Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 200224 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 924 PM EST Sat Jan 19 2019 .SYNOPSIS... An expansive area of low pressure will approach the region from the west tonight and pass over our area overnight Saturday night and early Sunday morning bringing a significant winter storm to the region. Low pressure moves across southern New England then out to sea late Sunday. Strong Arctic high pressure will build quickly into the Mid-Atlantic through the early part of next week resulting in very cold and dry conditions. Another area of low pressure will move across the Great Lakes and into southeastern Canada late Tuesday into Wednesday pushing a cold front into the region Wednesday. && .NEAR TERM /THROUGH SUNDAY/... Rain/snow line continues to creep to the north, and the transition line is now along or north of a line from around Reading to Doylestown to Trenton. Across the Lehigh Valley, southern Poconos, and northern NJ, moderate to locally heavy snow continues. The rain/snow line continues to lift to the north, and shortly after midnight or so, expecting a wintry mix of sleet and freezing rain, then a period of freezing rain across Carbon, Monroe, and Warren counties. Max snow amounts in the far northern areas will range from 6-8" (will bump up a bit from earlier forecasts), along with up to 0.20" of ice. Winter Storm Warnings remain in effect for the far northern zones, and for now, will not make adjustments to the Winter Weather Advisories, as there may still be some wintry precip as that line lifts north. Timing: The bulk of the precip falls tonight through Sunday morning with this winding down as the cold front moves through during the 15- 19z time frame Sunday. Winds: Late tonight into Sunday morning, a very strong southerly low level jet is expected to develop with 925/850 mb winds progged to reach 70/90 knots over the area as the warm sector moves in. There will be lots of moisture in play with rain continuing at this time with some indications a convective type line could develop even if it doesn`t actually produce lightning. Nevertheless, this could potentially bring very strong, even damaging winds, down to the surface. Not confident in this though and this will need to be handled as a "short- fused" type product situation, if needed. Then, following the passage of the cold front, expect strong NW winds to develop potentially gusting 30-40+ mph tomorrow afternoon into the evening along with rapidly falling temperatures. This could result in at least some scattered power outages with more significant problems possible in the far north in the areas that still may get more snow/ice. Flash Freeze: As mentioned above, strong cold front moves through NW to SE late morning into the early afternoon with rapidly dropping temps to values well below freezing. This will result in quick refreezing of wet/slushy surfaces causing very ice conditions. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... The beginning of the week will feature deep winter arctic cold, but dry conditions. Temperatures will continue the fall (from Sunday) and drop into the single digits and low teens across most areas. Mercury readings across the southern Poconos may reach as low as -5 by dawn Monday. As bad as the cold is, wind chills will be brutal with sub-zero readings in most areas and readings around -20 to -25 across the Poconos. Proper precautions against the cold will be required to be safely outdoors Monday. Dry weather is expected Monday and into Tuesday as high pressure builds in. Readings Tuesday morning will also be very cold, but temperatures will moderate by days end back into the low 30s S/E and low/mid 20s N/W. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The midweek period looks unsettled as of now since another H5 trough will be advancing from the Midwest and low pressure is expected to form along it. Another wet/white storm is envisioned with confidence on storm track and P-types low at this time. More arctic cold looks to follow this system. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...IFR and lower conditions as precipitation overspreads the region from southwest to northeast. All rain expected at MIV and ACY; precip has changed to rain at ILG, PHL/PNE, and TTN; RDG and ABE start as snow then quickly go over to sleet and freezing rain, then rain overnight. Main snow and ice accumulations occur at RDG and ABE. Low confidence on the timing of the precipitation type changes. Easterly winds around 10 knots, turning southeast or south toward morning (some gusts to 20-25 knots possible overnight mainly at ACY). A low- level southerly jet around 2000 feet overnight into early Sunday of 40-50 knots results in low- level wind shear. Sunday...MVFR/IFR conditions to start, then rapidly improving by late morning or afternoon as the precipitation ends. An abrupt wind shift to the northwest occurs by midday with winds increasing to 15- 25 knots with gusts to around 35 knots (highest during the afternoon/evening). Low confidence on timing