levels, and winds are expected to increase above advisory levels as well. There may be a brief period of gale force winds during the day Saturday. && .TIDES/COASTAL FLOODING... The combination of a new moon on Friday, along with an onshore flow may lead to areas of coastal flooding with the high tide Saturday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Robertson Near Term...MPS Short Term...MPS Long Term...MPS/Robertson Aviation...MPS/Robertson Marine...MPS/Robertson Tides/Coastal Flooding...Robertson is the U.S. government's official web portal to all federal, state and local government web resources and services.