Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 190040 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 740 PM EST Sat Nov 18 2017 .SYNOPSIS... Strong low pressure will pass through the region tonight into Sunday with widespread rainfall and milder temperatures. Rain will taper to snow showers on Sunday afternoon as much colder air surges back into the area along with gusty winds. The general weather pattern next week will feature mainly seasonable weather. There will be a chance of a few rain or snow showers Wednesday, but otherwise it looks mostly dry for the Thanksgiving holiday. && .NEAR TERM /THROUGH SUNDAY NIGHT/... As of 635 PM EST Saturday...Leading edge of warm advection rainfall has reached the Tug Hill Plateau east of Lake Ontario at 2330Z, and will be rapidly overspreading nrn NY and wrn/central VT over the next 1-3 hours. May see a mix with sleet in spots with onset of precipitation this evening, with temps near freezing at summit level and also on the northern slopes of the Adirondacks into portions of the St. Lawrence Valley. That said, generally looking for rising temps overnight, so still not expecting any winter weather impacts for the roadways. Previous Discussion...No big changes in the forecast after review of the 12z guidance. Deepening surface low in western Ohio is already down to about 988mb as of mid afternoon, and will continue to strengthen as it tracks to the northeast. All guidance are pretty close on track and intensity, so we expect the center of the low to track right up the St Lawrence Valley and by 12z Sunday, likely sitting nearly on top of Massena with a pressure somewhere in the 978-982mb range. The low will push rapidly to the northeast of the region Sunday, pushing a strong cold front through the area. Rain overspreads the area tonight, becoming more showery in nature tomorrow morning. The showers will transition to snow showers and as moisture pulls away, the coverage will take on an orographic look and be concentrated across the higher terrain of the Adirondacks and northern Greens. A tight pressure gradient will also develop as the low departs, resulting in a gusty west- northwest wind area wide. Regarding various elements of the forecast, here are a few items of note... Temperatures: it`s a tricky forecast, and prone to large errors. In general, southerly winds will be resulting in steadily warming temperatures for most of the region overnight. Sunday`s high temperatures will occur during the morning, with temperatures falling all afternoon to the upper 20s to low 30s by late day. Most of us will be in the 40s overnight. There is actually a couple of models that indicate portions of the Champlain Valley will rise into the lower 50s after midnight as a southerly low level jet develops. Wasn`t quite that bold in the forecast, but we can`t rule it out. It will be harder to scour out the colder air in eastern VT, but still everywhere will be above freezing. The immediate St Lawrence River Valley region will not see those southerly winds. Instead, a cold northeast wind will persist as is common in situations with lows coming up the valley. This will keep temperatures there in the low/mid 30s all night, so when the cold front moves through, there won`t be much of a temperature change. Winds: Southerly winds will increase overnight, at times a little breezy in the Champlain Valley. As mentioned above, a brisk northeast wind will persist in the St Lawrence Valley. The primary winds will be after the cold front passes. Strong cold air advection will keep the boundary layer well mixed. With winds around 40-45kts at 850mb, some of that wind will come down to the surface at times. Models today are a smidge weaker with the winds than yesterday, so thinking 35-40 mph gusts will be common. Could be some downslope enhancement, especially on the eastern side of the Adirondacks and Green Mountains for some local gusts Sunday afternoon around 45 mph. At this time these winds will be just below our wind advisory threshold, so won`t raise those headlines. However later forecasts will have to monitor that potential. Precipitation Type: Strong warming aloft this evening and overnight will mean rain. Can`t rule out isolated sleet pellet or two at the onset of the precipitation this evening as a dry boundary layer helps with evaporative cooling. There will be a quick crash of temperatures aloft and at the surface with the cold front passage, so as it moves through, any rain showers around will transition fairly quickly to snow. By late Sunday, any precipitation will be in the form of snow showers. Snowfall Accumulations: Not looking at much in the way of accumulation, as by the time the precipitation turns to snow, the bulk of the deep moisture will be pulling out. Expecting perhaps up to 1" at elevations from 800ft to 1800 ft. Maybe 2-3" or so at elevations above that. Nothing more than a flurry or light dusting at lower elevations. