FXUS61 KBTV 120009
Area Forecast Discussion
National Weather Service Burlington VT
709 PM EST Mon Dec 11 2017
A strong clipper low pressure system is expected to bring
widespread moderate to heavy snowfall across northern New York
and Vermont. Winter Storm Warnings and Advisories are in effect
for Tuesday and Wednesday. An arctic airmass will move in behind
the low pressure system bringing cold temperatures through
Friday before warming slightly over the weekend.
.NEAR TERM /THROUGH TUESDAY/...
As of 656 PM EST Monday...Winter Storm Warnings and Winter
Weather Advisories remain in effect for the North Country as
a vigorous clipper low is expected to bring significant snow to
the region starting during the pre-dawn hrs Tuesday.
Quiet wx conditions in the meantime with high pressure in place
across srn Quebec and increasing mid-upper level clouds from
west to east. Cold air is still draining into the Champlain and
Saint Lawrence Valleys with upr teens to lower 20s across the
northern tier of Vermont and most of northern New York. Expect
overnight lows to fall into the teens early this evening before
southerly flow and OVC conditions set in. Once southeasterly
flow ramps up, as the clipper starts to move into region, warm
air advection will surge into the region.
Warm advection snow will push into northern New York and into
Vermont during the pre-dawn hours. The trends in the near term
guidance continue to point to significant snow accumulating
across most of the North Country. Omega in the snow growth zone
amplifies with nearly 100% saturation in the DGZ which all
points to moderate to heavy snow across the North Country.
As the midnight shift described, the storm will move through in
two waves with significant differences in the locations of snow
accumulations. With the first warm advection snow, expect
strong south to southeasterly winds to push into the region
which will cause downsloping effects in the western Greens and
Adirondacks. These areas will be the last to see accumulating
snow and likely to see only see 3-6 inches initially whereas
the eastern slopes of the Greens and across the Saint Lawrence
valley will see 6-10 inches. The closed surface low looks to
drop just south of the forecast area which will lead to the dry
slot perhaps not making it all the way into the North Country.
With the location of that low track and the warm air advection
all day, is possible in the southern Champlain Valley and
Connecticut river valley that the temperature profile will warm
up enough to see some rain mix in but for the time being I
haven`t included that in the forecast. The second phase is the
orographic snow described in the Short Term.
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 401 PM EST Monday...The second phase of the system will
come Tuesday night into Wednesday as the low pulls into Northern
Maine. Cold air advection returns and the flow on the backside
of the low turns northwest. Once this happens we`ll move into a
more favourable upslope pattern where the western slopes of the
Greens and Adirondacks start to pick up some bigger numbers.
Froude numbers initially will be blocked Tuesday night into
Wednesday and so the snow should back up into the Champlain
valley. Expect during this second phase that the upslope
regions will pick up another 3-6 inches of snow while the rest
of the North County sees an additional 1-2 inches. The flow
aloft picks up fairly quickly during the day on Wednesday and
the flow becomes unblocked so we`ll be looking at the potential
for some blowing snow across northern New York with accumulating
snow moving back into the Northeast Kingdom.
Its going to be rather chilly on Wednesday as cold air
advection rips into the North Country. Expect highs in the teens
across Northern New York and in the low 20s across Vermont.
With gusty winds its going to be quite the shock to the system
to feel wind chills back into the single digits above and below
Some lingering mountain snow showers will continue in the
evening hours on Wednesday however the flow will be turning more
west to west northwesterly so with cold air and flow across
warm lakes we`ll be switching gears to a lake effect snow again.
Most of the accumulating lake effect snow will fall south of
Saint Lawrence county. Across the North Country, with a fresh
snow pack and cold air still pushing into the region expect a
chilly evening with lows in the single digits above and below
.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 330 AM EST Monday...Large scale picture shows mid/upper prevailing
across the eastern Conus...while energy and moisture from the
Pacific NW ejects into the fast flow aloft every couple of days.
Latest guidance supports the northern tier staying on the cool
side of these systems with several mainly light snow events
possible. Below are my daily thoughts for days 4 thru 7.
