Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 130834 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 434 AM EDT Tue Mar 13 2018 .SYNOPSIS... The strong coastal low will continue to move northeast offshore of New England today, then continue into the Canadian Maritimes tonight and linger there through the remainder of the week. Several surface troughs or fronts will likely rotate around this low through Friday. Canadian high pressure builds into the region Friday night through Saturday. A back door cold front may sink across the area Sunday into Sunday night, then high pressure pushes into the area later Monday. Another coastal storm is possible late Monday into late Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 330 AM fcst: Might have given up too soon on accums near and north of VAY to ACY as banding is really getting going now but we`re out there and staying with what we have until we know we`re wrong. Recent model trends suggest snow will last 1-2 more hours than we currently have fcst in our zone and taf products and there is going to be some 3/4 mi snow here and there between now and 9 am. While the primary forcing has shifted east slightly from midnight to about 60 miles offshore as you can see from the radar at 0830z... ie...a 50-60 NM westward shift in the storm track would probably have meant a much more substantial snowfall along the coast....not to be. Still, banding is occuring and snow ratios are higher so at elevation, there is going to be some significant accumulations with 5" amounts expected aoa 1000 ft along and north of I80. Otherwise at lower elevations...despite the surface temperatures cooling early today, accumulations may be more difficult on treated surfaces due to the lighter intensity. Most of the snow accumulations will occur prior to 9 AM today with an additional 1-2 inches possible Monmouth to Morris and Sussex Counties in nrn NJ after 12z. There should definitely be morning commute impacts near and north of I78. The Winter Weather Advisory was maintained as is, where an area of widespread 2-4 inches of snow is expected. I did drop Mercer county due to the fcst being under criteria Snow ends slowly from southwest to northeast later this morning. Mixed clouds and sun and blustery this afternoon with a northwest wind gusting 25-35 mph and maybe some scattered flurries except scattered snow showers Poconos. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... Becoming mostly clear. A westerly wind with scattered gusts 15-20 MPH. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... The strong coastal low will continue to linger across the Canadian Maritimes Wednesday, Thursday, and Friday. At the same time, high pressure will be building across the Deep South and southeastern states, as well as the Upper Mississippi Valley and western Great Lakes. This will keep a strong northwest flow across the area Wednesday, Thursday, and Friday. Each day, a surface trough/frontal boundary is forecast to move across the area as well. There will be a chance of showers each day from Wednesday through Friday. However, each day the chances and coverage get less. Wednesday has the greatest chance of showers as the low level lapse rates will be their greatest during the day Wednesday, as well as the low-mid level moisture. Wednesday is also expected to be the windiest day, with winds reaching at least 30-40 mph, possibly even higher later in the day and into the evening. With the strength of the winds, and the instability, we expect there to be some snow showers/squalls developing to our west and move into our area. Temperatures may warm into the upper 38s or low 40s for some areas, but with as hard and fast as the precipitation will come down, it may be more snow or a rain/snow mix for the warmer areas. The higher elevations of the Poconos may very well see an inch or two as they will be colder and have the greater potential to see snow. Any snow showers/squalls should diminish after sunset as the lapse rates weaken and moisture slides to our east. On Thursday, another surface trough is expected to move across the area while low level lapse rates increase again, along with low-mid level moisture. It is possible again for another round of snow/rain showers or squalls during the day. Again the Poconos have the better chance of seeing any accumulation as most other places may mix rain and snow. Although winds are not expected to be as windy as Wednesday, we should still see wind gusts 20-30 mph at times. Any precipitation that does form is expected to diminish after sunset as the lapse rates weaken and moisture slides to our east. For Friday, yet another surface trough is forecast to move across the area as the low to our northeast loses it`s grip on our area. The lapse rates are not as strong everywhere on Friday, and there is not as much moisture expected across the area. Therefore the chance for snow is mainly expected across the Poconos on Friday. By Friday night, high pressure begins to approach from the west, and drier conditions are expected. On Saturday, high pressure briefly builds across the area, then pushes south of the area. This will lead to dry conditions during the day Saturday. On Saturday night, an area of low pressure is forecast to pass just to our south while a short wave/vorticity impulse slides across the southern half of the area. The expectation is that any precipitation will remain to our south Saturday night. However, if any precipitation were to occur, it would most likely occur across the southern Delmarva in the form of rain. On Sunday into Sunday night, a back door cold front is forecast to move across the area from the north, before high pressure noses into the area from the north on Monday. This is expected to lead to dry conditions Sunday into Monday. However, the forecast then turns to the potential for...yet another coastal storm late Monday night through late Tuesday. As usual, there is uncertainty with the details, but the GFS, Canadian, and ECMWF all show the coastal storm with varying degrees of coldness and QPF. Still, there is the potential for some of the area to see another round of snowfall. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Early this morning...VFR CIGS occasionally IFR conds in snow with TAFS attempting to time the end of the IFR risk in snow beginning 08z-10z ILG and arriving RDG PHL MIV ard 11-13z and ABE TTN ard 13-15z. North to northwest wind with scattered gusts around 20 kt. Today after 15z....VFR sct-bkn aoa 4000 ft. Northwest winds 12-18 knots with gusts up to 30 knots. A few late afternoon snow showers are possible in the vicinity of RDG and ABE. Tonight...VFR conditions expected with westerly winds scattered gusts 15-20kt. Outlook... Wednesday...VFR CIGS early may lower to MVFR during the day. Snow or rain showers/squalls possible during the day. If snow showers/squalls occur, they would likely lead to temporary lower conditions. Westerly winds gusting to 25-30 knots. Moderate confidence. Wednesday night...MVFR CIGS possible early for some areas, becoming VFR overnight. West winds gusting to 30-35 knots. Moderate confidence. Thursday...Mostly VFR. However, snow or rain showers/squalls possible during the day, but not as widespread as Wednesday. If snow showers/squalls occur, they would likely lead to temporary lower conditions. Westerly winds gusting to 20-25 knots. Moderate confidence. Thursday night...VFR conditions overnight. Northwest winds may gust 20-30 knots. High confidence. Friday...Mostly VFR. However, snow or rain showers/squalls possible during the day, but not as widespread as Thursday and mainly for northern areas. If snow showers/squalls occur, they would likely lead to temporary lower conditions. Northwest winds gusting to 20-25 knots. Moderate confidence. Friday night...VFR conditions overnight. Northwest winds may gust 20- 30 knots. High confidence. Saturday...VFR. Northwest winds gusting 15-20 knots. High confidence. && .MARINE... Gales in progress most of the waters at this time with NAM MOS guidance a better indicator of gust transfer reality. The winds become northwest during the day and gales should gradually diminish later today. WW3 seas were very poor for this evening and we increased the seas by 3-5 feet this morning. We have no SJSN4 data so we`re not exactly sure of winds speeds over the upper part of DE Bay Tonight...SCA expected with isolated gale force west northwest gusts possible. Outlook... Wednesday-Wednesday night...Gale Watch in effect. Moderate-high confidence. Thursday-Friday night...Small Craft Advisory conditions expected. High confidence. Saturday...Conditions may lower below advisory levels. High confidence. && .TIDES/COASTAL FLOODING... Still a risk of coastal flooding this mornings high tide Ocean County to the DE Atlc coast area but at this time our merged TWL guidance still says just below. Wind direction near the 6am high tide will ultimately determine how much surge at high tide which is currently anticipated to be around 2 feet. We may need a last minute 430 am issuance there based on surge trends as the tide cycle marches up to high tide. An examination of the latest gridded ETSS and ESTOFS (GFS- based) and multi-model ensemble guidance indicates that coastal flooding is expected to be at worst, minor. On the coast of Delaware Bay, spotty minor flooding is forecast during the Tuesday morning high tide. Levels will be elevated on the tidal portions of the Delaware River, but they are expected to remain below advisory levels at this point. Beyond this morning, surface flow is expected to become strong and offshore, limiting the threat of flooding with subsequent high tides. However, confidence is a little lower on the NJ coast where surge will be higher, so coastal flooding cannot be ruled out for the Tuesday evening high tide. However, the astronomical tide will be lower for the evening high tide, likely limiting the threat. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Winter Weather Advisory until 10 AM EDT this morning for PAZ054-062. Winter Weather Advisory until noon EDT today for PAZ055. NJ...Winter Weather Advisory until 10 AM EDT this morning for NJZ007-009. Winter Weather Advisory until noon EDT today for NJZ001-008- 010-012>014-020-026. DE...None. MD...None. MARINE...Gale Watch from Wednesday afternoon through Thursday morning for ANZ430-431-450>455. Gale Warning until 6 PM EDT this evening for ANZ450>455. Small Craft Advisory until 6 AM EDT Wednesday for ANZ430. Gale Warning until 5 PM EDT this afternoon for ANZ431. && $$ Synopsis...Robertson Near Term...Drag 433 Short Term...Drag 433 Long Term...Robertson Aviation...Drag/Robertson 433 Marine...Drag/Robertson 433 Tides/Coastal Flooding... is the U.S. government's official web portal to all federal, state and local government web resources and services.