Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 220557 AFDOKX Area Forecast Discussion National Weather Service New York NY 157 AM EDT Sat Apr 22 2017 .SYNOPSIS... Low pressure over southern Canada will continue to move east overnight, dragging an occluded front across the area. 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 THIS MORNING/... Visibilities have lowered to around 1 SM with patchy areas under 1 SM, however, do not expect visibilities to drop to a quarter of a mile or less, so no dense fog advisory for the coastal areas. There were areas of drizzle and expected to be possible through 08Z, so added to the forecast. As the primary low continues to move east across southern Canada, it will drag an occluded front across the area overnight. A weak low along a warm front passes south of Long Island overnight. This has resulted in light northerly winds, which seems to have kept visibilities from falling as much as expected. With plenty of low level moisture and light winds, patchy to areas of fog, locally dense, is still possible overnight. High res models still indicate that fog/visibilities improve by daybreak as slightly drier air begins to work into the region. Temperatures will a few degrees, into the mid 40s to around 50, several degrees above normal. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... 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. && .LONG TERM /SUNDAY NIGHT 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 /06Z 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 are expected to continue through around 09z with with eastern terminals holding a few hours longer. Conditions then improve to MVFR before gradually improving to VFR around 15z at city terminals and around 17-18z at KISP, KBDR, and KGON. Timing of improving conditions in the TAFs may be off by 1-2 hours. There is also a possibility MVFR conditions hold longer into the day than currently forecast. There is a chance of light rain after daybreak through early afternoon mainly at coastal terminals, but confidence is not high enough at this time to include in TAF and visibilities should remain VFR. 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... Ocean seas have increased, mainly in an easterly swell, with buoys 44025 and 44017 near and just over 5 FT. This should be short lived however. Will hold off on SCA issuance as conditions improve with weakening winds. A Dense Fog Advisory remains in effect across much of the eastern waters as fog and low visibilities persist. Western LI Sound was included in the advisory earlier. Fog should become more patchy in nature early Saturday morning before finally clearing by daybreak. Winds back and lighten to the N/NE overnight. 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. && .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 early this morning for ANZ330-335-340-345-350-353. && $$ SYNOPSIS...FEB/DW NEAR TERM...MET/PW SHORT TERM...FEB LONG TERM...DW AVIATION...DS MARINE...MET/DW/PW HYDROLOGY...FEB/DW

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