for improvement to VFR. Outlook... Sunday night and Monday...VFR. Northwest winds 15-20 knots with gusts to around 30 knots, diminishing Monday night. Tuesday...VFR. Northwest winds 10-20 knots, diminishing by late afternoon. Wednesday and Thursday...Sub-VFR conditions possible with the chance for some snow to a rain/snow mix. && .MARINE... East to southeast winds tonight will increase to advisory levels, then become more southerly early Sunday morning. The passage of low pressure and a strong cold front will result in an abrupt wind shift to northwesterly during Sunday with a rapid increase in the winds as bitterly cold air pours in across the region. The gales may not fully take hold until the afternoon or evening, however will maintain the Gale Warning as is although did extend the end time to 23z/6pm Monday. Outlook... Sunday night and Monday...Gale Warning through 23z/7pm Monday due to a bitterly cold airmass and deep mixing. The warning may need to be extended into a portion of Monday night. Due to the bitterly cold air and strong winds, freezing spray is expected especially later Sunday night through Monday. As of now, looks like moderate ice accretion rates will be achieved and therefore issued a Freezing Spray Advisory. Tuesday...The conditions (winds) are anticipated to be dropping below Small Craft Advisory early. Wednesday and Thursday...Winds may increase to Small Craft Advisory criteria Wednesday then decrease through Thursday. Seas could remain at 5 feet or higher on the ocean waters. && .HYDROLOGY... With the trend toward warmer solutions, models indicate that the threat for heavy rain along the I-95 corridor has increased. Consensus of operational model solutions suggests a swath of 1-2+ inches in this general area. These totals have been observed to generate localized flooding on several occasions during the past few months. Additionally, there are indications that some of the rainfall may result from convection, especially late tonight into early Sunday morning. Should rainfall rates approach/exceed half an inch per hour, urban and small stream flooding is likely to occur, especially in the quickly responding basins within and surrounding the Philadelphia metro. River flooding is possible, but appears to be more likely if QPF exceeds the current forecast (i.e., widespread totals of 2+ inches). && .TIDES/COASTAL FLOODING... Onshore continues across the region, and will increase tonight and into Sunday morning. With the approaching full moon, the threat of coastal flooding will increase by Sunday morning`s high tide. However, winds are expected to become more southerly late tonight, which should mitigate a more substantial coastal flooding event. To this point, guidance continues to advertise mainly minor flooding, though models do tend to exhibit a low bias in these sorts of events. Notably, the Stevens Institute ensemble guidance does suggest potential for spotty moderate flooding, especially on the northern New Jersey coast. Also noteworthy is the potential for heavy rainfall tonight and Sunday morning, which may exacerbate coastal flooding owing to contributions from freshwater runoff. At this point, however, think widespread minor flooding is more likely on the New Jersey and Delaware Atlantic coasts, along Delaware Bay, and the tidal Delaware River, for Sunday morning`s high tide. Some locally moderate coastal flooding remains possible. As a result, we have issued a coastal flood advisory for the above-mentioned areas. As flow will become strongly offshore by Sunday afternoon, coastal flooding is not expected with high tides following Sunday morning`s. At this time, coastal flooding is not expected for the eastern shores of Chesapeake Bay. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Winter Weather Advisory until 1 PM EST Sunday for PAZ060>062- 103-105. Flood Watch through Sunday afternoon for PAZ070-071-101-102- 104-106. Coastal Flood Advisory from 10 AM to 3 PM EST Sunday for PAZ070-071-106. Winter Storm Warning until 1 PM EST Sunday for PAZ054-055. NJ...Winter Weather Advisory until 1 PM EST Sunday for NJZ007>010. Coastal Flood Advisory from 5 AM to 11 AM EST Sunday for NJZ012>014-020>027. Flood Watch through Sunday afternoon for NJZ012>019. Coastal Flood Advisory from 8 AM to noon EST Sunday for NJZ016. Coastal Flood Advisory from 10 AM to 3 PM EST Sunday for NJZ015-017>019. Winter Storm Warning until 1 PM EST Sunday for NJZ001. DE...Coastal Flood Advisory from 5 AM to 11 AM EST Sunday for DEZ002>004. Flood Watch through Sunday afternoon for DEZ001. Coastal Flood Advisory from 8 AM to noon EST Sunday for DEZ001. MD...Flood Watch through Sunday afternoon for MDZ008. MARINE...Freezing Spray Advisory from 1 AM to 6 PM EST Monday for ANZ430-431-450>455. Gale Warning from 8 AM Sunday to 6 PM EST Monday for ANZ430- 431-450>455. && $$ Synopsis...Staarmann Near Term...Fitzsimmons/Johnson/MPS Short Term...Fitzsimmons/Johnson Long Term...Fitzsimmons/Johnson Aviation...Gorse/MPS/Staarmann Marine...Gorse/MPS Hydrology... 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