Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 282332 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 732 PM EDT Wed Oct 28 2020 .SYNOPSIS... The remnants of Hurricane Zeta will move through the Mid-Atlantic Thursday into Friday. High pressure will build across the region on Saturday, exiting to the northeast Saturday night. A cold front will move through our area on Sunday night. High pressure will build across the southeastern states, influencing our weather through the middle of the new week. && .NEAR TERM /THROUGH THURSDAY/... The remnants of Zeta will be approaching our region through the day tomorrow, and the center should be off shore by late tomorrow. As we have been mentioning for the past several days, there are several risk factors for heavy rain, including a deep warm cloud layer and high precipitable water values. In a change from previous days, the forecast axis of heaviest precip has shifted south, now mostly south of the PA turnpike and I-195 corridor. More information on the hydrology concerns are discussed in the hydro section below. With the remnants of Zeta quickly approaching during the day, winds will increase quickly during the second half of the day. However, at this point, it still looks like winds should stay below wind advisory criteria. Thanks to the persistent cloud cover, we won`t see a big swing in temperatures from tonight into tomorrow. Lows will likely be within 10 degrees of the highs. && .SHORT TERM /THURSDAY NIGHT/... Rain will continue, even with the remnants of Zeta already offshore, as a low and mid level short wave trough will be digging in quickly behind it. However, by tomorrow night, our moisture advection will be limited. Thus, expect the intensity of the rain to decrease starting as early as tomorrow evening. We will start to see some significant cold air advection through the night. Consequently, some snow could mix with the rain in the higher terrain of the Poconos and NW NJ. Still think there will be little if any accumulation thanks to relatively warm ground and rain ahead of the snow. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The remnants of Zeta and the trailing secondary low pressure should be offshore by Friday morning, continuing to pull away to the east. Some rain will still be around the region but should be on the lighter side and will start to exit the region from west to east, finally ending most locations by Friday afternoon. Skies will remain cloudy through much of the day with some clearing possible as we head towards the evening. High pressure will slide across the Great Lakes region and into the Mid-Atlantic Friday night. Skies really clear as the flow turns more to the north-northwest. With clear skies in place, we radiate efficiently and temperatures should drop well into the 20s north and west of the I-95 corridor. Along the I-95 corridor and points to the south and east, temperatures will fall into the lower to mid 30s. The exception is along the immediate coast of New Jersey and Delaware where temperatures are more likely to stay in the mid/upper 30s. Additionally, winds should drop off and become light through the overnight period. This will allow for frost to develop and with the temperatures dropping down near freezing, we will likely need some form of frost/freeze headlines for late Friday night/early Saturday morning. The high will cross over our area on Saturday, quickly pushing off to the northeast as another low pressure system moves through Ontario and, with its cold front, makes its way eastward. Being between the departing high and the approaching cold front, we should have a very nice fall day in place with highs in the 40s to low 50s. Skies should be mostly clear through the day but we will start to see them creep back in from the east as the return flow brings some moisture back into our area Saturday night. A few light showers may occur, mainly along the coast late Saturday night but not confident enough to include in the forecast at this time. Overnight lows will warmer than the night before and mostly in the 30s to lower 40s. Low pressure will cross through Ontario and into Quebec on Sunday. Its attendant cold front will move through central Pennsylvania on Sunday, crossing through our forecast area Sunday evening. We should see some warming ahead of the front in the southwest flow and daytime highs will be into the 50s to lower 60s. The front will also bring a round of rain to the region and some fairly gusty winds as the gradient tightens up. The rain should taper off late Sunday night as the front exits offshore. A deep upper trough will also cross the region Sunday night and this will help to usher in some much colder air aloft. The timing of when the cold air arrives and the final showers exit the region will be important as it means we could see some mixed ptypes, especially across the southern Poconos and far northwestern New Jersey. For now, models show the precip exiting well before the cold air arrives so we leave out the mention of any mixed precipitation at this time. Behind the front, in the northwest flow, we should dry out and see skies clear once again. Another strong radiational cooling night is likely to take place and overnight lows will drop down into the 30s, with some upper 20s across the higher terrain of the southern Poconos. High pressure will move from the central plains to the southeastern states Monday through Tuesday, moving off the Atlantic coast on Wednesday. The deep upper trough cross the area on Monday and exits to our east Monday evening. We should be dry through the first half of the week with mostly clear skies. Temperatures will start off cool on Monday as the trough crosses the region, generally in the 40s, but as the high starts to take hold of our weather the airmass will modify and temperatures should be able to warm into the upper 40s/ lower 50s on Tuesday and then upper 50s to lower 60s by Wednesday. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 06Z...Ceilings will likely be waffling between MVFR and VFR for much of this period, though a few sites may have transient IFR conditions through this time. Mostly light southwesterly winds. Moderate confidence. Late tonight...Ceilings should lower quickly back to IFR or even LIFR. Winds will become light and variable, with the direction beginning to flip to northeasterly. Moderate confidence on the pattern, but low confidence on the timing details. Thursday...IFR conditions expected for most, if not all day. Ceiling should be the primary controlling factor, but visibility restrictions are possible too, especially in bands of heavy rain. If there is a long enough lull, there may be brief windows of improvement to MVFR, but this is unlikely. Northeasterly winds of 10 to 15 kt with gusts up to 20kt. Moderate confidence. Outlook... Thursday night...IFR or even LIFR ceilings are expected for much of the night. Northeasterly winds of 10 to 20 kt with gusts up to 30 kt, with the strongest winds at KACY. Non-convective low level wind shear is possible. Moderate confidence on pattern, but low confidence on timing of category changes. Friday...MVFR/IFR conditions possible through the morning with improvement to VFR expected by the afternoon. Northwest winds around 10 to 20 knots with gusts up 30 knots possible. Higher gusts possible, especially at KACY. Moderate confidence. Saturday...VFR conditions expected. Northeast winds in the morning will veer to the east and then southeast by Saturday night with speeds less than 10 knots. Moderate confidence. Sunday...Mainly VFR conditions but periods of MVFR are possible in rain, mainly in the afternoon/evening as a cold front crosses the terminals. Southwesterly winds 5 to 15 knots. Moderate confidence. Monday...VFR conditions expected. Northwest winds 15 to 20 knots with gusts up to 30 knots possible. High confidence. && .MARINE... Marine impacts likely from the remnants of Zeta late Thursday through Friday. For tonight, sub-advisory conditions are expected with an offshore wind around 5-10 kts and seas 1-3 feet. Winds and seas will begin to increase throughout the day Thursday. The strongest winds will be across the southern ocean waters by late Thursday afternoon and into the evening as the remnant low passes offshore along with heavy rain. Wind gusts of 35-40+ kts are expected mainly south of Atlantic City during this period. Seas in these areas will build up to 8 feet. The Gale Watch has been upgraded to a Gale Warning starting late Thursday afternoon. Additionally, a Gale Watch has been issued for the lower Delaware Bay as the aforementioned gale conditions could impact this area, but confidence is still too low for a warning at this time. A Small Craft Advisory has been issued for the upper Delaware Bay. Outlook... Thursday night through Friday...Northerly winds will continue to build after the remnant low of Zeta pulls away from the coast Thursday night with winds of gale force expected through at least the first half of Friday across the ocean waters. Seas will build to 6-9 feet with winds gusting up to 40 kts by around daybreak Friday across the ocean waters. Small craft advisory conditions are expected to persist across Delaware Bay during this time as well. Friday night through Saturday...Winds and seas will continue to decrease to below advisory criteria by the overnight period Friday night. Saturday will also be below advisory criteria with easterly winds 5-10 kts and seas 2-4 feet. Sunday through Monday...Winds and seas will increase throughout the day Sunday to advisory criteria. Expect offshore winds gusting 25-35 kts into the overnight period Sunday night with seas of 3-5 feet. Gale force wind gusts of 35-40 kts are possible, especially into Monday. && .HYDROLOGY... The remnants of Zeta will be moving through our region, bringing a few waves of heavy rain from Thursday morning through Thursday evening. At this point, we expect the heavy rain to be confined to the period from tomorrow morning through early tomorrow evening. However, light rain could linger Thursday night into Friday morning. Confidence is increasing that the axis of heaviest rain will be south of the PA Turnpike and Interstate 195 corridor, where a flood watch has been issued. Storm total rain of 2 to 4 inches is possible across the watch area. Elsewhere, storm total rain amounts of 1 to 3 inches is possible. Within the watch area, overland and road flooding as well as small stream flooding are possible. However, at this point, we are not expecting any flooding on main stem rivers. && .TIDES/COASTAL FLOODING... The combination of the remnants of Hurricane Zeta and a full moon Friday will lead to the potential for minor coastal flooding across portions of New Jersey, Delaware, and potentially the northern Chesapeake Bay. Astronomical tides will already be running high for the blue moon before accounting for surge from what will be a deepening low pressure system off our coastline. This will lead to easterly flow for the NJ coastline during the day on Thursday followed but strong northeasterly flow overnight on Thursday. This will push water into the back bays and will likely cause some minor tidal flooding especially across coastal NJ. Using guidance from the Stevens Institute there are hints that the tide gages could reach moderate flood stage however I`ve opted to keep the forecast currently minor. Per NHC, typically in these type storms the ETSS guidance typically under performs on the tidal surge so I`ve gone with a blend of the median of the Stevens ensemble guidance and a bias corrected ETSS/ESTOFS blend which worked out quite well running slightly higher than the raw ETSS guidance. Currently tidal flooding is not expected on the tidal Delaware river. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flood Watch from 6 AM EDT Thursday through Thursday evening for PAZ070-071-101>104. NJ...Flood Watch from 6 AM EDT Thursday through Thursday evening for NJZ016>027. DE...Flood Watch from 6 AM EDT Thursday through Thursday evening for DEZ001>004. MD...Flood Watch from 6 AM EDT Thursday through Thursday evening for MDZ008-012-015-019-020. MARINE...Gale Warning from 6 PM Thursday to 2 PM EDT Friday for ANZ450>455. Small Craft Advisory from 6 PM Thursday to 2 PM EDT Friday for ANZ430. Gale Watch from Thursday evening through Friday afternoon for ANZ431. && $$ Synopsis...Meola Near Term...Johnson Short Term...Johnson Long Term...Meola Aviation...Johnson/Meola Marine...Staarmann Hydrology...WFO PHI Tides/Coastal Flooding...Deal

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