Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 231435 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 935 AM EST Thu Feb 23 2017 .SYNOPSIS... Abnormally warm temperatures ranging 15 to 25 degrees above normal will continue through Saturday evening. Saturday will be the warmest day with highs in the 50s to around 60 and these temperatures could set new daily record highs across northern New York and Vermont. The above normal temperatures will lead to increased snowmelt and runoff which in turn will increase the potential for ice jams and river flooding. Widespread rain Saturday afternoon through Saturday night could further enhance the potential for flooding across parts of the North Country. && .NEAR TERM /THROUGH FRIDAY/... As of 934 AM EST Thursday...Quick update to the morning forecast mainly to adjust for hourly temperature and sky trends. Max temps just about occurring now across portions of the St. Lawrence Valley in the upper 50s before clouds come back in over the next 2 hours. Meanwhile further east skies will be generally clearing through early afternoon allowing temps currently ranging from the mid 30s to low 50s to warm sufficiently into the 50s area-wide. Best chance for showers comes around noon across northern New York along and ahead of a cold front passage, and then less so further east into Vermont as precipitation becomes more isolated/scattered in nature. Some convective elements to the showers out there this morning as well with lightning noted upstream northwest of Ottawa, and there`s a very slight chance a rumble could be heard across the St. Lawrence Valley but not likely eastward. Previous discussion...Well above normal temperatures will continue to through the day. Currently we are seeing temps ranging from the lower 30`s to low 50`s at 3am across the CWA. Normal lows for this time of year are single digits to very low teens. This will continue to lead to ice breakup in the rivers, especially northeast New York and areas along and north of Route 2 in Vermont where river ice still prevails. Weak low pressure system passing north of the area could bring some light precipitation to the St Lawrence Valley this morning. Early afternoon, a weak boundary associated with the low passes through the region and will bring some light rain showers, mainly in the higher elevations. Rainfall amounts though look to be less than a tenth of an inch for today. Still, the warm temperatures should still promote snowmelt/runoff and we should begin to see 1 to 3 foot rises on rivers late Thursday into Thursday night...but most of the main stem rivers are starting off low and should be able to handle the increase. A warm front associated with a low pressure system over the Central US will be to our southwest early on Friday and will eventually push up into the region late Friday before lifting north of the border by early morning Saturday. Early on Friday morning, temps could dip below freezing in the St Lawrence Valley and NEK which could see a couple hours of very light freezing precipitation, but seeing small window and that even more aggressive guidance still seems to be trending to low on temps, there does not look to be any significant impacts right now. Could be some embedded showers with this front, but again minimal QPF, generally around two tenths of an inch or less. This extra water along with the continued warm temps will lead to further rises for rivers through Friday night. High temperatures for today will be in the upper 40s to upper 50s and slightly cooler for Friday in the mid 40s to lower 50s. Well above normal for both days. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... As of 434 AM EST Thursday...Very active period of weather expected with near record to record warm, gusty south winds, and potential river flooding concerns. Have posted a flood watch for the entire North Country effective 00Z Saturday through 00Z Monday. Please refer to the hydrology section below for details relating to flooding potential As we begin Friday night, expectation is for a quasi-stationary sfc frontal bndry to be draped across north-central VT wwd across nrn NY (likely on the nrn slopes of the Adirondacks), wswwd to a deepening low pressure system across southwestern Michigan. The bndry will retreat nwd as a warm front as low pressure passes well to our west across Lake Huron and nrn Ontario. Thus, we`ll see rising temperatures in many areas Friday night as winds increase from the south. By daybreak Saturday, could see temps into the lower 50s across Rutland Co. and portions of St. Lawrence County, with temps rising thru the 40s elsewhere. Will probably see some low clouds and possible light shower activity Friday night, but low clouds should tend to scour out as we head into Saturday morning as we emerge into the warm sector. Saturday will be a breezy and very warm day with 850mb temps of +7 to +9C. Southerly gradient flow increases and should see widespread winds 15-25 mph with gusts to 30mph...and localized gusts 35 mph or so in the Champlain Valley with valley channeling. May see some locally higher gusts just in advance of the cold front, but those mesoscale details are still pending. Record high for Saturday at BTV is 56F. Given expected period of sunshine in advance of approaching cold front, should see a new record set with temps potentially into the lower 60s in many valley locations. Sharp/strong cold front approaches from the west bringing