Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 271131 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 731 AM EDT Thu Oct 27 2016 .SYNOPSIS... Rain mixed with wet snow across the mountains will develop from southwest to northeast over the North Country today. A slushy inch or so of wet snow is possible in the mountains...with up to 6 inches at the summits. As low pressure tracks toward our region...gusty southeast winds will develop along the western slopes and higher terrain by this evening and continue overnight. Rain will taper off by Friday afternoon before our next system arrives on Saturday. && .NEAR TERM /THROUGH FRIDAY/... As of 726 AM EDT Thursday...Minor update to increase arrival time of precip by 1 to 2 hours based on upstream surface obs and radar trends. Leading edge of snow is from Fulton to Syracuse to BGM which should arrive across southwest Saint Lawrence County by 16z and into the Champlain Valley around 18z...and northeast Kingdom by 21z. Otherwise...still expecting a mixture of rain/snow with mainly snow above 2000 feet...with some accumulation. All covered well in current forecast. The forecast challenge is timing of precip today...along with associated complex thermal profiles for determining ptype. Water vapor shows potent short wave energy across northern MI with good deep layer moisture advection over the Ohio Valley/western NY. Current surface analysis shows 1014 mb low pres over northern Indiana with greatest 3 hr pres falls toward western PA. Warm air advection precip is already overspreading western/central NY/PA at this time...with a mix of rain and snow depending upon elevation and precip rate. BGM reported 1sm -sn with leading edge of precip. Based on radar trends and following the 1000 to 500mb greater than 70% rh line off the GFS/NAM precip enters our southwest cwa by 15z...and quickly spreading into the Champlain Valley by 18z...and northeast kingdom by 21z today. Low level thermal profiles will be complex with some surface heating in the morning...warming bl temps into the mid 30s to lower 40s depending upon elevation. precip falls into a dry layer between 5000 and 15000 feet...expect some evaporational cooling to occur resulting in a mixture of rain/snow initially between 1000 and 2000 feet...with even a few wet snow flakes possible in the valleys. Soundings show freezing levels dropping between 1500 and 1800 feet during the higher precip rates late this afternoon...supporting a quick slushy inch or so of wet snow accumulation across the Dacks and Green Mountains. Depending upon precip rates and timing...this could make for a hazardous late afternoon/early evening commute across the higher terrain. An sps maybe needed to highlight this scenario. For tonight...initial band of warm air advect lift is located near the international border by 06z...with additional forcing arriving with potent short wave energy and strong upper level divergence signature. This combined with a deepening and closing off 5h/7h circulation moving from the Eastern Great Lakes into southern New England will produce additional precip across our region overnight into Friday. Models show good 1000 to 500mb rh with favorable 850 to 500mb q-vector forcing parameters from 06z to 18z Friday. Will continue to mention pops near 100% overnight...before tapering off from west to east on Friday. Given the track of surface low pres into the gulf of Maine and closed 5h/7h circulation...thinking additional moisture with area of rain and summit snow continues for most of VT on Friday...including the Champlain strongly blocked flow develops. Total qpf will range between 0.50 Saint Lawrence to 1.50 southern Greens and eastern Dacks. Given developing 925mb to 850mb low level jet of 40 to 50 knots from the southeast...expecting some impacts of terrain on qpf fields. Highest amounts will be along the se upslope regions from Ludlow/Killington to Stowe to Jay Peak...with some shadowing in the Champlain Valley/Northeast Kingdom initially. wind shift to the northwest on Friday...the northeast kingdom and western slopes/champlain valley will see some additional qpf. Snow levels become very tricky overnight into Friday as soundings show warm layer developing between 5000 and 7000 feet associated with southwest winds with cold pocket from 2500 to 3500 feet associated with upslope cooling on southeast winds. By 15Z Friday...cooling aloft occurs as winds change to the east then north by early afternoon and progged 850mb temps drop below 0c. Current thinking snow continues near the summits through early this evening...then changes to a wintry mix with pockets of freezing rain in the midslopes...before changing back to all snow by midday friday at the summits and cold rain below 2000 feet. Once again snow accumulations will be very elevation dependent with summits above 4000 feet seeing around 6 inches with several inches possible around 2000 feet and some minor ice accumulation in between. This should have very limited impacts...given elevation. Still anticipating breezy to gusty southeast winds along the western slopes from near Rutland to East Middlebury to Nashville tonight. The strongest winds will occur between 7 PM and 2 AM associated with 925mb to 850mb jet of 40 to 50 knots. Thinking localized surface wind gusts to 35 knots is possible with a few isolated power outages possible. Temperatures mainly in the mid 30s to mid 40s today...fall back only into the lower 30s to lower 40s overnight...with similar profiles expected on Friday. Hourly temps will drop several degrees when precip starts today and during higher precip rates...have tried to show this detail in grids. