Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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133 FXUS61 KPHI 132049 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 349 PM EST Fri Dec 13 2019 .SYNOPSIS... Low pressure across the southeast states will strengthen while moving across the Middle Atlantic region later tonight and Saturday. The low will then move up across New England and into eastern Canada through Sunday. High pressure will build over the area later Sunday before moving away Monday. Another low and its associated fronts will affect the area Monday afternoon through Tuesday. More high pressure will follow for the middle and end of next week. && .NEAR TERM /UNTIL 6 PM SATURDAY/... Mother Nature is cooperating with a freaky Friday forecast for your Friday the 13th. A strong area of low pressure continues to develop to our south over the Carolinas this afternoon. This low will continue to intensify and move towards the northeast and into our region through the overnight hours, bringing a whole slew of excitement as it does so. Strong WAA and PVA ahead of the surface low will continue to promote surface cyclogenesis and height falls ahead of the system as an energetic and strongly negatively tilted mid-level trough lifts out of the lower Mississippi River Valley and into the mid- Atlantic. A strong 150-kt 300 mb jet streak developing directly over the Delaware Valley will also provide forcing for ascent, and there is and will be plenty of moisture available with strong southerly flow off the Atlantic ahead of this system. PWATs from 1-1.5 inches will begin to advect into the region, thus, a widespread moderate to heavy rain event is in store for tonight. Light to moderate rain is currently overspreading the region, and will continue to fill in and increase in intensity through the evening. At this point, the heaviest rainfall is likely to fall just ahead of the surface low through 8 AM Saturday. The progressive nature of this storm will be the one saving grace, as the current track of the surface low takes it right across much of the Garden State. As the low moves overhead, rainfall rates will likely taper off a tad as we head into the later morning hours. Current hi-res models are suggesting another line of heavier rainfall will develop into the early afternoon. There is some CAPE associated with this line, thus we cannot rule out a clap or two of thunder. After this, we will begin to dry out, save for a few wrap around showers into the evening and early overnight hours. This could mix with some wintry precip for a brief time in the Poconos and Sussex County, NJ, but no significant impacts are expected at this time. Total rainfall accumulations are forecast to range from 1 to 1.5 inches across the region, with the potential for localized amounts to near two inches. Given the already sodden ground across Central and Northern NJ, this may lead to some flood concerns, which are outlined in the hydro section below. Otherwise, a warmer than average overnight tonight with lows in the mid to upper 40s across much of the area and above average highs in the mid to upper 50s Saturday. && .SHORT TERM /6 PM SATURDAY THROUGH SUNDAY NIGHT/... Quieter conditions Sunday and Sunday night as the low pulls off to the northeast and high pressure continues to build into the region. As low pressure lifts to our northeast, the pressure gradient behind it will tighten quite significantly. Winds above the surface increase as well and could mix down to the surface. This could potentially lead to wind gusts of at least 25-35 mph, with occasional higher gusts of near 40 mph late Saturday afternoon, Saturday night into early Sunday. High temperatures will be cooler in the low to mid 40s. Lows in the upper 30s Saturday night as the low pulls out of the area. && .LONG TERM /MONDAY THROUGH FRIDAY/... Monday thru Tuesday night... An area of low pressure will form across the lower Mississippi Valley Monday and then move NE into the Middle Atlantic area by Tuesday. The system is not strong as it nears, but much like the present system, it will deepen as it moves through. A shield of precipitation will develop and run ahead of the system, arriving across our area Monday. The precipitation will continue into Tuesday before tapering off. Right now, much of the precip will be rain, but the onset may contain some mixed or frozen precip, especially if it begins early enough Monday. Right now the rain/snow/rain-snow mix/ wording will be used, but as we get closer to the event, some sleet or perhaps some freezing rain may be added to the fcst. Highs Monday will be a little below normal, but by Tuesday, readings should climb above normal with low/mid 50s for the Delaware Valley (S/E) and mid/upper 40s for the Lehigh valley, Berks County and nrn NJ. A cold front will follow for Tue night, ending the milder temperatures. Wednesday thru Friday... Colder and drier air arrive across the area Wednesday and lasts into the end of the week. As high pressure noses in, fair weather is expected, so we will keep the fcst dry for Wed thru Fri attm. