Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
339 PM EST Wednesday Dec 17 2014
a developing area of low pressure off the coast of New England
will bring unsettled conditions to the north country through
Thursday as it tracks northeast into the Gulf of Maine. Rain
showers across the region today will change to snow tonight with
some light accumulations expected at the valley floor through
tomorrow, while higher elevations will see considerably more. High
pressure builds into the area Friday and will provide clear and
dry weather to the region through much of the weekend.
Near term /until 6 am Thursday morning/...
as of 339 PM EST Wednesday...as expected, much of the north
country is seeing a lull in precipitation this afternoon as the
primary surface low northwest of the County Warning Area from earlier this morning
is transferring energy to a developing low off the New England
coast. As this new low strengthens this evening and begins to
track north toward the Bay of Fundy precipitation will fill back
in and transition from rain to snow as thermal profiles cool on
developing northwest flow and cold air advection. Initially,
precipitation will be rather widespread but become more orographic in
nature as the night progresses and with Froude numbers off our
locally run 4km WRF indicating sub-critical to blocked flow.
Overall quantitative precipitation forecast isn't too tremendous though so thinking a dusting to
an inch of snow across the valley floor, with up to 4" across the
high peaks. Lows will generally run in the upper 20s to low 30s.
Short term /6 am Thursday morning through Friday night/...
as of 339 PM EST Wednesday...aforementioned surface low continues
it's slow trek northeastward from the Bay of Fundy Thursday
morning to the Gulf of St. Lawrence by Friday morning. Sufficient
low level moisture remains across the north country Thursday with
favorable conditions for upslope snows to continue across the
higher elevations of the Adirondacks and northern Green Mountains
through the day. While the valley floor will see little to no
snow, the climatology favored upslope locales along the northern greens
will see additional accumulations of 2-4" of snow. By Thursday
night though moisture begins to thin as the low pulls further east
and high pressure across the Great Lakes builds eastward. A few
lingering snow showers remain possible, but should end by early
Drier conditions are then expected for Friday and Friday night as
high pressure slowly builds into the region. Ample low level
moisture and continued northwest flow will keep plenty of clouds
around through much of the day Friday with likely a notable
clearing line in the western Champlain Valley on downslope flow.
By Friday night low levels dry out and we should see our first
clear night in quite some time with min temperatures falling back towards
seasonal normals in the teens.
Long term /Saturday through Wednesday/...
as of 339 PM EST Wednesday...high pressure over the weekend will
provide dry and partly cloudy to mostly sunny conditions, with maximum
temperatures in the middle 20s to low 30s. Min temperatures will see the middle teens
to middle 20s through Monday morning. Ridging aloft puts the north
country in S-SW flow...increasing temperatures into the middle 30s in
the valleys on Monday and Tuesday. The next threat for
precipitation will be Monday night into Tuesday as an upper level
shortwave moves along the SW flow. This will be followed by an
deepening upper level trough over the upper Mississippi Valley.
The GFS and European model (ecmwf) differ on timing, but keeping the north country
in the warm sector of this system will lead to a mostly rain event
at some point Christmas eve, as the surface low tracks to our
Aviation /21z Wednesday through Monday/...
through 18z Thursday...variable flight conditions persist across
the north country with MVFR to LIFR ceilings expected through the
entire period. Rain/rain showers will continue across all
terminals except krut...which will see more of a dry slot. As
night falls, and temperatures begin to cool, expect rain to change
to snow overnight with continues MVFR-IFR conditions. Cannot rule
out chance for LIFR/vlifr ceilings and visibilities within heavier snow
showers especially as winds shift northwest and upslope flow affects kmpv
and kslk. At the same time, this blocked upslope flow will keep
MVFR to IFR ceilings in the valleys.
Winds will generally be under 10 knots through the period,
shifting west northwest this afternoon.
Outlook 18z Thursday through Monday...
18z Thursday-00z Friday...MVFR with periods of IFR expected due to wintry
mixed precipitation associated with area of low pressure and
associated frontal system.
00z Friday-00z Sat...some MVFR in snow showers at mpv/slk but
elsewhere expect improvement to VFR.
00z Sat-00z Tuesday...VFR conditions expected under high pressure.
Increasing threat of precipitation late Monday.