period of moderate rainfall across nrn NY during the aftn, and across VT during the evening hrs. This will enhance runoff and bring main threat of minor to locally moderate flooding late Saturday into Saturday night. Overall rainfall amts generally 0.50 to 0.75", with locally up to 1" with orographic enhancement across the nrn Adirondacks. Negative tilt mid-level trough and sfc bndry shift east of our region during Saturday night, with strong low-level CAA. May see rain end as a period of wet snow or snow showers, especially across the higher terrain during Saturday night, with temperatures falling into the upr 20s to lower 30s by daybreak Sunday. Will see high pressure cresting into the nern CONUS by Sunday afternoon. Prevailing W-NW low-level flow on Sunday will result in much cooler conditions with afternoon highs generally in the low-mid 30s, except close to 40F in the CT River Valley with local downslope effects. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... As of 434 AM EST Thursday...A relatively fast and active WSWLY flow regime will persist through the extended forecast period, though the 00Z ECMWF and 00Z GFS differ on timing and track of embedded shortwave troughs potentially affecting the North Country. It continues to appear based on the 00Z ECMWF that a shortwave trough and associated surface low will pass to our south Monday/Tuesday, though the 00Z GFS is further north and quicker with this feature. Maintained low PoPs of 20-30 Percent Monday/Monday night for possible snow/rain showers. More significant low pressure develops in amplifying flow aloft and potentially passes to our west across the Great Lakes Wednesday into Wednesday night. This system would bring greater potential for widespread precipitation. Vertical temperature profiles favor a wintry mix changing to mainly rain. Overall, temperatures during the long- term period will remain above seasonal averages. && .AVIATION /15Z Thursday THROUGH Monday/... Through 12Z Friday...VFR conditions overall expected through most of the period. System will push north of the forecast area and swing a weak boundary through around 18Z. NY stations should see some brief showers and MVFR ceilings through 03Z. the boundary will weaken even more as it moves over VT stations. Showers are less likely but MFVR ceilings are still expected after 21Z through 03z. Winds will be southerly at 05-15 knots through 03Z before shifting to the west-northwest at 05-10 knots. Outlook 12Z Friday through Monday...Fog/BR possible Thursday Night into Friday...as weak backdoor front results in a wind shift to the north. Very gusty southerly winds develop...along with a line of showers with embedded heavier rainfall for Sat. Localized areas of turbulence and shear likely...along with MVFR conditions in the heavier showers. Rain transitions to mountain snow showers with lingering IFR vis possible at SLK/MPV Sat night into Sunday. MVFR possible again on Monday with more showers in the area. && .HYDROLOGY... As of 400 AM EST Thursday...A flood watch has been posted across the entire North Country effective 00Z Saturday through 00Z Monday. Overall scenario remains on track, with continued snowmelt and ripening of the remaining snowpack during the day Thursday with high temperatures expected well into the 50s areawide. A shallow cold front settles southward across our region during Friday morning, and will provide a focus for some initial light precipitation (0.10-0.25") later Friday morning into Friday afternoon. Will see a bit of a cooldown across nrn areas on Friday with highs in the lower 40s, but remaining in the upr 40s to lower 50s across s-central VT south of expected sfc frontal position. The boundary lifts back northward as a warm front Saturday with breezy and very warm conditions with record highs in the upper 50s to low-mid 60s in spots. Looking at additional thawing degree hours 600 to 700+ from 12z Thu thru Saturday, which will led to ice breakup for all basins. In addition, frontal rain band Saturday continues to appear very sharp with potential reflectivity fine line due to strong mid-upr level vort adv., strong low-level convergence, and low CAPE values. All in all, looking at potential 0.50-0.75" precip, with locally up to 1" in spots (highest across the nrn Adirondacks) as frontal rain band tracks from west to east thru the area. The combination of snowmelt and QPF are pushing NAEFS and GEFS ensemble river simulations into at least minor flood for the Ausable @ Ausable Forks, Winooski @ Essex Jct., and the Mad River @ Moretown, with several members approaching moderate stage. 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. So, ice jams could enhance potential flooding on some of the northern rivers, and would expect slightly higher overall threat of flooding as a result for the nrn basins. Can`t rule out an isold ice jam or two Thu/Fri with localized flooding, but bulk of the issues should hold off until Saturday coincident and after the best rainfall rates. We will continue to monitor river rises and river flood threat. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Flood Watch from Friday evening through Sunday evening for VTZ001>012-016>019. NY...Flood Watch from Friday evening through Sunday evening for NYZ026>031-034-035-087. && $$ SYNOPSIS...MV NEAR TERM...Lahiff/MV SHORT TERM...Banacos LONG TERM...Banacos AVIATION...MV HYDROLOGY...Banacos

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