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 154 PM EST Saturday...Deep cold trof rotating out of area during this period with building heights and zonal flow and surface ridging while the main surface high is located along the mid-Atlantic coast. Primarily dry and unseasonably cool with gusty NW winds of Sun-Sun ngt gradually diminishing and shifting W-WSW. Highs 25-33. Return flow Monday night means not as cold as Sun ngt-Mon morning with the exception of eastern VT and lows in the 20s with teens in NE VT and deep Adirondacks Vlys. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 154 PM EST Saturday...Primarily a very broad cyclonic flow pattern for the period with very minor disturbances and slight roller coaster of temperatures but largely below normal. There is an outside threat of a coastal storm Wed-Wed ngt but most current indications are keeping this a mid-atlantic and then out to sea storm with no impacts for our area but still worth monitoring for the next few days. Tuesday: High pressure sliding offshore for a return flow ahead of northern stream shortwave for moderating temperatures in the 40s. Northern shortwave and cold front move across area Tue ngt and largely exit by Wednesday. This will bring rain to mixed rain/snow showers and colder air once again. Wednesday: Cold front exiting region, although we still must look to our south and model trends about possible coastal. Currently, exiting drier conditions with some mountain snow showers possible with temperatures in the 30s/40. Thanksgiving: Quiet with surface high in control but the eventual approach of another northern stream shortwave by Thursday night. Currently dry with temperatures in the 30s. Thursday Night/Friday: Much of the energy with northern stream shortwave is in Canada but can`t rule out some isold/sct snow showers, especially in the mountains. Lows in the 20s and Highs in the 30s, a tad milder than Turkey day. Friday night/Saturday: We return to a more zonal flow with another minor shortwave and surface reflection moving along the Great Lakes and international border with some decent warm-air advection ahead of it for light snow/snow showers Friday night and scattered rain/snow showers on Saturday with temperatures in the mid-upper 30s. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... Through 00Z Monday...Expect a mix of MVFR/IFR as widespread rain moves into the region this evening. All terminals except MPV should see rainfall by 01Z with MVFR ceilings lowering to between 1000-2000 feet overnight. As a cold front moves closer anticipate some periods of IFR at SLK/BTV with a more prolonged period of LIFR at MSS under pressure driven northeast winds. After the front pushes across the region between 13-16z expect a sharp wind shift with gusty winds on the back side of the front. Winds will shift to northwest and gust between 20-30kts. With cold air building in the rain will abruptly switch to snow behind the front so there could be periods of IFR snow at MSS/SLK in the morning hours Sunday. Outlook... Sunday Night: VFR. Windy with gusts to 30 kt. Chance SHSN. Monday: VFR. NO SIG WX. Monday Night: Mainly VFR, with local MVFR possible. NO SIG WX. Tuesday: VFR. NO SIG WX. Tuesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA, Slight chance SHSN. Wednesday: VFR. Chance SHRA, Chance SHSN. Wednesday Night: VFR. Slight chance SHSN. Thanksgiving Day: VFR. Slight chance SHSN. && .MARINE... As of 245 PM EST Saturday...A Lake Wind Advisory is in effect for overnight and into Sunday. Southerly winds overnight will increase to 20-30 knots. A strong cold front will move across the lake during the mid to late morning on Sunday. Winds will quickly switch from south to west with the frontal passage and remain strong and gusty. Some gusts over 35 knots are possible during the afternoon. These winds will result in wave heights of at least 2 to 4 feet, producing very choppy conditions. These conditions may prove hazardous to those operating small craft && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Nash NEAR TERM...Banacos/Nash SHORT TERM...SLW LONG TERM...SLW AVIATION...Deal MARINE...Nash is the U.S. government's official web portal to all federal, state and local government web resources and services.