Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 200006 AFDOKX Area Forecast Discussion National Weather Service New York NY 806 PM EDT Sat Aug 19 2017 .SYNOPSIS... A weak cold front will pass through tonight, followed by high pressure building from the west Sunday into Sunday night. The region remains on the western periphery of the Bermuda High from Monday through Tuesday. A cold front approaches from the west Tuesday night then crosses the area on Wednesday. Canadian High pressure then builds in through Saturday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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AFD Issued to clear rip current headline which expired at 8pm. Latest radar trends show convection over central Pa beginning to weaken. 22z HRRR seems to be handling this well. Made some minor adjustments in Pops this evening, shading towards 22z HRRR (ignoring its typical spurious convection out ahead of main area). Should be dry throughout after midnight as northern stream shortwave trough exits to the NE. Low temperatures should be in the lower 70s in/just outside NYC, with 60s elsewhere.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Zonal upper flow ensues after the upper trough passage, with sfc high pressure building from the west. Sunday should be mostly sunny and quite warm, with high temps only a shade lower than those of today. Temps should respond to clear skies/light winds Sunday night by dropping into the 50s inland and in the Long Island Pine Barrens and the 60s most elsewhere, but only the lower 70s once again in outside NYC. && .LONG TERM /MONDAY THROUGH SATURDAY/... The region remains on the northern periphery of a western extension of the sub-tropical ridge Monday-Monday night, with zonal flow aloft. With no shortwaves embedded in the flow it should be dry with minimal cloud cover. Any clouds would be primary some isolated- scattered cirrus, but cannot rule out few-sct cu Monday afternoon along any seabreeze/differential heating boundaries. Highs Monday should be 5-10 degrees above normal, with the NYC Metro Area right around the 90 degree mark. With dewpoints progged in the lower-mid 60s Monday afternoon, heat indices should be within a degree or two of the air temperature. Lows Monday night should also be around 5-10 degrees above normal, with urban heat island areas only falling to the mid 70s. SW winds aloft on Tuesday as an approaching N stream closed low sharpens the flow ahead of it. GFS is the most aggressive of all models with any showers/thunderstorms Tuesday afternoon, so have limited pops to slight chance over the NW 1/2 of the CWA. Tuesday will be another very warm-hot day over the area, with highs again 5- 10 degrees above normal. Afternoon dewpoints though should be around 70 producing heat indices across NYC/Urban NE NJ in the mid 90s. Have increasing pops Tuesday night into Wednesday with the aforementioned northern stream closed low passing to the north, and its associated surface cold front crossing the area on Wednesday. With the region in the right rear quadrant of a 95-100kt 300 hPa Jet Wednesday, 1000-2000 J/kg of CAPE, 35-45kt of 0-6km bulk shear, and the region in the tail of a 30-35kt low -level jet, there is a low- end potential for strong to possibly isolated severe storms ahead of the cold front on Wednesday. Lows Tuesday night should be a degree or so warmer than on Monday night. Highs on Wednesday should be near normal (depending on how fast the cold front actually moves through). A mean trough sets up over the Northeast and Mid-Atlantic Wednesday night-Saturday. However dry low levels and predominately NW (occasionally W-WNW) low level flow should keep things dry. Temperatures should be near normal Wednesday night, then a few degrees below normal Thursday-Saturday. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... A cold front moves through the terminals tonight followed by high pressure for Sunday. VFR through the TAF period. Showers and thunderstorms to the west will weaken and diminish after sunset with no impact to the immediate NY metro terminals. While a weakening shower/storm cannot be ruled out at KSWF 01-03z, have left out of TAF due to low confidence. SW-W flow this evening 10 kt or less veers to the NW with the cold front passage overnight. NW winds are expected on Sunday around 10 kt, with some backing to the W and SW in the afternoon. .OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY... .Sunday Night-Tuesday morning...VFR. .Tuesday afternoon-Wednesday...A chance of showers and thunderstorms with MVFR or lower conditions possible. SW G20 kt possible late Tuesday. .Thursday...VFR. && .MARINE... Made minor changes this update to reflect the latest trends in observations and guidance. The forecast appears on track. A relaxed pressure gradient over the region will limit winds to around 10KT or less through Monday night, with seas/waves below Small Craft Advisory levels. The pressure gradient tightens ahead of a cold front Tuesday, with winds up to around 15KT. There should be a moderately tight pressure gradient over the region Tuesday night- Wednesday with sustained winds up to around 20KT and the potential for gusts to around 25KT, especially over the coastal ocean waters. Seas should build to SCA levels over the coastal ocean waters Tuesday night and remain so on Wednesday. The pressure gradient then slackens from Wednesday night into Thursday. Winds should be limited to around 15 KT or less on Wednesday night and 10KT or less on Thursday, with seas below SCA levels during this time frame. && .HYDROLOGY... It should be dry through Monday night, then no significant hydrologic impact is expected from any showers or thunderstorms on Tuesday. At this time, there is too much uncertainty to specify what, if any, hydrologic impact would be experienced from convection Tuesday night and Wednesday. It should then be dry Wednesday night-Saturday. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...None.
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