Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 301628 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1228 PM EDT Thu Mar 30 2017 .SYNOPSIS... High pressure will move offshore today. Low pressure moving through the Ohio Valley on Friday will redevelop near the New Jersey coast Friday night and move offshore on Saturday. Canadian high pressure will move into the area for Sunday and Monday. Low pressure over the Ohio Valley on Tuesday will move through the middle Atlantic Tuesday night and offshore on Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Dry weather continues today as high pressure slides through the region. Mid and high clouds will increase and thicken into this afternoon as clouds associated with low pressure over the Midwest stream into the Northeast and Mid-Atlantic. Temps on track to top off in the 40s in the Poconos and in the low to mid 50s elsewhere. Light NE winds will become SE through the afternoon as the high moves offshore. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... Low pressure will continue its track eastward tonight along a warm front positioned over the Midwest. The nose of a southerly low-level jet ahead of this system will be positioned over the Mid Atlantic tonight. Forcing for ascent over the region will predominately be provided by isentropic lift as warm, moist air overruns the low- level baroclinic zone situated over the Ohio Valley-Delmarva. PoPs increase from NW to SE this eve. Did not ramp up PoPs quite as fast as I would normally like to in this close to the event due to some notable timing differences with respect to onset of precip this eve. Did have enough confidence to increase to PoPs to likely for southern Poconos this evening and then eventually the remainder of the CWA overnight. QPF amounts will generally be light tonight (under one-quarter inch) with the deeper/stronger lift still upstream of the region. Despite the center of the high retreating to our northeast, CAD wedge will be reinforced in-situ owing to the effect of evaporative cooling when precip initially falls into an relatively dry boundary layer. Temperatures were populated using a blend with much of the weighting from the NAM 12km/NAM 3km nest as this model has shown to handle complex thermal profiles in CAD setups like this. Freezing rain is likely overnight tonight in the mountains of Carbon and Monroe Counties in PA and Sussex County, NJ as temperatures fall into the lower 30s. Held off on issuing a late second period Freezing Rain Advisory since areal coverage looks to be limited to the highest elevations (approximately above 1300 ft). However, places like Mount Pocono and High Point may see a few hundredths of an inch of ice accretion late tonight, especially on elevated surfaces such as trees and wires. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The primary players during the long term continue to be two southern stream systems that are expected to impact our region in the Friday- Saturday and Monday-Tuesday time frames. The first system will produce a wide swath of rainfall across the region, with localized amounts in excess of 1.5 inches, especially across the I-95 corridor. While urban and poor drainage flooding are possible, and have been mentioned in the HWO, we do not expect major impacts on rivers and streams. Freezing rain looks to persist into at least the morning on Friday along the higher elevations of Carbon, Monroe and Sussex (NJ) counties. Currently, our weather grids indicate a change over to just plain rain with temperatures rising above freezing in these high elevations by the afternoon. However, some of the colder model solutions indicate the potential for freezing rain to persist into Friday afternoon and perhaps Friday night. The latest storm total ice graphic was populating running the FRAM off our forecast database and represented an increase in the icing amounts ranging from a few hundredths of an inch in these counties at around 1000 ft in elevation to almost a quarter inch at above 1800 ft in elevation (isolated areas in Monroe County). These amounts may need to be increased if trends toward a prolonged icing event (i.e., freezing rain persisting into Friday afternoon/night) continue. Looking ahead to early next week, the next system is expected to bring more precip to our region, especially Monday night into Tuesday. This setup continues to look warmer compared to the previous system, given the absence of high latitude blocking, and would favor predominantly rain. Temperature-wise, daily means are expected to average near normal Friday thru Sunday, then around 5 to 10 plus degrees above normal Monday thru Thursday. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR. BKN-OVC CIGs will lower to 5000 ft by 00Z Friday. Winds will generally turn to the SE at 5-7 KT through this afternoon. CIGs lower from W to E tonight as precip arrives. Held off MVFR CIGS/VSBYs until closer to midnight EDT for ABE/RDG and until 07-09Z farther east toward I-95 terminals. However, there is a low chance that MVFR begins 2-4 hours earlier than that if precip moves in faster than currently forecast. PROB30 group covers this potential. SE winds 6-12 kt are expected tonight. OUTLOOK... MVFR possible in low clouds Friday and Friday night, then again Monday night into Tuesday. Otherwise, predominantly VFR. Southeast winds may gust 20 to 25 knots on Friday, and northwest winds may gust around 20 knots on Saturday. && .MARINE... Winds and seas below SCA today and tonight. NE winds 5-15 kt this morning will become SEly this afternoon and tonight. These SE winds will initially be light this afternoon but increase to 15-20 kt by late tonight. OUTLOOK... We have issued a Gale Watch from 18Z Friday to 09Z Saturday for the northern NJ coastal waters (ANZ450-451) for southeasterly wind gusts up to 35 knots during this time frame. Outside of the Gale Watch, a Small Craft Advisory is in effect for Friday and Friday night for the southern New Jersey and Delaware coastal waters. Hoisted a SCA for northern DE Bay in addition to lower DE Bay, but for Friday afternoon/early evening. A Small Craft Advisory may be needed on Saturday for northwest wind gust of 25 to 30 knots and seas of 5-8 FT, especially across the NJ coastal waters. Another SCA may be needed Monday night into Tuesday, as southeasterly winds and seas increase. && .TIDES/COASTAL FLOODING... Though astronomical tides will be gradually diminishing through the week now that we are past the new moon, the threat of minor tidal flooding along the NJ and DE Atlantic coasts increases by Friday. Tidal anomalies are currently around 0.5 feet above astronomical this morning. We expect this to continue today. Beginning tonight, a low pressure system will bring a prolonged period of onshore flow, further increasing the surge. Forecast tidal levels from the ETSS have trended slightly upward for tonight, indicating Reedy Point, Lewes and Sandy Hook could reach their minor coastal flood stage with the high tide cycle late this evening. These ETSS forecasts would fall just shy of threshold for Coastal Flood Advisory with spotty minor coastal flooding tonight. OFS guidance for tonight is significantly lower than ETSS. It seems the ETSS may be a bit overdone since with the expected SE wind direction and lighter wind speeds, we should not see a surge any higher than what we currently have tonight. The high tide of most concern is still Friday evening and Friday night, particularly along the northern and central New Jersey Shore. By this tide cycle, it will take a surge of 0.8 to 1.0 feet to reach minor flooding thresholds, which is likely. However, not sure yet if we will have another 0.3 feet surge to reach advisory thresholds. The exact magnitude of the surge will be dependent on how quickly the onshore flow develops and how strong it will be by Friday. Given the fetch and duration of southeasterly flow, some of the surge guidance is also raising water levels along the eastern shore of Maryland, particularly for the Friday evening high tide. At this time, none of the guidance reaches the minor flooding threshold, but this will bear watching. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 8 AM Friday to 5 AM EDT Saturday for ANZ452>455. Gale Watch from Friday afternoon through late Friday night for ANZ450-451. Small Craft Advisory from 2 PM to 8 PM EDT Friday for ANZ430. Small Craft Advisory from 8 AM to 8 PM EDT Friday for ANZ431. && $$ Synopsis...Franck Near Term...Klein Short Term...Klein Long Term...Franck Aviation...Franck/Klein/MPS Marine...Franck/Klein/MPS Tides/Coastal Flooding... is the U.S. government's official web portal to all federal, state and local government web resources and services.