Area Forecast Discussion
Issued by NWS Upton, NY

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125 FXUS61 KOKX 201614 AFDOKX Area Forecast Discussion National Weather Service New York NY 1214 PM EDT Thu Jul 20 2017 .SYNOPSIS... Hot and humid weather will continue across the Tri-State Area today. A weak cold front will pass across the area tonight into Friday. This cold front will stall south of the area late Friday and remain around through the weekend before finally moving south as a cold front early next week. High pressure follows through mid week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A batch of high clouds was pushing south across the Lower Hudson Valley and Long Island so sky grids were tweaked in the next few hours. Otherwise any adjustments made were to hourly temps and dewpoints based on recent trends. Given the flow is shown to be more westerly across coastal Fairfield County, CT highs were tweaked up here a bit which put them closer to observed values yesterday since I don`t see any reason they will run much cooler. Some tweaks were also made to bump up highs a bit along the Highway 25 Corridor of Suffolk County as well as at Montauk based on high temperatures from yesterday in addition to the latest observations. The rest of the forecast looks reasonable at this time and no other changes were made. Very juicy air will continue to flow off nearly 75 degree ocean water right into south facing shoreline areas as evidenced by the 77 degree dewpoint reached at JFK this morning. Heat Headlines continue and look justified. A deep WNW upper flow zonal flow existing today around an anomalously strong polar low moving across Hudson bay. At the surface weak diurnal surface/thermal troughing will develop over the region. Although marginal to moderate instability development is expected today...there is a lack of a distinct trigger to initiate convection. Highest instability/dewpoints are expected along the coast once again today...where the thermal trough/sea breeze could act as focus for isolated pulse convection across NYC/LI this afternoon if any weak vort energy tracks through. A localized strong wet downburst is possible. Otherwise...main story will be heat today. Deep mixing and warm temps aloft should have temps rising into the lower to mid 90s for much of the region. A few upper 90s possible for NYC/NJ metro. As was the case yesterday, deep mixing and subsidence will likely promote dewpoints to mix out into at least the the lower to mid 60s in the afternoon across areas N&W of the sea breeze (NYC/NJ metro and interior). Meanwhile...south coastal areas will likely see dewpoints hold in the lower to possibly mid 70s with sea breeze development off 75 degree ocean. Based on 95-100 heat indices being reached across the NY/NJ metro area as well as coastal SW CT and the Eastern 2/3rd of LI for a second day, have continued/expanded heat advisory into these areas. There is a low risk of rip current development this morning, which may become moderate for the beaches of Queens and Nassau County late today with coastal jet development. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... An active near zonal flow will develop as a anomalously strong polar low tracks through Northern Ontario/Quebec. A weak cold front approaches tonight as the first in a series of shortwaves tracks through the NE in the developing zonal flow. Main forecast challenge and concern for tonight into early Friday morning is progression of any MCS activity into the region. The shortwave energy emanating from the activity currently occurring over the Upper Mississippi River Valley/Great Lakes this morning will likely provide trigger for upstream convection (Eastern Great Lakes) this afternoon/evening which could track over the region tonight. Considerable model spread exists on the track and intensity of any activity across the region tonight. This is due to differences in the favorability of the environment (particularly mid-level lapse rates) and the unpredictability of the interaction of a yet to form convective complex with this environment. So overall the threat for a strong MCS passing through the region tonight into early Friday morning, with an associated flash flood and damaging wind threat, is low. Higher probability is for scattered shower and embedded thunderstorm activity as shortwave energy moves through the region and interacts with a moist and marginally unstable airmass over the area. An isolated strong storm is possible in this scenario, with a low chance for minor urban flooding. Pretty good agreement that any shortwave energy and convective activity pushes east by Friday morning. In its wake, deep W/NW flow and subsidence will favor a hot and dry day. Temps across the coastal plain will likely rise into the lower 90s to 95, with upper 80s to lower 90s interior. Deep mixing and subsident NW flow should promote lower dewpoints area wide. At this time, it appears that heat indices could marginally reach 95 degrees across the NYC/MJ metro and LI, but not enough confidence to extend advisory at this time as dewpoints may mix out more than forecasted. