Area Forecast Discussion
Issued by NWS Upton, NY

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492 FXUS61 KOKX 220953 AFDOKX Area Forecast Discussion National Weather Service New York NY 553 AM EDT Sat Apr 22 2017 .SYNOPSIS... Low pressure over southeastern Canada will continue to move east today as another wave of low pressure passes to the south of Long Island. High pressure will then slowly build into the region from the west tonight, and across the area on Sunday, then move offshore on Monday. A wave of low pressure will move off the Southeastern coast Monday, and track slowly north through midweek. High pressure will build back in for the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The NAM and HRRR continue to bring precipitation across the metropolitan NYC area and across Long Island, mainly this afternoon. Have increased probabilities across these region to likely, and increased rainfall slightly. See hydrology section. The northern stream trough and associated surface low across southeastern Canada was slow to track east along with a very weak wave crossing the Ohio Valley and into the mid Atlantic. Trends have been for low to the south to be far enough north for light rain across the southern half of the CWA today and into early this evening until the upper trough moves east. Little dry air was moving into the area on a light north flow and fog remains across much of the area with varying visibilities with visibilities generally 1 statue miles or greater. With more clouds and precipitation through today lowered high temperatures for today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... With the slower movement of the upper trough and weak building heights to the west, have probabilities into this evening along the coast, and just south of Long Island this evening. If the trough is slower to move east, precipitation may remain longer across eastern Long Island and southeastern Connecticut. Otherwise high pressure builds for the remainder of tonight. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... With the weak high to the north moving east and weakening farther the southern low now is expected to move north a little faster and have introduced probabilities into the region Monday morning. 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 /09Z SATURDAY THROUGH WEDNESDAY/...
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A wave of low pressure along a nearly stationary frontal boundary tracks south of the terminals through this afternoon. High pressure builds in from the west late today into tonight. IFR/LIFR conditions continue to hold on, but should see gradual improvements to MVFR through daybreak. Long Island and southern Connecticut terminals may stay lower a bit longer. MVFR conditions should gradually improve to VFR by middle to late morning. However, light rain is possible around 14z through early afternoon which could hold MVFR cigs several hours longer. Visibilities are likely to remain VFR in the light rain. Light N-NNE winds early this morning will gradually back to the NW today. Speeds should remain around 10 kt or less. Winds will stay to the right of 310 magnetic at city terminals. NW winds continue tonight. .OUTLOOK FOR 06z SUNDAY THROUGH WEDNESDAY... .Saturday Night-Sunday...VFR. .Sunday...VFR. .Monday...VFR during the day. Chance MVFR in rain at night. .Tuesday...Chance IFR in rain. NE gusts 20-25 KT near coast possible. .Wednesday...MVFR possible early, becoming VFR.
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&& .MARINE...
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An easterly swell was keeping seas at buoys 44017 and 44025 varying over 5 feet. With long period swells expected to continue into this afternoon have issued a small craft for hazardous seas on the ocean waters east of Fire Island Inlet. Swells are expected to subside mid to late this afternoon. Wind waves will remain under 5 feet with a light northerly flow. Visibilities have improved to over 1 nautical mile across the waters. However, across the ocean waters into early this morning there may be a few locations where the visibility is around 1 nautical mile at times. Winds and seas will remain below small Craft levels into Monday as a wave of low pressure passes near the ocean forecast waters today, and then high pressure builds from the north tonight into Sunday night. The high weakens Monday as low pressure moving off the southeastern coast begins to track slowly to the north. The low pressure system moving off the southeastern 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...
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Up to a tenth of an inch of rainfall is possible today into this evening, mainly from portions of northeastern New Jersey, across New York City, and Long Island. Lower amount possible to the north. Up to an inch of rainfall is possible Monday into Wednesday. No hydrologic impacts are anticipated at this time.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 4 PM EDT this afternoon for ANZ350-353.
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&& $$ SYNOPSIS...MET NEAR TERM...MET SHORT TERM...MET LONG TERM...MET/DW AVIATION...DS MARINE...MET HYDROLOGY...MET

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