Area Forecast Discussion
Issued by NWS Burlington, VT

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000
FXUS61 KBTV 130849
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
349 AM EST Sat Jan 13 2018

.SYNOPSIS...
A widespread mixed precipitation event will slowly taper off to
scattered snow showers by this afternoon, with highly variable storm
total snow and ice accumulation expected across the region. The
threat for localized flooding due to freeze up jams will continue
today as temperatures cool back into the single digits to mid teens.
High pressure with cool temperatures and dry conditions prevails
tonight into early this upcoming week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 324 AM EST Saturday...Water vapor shows an impressive short wave
trof digging across the mid Atlantic States with deep layer
moisture conveyor impacting the ne conus. This system will
continue to quickly lift se to ne across the ne conus this
morning with well defined mid/upper level dry slot moving from
central pa into southern VT by 12z Saturday. This dry slot along
with extremely complex thermal profiles will greatly impact
storm total snow, sleet, and ice accumulations across our
cwa...especially in the transition zone between snow and mixed
precip. This tight gradient is impossible to forecast, so
anticipate some areas especially in central cpv/central vt to
struggle to reach expected snow amounts, as change to snow is
delayed by several hours. Overall very little change to storm
total snowfall with 6 to 12 inches northern NY...4 to 8 inches
northern VT/CPV...and 1 to 4 inches southern/central Vt with ice
accumulation of 1 to 3 tenths. All current winter storm
warnings and advisories continue this morning.

The best mid level deformation and RAP 850 to 500mb rh is located
over northern NY into northern VT at 12z and lifts into the northern
CPV by 18z...before exiting our cwa by 21z. Based on this mid
level moisture trend...will taper precip off in grids/forecast
btwn 16z-20z today. Expect most of the heavier precip to be
confined to the northern cwa and mountains by 18z today...with a
period of favorable upslope snow possible. Temps continue to
fall under llvl caa as progged 850mb temps drop to -13c to -17c
by 00z Sunday...supporting highs single digits slv/dacks to mid
20s lower CT river valley. The combination of fresh snow and
clearing skies will result in cold overnight lows...with
readings between 5 and 20 degrees below zero. Given flash freeze
and wintry mix of precip falling at this time, expect areas of
difficult travel today with some isolated power outages possible
over central/southern VT due to ice accumulation and breezy
north winds.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
As of 343 AM EST Saturday...Broad surface high pressure will shift
to the northeastern US Sunday night, allowing for calm to light
winds and clear skies overnight. Effective radiational cooling
overnight will result in surface temperatures dropping to below
zero throughout the forecast area. This cold spell will be short
lived however, as southwesterly warm air advection starts to
increase Monday in advance of surface low pressure forming over
the Great Lakes. Temperatures will start to rise back towards
seasonal norms ahead of the clipper, with daytime highs in the
teens Monday and the mid to upper 20s by Tuesday.

During the daytime hours Tuesday, some light warm air advection snow
will move into the region from west to east as the Great Lakes
low moves northeastward up the Saint Lawrence Valley. The mainly
continental-sourced airmass will be lacking in moisture, so
would expect any snowfall accumulations to be light.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
As of 343 AM EST Saturday...The extended forecast will continue
to feature a fairly active, progressive pattern. Shortwave
energy aloft over northwestern Canada Monday will dig towards
the East Coast Wednesday, significantly amplifying the upper-
level flow. Once the colder continental polar airmass within the
trough digs into the southeastern United States and then pushes
offshore, a baroclinic zone will sharpen over the western
Atlantic. With favorable jet dynamics aloft and strong low to
mid level baroclinicity, a surface low will develop somewhere
off the MidAtlantic Coast Wednesday afternoon/evening. Models
are having a difficult time coming to a consensus on the track
of this low, thus lending to lower confidence in the forecast
for Thursday and Friday. If the upper level trough remains
positively tilted as it progresses eastward over the East Coast,
the developing low will be taken out to sea with no impacts to
the Northeast. However, if the trough sharpens and becomes
negatively tilted over the East Coast, the low will curve back
towards land, impacting northern New England and the Canadian
Maritimes. For now, current thinking is that the system won`t
have major impacts on Vermont/northern New York, however we
will be monitoring the situation closely over the coming days.
If the low does curve back towards northern New England, the
forecast area could receive some snow on the western fringes of
the storm.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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.

&&

.HYDROLOGY...
As of 128 AM EST Saturday...High flows and significant ice
movement has occurred on area streams and rivers over the past
18 hours due to heavy rainfall and excessive snowmelt.
Temperatures have fallen sharply behind an advancing arctic
frontal boundary tonight, and as such resultant runoff should
slow considerably into the late night and early morning hours.
Scattered ice jams and areas of high water/flooding will still
be possible, though the threat will be diminishing over time.
Additional Flood Warnings will be issued as necessary for any
new ice jam flooding overnight.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...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...Winter Storm Warning until 4 PM EST this afternoon for
     NYZ026>031-034-035-087.

&&

$$
SYNOPSIS...Taber
NEAR TERM...Taber
SHORT TERM...RSD
LONG TERM...RSD
AVIATION...Taber
HYDROLOGY...JMG



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