Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 301744 AFDOKX Area Forecast Discussion National Weather Service New York NY 144 PM EDT Thu Mar 30 2017 .SYNOPSIS... High pressure slides east across the region today. Low pressure will impact the area tonight through Saturday. High pressure builds in for the second half of the weekend. Another low pressure system may impact the area Monday night and Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Forecast remains on track. Northern stream shortwave energy slides east today with surface high pressure building in from the west. Tranquil and near seasonable conditions today as high pressure moves across. Increasing high and mid clouds expected in the afternoon ahead of the next approaching system. Highs generally in the lower to mid 50s under light winds...deep mixing and late March solar insolation. If high clouds come in a little thicker or earlier, temps could run slightly a degree or two cooler than forecast. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... Models in general agreement with a Central Plains closed low tracking through the Mid-Mississippi River valley today and into the Ohio Valley tonight. The low then begins to interact with the northern stream as it slides to the east coast by Saturday morning. Subtle difference exists in this interaction...which manifests in some timing and track differences with the resultant coastal surface low as it develops over the Virginia Piedmont Friday and tracks just south of the area Friday Night into Sat am. The main impact from this system for most of the area will be a soaking windswept rain developing late tonight into Friday morning and continuing through Friday night before tapering off Saturday morning. Ensembles generally clustered between 1 1/4 and 1 3/4 inches of liquid...with locally up to 2 inches signaled. Across interior portions of NE NJ/Lower Hud Valley/Southern CT...thermal profiles will be marginally cold enough to complicate the forecast late Tonight through Friday Night. Storm track will be critical...with a farther south track favoring cooler and more wintry mix potential...while a track over NYC/LI favors warmer thermal profile and more in the way of plain rain. At onset of steadier precip lat tonight/Fri am...evap cooling will increase the likelihood for a wintry mix of rain/sleet and snow across interior. Operational models all indicating warming aloft as Fri morning progresses but to differing degrees. With that said...March boundary layer warming should allow for precip in most areas to become mainly rain by afternoon...except elevations above 750-1000 ft or so. Late Fri Aft into Fri night...dynamics increase as closed low energy approaches and frontogenetic banding strengthens over the area to the north of the developing coastal low. At the same time low-level winds backing to the ne/n should allow the boundary layer to slowly cool. The question will be whether diabatic processes can overcome warming aloft from se llj to bring a period of heavier sleet...possibly mixed with snow. 90 percent exceedance snow/sleet forecast covers this low potential for a period of complete changeover to wintry precip. Another concern is that temperatures across interior...particularly higher elevations...could haver around/drop to freezing Fri night...introducing the potential for freezing rain. Marginal temp profiles will not support efficient icing...but the threat of hazardous travel from light icing exists. Based on above...this is a low confidence snow/sleet accum forecast for the interior. At this point the most likely outcome is varying combinations of mixed precip during the period with a light slushy accum of sleet/wet snow/fzra across the interior...especially elevations above 750-1000 ft...by the time everything winds down Sat am. In terms of winds...easterly winds increase Friday as a tight gradient develops between high pressure anchored over Se Canada and developing coastal low pressure. 950 hpa llj appears to peak at 45- 50 kt across LI/SE CT late Friday into Friday Night. Across the NYC metro and much of the coast...gusts of 30 to 35 mph are likely and peak gusts to 40 mph possible. The llj peaks across Eastern LI and coastal SE CT Fri Night...with gusts of 30 to 40 mph likely and a few peak gusts to 45-50 mph possible. Highest winds will be along immediate coast. The easterly winds will result in minor coastal flood concerns for the Fri night high tide. See tides and coastal flood section. