Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 201824 AFDOKX Area Forecast Discussion National Weather Service New York NY 224 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 this evening into 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 /THROUGH TONIGHT/... The heat was on across the Tri-State Areas as of midday with the temperature reaching into the 90s at Central Park for the 9th time this year. The Heat Advisory remains in effect through this evening due to the combination of hot temperatures and high humidity values. Via mixing, dew points have since dropped across the area with a peak value of 77 degrees noted at JFK which is up there climatologically for this part of the world. The main issue tonight centers around the complex of showers and thunderstorms (in technical terms a MCS or mesoscale convective system) currently across the western parts of Upstate New York. All operational models have been keying on for several runs that this feature could impact our area this evening into tonight. The 12Z guidance has come in with better agreement, especially on the higher resolution models mainly the NAM 3km, the HRRR and the RAP which are in very good agreement even with timing. The somewhat detailed NAM 12Z or operational WRF-NAM and even the 12Z operational GFS which has been weaker with this complex on most runs, have hold this feature together as it heads towards the Lower Hudson Valley by this evening. As a result of this, I have boosted PoPs significantly area-wide, especially from The City on west and north. There are still some signs as this complex gets toward The City it may weaken as it moves into the maritime influenced air mass, but if this complex can come in initially more vigorous it may have better shot to maintain some thunderstorm activity all the way to Long Island. If not, then activity here on The Island may be more showers with no thunderstorms. Timing also has sped up arriving in the western CWFA by 3-5 PM and moving through The City around 4-7 PM and Long Island/southeast CT mainly between 7 and 11 PM. CAPE Values as well as LIs progged are much greater on the WRF- NAM than the GFS which is why the GFS remains weaker with this complex as it heads further east toward us. SPC has pushed a Slight Risk for severe thunderstorms into western Orange County for this evening. I went ahead and added gusty winds and heavy rain as hazards from the Hudson River on west where confidence in this is greatest. In summary: * A complex of thunderstorms will approach the area this evening from the west and move east, possibly weakening as it moves toward the immediate coast. * Some strong to severe thunderstorms are likely, with gusty winds over 50 mph possible along with hail. * Downpours producing rainfall rates in excess of one inch per hour may occur in any heavier thunderstorms that could result in poor drainage flooding, especially in more urbanized areas. * Those outdoors with plans this evening should watch the sky and be aware for any alerts. Travel may be impacted by low visibility, ponding of water/poor drainage flooding and gusty winds that blow any objects over or around especially during the evening commute. In the wake of activity, patchy fog may form in areas that get heavier rain briefly and temps cool to near the dewpoint. This is mostly likely in Orange County this evening for a bit. Lows tonight will still be in the upper 60s in the coolest spots well north and west of The City with readings in the mid to upper 70s in more urban areas. Some spots may actually set a calendar day low during any heavier convection this evening as rain cooled air drops toward the surface in convective downbursts. 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 /FRIDAY/... 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 /19Z THURSDAY THROUGH TUESDAY/...
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...Convective Complex Likely to Impact Terminals This Evening... A weak trough will be near or just west of the NYC terminals for the remainder of this afternoon, while a cold front approaches from the eastern Great Lakes. A convective complex developing over western NY state ahead of the cold front, will race quickly SE this afternoon into early this evening. There is some uncertainty as to how much of the complex stays together, but it seems likely that it will have an impact on most of the terminals, especially from NYC and points north and west. Strong gusty winds are possible with this activity. For the most part, outside of the convection, VFR conditions will prevail through Monday. W-SW flow this afternoon around 10 kt, with some occasional gusts up to 20 kt. Coastal terminals have the best chance for gusts this afternoon. Winds will become Northerly behind the complex this evening, then W-NW overnight into Friday morning. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Occasional gusts up to 20 kt this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KLGA TAF Comments: Winds may vary W-SW early this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KEWR TAF Comments: Winds may vary W-SW early this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KTEB TAF Comments: Winds may vary W-SW early this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KHPN TAF Comments: Timing of showers and thunderstorms could be off by 1-2 hours this evening. KISP TAF Comments: Timing of showers and thunderstorms could be off by 1-2 hours this evening. .OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY... .Friday Afternoon through Saturday...VFR. .Saturday Night-Tuesday...Episodes of showers and thunderstorms with MVFR or lower conditions possible.
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&& .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 threat for a convective complex to track across the area this evening 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...CS SHORT TERM...NV LONG TERM...GC AVIATION...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.