Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
323 am EST Friday Jan 30 2015
a weak clipper like system will produce a widespread light snow
tonight into Friday...followed by upslope snow showers and
bitterly cold temperatures Friday night. High pressure will build
in for the weekend with temperatures much below normal.
Temperatures of 10 to 15 degrees below normal will persist into
the middle of next week.
Near term /until 7 am this morning/...
as of 1224 am EST Friday...winter weather advisories continue to
be in effect for entire forecast area through Friday evening.
Precipitation reaching the ground mostly in the form of snow as
temperatures around freezing or colder. Few warmer spots in the St
Lawrence Valley may see rain mix with the snow early this morning.
Otherwise, forecast still on track with water vapor imagery
showing baroclinic Leaf (bcl) developing over the eastern Great
Lakes associated with the clipper low. With that in mind, expect
best low level deformation of this system to affect the north
country into the middle morning hours with light snow showers.
Observations showing reduced visibilities around 1sm. There will
be a couple breaks in snow as southern edge of precipitation shield moves
northeastward, but with bcl development and cooling cloud heights,
expect moisture/snow showers to continue filling in this shrinking
Short term /7 am this morning through Sunday/...
as of 330 PM EST Thursday...the center of the clipper traverses
near the international border early Friday morning...then
redevelops off the southern New England coast in the afternoon as
the associated middle level trough digs and takes on a negative tilt.
This will result in the surface low slowing its eastward
progression into Gulf of Maine. The result will be a transition of
synoptic snow to upslope snow or snow showers across
Vermont...which will continue into Friday night. The snow will
taper off earlier across northern New York.
Behind the surface low and with passage of cold front...southerly
winds will shift into the north. This combined with lingering
moisture will produce upslope snow showers with Froude numbers
showing blocked flow. When all is said and done...expect 3-7 inches
of snowfall for the St Lawrence Valley...stretching across the
northern tier of our zones across the central Champlain Valley and
all of northern Vermont. Due to shadowing...Essex County New York and
the southern Champlain Valley and south central Vermont will receive
just a bit less...with 2-5 inches expected. Some locally higher
amounts are also possible...especially over the western slopes of
the northern Green Mountains.
The northwest flow will usher in colder air with non diurnal
temperature trend expected Friday. Drier air will also be
filtering in Friday allowing skies to clear across northern New
York. Pressure gradient will increase late Friday into Friday
night with coastal low deepening and high pressure building to
our west. These features will result in very cold temperatures
Friday night into Saturday. 925mb temperatures will fall to between -10c
and -20c Friday night...which will be reflected at the surface in
terms of Saturday morning lows ranging from a bit above zero
southern and eastern Vermont to the teens below zero across
much of northern New York. Combination of temperatures and wind will
likely result in some wind chill issues...with possibility of at
least advisories for late Friday night into Saturday.
Maximum temperatures Saturday under partly to mostly sunny skies will be
only in the single numbers to lower teens...although winds will
abate during the afternoon. Another front will drop into the area
from the northwest Saturday night. Not much in way of available
moisture...but enough for at least the mention of a chance of snow
showers...especially over the northern mountains.
Long term /Sunday night through Thursday/...
as of 322 am EST Friday...a ridge of high pressure will be over
the region Sunday night with temperatures well below zero Sunday
European model (ecmwf) and GFS models have trended further north with a low
pressure area moving northeast from the Ohio Valley Sunday
night...but models still have this low passing just south of the
benchmark (40n 70w) on Monday. Have gone with low chance probability of precipitation for
light snow across Rutland and Windsor counties in south central
Vermont on Monday. However...confidence in this is not very high
as Arctic air will be well entrenched across the region on
Monday...with highs in the single digits above zero...and dew
points mainly in the teens below zero on Monday. Any snow will
likely have a very difficult time reaching the surface on Monday
given the very dry air mass in place in the lower levels of the
atmosphere. Likely to be a very sharp south to north gradient of
snow versus no snow on Monday...with the best chances south of
the region on Monday. Would not be surprised to see area remain
dry on Monday.
A ridge of high pressure will build into the region Monday night
into Tuesday...with temperatures again well below zero Monday
night. Model guidance hinting at some lake effect moisture moving
northeast from Lake Ontario later Tuesday...so have gone with
slight chance probability of precipitation for snow showers across the Adirondacks and
Saint Lawrence valley later Tuesday. Expecting more snow showers
to develop across the region on Wednesday...with developing warm
air advection. Another Arctic cold front will bring another shot
of Arctic air to the region late Wednesday night and Thursday with
a chance for more snow showers Wednesday night and Thursday.
Aviation /08z Friday through Tuesday/...
through 06z Saturday...a low pressure area moving through the
region today will bring light snow and IFR conditions to the
region through the period. Expecting surface winds to shift to the
northwest by this afternoon withe surface wind gusts becoming
around 20 knots or greater between 21z-24z Friday and continuing
through 06z Saturday...as a surface low pressure area deepens off
the Maine coast.
Outlook 06z Saturday through Tuesday...
06z Saturday-12z Saturday...slow improvement as snow showers end.
Gusty northwest winds will result in areas of blowing snow.
12z Saturday-12z Monday...VFR.
12z Monday-00z Wednesday...mainly VFR as system slides south of
region. Could see some light snow across southern Vermont from 12z
Monday through 00z Tuesday as low pressure area passes south of
Vermont...Winter Weather Advisory until 1 am EST Saturday for vtz001>012-
New York...Winter Weather Advisory until 7 PM EST this evening for