Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 141723 AFDOKX Area Forecast Discussion National Weather Service New York NY Issued by National Weather Service TAUNTON MA 1223 PM EST Tue Nov 14 2017 .SYNOPSIS... High pressure slowly retreats to the northeast through Wednesday. A warm front approaches from the southwest Wednesday night, then lifts to the north Thursday morning, followed quickly by a cold frontal passage Thursday afternoon. High pressure then builds in to the west through Friday, then slides offshore Friday night. A complex low then impacts the area from Saturday into Sunday, followed by high pressure building in through Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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WFO Boston/Taunton is testing service backup for WFO New York today. 1230 PM Update... Showers are persisting along CT coast and south of Long Island, and are associated with a weak surface trough and low level moisture convergence. Had one spotter report from Haddam CT of a little sleet mixing in during past hour, but that shouldn`t last long. High-res models show little overall movement to this activity, since surface trough should remain nearly stationary, but gradually weakens everything thru afternoon, having most of it done by 3-4 pm. Adjusted PoPs to reflect this trend. Expect clouds to dominate this afternoon, although there will be breaks of sun from NE NJ into parts of NYC. Western edge of lower cloud deck, which has made slow westward progress from CT and Long Island, has made it into Queens and may edge a little farther west early this afternoon before retreating back to east. Forecast highs in 40s are on track.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... The 700-500 hPa northern stream trough exits to the east this evening, followed by northern stream ridging beginning to build in overnight. Given the dry low levels and best forcing remaining to the N, should remain dry - once again with the possible exception of a stray sprinkle across northern interior zones this evening. Lows tonight should be up to around 5 degrees below normal, with temperatures ranging from the upper 20s to mid 30s, except upper 30s in NYC and its immediate surrounding area. Northern stream ridging continues to build over the area on Wednesday, with subsidence under the ridge keeping things dry. Highs on Wednesday should be around 5 degrees below normal - mainly in the mid-upper 40s. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Northern stream ridging exits to the east Wednesday evening. A 700-500 hPa shortwave crossing the area late Wednesday night, followed by a deep-layered trough crossing the area Thursday. While it should be mainly dry Wednesday evening (maybe some isolated to scattered rain showers over the NW 1/3 of the CWA), the rain showers become likely over the area from W to E late Wednesday night and Thursday morning. The precipitation should tapper of from W to E Thursday afternoon as the trough axis exits to the east. Northern stream ridging begins to build in Thursday night, builds over the area Friday, then exits to the east Friday night. The ridge should keep the area dry during this time frame, with the possible exception of some light rain or snow moving into far western Orange County late Friday night ahead of the next system. The GFS is more progressive than the CMC and ECMWF with the system for this weekend. Given the relatively high amplitude ridging ahead of the system (and the GFS developing closed upper lows ahead of and behind the ridge), believe the GFS is too progressive. As a result, have used a blend of ECMWF/CMC for timing precipitation and temperatures Saturday-Sunday. Regardless of timing of the system, there is the potential for strong, gusty winds both ahead of and behind the system, with a 50-60kt 950-850 hPa jet progged before it and 30-40kt of flow at 950-850 hPa behind it. Cannot rule out gusts to wind advisory criteria Saturday/Saturday night depending on how deep/strong the low level marine inversion is. With the strong low level jet ahead of the system, there is the potential for locally heavy rainfall as well from Saturday night into Sunday as well. For now expect showers to develop from W to E on Saturday, possibly beginning as a wintry mix across northern interior zones. The showers should be fairly widespread by late Saturday afternoon and continue through Saturday night, then taper off from W to E on Sunday. For now went dry Sunday night/Monday as the system exits to the east and the region is under the based of a northern stream cutoff low over SE Canada. For now thought, it appears the low levels will be relatively dry, warranting a dry forecast at this time. For temperatures Wednesday night-Monday: Low should run above normal Wednesday night, followed by near normal temperatures Thursday and Thursday night, then below normal temperatures Friday. Temperatures return to near normal Friday night and Saturday, then go above normal Saturday night, then should be below normal Sunday-Monday. There is quite a bit of uncertainty though with temperatures Sunday-Monday depending on timing of the trough crossing the area this weekend and strength/orientation of the closed low over SE Canada early next week. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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High pressure over the Ohio Valley builds slowly east through Wednesday, while low pressure lifts up into the North Atlantic. The high will move offshore Wednesday night. Main concern is area of MVFR and even IFR ceilings, which were making slow progress W across CT and Long Island and were surrounding city terminals this morning. We are more confident that these low ceilings (most likely MVFR) will remain near KLGA and KJFK and not impact KEWR or KTEB, although it will be close. Trend will be for slow improvement after 21z, so that most terminals will improve to VFR between 21z and 00z Wed for the evening push. VFR conditions expected tonight and Wednesday, although MVFR ceilings should arrive at city terminals toward evening. Light N/NE winds through tonight will become E/SE Wednesday. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: MVFR ceilings may linger an hour or two longer than forecast. The afternoon KJFK haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KLGA TAF Comments: Fairly confident on timing of improvement to VFR. The afternoon KLGA haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KEWR TAF Comments: Low chance of MVFR ceilings (BKN025) early this afternoon, but more confident on remaining VFR. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Low chance of MVFR ceilings (BKN025) early this afternoon, but more confident on remaining VFR. KHPN TAF Comments: Fairly confident on timing of improvement to VFR. KISP TAF Comments: Fairly confident on trends in TAF. Slow improvement from IFR to MVFR late this afternoon, and to VFR later this evening. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY... .Wednesday night-Thursday...MVFR or lower possible in chance of showers. W-NW winds G20-30KT possible Thursday afternoon. .Thursday night-Friday...VFR. NW winds G20-30KT possible, strongest Thursday night. .Saturday... Sub VFR conditions possible by the afternoon and becoming likely towards evening. S-SW winds G20-25KT.
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&& .MARINE... Made minor changes this update to reflect the latest trends in observations and guidance. The forecast appears on track. As high pressure builds in from the west through Wednesday and low pressure lifts up into the north Atlantic, a N-NE flow will continue across the waters. Winds and seas are forecast to remain just below SCA criteria on the ocean waters, but its possible there could be a period of 5 ft seas today east of Moriches Inlet and closer to 20nm offshore. Winds and seas diminish on Wednesday with the high moving across the waters. A strengthening return southerly flow develops ahead of a cold front Wednesday night, followed by potential gale force gusts behind the cold front Thursday afternoon and night. High pressure then briefly returns late Friday into Friday night before another strong frontal system impacts the waters Saturday into Sunday. There is the potential for both pre- and post- frontal gale force gusts on all waters, especially on the ocean waters. Gale potential will continue to be highlighted in the Hazardous Weather Outlook (HWO). && .HYDROLOGY... No significant hydrologic impacts are expected through at least Saturday morning. There is the potential for a significant rainfall from late Saturday into Sunday, with locally heavy rainfall possible. At this time, it is too early to specify amounts or what the exact impacts, if any, will be. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ JWD

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