Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 210146 AFDOKX Area Forecast Discussion National Weather Service New York NY 946 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 overnight 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/... 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 overnight. Clouds increase ahead of the next wave of low pressure. In addition, stratus should encroach from the SE. Showers approaching NW zones, and should pass and weaken. Thereafter, upstream showers/thunderstorms will approach after midnight. With SE winds increasing, plus 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 mention of thunder. Showers and possible thunderstorms become likely to categorical late tonight into early Friday. && .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 /02Z FRIDAY THROUGH TUESDAY/... Weak low pressure will track from the Great Lakes into southern Quebec through Fri with a warm front remaining SW of the area. A wave of low pressure is forecast to develop on this boundary and pass S of the area Fri aftn/eve. VFR to start...with conds dropping to IFR/LIFR overnight. Already seeing signs of stratus on eastern Long Island and is more widespread over ern MA. A light E-SE flow will prevail tonight with areas of fog also developing. Area of showers moving through Central NYS may brush KSWF between 03-04z with low chc tstm. looks like shower activity will hold off until late tonight/early Fri morning. Isold thunder is possible...but coverage too low to include in tafs. Once again onset of IFR could be several hours off and timing of showers may need to be amended. Guidance all points to low clouds lingering through the day Fri with a light ely flow continuing. IFR likely at the coast...may be able to improve to low end MVFR for a few hours during the aftn...but confidence in forecast aft 15z is low. Could be additional showers around late in the day as wave of low pres passes to the S and frontal boundary moves through although coverage looks meager attm. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: vsbys could be lower between 11z and 15z. KLGA TAF Comments: vsbys could be lower between 11z and 15z. KEWR TAF Comments: vsbys could be lower between 11z and 15z. Conds may remain IFR all day. KTEB TAF Comments: vsbys could be lower between 11z and 15z. Conds may remain IFR all day. KHPN TAF Comments: vsbys could be lower between 11z and 15z. KISP TAF Comments: vsbys could be lower between 11z and 15z. .OUTLOOK FOR 00z SATURDAY THROUGH TUESDAY... .Friday night...IFR in the evening, with cold fropa and improving conds late. .Saturday...VFR. .Sunday...CHC MVFR/rain. .Monday...CHC MVFR/rain in the morning, VFR in the afternoon. .Tuesday...VFR. && .MARINE... 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, onshore flow and higher dew points over cool water, areas of fog develop overnight 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. && .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...24 MARINE...Fig/JM/PW HYDROLOGY...Fig/JM is the U.S. government's official web portal to all federal, state and local government web resources and services.