Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 130535 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1235 AM EST Sat Jan 13 2018 .SYNOPSIS... Today`s record warmth will be short-lived as a strong cold front across the St. Lawrence Valley late this afternoon moves steadily southeastward across the region this evening and overnight. Temperatures will very rapidly fall below freezing with passage of the front. Meanwhile, a developing low pressure system will track northeastward along the frontal boundary, bringing heavy mixed wintry precipitation to the region tonight through Saturday morning. Periods of heavy snow and sleet are expected, with localized ice accumulations up to a quarter inch across south-central Vermont. Difficult and icy travel conditions are expected areawide, especially late tonight and Saturday morning. Conditions will trend colder and drier for Sunday and Monday. There is a chance for additional snowfall Tuesday into Wednesday of next week. && .NEAR TERM /UNTIL 1 PM THIS AFTERNOON/...
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As of 1224 AM EST Saturday...Overall given the complex thermal profiles and associated ptype issues current forecast in good shape. Updated to capture latest trend...which show 0c sfc line from Essex County VT to Essex County NY with BTV down 27f and a sleet/snow mix. Will examine all 00z guidance...but may have to trim back snowfall amounts along transition zone over central VT, sleet will limit accumulation. Previous Discussion...Very dynamic weather pattern in place with near record to record warm temperatures / dewpoints/ and precipitable water values across the North Country this afternoon. High of 61F thus far at BTV, with a few locations 63-64F across wrn VT. In addition to the warm temperatures, dewpoints have reached the mid 50s. Along with gusty south winds and patchy fog, this has quickly eroded almost all of the existing snowpack at lower elevations, with significant loses at higher elevations per webcams (high of 53F at the Mt. Mansfield summit). Additional light to moderate rainfall into this evening and runoff will maintain the threat of river and ice jam flooding through tonight. Flood watch continues thru 12Z Saturday. Please refer to ongoing flood warnings for additional details. Next issue is the moderate to heavy mixed precipitation moving in during tonight. Sfc cold front with an extreme low-level temperature gradient was shifting sewd into the St. Lawrence Valley at 20Z. Temperatures will drop 10-20 deg / 2hr with the frontal passage, and will gradually be transitioning to mixed wintry precipitation by 22Z at KMSS, and by 01-02Z around BTV with N-NW wind shift. We`ll be seeing a "flash freeze" situation tonight, where temperatures dive sharply below freezing and any standing water will quickly freeze on roads and sidewalks. Will make for increasingly icy road sfc conditions from NW-SE as cold air sweeps in, even beneath the falling snow/sleet overnight. We`ve been monitoring the vigorous mid-level shortwave trough across the Tennessee river valley...which will shift newd along the frontal zone during the overnight hours. Excellent warm conveyor belt across nrn FL/GA/SC (1.8" PW values) will contribute to strong moisture advection and lift back across the frontal zone late tonight into Saturday morning, as the frontal zone bisects VT from SW-NE during the predawn hrs. Combined with frontogenetic forcing, should see periods of heavy mixed wintry precipitation, especially 06-15Z Saturday. No changes to the ongoing winter weather headlines, with Winter Storm Warnings across nrn NY into central/nrn VT, and Winter Weather Advisories for Rutland/Windsor/Orange counties. Will see freezing rain of brief duration across nrn NY and the nrn Champlain Vly (1-2 hrs), followed by sleet and snow. Snow will be of longest duration across nrn NY where favorably cold thermal profiles arrive first. Have 6-10" snowfall across nrn NY, with localized amts to 12" possible. Greater mixing with sleet in the Champlain Valley and n- central VT supports 4-8" snow/sleet, with a few spots maybe up to 10" along the intl border area in nwrn VT. South and east of a line from St. Johnsbury to Montpelier to Rutland, looking for more freezing rain (around 0.25" possible) and reduced snow/sleet accumulations of 2-4" with the prolonged icing. May see isolated power outages with the freezing rain across central/s-central VT, but overall ice loading not sufficient for widespread power issues based on current indications. Will also see strong north winds of 15- 30 mph develop across the Champlain Valley with low-level channeling of colder air filtering into the valley overnight. Strongest winds will be near the srn end of Lake Champlain, where valley narrows considerably. As surface frontal wave low pulls away across the Gulf of Maine, we`ll see lingering trowal/comma head snowfall across the Adirondacks and nrn VT through about 16-18Z, before exiting quickly to the north and east. Thus, should see snow winding down by early afternoon with some improvement to travel conditions later in the day along with partial clearing late afternoon into Saturday night. Temperatures will be sharply colder, with lows in the single digits across nrn NY and teens across VT, except low 20s far southeast. Temperatures rise just a few degrees on Saturday, and then we`ll see lows of -5 to -15F Saturday Night, and locally near -20F for Saranac Lake (KSLK).