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 316 AM EDT Thursday...Brief ridging at the surface and aloft builds in over the North Country for the first half of Friday night before heights begin to fall again ahead of weak low pressure which will pass north of the Canadian border on Saturday. Overnight temp forecast will be tricky as winds slacken in the wake of an exiting system to our east, but pick up again markedly after midnight from the southwest. Not expecting a whole lot of clearing, so think mins will be mild and slightly above freezing. Timing of lows I think will fall early across the St. Lawrence and Champlain Valleys before warming slowly through the night with increasing winds, but elsewhere likely follow the normal diurnal curve. Weak low passes north of the border on Saturday and while low/mid level moisture is abundant with this system, overall forcing is rather weak so even though we continue to highlight likely PoPs for showers, QPF will be light with temps pushing well above seasonal normals into the upper 40s east to mid 50s west. By nightfall, the deepest low level moisture begins to shift east as the low tracks off into the Canadian maritimes and thus precipitation will gradually taper to nil by Sunday morning as high pressure building eastward into the Great Lakes approaches. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 316 AM EDT Thursday...The extended period looks to be fairly dry with a fast zonal flow aloft Sunday trending towards ridging for Monday and Monday night. A strong low developing out of the northern plains Monday afternoon tracks north of Lake Superior Monday night to the tip of James Bay by Tuesday night pushing a dry warm front through the area. We remain mainly dry all the way through Wednesday with temps warming well into the 50s for Tuesday and Wednesday in increasing south/southwesterly flow. && .AVIATION /12Z Thursday THROUGH Monday/... Through 12z Friday...Several impacts to aviation expected over the next 24 hours associated with approaching storm system. Vfr conditions will prevail through 15z Thursday...with precip and mvfr cigs developing at MSS/SLK/RUT btwn 15z-18z...with a period of wet snow providing intervals of ifr vis at slk. The precip overspreads PBG/BTV and MPV btwn 18z-21z with mvfr cigs and potential brief period of ifr vis at MPV in -sn. Expecting mainly a cold rain by 00z at all taf sites with mvfr cigs...some ifr cigs are possible at MSS associated with northeast flow and MPV/SLK. Next concern is developing low level jet of 45 to 55 knots at 5000 feet lifting from southwest to northeast across our taf sites between 00z and 06z. This will create areas of turbulence and enhanced low level wind shear...especially when this jet interacts with the higher terrain. A few surface gusts between 30 and 35 knots can be expected at RUT between 00z-06z Friday with gusts up to 30 knots possible at BTV. Outlook 12z Friday through Monday... Precip will be slowly ending from southwest to northeast by 12z Friday with lingering upslope focused precip impacting mpv/slk. Profiles support mostly rain. As winds shift to the northwest on Friday morning...intervals of ifr cigs are possible at BTV/RUT/MPV/SLK...given the amounts of low level moisture available. A warm front feature lifting across our taf sites on Saturday morning will shift the winds to the southwest with some scattered showers possible...especially mss/slk. Expecting mainly vfr conditions with intervals of mvfr cigs possible across northern NY taf sites on Saturday. Gusty southwest up to 35 knots are possible at MSS with 30 knots expected at SLK/BTV on Saturday. Another wind shift to the west/northwest will occur Sat Night into Sunday with additional scattered showers. Drier conditions with vfr flight conditions for Sunday afternoon into Monday. && .MARINE... Southeast winds will increase 15 to 25 knots this afternoon with waves building 1 to 3 feet. These winds will continue until midnight before decreasing toward Friday morning. Additional gusty northwest winds are expected on Friday Afternoon. A lake wind advisory is posted for today. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Taber SHORT TERM...Lahiff LONG TERM...Lahiff AVIATION...Taber MARINE...Taber is the U.S. government's official web portal to all federal, state and local government web resources and services.