Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181145 AFDOKX Area Forecast Discussion National Weather Service New York NY 645 AM EST Sun Nov 18 2018 .SYNOPSIS... High pressure over New England will shift offshore today, with a weak warm front approaching tonight. A slow moving cold front will sag south of the region on Monday, followed by the passage of a weak offshore low on Tuesday. An arctic airmass will likely build in for the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Forecast is on track. Minor updates to hourly T/Td and winds based on latest obs and trends. Otherwise, despite high pressure over New England, skies will remain gray as jet induced cloud cover and pcpn move towards the area from the Ohio Valley. The high shifts offshore this aftn with the possibility of some light pcpn well N and W of NYC late this aftn as the entrance region of an upper jet streak with weak shortwave energy tracks into New England. Soundings indicate this would fall as snow, with only a coating expected through 6pm. Highs are expected to range from mid to upper 30s well inland to mid 40s near the coast. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... Guidance remains in good agreement with an amplifying pattern developing across the lower 48 early this week as a piece of the polar vortex breaks off and drops into Hudson Bay. This will result in a developing longwave trough east of the Rockies with a high amplitude ridge to the west. At the sfc, a weak frontal system will track from the mid Mississippi valley into the Mid Atlantic states by evening and continue through southern New England tonight. WAA will ensue tonight ahead of a warm front with temps slowly rising in the low levels. Pcpn is expected to gradually expand southward, although NYC and Long Island may remain mostly dry until Mon night and Tue. With the warming low level temperatures any snow across locations well inland this evening is expected to change over to plain rain overnight. Less than an inch of snow accum is expected before the changeover. Weak low pres continues towards the Canadian Maritimes on Monday with its cold front slowly pushing south of the area. PoPs decrease Mon aftn/eve as weak ridging moves through ahead of the next wave of low pres. There is some uncertainty in the track of this low which will depend on where the energy in the base of the upper trough tracks and the interaction between this and additional southern stream energy ejecting from the SE coast. This will also determine where the axis of heaviest pcpn will be. Pcpn overspreads the area late Mon night with all NWP guidance tracking the low S of Long Island on Tue. Colder temps across northern zones should gradually change the pcpn back over to snow into Tue morning. Boundary layer temps are progged to become marginally warm as the pcpn is lifting out which may lead to a changeover back to the liquid state before ending. At any rate, boundary layer temps will be marginal across the interior where accumulating snow is expected late Mon night into Tue, which will result in a wet snow. As such only anticipate 1-2 inches of accumulation. If the axis of heaviest pcpn shifts a bit further N or the wetter GFS verifies, could be flirting with advsy level snow. Areas from the CT coast and south are expected to remain all rain through the duration of the event. Temperatures are expected to range between 5 and 10 degrees below normal through Tue. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Fair wx Wed with the cwa between systems. An arctic front however arrives Wed ngt. The GFS and ECMWF both agree on this timing. Although the models are dry, some snow shwrs cannot be ruled out. Pops may need to be included in later forecasts. Dry wx fcst for Thanksgiving thru Sat with a 1040 or so high building in. Temps well blw average on Thanksgiving, then moderating a bit each day thereafter. Rain possible Sat ngt as a Pacific sys approaches. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... High pressure will slowly build from the NW this morning. The high moves offshore this afternoon with a warm front approaching tonight. VFR through this afternoon. There is potential for ceilings 2500- 3000 feet late this afternoon into tonight. Light precipitation moves into the terminals this evening north of NYC. KSWF may start off as some light snow, but will transition to rain towards midnight. Just some light rain is expected for the remainder of the terminals. W-WNW winds diminish through the early morning hours, veering to NW- N and then N-NE after day break. Winds continue to veer to the S-SE this afternoon. Speeds will be under 10 kt. .OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY... .Monday...MVFR possible with chance of rain. .Monday Night-Tuesday...MVFR or lower conditions possible in rain or wintry mix Monday night into Tuesday. NW winds gust 15kt in the afternoon. .Tuesday Night-Wednesday...Mainly VFR. low chance MVFR. W winds G15-20kt. .Wednesday Night-Thursday...VFR. NW winds 15G25kt. && .MARINE... High pressure passing over the waters today will keep conditions below SCA criteria through tonight. Winds and seas are forecast to remain below SCA levels through Wednesday. An arctic front move across the waters Wednesday night bringing SCA and low chance of gale conditions Wednesday night into Thursday. Winds and seas then fall below SCA levels on Friday. && .HYDROLOGY... QPF amounts between 1/4" and 1/2" are expected from late this afternoon into Tuesday. Some of this is expected to fall in solid form across interior locations. No hydrologic issues are expected through next Saturday. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO35 (162.55 MHz) will remain off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JMC/DW NEAR TERM...JMC/DS/DW SHORT TERM...DW LONG TERM...JMC AVIATION...BC MARINE...JMC/DW HYDROLOGY...JMC/DW EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.