Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 280329 AFDOKX Area Forecast Discussion National Weather Service New York NY 1129 PM EDT Tue Oct 27 2020 .SYNOPSIS... Weakening high pressure tonight gives way to an approaching weak wave of low pressure for Wednesday. Frontal boundary associated with weak low moves south of the region Wednesday afternoon into Wednesday night. Remnants of Zeta enters the area south of Long Island Thursday followed by an upper level trough Friday. Strong high pressure then builds into the area over the weekend followed by a second trough early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Forecast is on track. The forecast temperatures and dewpoints are within a few degrees of their respective observed values. Temperatures generally in the upper 40s to mid 50s are only expected to lower 3-5 degrees overnight. With initial temperature and dewpoint differences near 10 degrees, enough low level drier air will preclude any rain from making it to the ground. Low levels will become more moist later overnight with measurable rain forecast as it moves in from the west. There will be an increasing chance of light rain tonight as high pressure weakens and weak low pressure approaches from the south and west. Models continue to show the trend of RH increasing from approx 10kft and lower. An upper jet streak will be nearby, but not in the best position for upper divergence and enhanced synoptic lift for our area. Models however show some disorganized mid- level shortwave lift with increasing winds in the 850-700mb layer, and with models trending wetter in the QPF fields over the past 24 hours, will increase PoPs from the previous forecast. Greatest overall chances will be after midnight and NW of the city. Low temperatures will be a few degrees above normal. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... The best combination of moisture and lift for rain chances will be in the morning on Wednesday with all locations likely seeing some rain. Rainfall will be generally on the lighter side. Mid levels begin to dry out thereafter, so PoPs lower in the afternoon with partial clearing. Any clearing in the afternoon and evening will be replaced by increasing clouds Wednesday night in advance of tropical moisture approaching from the Gulf states. There is a slight chance that some areas see some rain before daybreak. Daytime temperatures will be near normal with nighttime temperatures above normal. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Thursday the remnants of Zeta enters the DelMarVa region promoting initially warm frontal showers locally. As the day progresses an area of precipitable water values around 1.2 to 1.6 inches soak the forecast area with heavy rainfall throughout the evening. QPF totals are around 1 to 1.5 inches with this initial round of rain could induce localized street flooding. The good news is the rain is progressive as a +160 kt jet streak over central New York quickly moves the system out of the area. A second round of moderate to heavy rain arrives Friday with the main upper level trough. This second system is more complex as the trough brings in 1000-500mb thickness less than 540dm meaning that there is a potential for mixed precip within the rain. Model soundings over the Lower Hudson Valley and northern Connecticut Friday morning does show snow possible but the low levels below 1000 to 500 ft may remain above freezing. Nevertheless have opted to include a rain snow mix in the grids for Friday morning. Accumulations are unlikely but cannot be ruled out as surface temperatures early Friday morning hover around 34-36 degrees. During the day the region warms into the low 40s. Over the weekend a strong high pressure system builds behind the trough into the Northeast. Dew points drop dramatically into the 20s and 30s particularly for our inland counties. This sets up the possibility of widespread freezing temperatures Saturday morning. The dry air zeros out the rain chances through most of the weekend. The high slides off to the east Sunday afternoon as the next trough enters the Northeast region. The trough and low pressure system could initiate additional showers late Sunday into Monday. Temperatures fall into the 50s to start the week following the cold front. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Weakening high pressure tonight gives way to an approaching weak wave of low pressure for Wednesday. Frontal boundary associated with the low eventually pushes south of the region Wednesday afternoon into Wednesday night. VFR conditions expected through the evening but deteriorating conditions expected overnight into Wednesday morning with ceilings dropping to MVFR and eventually IFR. Visibilities are expected to drop to MVFR. There will be some light rain moving across during this time. Improvement to VFR is expected Wednesday afternoon after the rain has ended. Winds are less than 10 kts through the TAF period. Wind direction is variable tonight into Wednesday morning before becoming more west to northwest Wednesday afternoon into Wednesday evening. ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty... Amendments are expected to better refine timing of MVFR and IFR which may vary a few hours from the TAF. Improvement timing from IFR to MVFR and MVFR to VFR could also vary a few hours compared to TAF. .OUTLOOK FOR 00Z THURSDAY THROUGH SUNDAY... .Wed night...VFR with W to NW flow. MVFR possible late with a slight chance of rain. .Thu...Rain developing with increasing NE winds. IFR possible by late in the day. .Thu Night...Rain with NNE winds 20-30 kt. Higher gusts possible near the coast. IFR. .Fri...Rain ending, possible mixed with snow mainly N of NYC. N winds gradually decreasing. NE-N winds near 20 kt with gusts 25-30 kt during the day along the coast. .Sat...VFR with light SW flow. .Sun...MVFR possible with SW winds near 15 kt with gusts near 20 kt. Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 && .MARINE... Winds and seas forecast on track with similar forecast and observed values. Winds will be light and mainly offshore tonight before shifting SW and increasing somewhat during Wednesday. The light winds and a lack of significant swell will sustain sub-advisory conditions on all waters through Wednesday night. By Thursday night winds and seas increase to above SCA criteria. Waves rise to 8-11 ft, with NE gales expected mainly on all but the western Sound and NY Harbor by late Thu night, and continuing into early Fri evening even as winds back N after the passage of low pressure, the combination of the remnants of Zeta plus an extratropical low developing to its west. Lingering hazardous ocean seas will continue into late Fri night. By Saturday morning sub SCA conditions return with south to southwest winds. The next system passes late Sunday night into Monday. Winds increase to 20-25kts out of the north with gusts possible up to 30kts with SCA conditions lasting until Tuesday morning. && .HYDROLOGY... No hydrologic impacts through Wednesday night. Areal QPF for Thursday into Friday averages around 2 to 2.5 inches. Most of this should be of long duration, with only nuisance impacts, but there could be a window for heavier rainfall and greater impact from late day Thu into Thu night. && .TIDES/COASTAL FLOODING... The high tide cycle on Fri is of concern for widespread minor to locally moderate coastal flooding as astronomical high tide levels rise in association with the full moon on Halloween, and as strong NE winds bring in surge. An early look per latest guidance suggests total tide departures of at least 1-1/2 to 2 ft and locally 2-1/2 ft, with a worst case about 1/2 foot higher than that. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JC/DJ NEAR TERM...JC/JM SHORT TERM...JC LONG TERM...DJ AVIATION...JM MARINE...JC/DJ/JM HYDROLOGY...JC/DJ TIDES/COASTAL FLOODING...

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