Thursday...deep mid/upper level trof across eastern canada will
result in favorable upslope flow...but 1000 to 700mb rh is progged
to slowly dissipate by 18z Thurs. Based on llvl caa and upslope
flow...expecting remaining moisture to be squeezed out across the
northern dacks/greens. Have mentioned chc pops with only minor
accumulation expected. Temps aft a chilly start will only warm into
the single digits/lower teens mountains to mid/upper teens warmer
valleys with brisk northwest winds. Weak surface high pres builds
into our cwa on Thurs Night into Friday...but next system approaches
our western fa by Friday. Very difficult to determine cloud
cover/winds and impacts of fresh snow pack will have on temps Thurs
Night/Friday Morning. Have trended toward cooler side of guidance
envelope with -10f slk/nek to single digits to around 10f cpv. Some
lake effect clouds could impact temps near BTV.
Friday/Saturday...Both gfs/ecmwf show next weak clipper like system
and associated boundary crossing our cwa. This system will be weaker
and have less impact than current clipper. Still anticipating a
period of light snow activity...given good 5h energy... some enhanced
mid level moisture...and great lake moisture interaction with
approaching boundary. Several inches likely in the mountains with a
dusting to an inch possible in the valleys. Have continued to
mention high chc pops in the grids. Progged 850mb temps btwn
-14c and -16c...support highs mainly single digits summits to teens
mtn towns to l/m 20s valleys.
Sunday...weak mid/upper level ridge and associated 1025mb high pres
builds into the ne conus. Extremely difficult to time systems in
fast flow aloft...along with amount of clearing and impacts on
temps. Have lowered pops slightly for Sunday...but timing of next
system could arrive quicker based on fast flow aloft. Clouds and
winds will impact temps...but have kept temps close to superblend
with lows mainly in the teens and highs in the 20s.
Monday...Guidance supports another clipper like system moving thru
the Ohio Valley into the NE CONUS. Have noted lots of uncertainty
in ensemble data and between 00z/12z guidance in track of surface
low...with some to our northwest... while others show a system to our
south. Have continued on the cooler side of guidance...thinking
surface pres will keep system suppressed to our south...with another
light snow event possible. 12z ECMWF shows favorable mid level
moisture...good deep layer lift... and moderate llvl waa signature.
Plenty of time and uncertainty...so have mention chc pops for
now...with temps holding in the 20s. Overall pattern will support a
net increase in snow pack across the mountains with cool temps
keeping snowpack fresh.
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Through 00Z Wednesday...Widespread IFR to LIFR develops at all
sites by early Tuesday Morning with significant impacts
anticipated through 04z this evening, before widespread snow
developed from southwest to northeast across our TAF sites
between 04z-08z. Visibility will quickly drop to IFR with
locally VLIFR in bursts of heavier snow expected at all sites
between 09z-15z Tuesday. Ceilings will vary from IFR at MSS to
MVFR at RUT/MPV/BTV/SLK/PBG...with periods of IFR possible.
Localized southeast winds gusts to 25 to 30 knots at RUT on
Tuesday morning with breezy northeast winds at MSS. Conditions
will slowly improve at RUT aft 18z. Some low level wind shear
likely at MSS/MPV with change of speed and direction...causing
increased shear and turbulence on Tuesday Morning.
Monday Night: Mainly VFR, with local MVFR possible. Chance SN.
Tuesday: Mainly MVFR, with local IFR possible. Definite SN.
Tuesday Night: Mainly MVFR, with areas IFR possible. Chance SHSN.
Wednesday: Mainly MVFR, with areas VFR possible. Chance SHSN.
Wednesday Night: Mainly VFR, with areas MVFR possible. Slight
Thursday: Mainly VFR, with local MVFR possible. NO SIG WX.
Thursday Night: Mainly VFR, with local MVFR possible. Slight
Friday: Mainly VFR, with local MVFR possible. Chance SHSN.
VT...Winter Weather Advisory from 1 AM Tuesday to 7 PM EST
Wednesday for VTZ001-002-005-009-011.
Winter Storm Warning from 1 AM Tuesday to 7 PM EST Wednesday
Winter Storm Warning from 1 AM Tuesday to 7 AM EST Wednesday
NY...Winter Weather Advisory from 1 AM Tuesday to 7 PM EST
Wednesday for NYZ027>031-034-035.
Winter Storm Warning from 1 AM Tuesday to 7 PM EST Wednesday