Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 112329 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 629 PM EST Thu Jan 11 2018 .SYNOPSIS... Gusty south winds will maintain very mild temperatures across Vermont and northern New York tonight and through much of the day Friday. In fact, temperatures will reach the low to mid 50s in many locations during the day Friday, along with periods of light to moderate rain showers. The relative warmth will be short-lived, however, as a strong cold front shifts into the region Friday evening into Friday night. Temperatures will very rapidly fall below freezing with passage of the front. Meanwhile, a developing low pressure system across the central Appalachians will track northeastward along the frontal boundary, bring heavy snow to northern New York, and heavy mixed wintry precipitation across central and northern Vermont, during Friday night through the morning and early afternoon hours on Saturday. Difficult and icy travel conditions are expected across the region, especially late Friday night 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 /THROUGH FRIDAY/...
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As of 629 PM EST Thursday...Minor changes made to the previous forecast for this early evening update. Temps all over the place at this hour with 40s and 50s west of the Green mountains, while eastward they`re still holding in the mid to upper 30s. Forecast still looks good for a gradual warming through the night as precipitation moves in across northern New York through midnight, then points eastward thereafter. Previous Discussion...Very mild temperatures expected over the next 24 hours across the North Country, with temperatures rising overnight into Friday morning into the upr 40s to mid 50s. Mid- level ridge continues to build across the mid-Atlantic states nwd into New York and New England this afternoon, with broad region of south to southwesterly gradient flow in place. With channeled low-level flow in the Champlain Valley, will see south winds increase to 20-30 mph with gusts to 35 mph, and 850mb temps surge to +8 to +10C by 12Z Friday. Temps will generally slowly rise overnight as a result. In terms of precipitation, embedded vort in SW flow across OH/wrn PA will shift newd, bringing increasing coverage of showers after 00Z across St. Lawrence/Franklin county, and after 07-08Z across the Champlain Valley and the remainder of the Adirondacks. PW values in 12z GFS/NAM reach 1.2-1.3"...quite high for mid-January. Also, seeing weak elevated instability (up to 100 J/kg) in the NAM soundings late tonight into Friday morning. Will see some embedded periods of moderate to briefly heavy (convective) rain late tonight through Friday morning. Can`t rule out a rumble of thunder, but have not included in the official forecast attm. Rainfall of 0.5" to 1" generally expected, with the highest amts across south facing portions of the Adirondacks into the Green Mtns. With dewpoints rising into the 40s, also expect some patchy fog overnight, especially in sheltered spots where low- level winds/mixing will be less. Daylight hrs Friday, temps generally low-mid 50s until strong arctic front reaches the St. Lawrence Valley around 20Z or so, with temps falling across nrn NY late with developing mixed precipitation (see short-term discussion below). Elsewhere, will see melting/compacting snowpack with some continued patchy fog in spots with dewpoints potentially near 50F for several hrs Friday morning/early afternoon.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 303 PM EST Thursday...Frontal zone and associated wave of low pressure brings wide range of conditions to the North Country Friday night into Saturday, with trend toward sharply colder temperatures as arctic air mass moves in from NW-SE. We`ve upgraded to Winter Storm Warnings across northern NY, the Champlain Valley, and central/nrn VT for Friday night through 4pm Saturday. For Rutland/Windsor/Orange counties in s-central VT, a Winter Weather Advisory has been posted from 9PM Friday through 4PM Saturday for moderate sleet/freezing rain mix. Forecast generally remains on track. As frontal wave tracks newd across NJ/srn New England late Friday night, will see strong QG forcing and narrow axis of frontogenetic enhanced UVV across our region, especially 06Z thru 15Z Saturday. Vertical temperature profiles support mainly snow across the St. Lawrence Valley and nrn Adirondacks, with warm layer aloft resulting in a significant mix of sleet in the Champlain Valley/central VT, and potential for freezing rain accumulations around 0.2-0.3" across central/s-central VT. Appears widespread 6-10" snowfall is likely across nrn NY, perhaps into far nwrn VT. Forecast becomes much more difficult further south and east, with generally 4-8" snow/sleet in most of the Champlain Valley/nrn VT, with lesser snow/sleet to the south and more potential ice accumulation. Overall frozen QPF generally 0.5-1", so can`t rule out higher ice accumulation in spots. Will see widespread travel difficulties, with additional impact of scattered power outages across central/s-central VT, pending exact zone of best freezing rain potential. We`ll continue to monitor those finer details. Temperatures fall quite rapidly with frontal passage Friday night, so could see some flash freeze issues as well, with any standing water/wet roadways quickly turning to ice underneath the falling snow/sleet. Best snowfall rates of 1"/hr should occur pre-dawn hrs Friday into Saturday morning, when the most difficult travel is foreseen. Commahead precipitation gradually pulls away Saturday afternoon, with just a few lingering snow showers late into Saturday evening. Northwest flow brings continued CAA, and partial clearing will yield overnight lows of zero to 10 below...locally to -15F around Saranac Lake by early Sunday morning. Any unwanted snow should be cleared Friday before the next surge of arctic air, as the snowpack will become extremely dense/icy and very difficult to move thereafter. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 303 PM EST Thursday...In all honesty, my focus was more on the upcoming significant storm, so only performed a cursory view of the 12z model guidance and kept with the model blend output for ingest into the forecast. Still looking dry and COLD for Sunday and MLK Day, with highs in the single digits and teens and lows below zero. For the middle of the week, it`s starting to look potentially "interesting". Model trends over the last few runs have been to develop a fairly deep cut-off upper level low over the Great Lakes Tuesday. At 500mb, this low then slowly drifts east, and by Thursday has only gone as far as to make it over the top of us. The upper low will spawn surface low development off the mid-atlantic coast that will likely drift northward over New England Wednesday. At the very least, it looks like a period of unsettled weather. Kept with the blend which has roughly 40-60% PoPs through the period. At this point, kept it all snow, but if the 12z ECMWF and it`s stronger/deeper surface low ends up correct -- we could be looking at enough warm air tapped from the Atlantic to created a mixed p-type event. The ECMWF would also suggest potential western slopes of the Green Mtns wind event. Long way off, so just stay tuned. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Through 00Z Friday...VFR to give way to widespread MVFR later tonight into Friday as periods of rainfall move across the region in advance of a strong cold front. Most prevalent MVFR to first affect KSLK/KMSS this evening, then advance slowly east into Champlain Valley and other VT terminals later tonight and especially on Friday. Some IFR possible, especially at KSLK during these later periods. Winds generally south to southwesterly in the 6 to 12 kt range, though considerably stronger at KBTV and to a lesser extent at KRUT. At KBTV gusts to 30 kts likely overnight into Friday morning. Given stronger southwest flow aloft, LLWS to 45 kt will be maintained at many terminals through much of the period which could cause moderate turbulence on any approaches/departures. Cold front to begin crossing the region from northwest to southeast toward the end of the forecast cycle, but for now have only shown the wind shift at KMSS as other terminals will still lie just ahead of the boundary by 00Z Saturday. Outlook... Friday Night: Mainly MVFR, with areas IFR possible. Definite SN, Definite RA, Definite FZRA, Definite PL. Saturday: Mainly VFR, with areas MVFR and IFR possible. Definite SN, Definite FZRA. Saturday Night: VFR. Chance SHSN. 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. Slight chance SHSN. Tuesday: Mainly MVFR, with local IFR possible. Chance SHSN. && .HYDROLOGY... Continued concern for isolated ice jams - mainly during Friday/Friday Eve - following a 36-48hr period of above freezing temps and max temps into the 50s late Friday morning in valley locations. 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. The bitterly cold temperatures we`ve seen over the past couple of weeks have resulted in increasing river ice coverage and strength across the North Country. We are anticipating accumulated thawing degree hours between 400-500 Thursday through Friday, with temperatures 45-50F Thursday afternoon and night and upper 40s to mid 50s on Fri before a cold frontal passage toward 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 0.25-0.50" early Friday and snowpack SWE 2-4 inches, there is certainly some isolated threat of getting river rises on the order of 2-3 feet, with crests most likely during the daytime/eve hours on Friday. If river ice movement does occur, issues may linger into Friday night or Saturday, even as temperatures drop back below freezing behind the cold front. Persons with interests along rivers should continue to monitor this developing situation. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Storm Warning from 7 PM Friday to 4 PM EST Saturday for VTZ001>003-005-006-016-017. Winter Weather Advisory from 9 PM Friday to 4 PM EST Saturday for VTZ010>012-019. Winter Storm Warning from 9 PM Friday to 4 PM EST Saturday for VTZ004-007>009-018. NY...Winter Storm Warning from 4 PM Friday to 4 PM EST Saturday for NYZ026-027-029>031-034-087. Winter Storm Warning from 7 PM Friday to 4 PM EST Saturday for NYZ028-035. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos/Lahiff SHORT TERM...Banacos LONG TERM...Nash AVIATION...JMG HYDROLOGY...Banacos/Hastings

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