Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 242342

Area Forecast Discussion
National Weather Service Burlington VT
742 PM EDT Mon Oct 24 2016

The North Country will remain in cyclonic flow with variable
cloudiness and cooler than normal temperatures through most of
the week. A weak upper disturbance embedded in northwest flow
aloft will bring mostly cloudy skies tonight through Tuesday.
This feature will bring a chance of light rain showers in the
valleys. Snow showers are expected across the Northern
Adirondacks and north-central into northeastern Vermont tonight
through Tuesday. High pressure brings briefly drier conditions
Wednesday into Wednesday night. A more significant wave of low
pressure approaching from the Great Lakes and Ohio Valley will
bring periods of rain, generally late Thursday into the first half
of Friday. Precipitation may begin as a wintry mix across higher
terrain areas on Thursday before changing to rain.


As of 740 PM EDT Monday...Precipitation arriving on-cue in broad
NW flow coming from Quebec down across northern higher terrain in
VT. Previous forecast well covered and these trends expected to
continue overnight.

Previous discussion issued at 253 pm...Little overall change in
the large- scale pattern during the next 24 hours across northern
NY and VT. Deep layer W-NW flow continues west of mean mid-level
trough axis, but within broad upper level trough across the nern
CONUS and sern Canada. This is contributing to below climo average
temps this afternoon, with readings generally in the mid-upr 40s,
and only in the upr 30s across the Northeast Kingdom.

Will see increase in cloud cover overnight as embedded shortwave
trough translates sewd out of srn Quebec across the area, with
cloud heights generally 3-5kft. Limited moisture (PW values
0.3-0.4"), however orographic ascent will bring light rain/snow
shower activity overnight into the day Tuesday, especially across
the nrn Adirondacks and nrn Green Mtns into far nern VT. Freezing
levels initially around 2500ft this aftn, will generally fall to
near 1000ft during the pre-dawn hours Tuesday. Thus, will see
falling snow levels overnight, and then rising a bit during the
day Tuesday. Not expecting any snow accumulation in the Champlain
Valley, but could see a dusting to 1" for towns in central/nrn VT
and across the nrn Adirondacks. The highest summits of nrn VT
could see 2-4" snowfall, including at Jay Peak and Mt. Mansfield
by Tuesday evening. Winds will generally continue from the NW.
Generally 10-20 mph gusting to 25 mph thru early evening,
diminishing to near 10 mph overnight, and increasing again to
10-20 mph for Tuesday. Low temps tonight generally low-mid 30s,
except 28-32F 1-2kft elevational band. Highs on Tuesday generally
low to mid 40s under cloudy skies.


As of 332 PM EDT Monday...The upper level trough will slowly drift
towards the east as persistent cold air advection continues to
provide below normal temps in the short term through the mid week.
The continued northwest flow aloft will cause some light upslope
snowfall. The flow will be unblock so areas with the highest
accumulations will be in the western upslope locations such as
Underhill, Jericho, Bolton etc. However with total qpf will be
less than 0.10 which ultimately means we`ll only see an inch or
two of snow fall.

Wednesday we will be in sort of a lull between two systems. Expect
cloudy conditions in the higher terrain with some breaks in the
cloud cover in the Saint Lawrence and Champlain Valleys. The low
and mid level moisture will be decreasing and so while the
orographic forcing is still favourable for snow I dont anticipate
much in the way of accumulation along the ridgeline Wednesday. The
cold air advection even as a weak ridge starts to build in. Expect
max temps to remain below normal as the entire column of air above
925mb is below 0C. Highs will be in the upper 30s to around 40 in
the valleys.


As of 425 PM EDT Monday...By Thursday the pattern picks up again
with several chances for rain and snow. The upper level trough
builds back in thus the upper level flow will remain west to
northwest through the end of the week and into the weekend.

The first surface low pressure system will track through the Great
Lakes into New England on Thursday night and should bring quite a
bit of warm advection to the area. The rain vs snow forecast will
be quite tricky as the overnight temps will be supportive of snow
however the warm air advection will be advancing rapidly with a
southerly 850mb jet of 40-50kts bringing warmth from the Atlantic
west of the spine of the Green mountains. However on the eastern
side of the Greens the cold air will be trapped longer due to the
high pressure system located over Nova Scotia. So I anticipate
precip beginning first as snow across the entire area however by
mid morning on Friday that will transition to a mix of rain and
snow except for areas east of the Green mountains. Temp profiles
in the higher terrain suggest they will stay all snow.

The bigger issue will be the potential for gusty downslope winds.
The track of the low pressure system will be critical as if the
GFS is correct the low tracks across the CT/MA/NY border and the
winds will be due east over the southern Green mountains. However
the EC is slightly further north and thus the strongest winds
dont turn east until the system is already east of the forecast
area. If the GFS is correct there will be a 35-45kt 850m easterly
jet over the southern Greens which would be supportive of
downslope gusty winds. We will need to continue to monitor that
as the forecast becomes clearer.

Next system arrives late Saturday into Sunday with additional
chances for precipitation however most of the guidance is warm
enough that the system will produce mainly just rainfall. Based on
GFS and EC soundings the entire column below 850mb is positive so
based on the 12z suite of guidance I anticipate rain and max temps
in the mid to upper 40s and lows in the 20s to mid/upper 30s.


.AVIATION /00Z Tuesday THROUGH Saturday/...
Through 00z Wednesday...OVC VFR ceilings to predominate most of
this TAF period under cold cyclonic flow aloft. Potential for
scattered rain/higher elevation snow showers after 07z. In the
snow showers, visibilities may briefly drop to IFR with ceilings
in the MVFR range. The best shot at seeing snow showers will be at
MPV and SLK. Northwest winds stay steady 8-14 kts. Gusts to 25 kts
abate early this evening, and pick up to around 20 kts on Tuesday
as mixing depth increases.

Outlook 00z Wednesday through Saturday...

00Z Wednesday through 12Z Wednesday: Isold/sct rain and snow
showers will persist vcnty of the nrn Adirondacks/nrn Greens
Tuesday aftn into first half of Tuesday night. Could see intervals
of MVFR conditions at SLK, and possibly also at MPV. At the
remaining TAF sites, BKN-OVC conditions but with VFR ceilings
expected. Winds NW 8-15kts.

12Z Wednesday Through 12Z Thursday: Surface high pressure across
the region will bring generally VFR conditions and lighter winds.

12Z Thursday Through Saturday: Low pressure system approaching
from the Great Lakes/Ohio Valley brings developing rain Thursday
afternoon into Thursday night, with MVFR and intervals of IFR
conditions possible. After a brief break on Friday, another wave
of low pressure brings additional showers and possible MVFR
conditions on Saturday.


AS OF 308 PM EDT MONDAY...Lake Wind Advisory continues through
this evening with northwest winds 15-25kts and waves 2-4kt.
Highest waves along eastern shores exposed to a greater fetch on
northwest winds; specifically those locations adjacent to the open
waters north of the Charlotte Ferry and south of Valcour Island.
Expect these strong winds and waves to gradually diminish
overnight as wind speeds decrease slightly to 10-20kts.




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