Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 192348 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 648 PM EST Thu Jan 19 2017 .SYNOPSIS... A building ridge of high pressure both aloft and at the surface will occur across our region...while plenty of low level moisture will produce lots of clouds and patchy fog overnight. Given the depth of moisture...expecting the higher summits to be above the low cloud deck on Friday...with other areas of clearing also possible. Temperatures will continue to be very mild with highs mainly in the 30s to near 40 and lows in the mid 20s to mid 30s. The next system will impact our region late Monday into Tuesday with a wintry mix likely. && .NEAR TERM /THROUGH FRIDAY/...
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As of 648 PM EST Thursday...Low level moisture resides over the North Country under building high pressure and persistent inversion. Expect continued low level clouds overnight with light to calm winds. Currently seeing Temp/dewpoint spreads of 1F to 7F and as temperatures fall a little bit throughout tonight into Friday morning, isolated areas of patchy fog/freezing fog may develop where any breaks in clouds occur. Previous Discussion...Forecast challenge will be areal coverage of low clouds/patchy fog...followed by impacts on temps. Water vapor shows building ridge of high pres with subsidence/dry air aloft...which has suppressed moisture enough to support a few breaks across the dacks. Very difficult to determine if dry air aloft is strong enough to erode low level moisture/clouds and produce some clearing. If this was to occur...fog/br would quickly develop as temps would drop below cross over values...given current dewpoints in the upper 20s to lower 30s. Have continued to show some clearing across the summits tonight...with temps holding mainly in the mid 20s to lower 30s most locations. Given boundary layer moisture and light winds...combined with additional snow melt...some areas of patchy fog/br are possible overnight...especially Saint Lawrence Valley and protected valleys. Friday...little change in overall pattern expected...except soundings show shallower moisture. This will support more clearing especially southern sections and summits. Expect clouds to linger the longest over the Saint Lawrence and Champlain Valleys on light winds will limit mixing of boundary layer moisture. Temps will be tricky with progged 925mb to 850mb values around 0C...but mixing will be limited with high pres directly overhead. Thinking mainly near freezing summits to lower 40s warmer valleys which experience some sun on Friday afternoon...if more sun develops than expected highs will be 3 to 5 degrees warmer across the board.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 330 PM EST Thursday...Relatively quiet weather continues into the Friday night/Saturday time frame. An upper level ridge will be building into the North Country which should block some of the energy that will be heading into the Great Lakes. The strong inversion that will be trapping low level moisture will become eroded on on Friday evening and so low level clouds begin to move out of the area but a persistent mid deck will keep the area mostly cloudy through the day. There will be some light warm air advection that pushes into the region and so it wont take much to generate some light stratiform rain/snow especially in the higher terrain. Temperatures will remain above normal in the continue very mild with lows Friday night from the lower 30s and Saturday highs in the upper 30s to lower 40s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 330 PM EST Thursday...The end of the weekend should remain quiet before the weak upper level ridge breaks down. Then we move into a more uncertain time period from Monday through Wednesday. The one certainty is that we should be well above normal for temperatures to start the week. The most significant portion of the forecast is the potential for a phased low pressure system that will impact us early in the week. A southern stream upper level trough will dive south of the mid-Atlantic region over the Carolinas while a surface low develops over the DelMarVa peninsula. By Monday evening the GFS and EC show the system phasing and increasing in intensity. The trend in the guidance has been to bring the low close to the coastline Monday Night into Tuesday sliding the surface low inside of the benchmark. If that scenario plays out then we would trend colder than previous runs and we will see a wintry mix. I`m hesitant to go straight snow, however, because 1000-500mb thicknesses remain closer to 542-545 dam. So I chose to use a thickness based approach for precip type for the event leading to a mix of snow and sleet. The big take away is that the trend was more from rain and freezing rain to more of a wintry mix. This will be something continue to keep an eye on moving forward. I agree the previous forecaster in that there is some concern based on the potential for gusty southeasterly downsloping winds, especially along the western slopes of the Green Mountains later Monday afternoon into Monday night as mean 925-850 mb flow may exceed 40 knots. This will eventually predicate some adjustment of model qpf fields as valley/terrain shadowing/enhancement effects will be magnified. Higher-res guidance will certainly provide more detail as we draw closer in time. Variable conditions are expected behind that system as with synoptic flow stays southwesterly. This results in no significant change in our airmass through the mid week. Expect several shortwaves to pass through the area but at this point there isn`t a significant amount of confidence in timing. The idea of a daily threat of scattered rain/snow shower activity seems the way to go so I continued that from the previous forecast. Temps will continue in the mid 30s to lower 40s during the day time with overnight lows averaging in the upper 20s to lower 30s. && .AVIATION /00Z Friday THROUGH Tuesday/...
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Through 00Z Saturday...This evening starts with MVFR conditions outside the northern Champlain Valley and VFR conditions at PBG/BTV. MVFR cigs will plague the North Country terminals with IFR possible mainly after 05Z. With cross over temperatures ranging from the upper 20s to low 30s, there a chance for MVFR/IFR fog development in the light to calm winds high pressure is providing overnight. Strong inversion will keep MVFR cigs across the North Country, except RUT, through the late Friday morning/early afternoon. BUFKIT models indicate inversion breaks up in the afternoon, allowing for breaks in cloud cover and cigs to lift. Winds will continue to be light on Friday, generally 5 kts or less. Outlook 00Z Saturday through Tuesday...Areal coverage and cigs heights associated with plenty of low level moisture continues to be the aviation focus for Friday night into Saturday. A few sprinkles or flurries possible Saturday with general mvfr mountains to vfr valleys. Next system spreads a wintry mix across our taf sites late Monday into Tuesday with widespread mvfr to ifr conditions likely...along with breezy southeast downslope winds possible at Rutland.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...KGM/Taber SHORT TERM...Deal LONG TERM...Deal AVIATION...KGM is the U.S. government's official web portal to all federal, state and local government web resources and services.