Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 202249 AFDOKX Area Forecast Discussion National Weather Service New York NY 649 PM EDT Thu Apr 20 2017 .SYNOPSIS... A stationary front remains south of the region through Friday. A low pressure wave slowly approaches the region tonight into Friday, not moving across until Friday night. High pressure builds from the north Saturday. Weak low pressure will pass to the south Saturday night into Sunday night. Another wave of low pressure will move off the Southeast coast on Monday, and track slowly north through early Wednesday. High pressure builds back across the area on Thursday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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Mid/upper level trough passes across the Great Lakes region tonight. Surface low does the same, with occluded front tracking across PA, and Warm front approaching from the SW tonight. Some clearing occurred earlier, but clouds will increase ahead of the next wave of low pressure. In addition, stratus should encroach from the SE. Upstream shower progression will need to be watched, as they likely approach late this evening and through the overnight. With winds turning southeast and increasing, plus the shower coverage increasing, grounds will become moisture laden, leading to the development of low clouds and fog. Lows were a blend of MET and NAM12, upper 40s to lower 50s. Went a little on the cooler side with low temperatures because of advection of the relatively cooler air over the waters across the region. Also, models are indicating some elevated instability moving in with slightly negative Showalter indices. Most forcing and jet dynamics are north of the region so not much of a forcing mechanism to give extra strength to any showers or thunderstorms. Will maintain slight chance. Showers and possible thunderstorms become likely to categorical late tonight into early Friday.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Rain showers continue along with the fog early Friday. Fog could be dense early along the coast. Could still have some thunderstorms with probabilities of those being slight chance. Rain shower chances eventually decrease Friday afternoon from west to east as instability lowers but the forecast trend compared to previous forecast shows a lingering of the showers into the day and likewise a lingering of the fog across coastal sections. That low to the west is slow to move in. The SE flow and inversion just above the surface will keep more moisture trapped in the low levels. The temperatures during the day reflect this theme; a blend of the MET (2/3) and NAM12 (1/3) with some minor adjustments yields a range of lower 50s to lower 60s for highs. Friday night is when the low along with its occlusion will be moving southeast of Long Island. Mainly dry weather is expected. The winds switch to a more north to northwest flow while remaining light. Out east towards Southeast Connecticut and Eastern Long Island, some fog could redevelop Friday night with residual leftover ground moisture and more onshore flow over there. The lows were a blend of MET/MAV/ECS with minor adjustments conveying a range of mid 40s to lower 50s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Unsettled weather likely for much of the weekend and into next week as a cold front stalls south of the region on Saturday and a low pressure system moves near the area. Latest guidance trends continue to push the greatest precipitation further south over the weekend. The low may meander off the coast for a couple days with high pressure building to the north. This would result in an unsettled weather pattern with below normal temperatures into the middle of the week. High pressure builds back across the area on Thursday. A southwesterly flow on Thursday will allow temperatures to bounce back to above normal levels for this time of year. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... A stationary front will remain to the south through Friday. Weak low pressure and associated front will pass late tonight into Friday morning. Showers expected overnight into early Friday morning with patchy fog. VFR to continue into tonight. Easterly winds becoming more SE, generally under 10KT. Rain arrives between 04-06Z, however it could arrive a few hours earlier than currently forecast. Cannot rule out thunder but confidence is too low to currently include in TAFs. IFR ceilings return tonight with passing front and the development of fog. Expecting fog to remain through Friday morning which could fluctuate at times. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Timing of rain could be a few hours earlier than forecast. KLGA TAF Comments: Timing of rain could be a few hours earlier than forecast. KEWR TAF Comments: Timing of rain could be a few hours earlier than forecast. KTEB TAF Comments: Timing of rain could be a few hours earlier than forecast. KHPN TAF Comments: Timing of rain could be a few hours earlier than forecast. KISP TAF Comments: Timing of rain could be a few hours earlier than forecast. Vsby could be lower than forecast Friday morning. .OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY... .Friday...IFR and ISO TSTM early, then improvement to MVFR in aftn. .Friday night...MVFR in the evening, then VFR by late. .Saturday...VFR. .Sunday...CHC MVFR/rain. .Monday...CHC MVFR/rain in the morning, VFR in the afternoon. .Tuesday...VFR. && .MARINE...
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Overall, the pressure gradient remains weak through Friday night. Current ocean seas are between 3 to 4 feet. With winds staying near 10 kt or less and being primarily onshore much of the time period, these seas are expected to remain nearly constant. Overall, sub SCA conditions are expected through Friday night. Also with the weakness in the pressure gradient, and more onshore flow, areas of fog develop tonight into Friday on the water, which potentially could become dense. Eventually expecting fog to dissipate Friday afternoon but fog could return for at least some of the waters, mainly eastern, Friday night. Will monitor for possible dense fog advisory overnight into early Friday morning. Tranquil conditions across the area waters are expected Saturday through Monday. As high pressure remains to our north, the pressure gradient will increase resulting in a strengthening easterly flow. Small craft wind gusts will become likely on the ocean waters toward Tuesday morning and continue into Tuesday evening. Wind gusts may also approach small craft levels across the eastern Long Island Sound and the eastern Long Island bays. With the prolonged east flow, by late Tuesday afternoon ocean seas will likely build to small craft levels and remain into early Wednesday morning. As high pressure builds across the area waters later on Wednesday and into Thursday seas and winds will drop below small craft levels.
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&& .HYDROLOGY... Rain amounts through Friday will amount to under a half inch. However, with any thunderstorms, locally heavier rainfall amounts will be possible. Minor flooding will be possible in these thunderstorms especially in poor drainage and low lying areas. Precipitation amounts for the extended period will have no hydrologic impacts across the hydrologic service area. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...Fig/JM NEAR TERM...JM/PW SHORT TERM...JM LONG TERM...Fig AVIATION...CB MARINE...Fig/JM/PW HYDROLOGY...Fig/JM

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