Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 211916

Area Forecast Discussion
National Weather Service Burlington VT
316 PM EDT Fri Oct 21 2016

Mid-level longwave trough digging south and east from Canada west
of the North Country continues to dominate the region. Trough
is starting become negatively tilted and will continue into early
Saturday, keeping frontal boundary and associated surface low
pressure system over the region through Saturday night/early
Sunday. As the system moves past, colder air will filter
in bringing with it northwest flow producing upslope rain and
snow showers in higher elevations from early Sunday morning
through Tuesday. Another surface low pressure system looks to
affect the Northeast Thursday and into Friday.


As of 252 PM EDT Friday...Precip continues to shift more
westward with more widespread breaks across the Adirondacks. Eastward
momentum and additional moisture shift will slide into the region later
this afternoon/evening.

Wind direction continues its shift over the region bringing with
it falling temps as earlier temps in the 60`s and 70`s have
drifted back down to 40`s out west of the Adirondacks and 50`s and
60`s across VT. Moisture from coastal system is starting to feed
into the NE low pressure system and should continue to do so into
tonight, bringing with it increased moisture across central and
northern NY. This combined with diffluent mid- level flow will
result in possible periods of moderate rain over VT, especially
during the overnight.

Saturday morning, models find more consensus on surface low
positioning along the southern New England coast, traversing
northward during the day. This means deep NW flow over the North
Country will bring in colder air and widespread terrain enhanced
rain showers throughout the day and into the early evening.


As of 312 PM EDT Friday...Extremely challenging and complex forecast
associated with low level thermal profiles and associated snow
levels. GFS/NAM/ECMWF and GEM are all in excellent with evolution
of negatively tilted and closing off 7h/5h circulation across
eastern NY by 21z Saturday and coastal low pressure being captured
and becoming vertically stacked over southern Canada by 06z
Sunday. This synoptic scale pattern will support a 12 to 18 hour
period of favorable deformation and upslope focused precip on
Saturday Night into midday Sunday.

The difficult question to answer is how cold are the thermal
profiles...and associated snow levels. NAM is much colder and faster
bring in the colder air...on brisk northwest winds...while GFS/ECMWF
are slower and much warmer in the boundary layer to 925mb layer.
This makes for a huge difference on impacts associated with snow
levels between 1200 and 1500 feet as supported by the NAM or 2000
feet or higher with limited impacts per the GFS/ECMWF solutions.
Interesting to note NAM BUFKIT data showing 1.20" qpf falling as
all snow...while GFS BUFKIT shows only 0.32". Given the lack of cold
air upstream and very warm ground temps from recent
warmth...thinking snow will initially have difficulties the mountains towns on Saturday evening.

Have noted progged 850mb temp near 0C from KMSS to KBTV to KVSF at
00Z...while the 925mb 0C isotherm is still back northwest of our cwa
thru 06z Sunday...supporting snow levels above 2000 feet. Thinking
during heavier precip rates...especially on Saturday Night...column
will cool enough to support some wet accumulating snow in the
mountains towns of the Dacks and portions of the green mountains in
VT...mainly above 1500 feet. Have in the grids a dusting to several
inches of wet snow for Lake Placid...Tri Lakes Area...Newcomb...and
across the higher terrain of central Clinton and Franklin Counties.
Given the complex thermal profiles expecting a sharp snow gradient
as you climb in elevation with 8 inches or more possible above 4000
feet across the northern Dacks.

For the Green Mountains in Vt the colder air arrives first in the
central/southern portion...then advects north as closed cyclonic
circulations moves northeast. Thinking a similar type scenario plays
out with a dusting to several inches of wet snow likely between 1500
and 2000 feet...for towns like Killington...Bread
Loaf...Walden...Belvidere...and base area of local ski resorts.
Also...expecting a sharp snowfall gradient based on elevation with
Mansfield to Jay Peak having the potential of 6 or more inches by
Midday Sunday. A few wet snowflakes could mix in at times in the
valleys late Saturday Night...but no accumulation is expected.

