Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 200542 AFDOKX Area Forecast Discussion National Weather Service New York NY 142 AM EDT Fri Jul 20 2018 .SYNOPSIS... High pressure will remain over the area through Friday night. Low pressure will move up the coast and affect the region over the weekend. A frontal boundary will remain in the vicinity through mid-week. && .NEAR TERM /THROUGH TODAY/... Forecast remains on track with just some minor adjustments to reflect current observations. Otherwise, clear skies tonight as the core of the sfc high shifts to our ENE, allowing low level flow to come out of the S-SE. Winds tonight will be light. Low temps tonight were guidance blend, with 50-55 interior eastern Long Island, 55-60 inland, 60s most elsewhere, near 70 in midtown NYC. A moderate rip current risk continues at the ocean beaches late today due to 2-3 ft S-SE swells. && .SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/... Deep later ridging will remain along the New England coast, with onshore flow. Skies will still be mostly sunny, with high temps in the lower/mid 80s per guidance blend which has done well of late. Expect some patchy fog away from the urban areas late Fri night, also areas of low stratus to develop across E Long Island and SE CT. Low temps should be close to those fcst for tonight. Friday rip current outlook for the ocean beaches: Moderate for NYC/Nassau, Low for Suffolk. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... A highly anomalous pattern setting up for the weekend for this time of year. A blocking pattern sets up for this time period as a cutoff low over the Great Lakes region slowly moves south and weakens. We will be on the eastern side of the associated upper level trough which will help steer a small but potent low pressure system that will develop off the coast of the Carolinas and head toward our area beginning late Friday night. There are still some timing differences among the operational models with the onset of rain from this low, but much, if not all of Saturday morning should be dry. Rain should begin to move into the region from south to north Saturday afternoon, but the more moderate to heavy rain moves in for Saturday night. Conditions taper off Sunday, but chances for rain continue as a frontal boundary remains in the vicinity through mid- week. In regards to the rain, there are signals that show a period of heavy rain is possible, such as PW greater than 2.50", which is higher than the 2.14" daily max given climatology. WPC has our area in a marginal risk for excessive rainfall. A 40-50 kt LLJ approaches the area overnight, but weakens in both the NAM and GFS before coming onshore. Some operational rainfall forecasts showing more than 2 inches, with the previously mentioned PW, locally higher amounts of 3+ inches are possible, especially in any convection. Also, if the low tracks near the Gulf Stream, that could help to intensify the storm further. There is still uncertainty with this system and where the axis of heavy rain will fall as the ECMWF does show the axis of heaviest rain over Long Island and Connecticut, while the NAM and GFS are more over New York City and northeast New Jersey. Flash flooding is a possibility, especially if this axis is over New York City and northeast New Jersey, but again, it is still too soon to pinpoint where. As for severe threat, 0-6 km bulk shear of greater than 40 kt, 700-500 mb lapse rates of 5.5-6 deg C, 850 mb winds of 40-50 kt, and K index of greater than 35 point to some threat of severe weather. However, lifted index and MUCAPE are not that impressive. Of note are some high helicity values as well as EHI values approaching 1, which indicate tornadoes are possible. SPC has not placed any part of our area in a severe risk yet, but isolated to scattered thunderstorms are possible given the above conditions, some with gusty winds approaching 40 mph or a weak tornado. The rest of the week remains unsettled as the frontal boundary associated with the low remains in the vicinity. It seems as the heaviest rain remains to our west, but there is generally a chance for showers and thunderstorms through Thursday night. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... High pressure gradually shifts towards the Canadian Maritimes through the TAF period. VFR. Light SW to variable flow overnight becoming SE around 10 kt by noon. Winds diminish tonight, becoming more easterly by 12z Saturday. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .Friday Night...VFR. .Saturday...Conditions lowering by evening to MVFR or lower in SHRA/TS. NE-SE winds 20G30kt possible. LLWS possible. .Sunday...Conditions briefly improving to VFR during the afternoon- eve. .Sunday night-Tuesday...Chance SHRA/TS with local MVFR or lower conditions. && .MARINE... With high pressure firmly in control through Friday, winds and seas remain rather tranquil, with a 2-3 ft SE swell on the ocean. Winds and waves increase Saturday with the approach of a low pressure to our south. Waves build to 5 ft on the ocean waters by Saturday afternoon, with 10 ft waves possible by Sunday morning on the eastern ocean zone. Thereafter, waves diminish as the low heads inland. Wind gusts of 25 kt over the ocean by Saturday afternoon over the ocean waters and over all waters by Saturday night. Winds come down below 25 kt Sunday morning over all waters. Winds for the rest of the long term should remain below 25 kt, but waves should generally remain above 5 ft for the ocean waters due to an extended period of onshore flow. && .HYDROLOGY... Rainfall of at least 1 to 2 inches expected from late Saturday into Sunday. Locally higher amounts are possible, especially in any thunderstorms that develop. The location of the axis of the heaviest rainfall is still uncertain, but if this axis sets up over the metro area, flash flooding will be more likely. Right now, it still looks like minor urban and poor drainage flooding. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...Goodman/JP NEAR TERM...BC/Goodman SHORT TERM...Goodman LONG TERM...JP AVIATION...JC MARINE...Goodman/JP HYDROLOGY...Goodman/JP EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.