Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 260300 AFDOKX Area Forecast Discussion National Weather Service New York NY 1100 PM EDT Thu May 25 2017 .SYNOPSIS... Low pressure tracks through the Tri-State Region tonight and off the New England coast Friday into Friday night. High pressure builds down from southeastern Canada for the weekend. This high then retreats to the northeast early next week as weak low pressure tracks to the south. A cold front approaches from the west on Tuesday, then crosses the area Tuesday night. This front then stalls out nearby as high pressure builds in from the southwest, producing potentially unsettled weather for the middle of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Updated probabilities and weather across the far eastern zones for showers and scattered thunderstorms with area moving north northeast over the ocean waters. HRRR indicating area will remain next couple of hours, so have categorical and likely probabilities. Middle level dry air continue moving over the region into this evening as impressive upper level low begins tracking from the Ohio Valley into the Middle Atlantic region. A vigorous vorticity max will round the base of the upper trough and approach the northeast as the trough goes negatively tilted tonight. Light rain remains across southern Connecticut with patchy drizzle into northeastern New Jersey. Patchy to areas of fog with visibilities around 1 mile, and up to 3 miles, were across the region. No significant rain is expected however as lift is weak and saturation is confined to the lowest 5 kft. Moisture and lift increase after 03z from south to north as the upper low and energy approach. Significant DPVA and steepening lapse rates will support showers and scattered thunderstorms. The CAPE is elevated as the low levels are inverted. The best instability appears to lie along and East of the Hudson River. Due to the anomalous nature of the upper low and strength of the energy, feel thunder is possible anywhere across the area overnight. High resolution mesoscale models, such as the HRRR, NAM-3km, and NCAR and SPC SSEO ensemble all support this reasoning. The normalized probability of greater than 40 dBZ on the SPC SSEO is over 90 percent across Long Island and southeast Connecticut 06z-12z with slightly lower percentages further west. No severe weather is forecast. Surface low pressure will move along or near the Long Island coast overnight so winds will not be as strong as earlier today. The warm front may even briefly move across portions of eastern Long Island before the low lifts to the north and east. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Upper low and surface low become vertically stacked as they move off the New England coast on Friday. Wrap around showers and possible thunder linger for a few hours around day break across eastern Connecticut and the Forks of Long Island. Otherwise, clouds will be slow to clear as moisture lingers below 10 kft. NW downsloping flow should help to create some breaks in the clouds, especially across the western half of the area. These breaks will help boost temperatures into the 70s, with cooler readings in the middle to upper 60s further east where clouds linger longest. Model soundings indicate some instability between about 5 and 10 kft, so clouds may fill back in with any breaks. There is also the possibility of a few iso-sct showers. No thunder is forecast since the instability does not look to get much above -5C with heights building aloft behind the upper low. Weak ridging passes Friday night as high pressure moves into the region from the west. Lingering moisture will keep skies partly to mostly cloudy with lows near normal values. && .LONG TERM /SATURDAY THROUGH THURSDAY/... The region is in between two shortwaves passing to the north and south Saturday and Saturday night, so with most significant forcing outside of the area, have at most slight chance pops in this time frame, with temperatures near to slightly above normal. Onshore flow will dominate from Sunday through Monday. The result will be mainly gray sky conditions with spotty light rain or drizzle mainly over higher elevations mainly to the N/W of NYC from Sunday into Sunday night as a northern stream shortwave ridge crosses the area. A 700-500 hPa shortwave approaches late Sunday night and crosses the area on Monday, making for a more widespread rain over the region then. With the onshore flow/damming high, have undercut guidance by mixing in NAM and ECMWF 2-meter temperatures. Highs will run 5-10 degrees below normal Sunday and Monday and lows a few degrees above normal Sunday night (due to reduced diurnal range). A broad closed low slow tracks from Ontario into western Quebec from Monday night through Thursday, with shortwaves rotating around the base of the low from time to time. the timing of these shortwaves is somewhat difficult this far out, but for now it appears that most energy will be focused mainly to the N of the region. As a result, there is a chance of isolated to scattered showers - mainly over northern portions of the Tri-state. Also, cannot rule out an isolated rumble of thunder Tuesday/Tuesday night with the passage of a surface cold front. Temperatures Tuesday-Thursday should run near to slightly above normal. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/...
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A warm front lies just south of the terminals this evening. A weak low center then passes through during the late night hours. IFR/LIFR conds improving to MVFR at times with shra/tstms. TSTM chances drop off after around 06-08z with a return to prevailing IFR/LIFR for the rest of the night. East to NE winds around 10 kts for most terminals this evening, turning variable in direction for a couple of hours within roughly 04-08z for most terminals before a NW flow on the backside of the low gets established. Improving back to VFR by Friday afternoon. W-NW gusts 20-25 KT. Winds generally south of 310 magnetic. SHRA possible. .OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY... .Friday night...VFR. .Saturday...VFR. .Saturday Night-Monday...MVFR/IFR possible in showers. E/SE winds. .Tuesday...Improving to VFR. S/SE winds.
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&& .MARINE... Updated weather and probabilities for showers and scattered thunderstorms early this evening across the far eastern ocean waters and into the eastern Long Island Sound. With nearshore wind gusts, and across the waters, below 25 KT the small craft advisory for the bays and New York Harbor and Long Island Sound was allowed to expire. Easterly winds will gradually weaken into this evening as the pressure gradient relaxes. Seas on the ocean will remain at small craft levels through Friday and the small craft was converted to a hazardous seas small craft. These seas will gradually subside Friday night with sub-SCA conditions elsewhere. A light pressure gradient over the region Saturday-Tuesday should limit winds to 10 kt or less. Given the absence of any significant swell, in addition, conditions should be below small craft advisory conditions over the waters around Long Island Saturday-Tuesday. && .HYDROLOGY... An additional 0.50 to 1.0 inches of rain is forecast through Friday morning. The highest amounts will likely occur across eastern Connecticut and eastern Long Island. Locally higher amounts are possible where thunderstorms occur overnight. Minor urban and poor drainage flooding is possible. It should then be mainly dry Friday night-Sunday. Another round of rain is possible from Sunday night into late Monday. At this time, it is to soon to specify, what, if any, hydrologic impact will be experienced from this system. && .TIDES/COASTAL FLOODING... A Coastal Flood Warning continues for moderate flooding potential for the south shore back bay locations of Nassau County for tonight, and advisories are in place for minor flooding potential for areas adjacent to western Long Island Sound, NY Harbor, and the south shore back bays of the western Long Island. Minor flood thresholds could briefly be touched along the eastern bays of LI and SE CT. How quickly easterly winds begin to weaken this evening will be key to the potential for seeing widespread versus localized moderate coastal flooding along the southern bays of Western LI. Less than 1/2 ft of surge is needed in many places to reach minor flood thresholds. The threat for minor coastal flooding is likely to continue during the nighttime high tides for the southern bays of Western LI/NYC through the Memorial Day Weekend. While along western Long Island Sound, lower NY Harbor, and eastern Great South Bay...minor coastal flooding is possible at those times. Beach erosion is expected with the prolonged easterly sweep...but the potential for dune erosion looks to be low and localized. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Coastal Flood Advisory until 1 AM EDT Friday for CTZ009-010. NY...Coastal Flood Advisory until 1 AM EDT Friday for NYZ071>073- 078-176-177. Coastal Flood Advisory until midnight EDT tonight for NYZ080. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 6 PM EDT Friday for ANZ350-353-355.
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