Upslope parameters look very favorable with northwest 925mb to 850mb
winds of 35 to 45 knots...strong uvv`s signature across the
northern Dacks and western slopes...and plenty of 850 to 700mb
backside moisture. Thinking additional qpf values will range from
0.05 to 0.15 Saint Lawrence and Lower CT River Valley with near 0.50
eastern CPV/parts of the Northeast...and up to 1.0 northern Dacks
and parts of the central/northern Green Mountains from Mansfield to
Jay Peak.

Next concern will be developing winds associated with tightening
pressure gradient with 979mb low pres. Soundings show strong low
level wind fields of 40 to 50 knots...with bottom of the mixed layer
winds around 35 to 40 knots Sat Night into Sunday. Still some
questions how much mixing occurs with precip and clouds...but
thinking as drier air develops on Sunday...surface wind gusts
between 35 and 45 mph will be possible...with even higher gusts on
exposed mountain summits. For people adventuring out to experience
the first snow of the season in the mountains...please be prepared
for mid winter conditions on Sunday...especially near the summits.

Temps will range from the mid/upper 20s mountains to upper 30s/lower
40s warmer valley locations near Lake Champlain on Saturday night
and only warm 3 to 5 degrees on Sunday with brisk northwest winds.


As of 315 PM EDT Friday...After a prolonged warmer than normal period
through the summer and into the first 20 days of October...a
prolonged period of BELOW normal temperatures are in store for the
north country...Fall is here!

This weekends cut-off low will still strongly influnence our weather
through Tuesday. The cut-off lifts into Quebec but the cool,
cyclonic and marginally unstable flow will persist through Tuesday
with the typical climo-favored upslope rain/snow showers but less
than the weekend.

Still cyclonic flow in trof pattern but lessening influence by
Wednesday with Surface high moving into region for dry day but
still cool. Another shortwave moves into the trof with a surface
low and warm front for Thu and possibly Fri which brings back more
inclement weather but not like this last system. Some mountain
rain/snow but timing later thursday should keep just rain for

Highs in the 40s through Thursday and back to seasonable L50s by


.AVIATION /19Z Friday THROUGH Wednesday/...
Through 18z Saturday...Varying flight conditions across the North
Country with persistent low clouds/IFR/MVFR in NY and rains at
KMSS with VFR/MVFR in VT. However...surface cold front moving
south across Champlain Valley has brought IFR/LIFR cigs and this
trend will continue elsewhere.

Precipitation will be in rounds...except at KMSS where it will be
persistent through period. Showers moving North into Taf sites
this afternoon and exiting by evening then just some isold/sct
showers til 15z Sat when more persistent showers/rain returns.

Primarily IFR/LIFR tonight with clouds/drizzle and IFR Saturday
with clouds and showers/rain.

North winds in NY and Champlain Valley will move into rest of VT
and eventually shift to NW for Saturday with 10 knots or less
tonight but increasing and gusty by late Saturday.

The end result...deteriorating conditions with little no changes
through period.

Outlook 18z Saturday through Tuesday...

18z Saturday through 00z Monday: A prolonged period of unsettled
conditions is expected with widespread MVFR/IFR in periods of

00z Monday through 00z Wednesday: A mix of VFR/MVFR with upslope
showers in NW flow.


As of 315 PM EDT Friday...Through early this afternoon the heaviest
rainfall has been located over the Saint Lawrence Valley and
Northern Dacks (1 to 3.5 inches)...the amounts tapering off
sharply with < 0.75 inch across the central/southern Champlain
Valley and most of VT. Moving forward thinking additional rainfall
will range between 1 and 2 inches with some isolated higher
amounts along the western dacks possible. Several periods of rain
still anticipated for system tracks along the coast and
Atlantic moisture is advected back into the region tonight. Given
the long duration and breaks in the precip intensity/coverage...we
are not anticipating any hydro related issues associated with this
event. However...some minor urban and street flooding is possible
associated with the heavier rainfall rates through Saturday with
leaves clogging storm drains. Otherwise...some modest rises in
local rivers and streams are likely this weekend...but no
widespread flooding is anticipated.




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