Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
139 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 Saturday night/...
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 through Thursday/...
as of 254 PM EST Thursday...very little change to previous
forecast thinking for the extended period as todays 12z model
suite remains in good agreement keeping any major systems away
from the north country.
Lingering snow showers remain possible mainly across the higher
terrain Sunday as an Arctic front pushes into the region. Tricky maximum
temperatures forecast at this time based on frontal passage timing, but
based on falling 925-850mb temperatures through the day think highs will be
early in the morning and slowly fall off through the day. Meanwhile,
still monitoring the potential development of surface low pressure
over the Tennessee River valley late Sunday into Sunday night which
will intensify off the eastern Seaboard Monday. Latest trends of the
12z European model (ecmwf) and GFS continue the idea that this south stream energy
doesn't phase with the northern stream trough digging through the
Great Lakes which never becomes negatively tilted and remains an
open wave at 500mb. This results in a more westerly track of the
surface low initially, causing it to pass well to our south and east
of the benchmark. So basically a non-event for US, sigh.
Beyond Monday pattern turns cold and dry for Monday night through
Tuesday night as a strong 1030mb high settles over the middle-Atlantic
and northeast. Temperatures will struggle to warm into the single digits
Tuesday and fall below zero area-wide both nights. This will be a
brief blast of clod though as the high shifts east off the coast for
Wednesday with southerly return flow warming temperatures back into the
teens and 20s. Next chance for snow comes with a clipper system
shifting through the area Wednesday and Wednesday night.
Aviation /07z 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