National Weather Service Burlington VT
1237 PM EST Sun Jan 7 2024
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 347 AM EST Sunday...The potential for a significant
system to impact the North Country Tuesday night through
Wednesday continues to increase. Let`s go over a brief synopsis
of what is expected and then we will touch on the individual
elements and hazards. A
deepening mid-
latitude cyclone is
expected to move from the central US to the Great Lakes Region
and then the Ottawa Valley Tuesday night into Wednesday morning.
A strong high pressure system will continue to remain anchored
across eastern Quebec which will set up an impressively strong
pressure
gradient across the North Country. In addition to the
strong
gradient, a plume of Gulf of Mexico
moisture will quickly
advect northward allowing for both
moisture and warm air
advection across the region.
With a strong warm front slated to
push through the region Tuesday night into Wednesday, a brief
period of heavy wet snow is looking increasingly likely before
snow changes over to rain Wednesday night and melts much of this
snow and likely much of the snow that is currently falling.
Now, let`s discuss hazards.
First, let`s talk winds. The signal for strong to damaging
winds only continues to get stronger over the past several days.
Looking at past
high wind events, there are several key
features of note: A
low pressure system moving over the Ottawa
or St. Lawrence Valleys, strong high pressure to our northeast,
and a
deepening mid-
latitude cyclone. All three of these boxes
are checked off Tuesday night into Wednesday as a possible
sub-980
mb low moves across the Ottawa Valley Tuesday night and
Wednesday morning. The probabilistic values based off the
ECMWF
(which tends to be a little on the high side) continues to show
80-100% chance of wind gusts in excess of 55 mph and 40-60%
chance of winds in excess of 70 mph along the western slopes of
the Green and Adirondack Mountains. It`s hard to ignore these
signals when the conceptual model aligns so perfectly in this
scenario. Given this, we have issued a
high wind watch from 10
PM Tuesday through 1 PM Wednesday for the western slopes of the
Green and Adirondack Mountains as well as portions of
northeastern Vermont. As we begin to enter the high-res model
temporal resolution, it`ll be interesting to see the potential
for
mountain wave activity given a 70-80
knot low level jet with
a forecasted
inversion near mountain top level. These strong
winds will be monitored closely in the coming days as this has
the potential for a significant wind event across the North
Country.
Now, let`s talk heavy wet snow. Before the warm air
advection
is able to displace the cold air in the lower levels, a warm
front and associated
burst of
isentropic lift should yield some
potentially significant values of heavy wet snow across portions
of southern Vermont. Snow ratios Tuesday night are expected to
be in the 8:1 range, maybe even lower,
with 2-6 inches possible
across southern Vermont with a sharp
gradient of little to no
snow accumulation near the International Border. This
burst of
heavy wet snow is
likely to coincide with increasing winds which
may increase the
probability of
power outages.
Last but not least, let`s talk
rainfall and potential
hydrology
issue. There is pretty good model consensus that
we will see
between 0.75" to 1.5" of new rainfall associated with the storm
system on Wednesday. In addition,
it looks like we could add
around a half of an inch of snow melt as well. This rain and
snow melt will likely trigger some rapid river responses on
Wednesday and Wednesday night but guidance continue to suggest
rivers will remain within bankful. We will continue to monitor
the
flood threat as a cold ground is largely hydrophobic and all
rain will immediately run off into area rivers.
Rivers are
likely to
crest by Thursday morning with a few light
mountain snow showers possible with northwest
flow aloft. There
is a potential for a decent
shortwave to move across the region
Thursday night into Friday which could bring some minor snow
accumulation but shouldn`t be anything too impactful. Yet
another storm system looks to be on the horizon for next weekend
with models a little uncertain on the track. Several models
have been fluctuating between a Nor`easter and an inland runner
but the 00Z deterministic and ensemble guidance currently favors
an inland runner. If this happens, expect another round of
gusty winds and mixed precipitation. Stay tuned.