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&& .SHORT TERM /1 PM THIS AFTERNOON THROUGH SUNDAY NIGHT/... As of 346 PM EST Friday...Strong 1040 mb high pressure will moves slowly across the area Sunday while a weak short wave trof aloft moves by without any fanfare. So Sunday looks to be mostly sunny and quite cold with highs from the lower single numbers in the north to low teens in southeast VT. Mainly clear skies and calm winds Sunday night will allow temps to fall to 10 to 20 below with a few outliers either side of that. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 346 PM EST Friday...A very active long term forecast period is in store with a deepening long wave trof over the CONUS. Models start out in reasonable agreement with the trof closing off as it moves southeast across the great lakes with ridging aloft over our region and high pressure persists at the surface. However, the evolution of the trof and surface low pressure is quite different as it approaches the northeast US Wed-Thu. GFS/CMC has a positive tilt trof with the surface low out to sea east of the mid-Atlantic coast while the ECMWF develops a new closed low off the mid-Atlantic coast and the surface low right up the coast toward New England and into the Gulf of ME. Result is rather low confidence in the Wed-Fri time frame so for now keeping snow showers in the forecast through that period regardless as one way or another the upper trof should bring a chance of precip. Temperatures start out on the cold side Monday with high pressure but return closer to seasonable levels for the rest of the week. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
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Through 06Z Sunday...Mvfr/ifr currently across our taf sites early this morning with mixed precip occurring. The combination of snow and sleet will produce ifr vis at slk/pbg/btv/mpv and rut with lifr conditions in periods of moderate snow at mss. All sites transition to snow/sleet before ending as a period of light to moderate snow btwn 10z and 16z Saturday...with ifr/lifr conditions. Expect major impacts to both air and ground ops at all taf sites thru 18z Saturday...with associated deicing/snow impacts. Additional light icing still possible at mpv/rut and pbg thru 10z...before profiles cool to support mostly snow. Gusty north/northwest winds of 15 to 25 knots will produce areas of blowing/drifting snow...especially kmss. Improving conditions developing by 18z with vfr. Outlook... Sunday: VFR. NO SIG WX. Sunday Night: VFR. NO SIG WX. Martin Luther King Jr Day: VFR. NO SIG WX. Monday Night: Mainly VFR, with local MVFR possible. Chance SHSN. Tuesday: Mainly MVFR, with areas VFR possible. Chance SHSN. Tuesday Night: VFR/MVFR conditions possible. Chance SHSN. Wednesday: Mainly MVFR, with local IFR possible. Chance SN.
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&& .HYDROLOGY... Flood watch has been issued from 12z Today to 12z Saturday for the combination of snow melt, rainfall, and ice jams causing localized flooding on area streams and rivers. The greatest threat for ice jam or main steam flooding includes but not limited to the following rivers: the Ausable, Mad, Missisquoi, and Lamoille Rivers, along with the Otter Creek. Continued concern for isolated ice jams - mainly today into tonight from a 36-48hr period of above freezing temps with max temps into the 50s. River ice breakup will not be widespread, but it appears that the mild temperatures will exist long enough to get some river ice movement across the North Country. Thus, rivers will need to be watched during this time frame. We are anticipating accumulated thawing degree hours between 400-500 by this evening, with temperatures today in the upper 40s to mid 50s, before a cold frontal passage this evening. Preliminary ice thickness reports/estimates indicate most rivers have ice less than a foot thick, with some of the northern waterways having ice perhaps as much as 18 inches thick in spots. As a general rule, river rises of 2-3x the ice thickness is needed to breakup river ice. Given potential QPF 0.50-1.50" and snowpack SWE 2-4 inches, there is certainly some threat of getting river rises on the order of 2-4 feet, with crests most likely this evening. If river ice movement does occur, issues may linger into Saturday, even as temperatures drop back below freezing behind the cold front. Persons with interests along rivers should continue to monitor this developing situation. && .CLIMATE... Record Highs for January 12th: Burlington, VT......55F.....1980. (New Record: 61F so far today) Montpelier,VT.......53F.....2017. St. Johnsbury, VT...54F.....1980. Massena, VT.........50F.....2017. (New Record: 57F so far today) && .BTV WATCHES/WARNINGS/ADVISORIES...
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VT...Flood Watch until 7 AM EST this morning for VTZ001>012-016>019. Winter Storm Warning until 4 PM EST this afternoon for VTZ001>009-016>018. Winter Weather Advisory until 4 PM EST this afternoon for VTZ010>012-019. NY...Flood Watch until 7 AM EST this morning for NYZ026>031-034-035- 087. Winter Storm Warning until 4 PM EST this afternoon for NYZ026>031-034-035-087.
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&& $$ SYNOPSIS...Banacos NEAR TERM...Banacos/Taber SHORT TERM...Sisson LONG TERM...Sisson AVIATION...Taber HYDROLOGY...Banacos/Hastings/Taber CLIMATE...Banacos

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