Area Forecast Discussion
Issued by NWS Upton, NY

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047 FXUS61 KOKX 180341 AFDOKX Area Forecast Discussion National Weather Service New York NY 1041 PM EST Sat Feb 17 2018 .SYNOPSIS... Low pressure passes to our southeast overnight, followed by high pressure for Sunday. The high then slides offshore through Monday. A warm front approaches from the southwest Monday night, then lifts to the north Tuesday, followed by a slow moving cold front crossing the area during the middle week. High pressure may briefly build in to close the upcoming work week, before another frontal system approaches for the weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Rain/snow line, based on Dual-pol, has made progress to south coast of LI/NYC as of 03z, but is also eroding as it does so. Meanwhile, back edge of steady accumulating snow is beginning to make progress eastward into Orange county. Widespread reports of 5 to 8" across interior NE NJ and Lower Hud as of 10 pm. Generally 2 to 5" across NYC metro, 3 to 6" across SW CT, and 1 to 3 across LI/SE CT as of 10 pm. Based on low pressure deepening to the se of Buoy 44066, expectation is that rain/snow line does not much make much progress north of Belt Pkwy/Southern State across western LI, and stalls btwn Sunrise HWY and LIE across Suffolk County over the next couple of hours. This is fairly consistent with previous forecast and NAM. Expectation of a significant snow gradient across LI, from around an inch across the south shore of the south fork of LI to 4 to 7 inches for the hills of NW Suffolk and Nassau County. Heaviest total snow, 6 to 10", expected across NE NJ/Lower Hud and Southern CT based on upstream obs and most persistent moderate to heavy snow banding continuing over the next few hours with surface temps in the upper 20 to lower 30s. WSW`s remain as is. Snow should begin to taper from w to e between 6z and 10z. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Ridging at the surface and aloft occurs on Sunday, with high pressure shifting offshore on Sunday night. Dry weather through the period with a mostly clear sky. Sided with the colder side of guidance for temperatures due to a fresh snow pack. && .LONG TERM /MONDAY THROUGH SATURDAY/... Anomalously strong Bermuda/East coast ridging develops early this week and continues into midweek, in response to deep western troughing. The western trough will gradually shear NE in piecemeal fashion for the late week/weekend, resulting in a transition to a bit more suppressed but active confluent sw upper flow. At the surface, high pressure slides off the coast on Monday, and then becomes established under the upper ridge by midweek. Meanwhile a slow moving frontal system will cross through the Mississippi river valley the first half of the week. Its warm front likely approaches Monday Night with rain and then gets pushed north of the region on Tuesday. An unseasonably warm SW flow is likely Tue/Wed under deep layered ridging, with highs around 70 possible for NYC/NJ metro and areas N&W on Tue and lower to mid 70s on Wed. Meanwhile south coastal areas may struggle to get out out of the 50s due to the cold water temp. Coastal advection stratus/fog and nocturnal radiation fog is possible during this time as well. Models in general agreement with the eastern ridging breaking down enough, to allow a stream of shortwave energy to approach and push an approaching cold front towards and through the region Wed night. This likely brings another round of rain to the region Wed night through Thursday. Potential for brief ridging Friday, before next shortwave and associated frontal system affect the region on Saturday with another round of rain. Temps during the period expected to average well above average, with high temps potentially 25-30 degrees above normal Tue and Wed for NYC/NJ metro and areas N&W.. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... Deepening low pressure south of Long Island tracks to the northeast overnight, and then moves well east Sunday morning as high pressure builds to the west. The high builds over the terminals Sunday, then moves off the northeast coast Sunday night. Snow, with a rain/snow mix along the south shore of Long Island will be ending overnight into early Sunday morning, 08Z at KSWF to 12Z at KGON. IFR to LIFR will quickly improve to VFR as the precipitation ends. Snowfall rates could reach 1 inch, to as high as 2 inches, per hour during the heaviest snowfall, mainly across Long Island, and into southeastern Connecticut. Total snow accumulations: 3 to 6 inches, KJFK, KISP, KSWF, KGON 6 to 8 inches, KEWR, KTEB, KLGA, KHPN, KBDR. East to northeast winds 10 kt or less will back to the north and northwest as the low tracks south of Long Island. NW winds will increase to 10-15 kt, with gusts 18 to 25 kt during the day Sunday. Gusts and winds diminish late in the afternoon, after 19Z, and then become light and variable by 00Z Monday. .OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY... .Sunday night-Monday...VFR. Becoming MVFR to IFR in rain and possibly fog Monday afternoon. .Tuesday...MVFR or IFR possible in the morning and again at night, otherwise VFR with SW wind G20KT possible. .Wednesday...VFR. Chance of showers with MVFR. .Thursday...MVFR in rain. && .MARINE... SCA for the ocean waters for Sunday morning into early afternoon with increasing winds and seas. There could be some gusts to 25 kt Sunday morning over the Eastern Sound and eastern bays, but coverage didn`t warrant an advisory. Sub-sca conds otherwise tonight and from late Sunday afternoon through Sunday night. Generally sub-advsy winds expected Mon through Wed, but a persistent 15 to 20 kt SW flow may have sea building to SCA levels Tue/Wed. Seas should subside Wed night into Thu as a weak cold front passes through and winds become offshore. && .HYDROLOGY... Around 1/2 to 3/4 an inch of liquid equivalent is expected Saturday night with locally higher amounts. With most, if not all of this falling in the form of snow, no hydrologic impacts are expected. No significant hydrologic impacts are expected from Sunday through the end of next week. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Warning until 7 AM EST Sunday for CTZ005>012. NY...Winter Weather Advisory until 7 AM EST Sunday for NYZ067-068- 074-075-079>081-178-179. Winter Storm Warning until 7 AM EST Sunday for NYZ069>073-078- 176-177. NJ...Winter Storm Warning until 7 AM EST Sunday for NJZ002-004-006- 103>108. MARINE...Small Craft Advisory from 6 AM to noon EST Sunday for ANZ350- 353-355. && $$ SYNOPSIS...JC/NV NEAR TERM...JC/NV SHORT TERM...JC LONG TERM...NV AVIATION...19 MARINE...JC/NV HYDROLOGY...JC/NV EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.