Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 220600 AFDOKX Area Forecast Discussion National Weather Service New York NY 100 AM EST Wed Nov 22 2017 .SYNOPSIS... A cold front passes through early Wednesday as intensifying low pressure tracks well southeast of the region. High pressure builds in Wednesday through the end of the week. A cold front crosses Saturday night, with high pressure building in from the west for the beginning of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Rain event evolving very rapidly overnight. As of Midnight, rain is rapidly developing and expanding up the I-95 corridor from VA. Baroclinic leaf deformation evident SC to southern New England on satellite with subtropical cyclogenesis off the NC coast. The phasing of approaching northern stream energy from the Great Lakes with this southern stream energy, should result in a favorably strong right entrance jet region over the region late tonight into Wednesday morning. This lift interacting with Gulf/Atlantic moisture advecting up the coast should allow for a soaking rain across eastern half of the region by sunrise. In fact, high res models indicating potential for some weak instability promoting a period of heavy rain and perhaps an embedded rumble of thunder. The exact location of deformation zone will determine how far west the heavier rain develops, with high-res models clustering across LI/CT. With large scale lift, a period of light to moderate rain likely for NYC/NJ metro, with just some lighter rain potential to the NW. Rain develops late tonight from southwest to northeast, mainly between starting at 4 AM Total rainfall amounts generally between a half to 1 inch for Eastern Long Island and eastern Connecticut, with low prob of 1 1/2 inches. To the west, rainfall will taper to about about a 1/10 to 1/4 of an inch for the NYC/NJ metro, with lower totals NW of NYC/NJ metro. Temps will stay steady or rise for the interior. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... Once the cold front passes during the morning, conditions are likely to quickly improve from west to east during the early afternoon with drier air ushering into the region. With cold air advection following the front, the end result will be falling temperatures throughout the day along with an increase in breezy NW winds by afternoon. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Continued agreement with the operational models for the first part of the long term period. High pressure at the surface, with the center over the Mid-Atlantic states, will keep the area dry for Thanksgiving. Cold air advection continues as noted in 12Z GFS soundings, so conditions will be much cooler than Wednesday. Given forecast soundings and 850 temperatures in the 0 to -4 C range for much of the area, highs should only reach the lower 40s, which is below normal for this time of year. Normal highs should be in the lower 50s. A cold front does pass north of the area, with a wind shift to the west, then west-southwest by the afternoon. High pressure pushes off the East Coast late Friday into Friday night as a warm front over the Eastern Great Lakes lifts well north of the area. Warm air advection doesn`t seem to kick in until Friday evening, so dry and continued cool for Friday, but slightly warmer than Thursday with highs in the middle to upper 40s. Another cold front approaches the area late Saturday and passes through Saturday night. Southwesterly flow ahead of the front will bring temperatures to normal levels to above normal levels, in the upper 40s to upper 50s. 12z GFS has trended drier with this run, which will warrant only slight chance for the entire area as there isn`t much moisture for the front to work with. It may be cold enough at the start for some frozen or freezing precipitation in much of Orange County Saturday morning, however, it will quickly change to rain. A surface trough or secondary weak cold front moves through on Sunday with a reinforcing shot of cold air. Some instability with the colder air aloft associated with the upper level trough may produce some light rain showers across the area, mainly for portions of Long Island. High pressure then keeps the area dry through the beginning of next week. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... A cold front approaches from the west early this morning, then crosses the area later this morning. A coastal low passes to the east of Long Island this afternoon. High pressure then builds in from the west into tonight. MVFR conditions develop towards daybreak as rain overspreads the terminals, except IFR conditions at KHPN/KISP/KGON. There is a chance that the city terminals have IFR conditions during the morning, as well, but confidence in this is too low to put in the TAFs at this time. Rain likely ends by around noon for the city terminals and points west, and early afternoon farther east. There is a low chance for isolated thunderstorms at KGON and KISP from around 9-15z. Winds become light and variable throughout by daybreak. Winds then shift NW and increase by mid morning, mainly to the right of 300 true/310 magnetic. 20-25KT gusts become frequent during the afternoon, then taper of during the evening. .OUTLOOK FOR 06Z THURSDAY THROUGH SUNDAY... .Late tonight-Friday night...VFR. NW winds G15-20KT possible late tonight/Thursday morning. SW winds G15-20KT possible Friday night, mainly at eastern terminals. .Saturday-Saturday night...MVFR possible. W-NW winds G15-20KT possible Saturday night. .Sunday...Becoming VFR. NW winds G20-30KT possible. && .MARINE... SCA continues for the ocean waters as seas will be slower to subside. A cold front will be moving east of the forecast waters this morning as high pressure builds to the west, with marginal SCA gusts likely all waters in its wake. 5 to 6 ft waves on the ocean waters on Thursday will continue as a northwest flow shifts to the west-southwest. Waves will diminish Friday, generally coming down below 5 ft for most areas on the ocean by Friday afternoon. Waves increase again on the ocean late Friday night as a southwesterly flow sets up ahead of an approaching cold front, diminishing Saturday night. Winds should generally remain below 25 kt until Sunday afternoon as a northwest flow strengthens behind the passage of a cold front. Winds should remain above 25 kt from Sunday evening throughout the rest of the long term. && .HYDROLOGY... Rain this morning of up to 1.5 inches across Long Island to SE CT leads to urban ponding. Otherwise, No hydrologic problems are anticipated the next 7 days. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 AM EST Thursday for ANZ350-353- 355. && $$ SYNOPSIS...CB NEAR TERM...Tongue SHORT TERM...CB LONG TERM...JP AVIATION...Maloit/JC MARINE...CB/JP HYDROLOGY...CB/JP is the U.S. government's official web portal to all federal, state and local government web resources and services.