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Good model consensus that low pressure will be tracking south of Nantucket on Saturday, then further out to sea Saturday night. As this occurs, light precipitation on the back side of the system will taper off through the day. Time heights show a lack of deep lift, and therefore no ice crystals introduced, precluding snow. As a result, some mixing with sleet was included in the forecast early Saturday, with mainly rain expected across the majority of the area. Any precipitation ends by Saturday evening at this time, with fair weather then settling in for Sunday as high pressure builds in. Increasing clouds on Monday as both northern stream and southern stream moisture converge on the region. The ECMWF and GFS then continue a latitude battle with regard to the southern stream low, with the GFS about 150 miles north of the ECMWF. As a result of this uncertainty several days out, the probability for rain has been limited to the chance category. High pressure builds in in the wake of the low for Wednesday, then another low may impact the area at the end of the week. Increasing clouds with a low chance for rain have therefore been forecast for Thursday. A blend of guidance was used for temperatures except for Monday night, where the forecast was weighted heavily towards to raw model data. In this case, the potential clouds and rain would likely limit the climatology influence evidenced by MOS. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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VFR conditions are expected through the first half tonight as high pressure remains over the region. MVFR conditions move in after 06Z Friday as low pressure approaches. Conditions gradually fall towards daybreak, with IFR conditions or less developing after 14-15z in rain. At KSWF, a mix of rain and ice pellets will be possible. South-Southeast flow develops this afternoon with wind speeds remaining below 10 kt. Winds lighten this evening and overnight with speeds falling to 5-6kt or less. Late tonight, the wind direction becomes more easterly, and during the morning hours on Friday, speeds will increase to 10-15kt, with gusts into the 20 kt range. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Timing of southerly flow could off by +/- 1-2 hours. KLGA TAF Comments: Timing of southerly flow could off by +/- 1-2 hours. KEWR TAF Comments: Timing of southerly flow could off by +/- 1-2 hours. KTEB TAF Comments: Timing of southerly flow could off by +/- 1-2 hours. KHPN TAF Comments: Timing of southerly flow could off by +/- 1-2 hours. KISP TAF Comments: Timing of southerly flow could off by +/- 1-2 hours. .OUTLOOK FOR 18Z FRIDAY THROUGH MONDAY... .Friday afternoon...MVFR/IFR conditions in rain in the afternoon. SE winds G20-25 KT at the coast. .Friday night and Saturday...MVFR/IFR in rain with gradual improvement by Saturday afternoon/evening. E/NE winds G20-30KT at coastal terminals. .Sunday-Monday...VFR. .Tuesday...Chance of sub-vfr in rain.
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&& .MARINE... Winds and seas into tonight as high pressure moves across the waters. An approaching low pressure system will increase the pressure gradient across the waters and expected to bring SCA conds to the nearshore waters Friday morning and likely continuing into Saturday. Gale force winds gusts are possible across the ocean waters Fri afternoon through Friday night...warranting a gale watch. Ocean seas expected to build to 7 to 11 ft on the ocean and 3 to 5 ft on LI sound Friday night with good easterly fetch. Marginal gales will be possible into Saturday, before conditions subside to Small Craft Advisory levels by Saturday night. High pressure building over the waters will result in relatively light winds Sunday into Monday. Seas at or above 5 ft may linger into the day on Sunday on the ocean, then all waters will fall below Small Craft Advisory criteria for Sunday night and Monday. Winds will increase on Monday night and Tuesday as low pressure passes near the waters. && .HYDROLOGY... Between 1 1/4 and 1 3/4 inches of QPF is likely from tonight through Saturday morning...with locally around 2 inches. While there could be some urban and poor drainage nuisance flooding, flood impacts along rivers and streams are not expected. Heavy rain during the time of high tide Friday Night could exacerbate roadway flooding in low-lying coastal communities. Additional rainfall of around an inch is possible Monday night and Tuesday. && .TIDES/COASTAL FLOODING... An approaching low pressure system is likely to bring widespread minor coastal flood impacts to vulnerable coastal communities along lower NY/NJ harbor, southern bays of LI/NYC, and western LI Sound during the Friday Night high tide cycle. Locally moderate flooding is possible along the southern bays of western LI. Tidal departures of 1 to 1 1/2 ft are needed to reach minor flood levels and 2 to 2 1/2 ft for moderate flood levels during that time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 11 AM Friday to 8 AM EDT Saturday for ANZ330-335-338-340-345. Gale Watch from Friday afternoon through Saturday morning for ANZ350-353-355. && $$ SYNOPSIS...12/NV NEAR TERM...MD/NV SHORT TERM...NV LONG TERM...12 AVIATION...JP MARINE...12/NV HYDROLOGY...12/NV TIDES/COASTAL FLOODING...

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