Area Forecast Discussion
Issued by NWS Burlington, VT

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115 FXUS61 KBTV 252018 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 318 PM EST Sat Feb 25 2017 .SYNOPSIS... A strong cold front will continue move eastward across the North Country this afternoon and early evening. The leading edge of the front will have strong gusty winds and heavy rain. Rain will continue behind the front continuing the potential for ice jams and river flooding through the weekend. Tonight, lingering snow showers concentrated over the higher terrain will taper off Sunday morning. More seasonable weather returns Sunday with some light snow in the higher elevations before a quieter period of weather to start the work week. && .NEAR TERM /THROUGH SUNDAY/... As of 318 PM EST Saturday...Strong cold front moving through Northern New York this afternoon has produced strong gusty winds, heavy rain and isolated lightning/thunder. Gusty winds out ahead of the front from strong 850mb jet...CXX VWP showing 50kts at 850mb has also helped with deeper mixing and strong WAA, resulting in temperatures in the 60s to around 70. Expect the leading edge of to reach the Champlain Valley around 22Z, continuing east into central VT around 00Z and eastern VT shortly thereafter. The very warm temperatures and the heavy rain that is moving eastward across the area will continue the flood threat. Already have some areas/rivers flooding (see FLW`s) and expect the rain this afternoon and evening to result in runoff reaching the rivers and rivers cresting on Sunday. Observed 6-hourly rainfall amounts have generally ranged from quarter inch to half inch. Rain will continue with still some embedded areas of moderate to heavy rain possible into this evening. Expect the back edge to move out of the SLV around 03Z, CPV after midnight/05z. Lingering precipitation focused around the higher terrain is expected through Sunday morning. Also behind the front, the cold air advection surges in and we will see 25-35 degree diurnal swings with lows in the mid-upper 20s expected. Thus the precip lingering behind the anafront will likely end as end as a period of rain/snow in the valleys and heavy wet snow in the higher elevations where several inches of accumulation are possible. Sunday, some gusty winds of 30kts or less are possible in lingering PGF before subsiding in the afternoon. Drier air will move in with slight ridging at the surface. Max temperatures in decreasing cloud cover will generally be in the 30s. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 318 PM EST Saturday...Ridging at the surface continues Sunday night, but a mid level shortwave will near the international border Monday morning. Models disagree how far south the shortwave will reach, but with limited moisture available, have kept only slight chance POPs throughout the period, mainly for higher terrain near the international border. With increased cloud cover possible from the shortwave and generally moderating temperatures as low level flow becomes for SW, expect min temperatures Sunday night to be in the 20s. Increasing 500mb heights indicative of continued moderating temperatures in SW flow on the NW edge of surface ridge will have Monday and Monday night dry with max temperatures in the 40s and mins in the 20s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 318 PM EST Saturday...Tuesday the area will remain under slight ridging aloft, but moisture and weak vorticity attempt to move in from the south. NAM and GFS in agreement bringing precipitation into at least the southern half of the forecast area Tuesday afternoon, while ECMWF wait for developing low to bring precipitation Tuesday night-Wednesday. This system associated with deepening 500mb trough over the northern plains states. Details of track of developing surface low and strength continue to be under debate. Overall 12Z GFS and ECMWF show the surface low to track near the international border, which could start precip as rain through most of Thursday before the associated cold front moves through. Lingering snow showers possible late Thursday. Overall still time for models to focus around a solution. && .AVIATION /20Z Saturday THROUGH Thursday/... Through 18Z Sunday...Active weather is descending on the area this afternoon with a line of showers and isolated thunderstorms moving from west to east across the area between 18z and 02z. During this time expect MVFR/IFR conditions for both ceilings and visibilities due to the showers and isolated storms. Gusty south winds...in the 20 to 30 knot range...will exist in advance of the precipitation...then shift to the southwest and west after 02z through the remainder of the period. Winds will taper down a bit...but still be gusting in the 15 to 25 knot range. As precipitation ends after 02z...visibilities will improve into the VFR category and in the MVFR/VFR categories for ceilings. Outlook 18Z Sunday through Wednesday... 18Z Sunday - 12Z Tuesday...Mainly VFR under high pressure. 12Z Tuesday - 00Z Thursday...VFR with chance MVFR/IFR rain showers. && .HYDROLOGY... As of 430 AM EST Saturday...The flood watch remains in place and is effective through Sunday evening. The record setting warmth from Thursday through Saturday has already melted out a significant portion of our snowpack with more warm air this afternoon. The snow melt will combine with periods of heavy rainfall associate with a cold front and produce significant rises on nearly all rivers and streams across the region. And the ground is also frozen, so not much will soak in. Complicating matters is that some rivers, especially across northern/northeast VT and in the Adirondacks are still ice covered. Thus as the water levels rise and the ice weakens, we`ll start to see ice movement. Which could very well then get stuck in bends in the river or along bridges or where the rivers go from a steeper to more gentle slope. By their nature, ice jams are impossible to predict but can result in localized flooding occurring quickly. In general, it takes the river to rise 1.5 to 3 times the thickness of the ice to start the breakup process. Based upon NERFC forecasts as well as ensemble river simulations we continue to look at the Winooski @ Essex Jct, and the Mad River @ Moretown for the primary focus of more significant river flooding. Best river response will be late Saturday through Saturday night due to runoff from snowmelt and expected rainfall. Thickest river ice is in place across nern NY basins and nrn VT, including the Chazy, Ausable, Winooski, Lamoille, Missisquoi, and Passumpsic. Uncertainty in the river forecasts are due to unknown exactly how much snow melt we are getting and how much rainfall we will see on Saturday. Those uncertainties are pretty large, so forecast changes are possible as we move closer to the main event on Saturday. && .CLIMATE... Several more record high temperatures are expected to be broken tomorrow on February 25, 2017. Here are the current records for our long standing sites: Burlington, VT 55|1985 Montpelier, VT 59|1985 St. Johnsbury, VT 60|2016 Massena, NY 50|1956 Mount Mansfield, VT 49|1961 && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Flood Watch through Sunday evening for VTZ001>012-016>019. NY...Flood Watch through Sunday evening for NYZ026>031-034-035-087. && $$ SYNOPSIS...Deal/KGM NEAR TERM...KGM SHORT TERM...KGM LONG TERM...Evenson/KGM AVIATION...Evenson HYDROLOGY...Banacos CLIMATE...Lahiff

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