Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
937 PM EST sun Mar 1 2015
light snow tonight will gradually taper off to snow showers on
Monday. Total snow accumulations will generally be in the 1 to 3
inch range with slightly higher amounts possible in the mountains.
High pressure builds into the region Monday night and Tuesday for
drier weather...but then another trough of low pressure will move
into the northeast late Tuesday into early Wednesday and bring
another round of snow...and possibly some mixed precipitation...to
Near term /until 7 am Monday morning/...
as of 936 PM EST Sunday...updated probability of precipitation to reflect current
conditions. Radar showing back edge of synoptic driven snow from
near Saranac Lake to the northern Champlain Valley. Snow has
tapered off to north and west, and continues to south and east.
Organized snowfall will diminish from west to east as upper
trough embedded in zonal flow exits the region. Snow will
transition overnight to orographically driven snow showers as
westerly low level flow takes hold and moisture remains in the
boundary layer. Quantitative precipitation forecast and snow amounts from previous forecast still
look good, with snow characterized as light and accumulations of
one to two inches overnight. Forecast temperatures tracking nicely
with observed, and no changes there.
Short term /7 am Monday morning through Tuesday night/...
as of 324 PM EST Sunday...best potential for additional light
snow on Monday will be over the mountains as upper trough moves
across the area in the morning followed by pronounced drying
during the afternoon. Temperatures will be several degrees below
normal on Monday...so not too bad of a day. Clearing skies and
light winds Monday night will allow for strong radiational cooling
and lows getting down into the single digits above and below zero.
The pattern quickly changes on Tuesday as southwest flow aloft
develop and a surge of warmer air aloft moves up into the region
by Tuesday night. Thus looking at warm air advection snows to
develop late Tuesday afternoon and continue through the first half
of the night. Can see picking up anywhere from 1 to 4 inches of
snow with the warm air advection. Thermal profile changes to
indicate perhaps some mixed precipitation...but by the time this
happens most of the precipitation will be out of the area as drier
air aloft quickly moves in by Wednesday morning. So for now
keeping most of the event as snow. Highs on Tuesday will be in the
20s and then not fall much Tuesday night with all the clouds and
snow over the area.
Long term /Wednesday through Sunday/...
as of 324 PM EST Sunday...on Wednesday a weak low pressure system
will be tracking across southern Ontario/Quebec by Wednesday
morning. It will continue to bring a chance of widespread
precipitation across the area although the chances will quickly
diminish by middle morning into the afternoon. Both the 00z and the
12z suite of guidance have trending away from the warm sector
reaching the btv area. That would result in significantly cooler
temperatures aloft resulting in less of a chance for significant
mixed ptypes across the forecast region. The 12z European model (ecmwf) actually
keeps the surface/925/850/700mb 0c lines all south of the area
during the time period resulting in almost all snow whereas the
GFS is slight more northerly in its track leading to some mixed
precipitation. The guidance has come into fairly good consensus
that the bulk of the precipitation will fall mostly towards the
end of the short term (late Tuesday night/early wednesday) as the
initial burst of warm air advection pushes into the region. By 18z
Wednesday however the 1000-700mb layer relative humidity dissipates in both
models and the precipitable waters drop from 0.7" to 0.25" by 18z. So the moral
of the story is that there should be wide spread precipitation
early in the morning and then quickly ended across the area as a
cold front comes through by 18-00z. The surge of warm air
advection in the morning will warm the entire region to above 35f
getting close to 40f by early afternoon and then quickly dropping
off due to the cold front and high pressure subsidence that will
build into the region.
Thursday...the surface low will push out of the area giving way
to another building surface ridge below a weak upper level trough.
The high pressure will combine with the cold front from Wednesday
to keep temperatures in the lower teens to single digits across the area.
There could be a few lingering showers from overnight as some of
the upper level energy could squeeze out some orographic snow but
thats about it. Overnight lows will be around zero to just below
in the notorious cold spots.
Friday...high pressure will dominate the area with dry weather
and temperatures about 10 degrees below normal in the lower 20s across
the area in a gradual warming trend into the weekend. Overnight
lows will be in the lower teens with a few isolated areas seeing
Saturday/Sunday...the gradually warming trend towards more
seasonable temperatures should continue with temperatures warming to around
freezing if not slightly above under moderate westerly winds. A weak
disturbance could bring some scattered snow shower activity along
the international border and the higher terrain above 1500 feet.
Aviation /03z Monday through Friday/...
through 00z Tuesday...a variety of flight categories is
anticipated over the next 24 hours with areas of light snow and
snow showers. Periods of light snow will continue through the
overnight hours with additional scattered snow showers developing
on Monday. Looking at mainly VFR/MVFR at btv/pbg with downsloping
winds and dry low levels limiting coverage/intensity of
snow...although some brief periods of IFR possible. Mss also
likely mainly MVFR on the northwest edge of precipitation shield.
More noticeable impacts at rut/mpv/slk where IFR likely
tonight...and continuing at mpv/slk on Monday. Due to expected scattered
nature of snow showers on Monday outside of slk/mpv...any taf site
may experience a few brief periods of IFR as well. South winds
5-10 knots (with gusts up to 20 knots at btv) tonight turn
west/northwesterly on Monday and become quite gusty again with
widespread 20-30 knot gusts likely.
Outlook 00z Tuesday through Friday...
00z Tuesday-18z Tuesday...VFR conditions developing as high
pressure builds in.
18z Tuesday-00z Thursday...MVFR/IFR in mixed precipitation as low
pressure system tracks up through St Lawrence Valley.
00z Thursday through 12z Friday...mainly VFR with brief periods
of MVFR/IFR in snow showers as system slides off to southeast.
12z Friday Onward...VFR under building high pressure.