Area Forecast Discussion
Issued by NWS Upton, NY

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402 FXUS61 KOKX 220027 AFDOKX Area Forecast Discussion National Weather Service New York NY 827 PM EDT Fri Apr 21 2017 .SYNOPSIS... Low pressure over southern Canada will continue to move east this evening, dragging an occluded front across the area tonight. High pressure then slowly builds in from the west on Saturday before building across the area on Sunday and then offshore on Monday. A wave of low pressure will move off the Southeast coast Monday, and track slowly north through midweek. High pressure will build back in for the end of the week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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As the primary low continues to move east across southern Canada, it will drag an occluded front across the area tonight. A weak low along a warm front passes south of Long Island overnight. Drizzle or sprinkles are possible, especially eastern locales due to low level saturation. With plenty of low level moisture and light winds, patchy to areas of fog, locally dense, is expected over much of the region late this evening and into the overnight hours. This should clear or improve by daybreak as slightly drier air begins to work into the region. Temperatures tonight will only fall into the mid 40s to around 50, several degrees above normal.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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With high pressure gradually building into the region from the west, Saturday should remain dry. Rain should stay just south during the day. Northwest flow will allow for some mid-level drying during the day, leading to at least periods of sunshine. Temperatures will rise into the low 60s, near normal for this time of year, before falling into the mid 40s at night.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/... A split upper flow across the Eastern U.S. will feature a departing shortwave trough across the Northeast at the onset of the period, with an anomalously far south closed low moving into the southeast. The latter of which will likely bring some inclement weather to the area for the first half of next week. High pressure will initially be in place Sunday into Monday with some uncertainty to the northern extent of the rain shield during this time. A confluent upper flow will reside across the area at the start of the period, with a deep layered W/SW flow converging with the northern branch of the polar jet. Initial thinking is this should keep the area under subsidence and drying, but any shift in this zone could bring light rain/clouds in sooner. The best timing for a steady rain appears to be Monday night through Tuesday night as the upper low moves offshore and warm, moist air overruns the region. This mainly appears to be an overrunning rain event. Up to an inch rainfall seems to be a reasonable possibility at this time. High pressure follows Wednesday night into Thursday with model differences on the amplitude of a deepening western trough and the ridging east of the Mississippi River Valley. A weakening cold front works across the area on Thursday per the GFS and GGEM, while the ECMWF dissipates it to the west. Leaned toward the ECMWF at this time, but these details are far too early to resolve. As for temperatures, near seasonable levels through mid week, if not a bit cooler during the daytime due to cloud cover and rain. A significant warmup is possible for the end of the week with warming heights aloft. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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A warm front remains south of the area...with a weak wave of low pressure tracking east along it this evening. A weak cold front moves through the region overnight. Weak high pressure will nudge in from the west for late Saturday into Saturday night. IFR/LIFR cigs expected through 03-07z with eastern terminals holding LIFR cigs longer closer to 07z. Gradually improving conds to MVFR then VFR into early Sat morning, with KGON and KISP taking longer and may not completely improve at these terminals until 10-12z. Winds diminishing late this evening and backing to the N and remaining light overnight. N-NW wind over 5 kts starts to punch in towards mid morning, with winds speeds around 10 kts by the Saturday afternoon. 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: LIFR to IFR conditions with gradual improvement after 7z. KLGA TAF Comments: LIFR conditions much of the night with gradual improvement after 7z. KEWR TAF Comments: Prevailing IFR cigs...with LIFR conds possible from 03z-07z. Gradual improvement begins after 07z. KTEB TAF Comments: Prevailing IFR cigs...with LIFR conds possible from 03z-07z. Gradual improvement begins after 07z. KHPN TAF Comments: Prevailing LIFR conds, with gradual improvement after 08z. KISP TAF Comments: Prevailing LIFR cigs...with IFR visibility from 02z to 07z. Gradual improving conditions after 8z, but timing of improvement may be delayed by 2-3 hours. .OUTLOOK FOR 18z SATURDAY THROUGH WEDNESDAY... .Saturday...VFR. NW winds 10-15 kt. .Sunday...VFR. .Monday...CHC MVFR in rain. E/NE winds. .Tuesday...CHC IFR/MVFR in rain. CHC E/NE gusts 20-25 KT. .Wednesday...Improving conds. N winds.
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&& .MARINE...
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A Dense Fog Advisory remains in effect into the early morning hours across the eastern waters as fog and low visibilities persist into the overnight period. Did expand across western LI Sound earlier. Fog should become more patchy in nature early Saturday morning before finally clearing by daybreak. Initial east winds may peak at 20 kt or so eastern waters for a short time. Seas across the eastern ocean waters, south of the south fork, have approached or remain around 5 ft. This should be short lived however. Will hold off on SCA issuance as conditions improve with weakening winds. A generally weak pressure gradient will result in winds 15 kt or less late tonight through Saturday night as high pressure builds into the region. High pressure over the waters will result in sub-sca conditions Sun into Mon. A low pressure system moving off the southeast coast Monday will track slowly north through midweek. A prolonged and increasing easterly flow will set up from Monday night into Wednesday. There may be a period of gusts approaching small craft levels on the ocean waters Tuesday and Tuesday night. However, with the easterly flow, ocean seas are expected to build to small craft levels by late Monday night and remain into Wednesday. As the low tracks through the forecast waters and weakens Wednesday winds will remain below small craft levels, but seas will be slow to subside below small craft.
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&& .HYDROLOGY... Up to an inch rainfall seems to be a reasonable possibility Monday night into Wednesday. No hydrologic impacts are anticipated at this time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Dense Fog Advisory until 4 AM EDT Saturday for ANZ330-335-340- 345-350-353. && $$ SYNOPSIS...FEB/DW NEAR TERM...FEB/PW SHORT TERM...FEB LONG TERM...DW AVIATION...JE MARINE...FEB/DW/PW HYDROLOGY...FEB/DW

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