Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 141031 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 531 AM EST Wed Feb 14 2018 .SYNOPSIS... Several weak disturbances will move across the region today through Thursday, then a cold front crosses our area Thursday night into Friday. High pressure builds across the region Friday night into Saturday before shifting into the Canadian Maritimes late Saturday into Sunday. Low pressure is forecast to quickly track close to our region Saturday night before moving out to sea Sunday morning. High pressure builds in later Sunday before moving offshore Monday, then a warm front arrives Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Due to reports of black ice and freezing rain, including vehicle accidents, across parts of northern NJ and Pocono Mountains in eastern PA, felt it was prudent to issue a Winter Weather Advisory for Monroe, Warren, and Sussex counties for a few hours this morning to cover the morning commute. For the rest of the Lehigh Valley and northwest NJ, the freezing rain is more patchy, so the SPS should cover ice issues outside of the Advisory. The precip across the northern zones is on track to be out of the region by 8 am, and surface temps should begin to rise above freezing. Otherwise, high pressure is centered over the Southeast U.S., and return flow behind the high will allow for continued WAA. Clouds will scatter out this afternoon, and temperatures will be around 10 degrees above normal, topping off in the 40s north and west of I-95 and in the low to mid 50s south and east of I-95.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... Low pressure developing over the lower Great Lakes and Tennessee Valley will lift to the north and east tonight. Rain develops later this evening, and continues through most of tonight before tapering off by daybreak Thursday. The swath of heaviest rain will move across central NJ, where up to 1/4" QPF will fall. Otherwise, total rainfall will range from 1/10" to 2/10". && .LONG TERM /THURSDAY THROUGH TUESDAY/... Summary...Rather mild and wet at times Thursday and Friday; increasing potential for some wintry precipitation and colder air Saturday into early Sunday; turning much warmer early next week. Synoptic Overview...A positively tilted upper-level trough centered in the vicinity of Hudson Bay will send several spokes of energy into the Eastern U.S into the weekend. Significant short wave energy though Saturday into Sunday looks to sharpen the southern part of the trough enough to help focus surface low pressure near the Mid- Atlantic, however the flow looks progressive. Late in the weekend and especially early next week, the pattern becomes more amplified as a significant trough develops in the West with a strengthening ridge in the East. This will open the door for much warmer air to surge across our region starting Tuesday, although this will probably be accompanied by some showers. For Thursday and Friday...Several short waves will be traversing the area within a southwest flow aloft. This will assist in warm air advection ahead of a cold front that gradually arrives in our area Thursday night. Much of the more organized precipitation, which is expected to be in the form of just rain, looks to be along and especially behind the surface cold front. There appears to be two separate rounds of rain, one Thursday morning as a shot of stronger warm air advection occurs with a warm front then the second arrives Thursday night and Friday morning. Some fog should occur at times, especially near and west of the fall line. The precipitation should tend to weaken later Friday as the front settles farther south of our area and the low-level flow becomes a bit more anticyclonic. The precipitation is anticipated to end across the northern areas before the airmass gets cold enough for any mixing or changeover. High pressure then builds eastward and encompasses our region Friday night. This will bring in colder air along with notably drier air. For Saturday and Sunday...The consensus of the model guidance continues to increase regarding a storm system affecting our area during this time frame. The flow is progressive though therefore the surface feature will be moving by fast Saturday night into very early Sunday. Short wave energy from the northern stream looks to link up with a short wave tracking east-northeastward from the Southern Plains. The more interaction now with these features allows the trough to sharpen a bit for a time as it shifts eastward. This increases the downstream large scale ascent and organizes surface low pressure. Surface high pressure initially over New England is forecast to give way, however some signal of cold air damming looks to be in place at least near and west of the fall line. A blend of some of the model guidance shows an area of snow, a wintry mix zone then perhaps some rain farther south. The precipitation types will depend on the track of the surface low and how much warming aloft can occur despite the system moving quickly. For now, used a blend of the GFS and ECMWF 1000-850 mb and 850-700 mb partial thicknesses which the precipitation types were derived from. Given uncertainty with the details, kept it as rain and snow at this point. A swath of some accumulating snow cannot be ruled out, however the details have yet to be determined at this range. Given the systems speed, Sunday may start out dry. Held onto some precipitation mention very early on Sunday, then high pressure looks to quickly start building in Sunday afternoon and night. For Monday and Tuesday...The pattern is forecast to change into an amplified one, with a large trough settling in across the West while a ridge strengthens in the East. This will set the stage for another round of warming in the East during this time frame. As high pressure shifts offshore Monday morning, a return flow sets up along with warm air advection. This will be via a warm front arriving late Monday into Tuesday. This warm front should work northward Tuesday, with showers with it. It could be rather wet Tuesday if the warm front is slower to lift north, allowing for more of an overrunning setup and this could hold temperatures down some especially across the north. At this forecast time range, we continued with a time of chance PoPs. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today (through around 13Z)...Generally VFR into daybreak. MVFR CIGs possible across KABE/KRDG, and some light mixed frozen precip with VFR VSBY mainly at KRDG/KABE as well. Otherwise, dry conditions for the rest of the terminals. LGT/VRB winds. Moderate confidence. Rest of today (13Z through 00Z Thursday)...VFR. Clouds should scatter out throughout the day. SW winds less than 10 kt. Tonight...MVFR/IFR CIGs/VSBYs in rain and fog. Light and variable winds. OUTLOOK... Thursday and Friday...Sub-VFR conditions due to low clouds/fog and some rain especially Thursday morning and then again later Thursday night and Friday morning. Times of VFR should occur otherwise. Southwest winds around 10 knots Thursday, becoming west and northwest Friday around 15 knots with gusts possibly to 20-30 knots. Winds diminish Friday night. Low to moderate confidence. Saturday and Sunday...Conditions should lower to MVFR/IFR as rain/snow or a wintry mix moves across the area Saturday night into early Sunday. Low confidence with the details.
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&& .MARINE... Today...Winds and seas will remain below SCA criteria. However, in the afternoon, southwesterly winds are expected to increase with gusts around 20 KT possible. Tonight...VSBY restrictions in rain/fog as low pressure passes through the region. SW winds 15-20 kt. Winds and seas below SCA criteria. OUTLOOK... Thursday and Friday...Southwest winds Thursday and much of Friday within a warm airmass therefore mixing less than ideal. As a result, conditions should be below Small Craft Advisory criteria. Seas however may start to build to around 5 feet Thursday night on the ocean zones. Winds shift to the west and northwest later Friday afternoon and night and increase with potential wind gusts to 25-30 knots. Saturday and Sunday...The conditions will depend on the track and strength of low pressure, however at this time the conditions are forecast to generally be below Small Craft Advisory criteria. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Winter Weather Advisory until 8 AM EST this morning for PAZ055. NJ...Winter Weather Advisory until 8 AM EST this morning for NJZ001- 007. DE...None. MD...None. MARINE...None.
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&& $$ Synopsis...Gorse Near Term...MPS Short Term...MPS Long Term...Gorse Aviation...Gorse/MPS Marine...Gorse/MPS

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