Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 010816 AFDOKX Area Forecast Discussion National Weather Service New York NY 416 AM EDT FRI JUL 1 2016 .SYNOPSIS... A warm front approaches from the south today, followed by a cold front crossing the Tri-State tonight. High pressure will build in for the holiday weekend. Low pressure may track close enough on Monday night and early Tuesday to spark a few showers and thunderstorms, then fair weather will return through Thursday followed by low pressure for next weekend. && .NEAR TERM /THROUGH TONIGHT/... ** MARGINAL TO SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE TRI-STATE THIS AFTERNOON AND EVENING ** A 850-500 hPa trough moves across the Great Lakes today,with the trough axis pushing across the area tonight. Ahead of it, winds veer from the SSE-SE at the surface to SW-WSW at 500 hPa, with a Bulk shear of 30-40kt. In addition to the speed and directional shear, 1000-2000 J/kg of CAPE is forecast over most of the region (only 500-1000 J/kg over Eastern Long Island and coastal SE CT). Furthermore the region will be under the surface theta-e ridge and have a 25-30kt 950 hPa jet pass just to the south. Given the shear, CAPE, abundant low level moisture and forcing from the low level jet and an approaching warm front (and cold front by late afternoon), the ingredients exist for strong to severe storms across the Tri-State from mainly this afternoon into this evening. Bulk Richardson numbers in the 15-40 range, along with hodographs suggest potential for some isolated supercells and possibly some bowing segments as you get towards late afternoon/early evening. Consistent with this, SPC has placed NYC, NE NJ, the Lower Hudson Valley and most of Fairfield County in a slight risk for severe thunderstorms, and the remainder of the CWA in a marginal risk. The main threat is from damaging winds, with a secondary threat from large hail. In addition, given the anticipated low level helicity, as evidenced by Vorticity Generation Parameter from around 0.25-0.5 and Energy Helicity Index of 1 to 2.5 across mainly the W 2/3 of the CWA (highest over NE NJ/Lower Hudson Valley), LCLs forecast down to around 800-900m there is a small chance for tornadoes, highest west of the Hudson River. In addition to the severe threat, with the abundant low level moisture, there are some potential hydrologic concerns as well. Refer to the hydrology section of the AFD for details. The threat for storms falls off fairly rapidly from west to east this evening (maybe lingering into the first part of the overnight hours far eastern zones), as the surface cold front reflection of the upper trough pushes to the east. Highs today were based on a blend of MAV/MET/ECS guidance, NAM 2-meter temperatures and a mix down from 975-900 hPa per BUFKIT soundings. Highs should be near normal. Lows tonight were based on a blend of MET/ECS/MAV guidance and NAM 2-meter temperatures, with values forecast to be near normal. && .SHORT TERM /SATURDAY/... Saturday will feature rising heights aloft, as the aforementioned upper trough lifts to the northeast. The low-mid levels dry out fairly quickly, so should see minimal, if any cloud cover - except for maybe some diurnal cumulus over mainly higher elevations over far N/W portions of the CWA. Highs on Saturday were based on a blend of MAV/ECS/MET guidance, NAM 2-meter temperatures and a mix down from 825-775 hPa per BUFKIT soundings. Highs should be near to slightly above normal. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Saturday Night through the day Monday will feature fair weather with near normal temperatures as high pressure moves slowly east across the area. Day time heating will develop inland troughs that will aid the development of weak sea breezes both Sunday and Monday afternoon. Monday Night through Tuesday Morning, forecast models show a weak upper level short wave advecting east along the southern edge of the polar jet stream. There are enough differences in model track guidance to include at least a 20% POP for widely sct TSTMS after 8 pm during Monday evening with both the latest operational runs of the ECMWF and the NAM forecasting measurable QPF across NYC during this time. If the track becomes suppressed and remains further south of the area, fair weather will occur. If the track lifts further north, then heavier showers and TSTMs could occur. Stay Tuned. Tuesday Afternoon through Wednesday Night will feature fair weather with day time temperatures averaging slightly above normal in the mid to upper 80s across the NYC Metro area. Thursday through Friday, two successive troughs of low pressure may cause mainly diurnal widely sct TSTMs during each afternoon as humidity increases in an uncomfortable maritime tropical air mass with day time highs in the mid and upper 80s. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... A cold front approaches late today and passes through this evening. VFR, however there will be chance of tempo or prevailing cigs of 2000-3000FT after around 14Z, primarily east of the city, but may include the city terminals as well. Showers will be possible starting 12-14Z, but will be most likely for a few hours starting 20-21z for most terminals. TSTMs possible with westerly gusts over 40KT during this period as well. Winds otherwise SSE mostly 10-15KT most of the day. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .Friday Night...VFR NW gusts to 20 kt possible late. .Saturday-Sunday Night...VFR. NW-W flow Saturday and WSW-SW flow Sunday. Gusts up to 20KT for both days. Winds diminish at night. .Monday...VFR. .Monday Night-Tuesday...Mainly VFR. Slight chance for Showers/Thunderstorms. && .MARINE... ** STRONG TO SEVERE THUNDERSTORMS LIKELY OVER THE WATERS AROUND LONG ISLAND THIS AFTERNOON AND EVENING ** A light to moderate pressure gradient over the waters around Long Island through Saturday will keep sustained winds to 15 kt or less. Some gusts to around 20 kt are possible due to an approaching/passing cold front from late this afternoon into Saturday. Seas should run 4 ft or less, and waves 2 ft or less through Saturday as well. Saturday Night through Monday...Winds and seas are forecast to remain below Small Craft Advisory/SCA levels of 25 knots across local coastal waters and 5 feet across Atlantic Ocean Coastal waters. Monday Night through the day Tuesday...Winds and seas may reach SCA levels as a wave of low pressure tracks east, passing just south of the Atlantic Ocean coastal waters. This low may bring showers and TSTMs along with reduced VSBY. Stay tuned to forecast updates. && .HYDROLOGY... Around 1/3-2/3 of an inch of basin average precipitation is expected into this evening. However with precipitable waters forecast to be around 1.75 inches, and the potential for strong convection, locally heavy rainfall is possible. Areas receiving locally heavy rainfall could experience minor flooding of urban/poor drainage areas. With a forecast storm motion of 20-30kt, storms should be moving fast enough to minimize the flash flood threat, unless localized training occurs. It should be dry from late tonight into Monday. From Monday night through early Tuesday, there is a chance of rain depending on the future track of low pressure passing south of the local area, with amounts ranging from 0 to 1 inch plus. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...Maloit/GC NEAR TERM...Maloit SHORT TERM...Maloit LONG TERM...GC AVIATION...JC MARINE...Maloit/GC HYDROLOGY...Maloit/GC is the U.S. government's official web portal to all federal, state and local government web resources and services.