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... Rest of Today...Ceilings have lowered to IFR this afternoon and visibilities will also lower as rainfall moves into the area. East to northeast winds around 5 to 10 knots. --High confidence. Tonight...IFR conditions expected to continue through the overnight ours with periods of LIFR possible as rain moves across the area. Periods of moderate to heavy rain will occur at times helping to reduce visibilities. Light east to northeast winds around 5 knots may become light and variable for some areas. --High confidence on IFR occuring, with lower confidence on how low conditions will get. Saturday...IFR conditions will continue through much of the day Saturday. A break in the steady rainfall will transition to drizzle around daybreak for several hours, before another period of moderate to heavy rainfall briefly moves across the area round midday. Light and variable winds will increase out of the east to southeast around 5 to 10 knots. Winds will shift to the south to southwest and increase to 10 to 15 knots with gusts around 20 knots to 25 knots during the afternoon. --Moderate confidence. Outlook... Saturday night...An improvement to MVFR is possible during the evening hours and may improve to VFR overnight. Winds become westerly around 10-15 knots with gusts of 20-30 knots possible at times. --Moderate confidence. Sunday...MVFR ceilings may develop after sunrise for a few hours, before lifting to VFR by late morning into the afternoon. West winds 15-20 knots, with gusts 20-30 knots. --Moderate confidence. Sunday night...VFR conditions expected. West winds early, become light and variable overnight. --Moderate confidence Monday thru Tuesday night...MVFR or IFR expected with low CIGS. Rain/snow and fog expected. Wednesday...VFR returning to the area. && .MARINE... Seas have increased already today and have reached 5-7 feet. Therefore, we have started the Small Craft Advisory as of now. Winds will remain around 10 to 15 knots out of the east with gusts around 20 knots. Winds will turn more to the south and then southwest on Saturday increasing to 15 to 20 knots with gusts around 25 to 30 knots starting late afternoon/early evening. Seas will remain elevated through Saturday. OUTLOOK... Saturday night...Gale Watch in effect for all waters, including Delaware Bay as 35-40 knot wind gusts could develop behind a departing low pressure system. Sunday...Gale Watch continues for the Atlantic coastal waters as wind gusts could continue to reach 35 knots through midday before diminishing to advisory levels during the afternoon. Sunday night...Winds lower below advisory levels overnight and seas subside below 5 feet as well. Monday thru Tuesday night...SCA expected. Rain and fog expected. && .HYDROLOGY... Rainfall amounts will range from 0.50-1.00 inches for portions of eastern Pennsylvania, northwestern New Jersey, and northern Delmarva. This rainfall amounts will not cause more than some ponding on roadways and nuisance type flooding. However, farther east, rainfall amounts are forecast to range from 1.00-1.50 inches, with some spots potential reaching 2 inches, especially across northeastern New Jersey, portions of coastal New Jersey, and southern Delaware. Again, ponding on roadways and poor drainage type flooding will be likely in these areas. However, for portions of northern and central New Jersey, as well as Bucks county have the potential for more widespread flooding impacts, including some river and creek/stream flooding. Therefore a Flood Watch has been issued for Bucks County in Pennsylvania, as well as portions of northeast and central New Jersey. The majority of the rainfall will occur tonight and the faster responding creeks and roadway flooding would occur tonight into early Saturday morning. However, some larger rivers, like the Passaic and Millstone, would not flood until later Saturday into Saturday night. && .TIDES/COASTAL FLOODING... Confidence has increased that we will see minor tidal flooding on the Atlantic oceanfront, south shores of the Raritan Bay and adjacent back bays. Astronomical tides remain high thanks to the full moon which just occurred on Thursday. We will have persistent onshore flow through much of the day tomorrow. A coastal flood advisory has been issued for the Atlantic oceanfront and the south shores of the Raritan Bay. For the Delaware Bay and tidal portions of the Delaware River, spotty minor flooding is likely, but there is less confidence there will be widespread minor flooding, so have held off on any advisory in these areas for now. We will see an abrupt shift to offshore flow by Saturday night. Therefore, not expecting the coastal flooding to continue into subsequent high tide cycles. With only a brief period of southerly flow, tidal flooding is not expected on the northeastern shores of the Chesapeake Bay. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flood Watch from 9 PM EST this evening through Saturday morning for PAZ105-106. NJ...Flood Watch from 9 PM EST this evening through Saturday morning for NJZ008>010-015. Flood Watch from 9 PM EST this evening through late tonight for NJZ012>014-019-020-026-027. Coastal Flood Advisory from 7 AM to 1 PM EST Saturday for NJZ012>014-020-022>027. DE...Coastal Flood Advisory from 7 AM to 1 PM EST Saturday for DEZ003-004. MD...None. MARINE...Gale Watch from Saturday evening through late Saturday night for ANZ450>455. Small Craft Advisory until 6 PM EST Saturday for ANZ450>455. Gale Watch from Saturday evening through Sunday morning for ANZ430-431. Small Craft Advisory from 1 PM to 6 PM EST Saturday for ANZ430- 431. && $$ Synopsis...O`Hara Near Term...Davis Short Term...Davis Long Term...O`Hara Aviation...Davis/Robertson/O`Hara Marine...Davis/Robertson/O`Hara Hydrology...Robertson/Kruzdlo Tides/Coastal Flooding...Johnson

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