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Although this period will start dry on Friday night, there is an increasing chance of multiple rounds of heavy showers and TSTMs from Saturday afternoon through Monday night. The weather pattern favors the development of several Meso Convective Systems/MCSs caused by short waves rotating SE arnd a canadian polar vortex. There is considerable uncertainty regarding their track and intensity, depending on where they actually develop. Adding to this complexity is where the approaching warm front stalls late Saturday - Sunday, and the subsequent development of a low pressure wave along the front late Sunday - Monday. There is the potential for heavy showers, TSTMs, and strong gusty winds during this time. Stay tuned. Weather conditions will finally improve with the passage of a cold front early Tuesday, bringing more comfortable late July weather to the area next Tuesday through Thursday. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... A weak trough will be near or just west of the NYC terminals this afternoon, while a cold front approaches from the eastern Great Lakes. VFR conditions are forecast through today. W-SW flow this afternoon around 10 kt, with some occasional gusts 15 to 20 kt. Coastal terminals have the best chance for gusts this afternoon. There is also a low chance for an isolated thunderstorm at the coastal terminals along the seabreeze, but confidence is too low to put in TAFs at this time. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Amendments may be needed due to timing of gusts this afternoon. The afternoon KJFK haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KLGA TAF Comments: NE flow may end sooner than forecast. Amendments may be needed due to timing of gusts this afternoon. The afternoon KLGA haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KEWR TAF Comments: Amendments may be needed due to timing of gusts this afternoon. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Amendments may be needed due to timing of gusts this afternoon. KHPN TAF Comments: Wind may be more variable late morning/early afternoon. KISP TAF Comments: Amendments may be needed due to timing of gusts this afternoon, and for isolated thunderstorms this afternoon. .OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY... .Friday and Friday Night...VFR. .Saturday...MVFR or lower possible with a chance of showers and thunderstorms. .Sunday-Monday...MVFR or lower possible with a chance of showers and thunderstorms. && .MARINE... A weak pressure gradient over the region will keep sub Small Craft Advisory/SCA conditions through Friday. Although winds and seas are forecast to remain below SCA levels of 25 kt and 5 ft from Friday Night through Monday, there will be several rounds of showers and TSTMs starting Saturday afternoon through Monday. Winds and waves may be briefly higher in and around TSTMs. Stay tuned to possible Marine Weather Statements and/or Special Marine Warnings during this time. Note that areas of fog may temporarily reduce the VSBY to near 1 NM Saturday afternoon and night as a warm front moves north across the coastal waters. Depending on the exact track of the stalled front, southerly swells may begin to increase through the weekend into early next week, with a low probability for SCA conditions on the ocean by Monday. Weather conditions will improve following the passage of a cold front on Tuesday morning, when winds become offshore. && .HYDROLOGY... There is a low threat for a convective complex to track across the area tonight into early Friday morning. The main threat if this activity materializes would be minor urban flooding, with a low threat for flash flooding. There is a low chance for additional urban flooding from Saturday afternoon through Monday night as a slow moving front interacts with a moist and unstable airmass. This will bring a threat for periods of heavy showers and thunderstorms. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory until 6 PM EDT this evening for CTZ009. NY...Heat Advisory until 6 PM EDT this evening for NYZ069>071-078- 080-177-179. Heat Advisory until 8 PM EDT this evening for NYZ072>075-176- 178. NJ...Heat Advisory until 6 PM EDT this evening for NJZ004-006- 103>108. MARINE...None. && $$ SYNOPSIS...GC/NV NEAR TERM...NV/CS SHORT TERM...NV LONG TERM...GC AVIATION...JE/DW MARINE...GC/NV HYDROLOGY...GC/NV is the U.S. government's official web portal to all federal, state and local government web resources and services.