Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 191802 AFDOKX Area Forecast Discussion National Weather Service New York NY 202 PM EDT Mon Jun 19 2017 .SYNOPSIS... A cold front approaches from the west today, then crosses the Tri-State tonight, followed by a trough of low pressure building into the area on Tuesday. Weak high pressure builds in Tuesday night. A weak system crosses the area on Wednesday, followed by a return to high pressure on Thursday. A series of frontal systems then cross the area for Friday into the weekend. && .NEAR TERM /THROUGH TONIGHT/... **SEVERE THUNDERSTORM WATCH IN EFFECT THROUGH 8 PM** Severe thunderstorm watch coordinated with the Storm Prediction Center is now in effect through 8 pm. Scattered convection is already developing ahead of the main cold front. Main concern today remains the potential for severe weather and flash flooding. Visible satellite imagery as of 1700Z shows cloud streets gradually dissipating, indicating that convective inhibition is eroding. CINH will be somewhat slower to erode across portions of CT and Long Island where marine influence is strongest. This is timing well with a leading short wave now approaching eastern NY/PA, to support gradually intensifying storms through the early afternoon. The main impact will be ahead of a slow-moving upper trough and attendant cold front. A 110-120 kt upper jet moving into the Northeast will place the area in the favorable rear-quadrant, enhancing upward motion across a heavily populated corridor. Strong, largely unidirectional flow and ample forcing for ascent between a well-defined upper short wave and the approaching cold front should act to support linear development, with multiple line segments and/or a larger line approaching the area from the west this afternoon. Although the primary threat will be damaging winds, and to a lesser extent hail, ample heating ahead of the line may support the development of a pre-frontal trough, allowing surface winds to back more south-southeast direction. The increasing low-level wind shear/SRH combined with lowering LCLs as moisture advects northeastward may support the threat of a tornado or two, particularly with any discrete convection that can develop ahead of the line. The latest SPC outlook shows an enhanced threat of severe weather across the majority of the forecast area including the NYC metro, with a slight to marginal risk across eastern CT and Long Island where a marine influence will prevail. As the upper trough moves eastward, the forward progression will gradually be slowed due to a strong Atlantic high pressure system. Most recent model runs suggest the front may stall across the area, with southwesterly flow continuing to advect moisture, represented by 2+ inch PWAT values, across the area. As such, the threat of flash flooding may linger through the night. See the hydrology section for more information. A high risk of rip current development is expected for Atlantic Beaches into this evening due to persistent SE Swells. && .SHORT TERM /TUESDAY/... Mainly eastern areas could experience a few lingering showers early Tuesday morning as the last shortwave exits to the NE. Otherwise, the region will be under SW flow aloft on Tuesday, with a northern stream shortwave passing to the N. Most, if not all, guidance suggests the core of the forcing with this shortwave will pass to our north as well, so have gone with a dry forecast for the remainder of the day. With a mostly sunny sky on Tuesday across the area by afternoon, Tuesday should be warmer than today over eastern areas, and around today`s highs over western areas. Most locations should be around 5 degrees above normal. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... An upper level trough swings through the area Tuesday night into Wednesday. While moisture appears to be limited with this system, it may be enough to touch off a few showers on Wednesday afternoon. Weak ridging aloft and an associated surface high then build in for Thursday, resulting in a mostly sunny day. Thereafter, model solutions begin to diverge as a series of upper level disturbances pass through the region from Thursday night into the weekend. Each of these have the potential to produce showers and/or thunderstorms, but the exact timing and location of any precipitation will have to be refined. In general, kept PoPs through this period to 30% or less. Also worth noting is a tropical disturbance currently near the Yucatan Peninsula, which has the potential to feed tropical moisture into the area during the Friday- Saturday time period. At this point this solution appears somewhat less likely, but it bears watching nonetheless. Finally, models differ on the evolution of a longwave trough developing over the Upper Midwest next weekend, with associated sensible weather differences for our area on Sunday. Daytime highs will remain seasonable through the period, with overnight lows about 5 degrees above normal. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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** HIGH IMPACT WEATHER EVENT WITH POTENTIAL FOR STRONG TO SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING ** A cold front will slowly approach and then move across the terminals tonight. VFR at most terminals this afternoon. Some IFR/MVFR still being observed across eastern CT and Long Island. S-SW winds have increased to 12-15kt with gusts 20-30kt at most terminals, and could be a little stronger at KJFK. Potential remains for strong to severe tstms this afternoon and evening, with strong winds and heavy rainfall. Isold-sct activity has begun at KSWF and just west of KEWR/KTEB. An organized line of storms should arrive later this afternoon, and may be slow to move across the lower Hudson Valley and NYC Metro terminals. Most likely time of impact for NYC metro looks to be 21Z-24Z, with perhaps some lingering storms until 02Z. Activity should weaken as it moves east across Long Island and CT, so impact at KGON/KISP and possibly KBDR should be less than north/west. 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: Amendments possible this afternoon and evening for any showers/thunderstorms. KLGA TAF Comments: Amendments possible this afternoon and evening for any showers/thunderstorms. KEWR TAF Comments: Amendments possible this afternoon and evening for any showers/thunderstorms. KTEB TAF Comments: Amendments possible this afternoon and evening for any showers/thunderstorms. KHPN TAF Comments: Amendments possible this afternoon and evening for any showers/thunderstorms. KISP TAF Comments: Chance conditions improve to VFR. Amendments possible this afternoon and evening for any showers/thunderstorms. .OUTLOOK FOR 18Z TUESDAY THROUGH FRIDAY... .Tuesday...VFR. SW-WSW winds G15-25KT possible in the afternoon. .Tuesday night...VFR. W-NW winds G15-25kt possible. .Wednesday...A brief period of MVFR is possible with any shower and/or thunderstorm. .Wednesday night...VFR. .Thursday...VFR. SW winds G15-20KT possible in the afternoon. .Friday-Saturday...Chance of showers/tstms with MVFR or lower conds. Gusty S-SW winds.
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&& .MARINE... SEVERE THUNDERSTORM WATCH IN EFFECT THROUGH 8 PM FOR THE LONG ISLAND SOUND, NEW YORK HARBOR AND THE SOUTH SHORE OF LONG ISLAND WEST OF FIRE ISLAND... Scattered convection is now developing ahead of the main system and may impact the coastal waters through the early afternoon. Stronger, more widespread thunderstorms with potentially damaging wind gusts will be possible later this afternoon into the evening ahead of a slow-moving cold front. Outside of thunderstorms, a strengthening low-level jet today should support gusts to SCA levels on all waters, continuing into tonight. By Tuesday morning, though winds should subside to 15 kt or less, but it appears seas, at least in the outer portion of the coastal ocean zones, should remain around 5 ft, so have extended the SCA there through 22z Tuesday. Seas on the ocean waters will likely remain above 5 ft due to residual southerly swells into Wednesday morning. Otherwise, expecting sub SCA conditions across the waters until Friday afternoon into the weekend when waves on the ocean could again reach 5 ft. Winds should remain below SCA criteria through the period. && .HYDROLOGY... For the western parts of the region (Nassau County and west as well as New Haven County and west), there will be a chance of flash flooding from this afternoon into tonight. This is where there is total basin average rainfall between 1 and 2 inches expected...with locally higher amounts possible (maybe 3+"). Rainfall rates in excess of 1-2"/hr are possible in any training deep convection. To the east, with the bulk of the rain occurring at night, as the convection should naturally weaken, less than 1" is expected (with locally higher amounts) so mainly poor drainage/urban flooding would be the main threat there. No hydrologic impacts are anticipated Tuesday-Sunday. && .EQUIPMENT... * KOKX Weather Radar is scheduled for maintenance starting on Friday June 23rd for a period of 3 days. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Flash Flood Watch through late tonight for CTZ005-006-009-010. NY...Flash Flood Watch through late tonight for NYZ067>075-176>179. High Rip Current Risk until 9 PM EDT this evening for NYZ075- 080-081-178-179. NJ...Flash Flood Watch through late tonight for NJZ002-004-006- 103>108. MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ330-335-338- 340-345-350-353-355. && $$ SYNOPSIS...FEB/Maloit NEAR TERM...MD SHORT TERM...Maloit LONG TERM...FEB AVIATION...BC MARINE...FEB/Maloit HYDROLOGY...FEB/Maloit EQUIPMENT...

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