Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
335 PM EST Monday Feb 8 2016
occasional light snow will occur overnight into Tuesday morning with
accumulations generally a dusting to several inches across the north
country. A deepening trough of low pressure will produce additional
snow showers through Friday...before the coldest air mass of the
season arrives over the weekend. Temperatures will be near normal
this week...but will drop way below normal by the weekend.
Near term /until 6 am Tuesday morning/...
as of 330 PM EST Monday...forecast challenge tonight will be
areal coverage of light snow across our County Warning Area...given the very dry low
levels from weak surface high pressure ridge. Kvsf surface dewpoint is
currently -13f...indicating the very dry low levels with relative humidity values
in the middle to upper teens. Expect virga with initial band lifting
across central/southern Vermont late this afternoon. All guidance
continues to show 850 to 500mb moisture deepening from a combination
of upper level trough over the Ohio Valley and departing ocean storm.
This moisture along with some very weak lift from 500 mb vorticity rotating
through our region. NAM/GFS and latest rap show the best combination of
lift/moisture moves from south to north across our region between
00z and 09z tonight...with developing dry slot impacting our
southern regions by 12z Tuesday. Quantitative precipitation forecast for this minimal event will be
very light and generally under 0.10 with snow accumulations of a
dusting to 2 inches. Given the light winds between surface and 850mb
not expecting much terrain enhanced snowfall with a very uniformed
snowfall anticipated. Temperatures will range from the upper teens
to middle 20s most locations.
Short term /6 am Tuesday morning through Wednesday night/...
as of 330 PM EST Monday...models in excellent
agreement with development of deep full latitude middle/upper level
trough across the Great Lakes/NE Continental U.S....but have some differences on
timing of individual short waves and available moisture. A few
lingering snow showers are possible on Tuesday...but area seems to
be between systems with very light accumulation expected. Temperatures will
be tricky on Tuesday with a sharp 850mb thermal gradient from
southwest to northeast across our area. Temperatures range from -7c
southern Saint Lawrence to -14c Northeast Kingdom...which will
result in highs from the middle/upper 20s to middle/upper 30s across our
region...with warmest values in the west. Northeast winds will keep
immediate Saint Lawrence valley in the middle 20s...while
Potsdam/Canton should warm into the middle 30s.
Additional short wave energy associated with 500 mb vorticity and weak
surface low pressure will produce additional snow showers on Tuesday night
into Wednesday night. Once again...northwest flow aloft and developing
cold pool aloft...precipitable water values are only between 0.15 and 0.25. This
supports only light quantitative precipitation forecast/snowfall amounts...but given fluff
factor...several inches are possible in the mountains. Best dynamics
and moisture arrives around 12z Wednesday...but quickly shifts east in
progressive flow aloft. Will mention chance probability of precipitation valleys to likely in
the mountains on Wednesday...with several inches of snow possible.
Temperatures will remain near normal for Wednesday...but slowly fall by
Wednesday night under low level cold air advection on northwest surface
to 850mb flow of 15 to 30 knots. Some localized upslope enhancement
is possible Wednesday night...but moisture profiles are very limited.
Long term /Thursday through Monday/...
as of 317 PM EST Monday...the region will remain under the influence
of an upper level trough on Thursday...resulting in the continued
chance of snow showers. Shortwave moving through the the base of
the trough and passing to our south may allow for a steadier
period of light snow...with some minor accumulations of a dusting
to an inch or two possible. Chances for any light snow or snow
showers decrease Thursday night as this disturbance exits to the
east. Min temperatures Friday morning expected to range from 5 above to 5
More snow showers on Friday as an Arctic cold front moves into the
region. Threat of snow showers continues Friday night as front
pushes south across the area along with deep upper low. European model (ecmwf)
indicating development of surface low along the Arctic
boundary. This would keep chance for light snow into
Saturday...but GFS shows any low development well offshore with
snow showers ending in most spots by Saturday morning. Have gone
with chance probability of precipitation for Friday night...but continued with a mainly
dry forecast for Saturday.
Big story for the upcoming weekend will be the Arctic chill...with
the coldest temperatures of the winter season to this point expected.
High temperatures Friday as the front moves into the region will be in
the upper teens and lower 20s. Lows Saturday morning will range
from 5 above to 5 below in most areas...but will hold fairly
steady Saturday with highs mainly in the single digits as 850 mb
temperatures expected to bottom out around -30c. Brisk northwest winds
will result in wind chill temperatures well below zero. Coldest temperatures are
expected Saturday night when lows will range from 5 to 15
below...with lower readings in the normally colder locales. Maximum
temperatures on Sunday only 5 to 10 above with some sunshine. Another
night of subzero temperatures Sunday night...then a moderation begins on
Monday. As high pressure departs to the east...return southerly
flow develops. The result will be increasing clouds along with maximum
temperatures in the 20s.
Aviation /21z Monday through Saturday/...
through 18z Tuesday...VFR conditions across forecast area this
afternoon...but conditions will be deteriorating later today and
especially this evening. Light snow will spread from southeast to
northwest across the region between 21z and 03z Tuesday with
ceilings lowering to MVFR and visibilities to IFR within a couple
of hours of onset of snow. These conditions will persist overnight
into early Tuesday...with some improvement to MVFR at most sites
by late in the period. Winds will be north to northeast 5 to 10
kts today...with gusts 15 to 20 kts at mss. Winds become light and
Outlook 18z Tuesday through Saturday...
18z Tuesday-00z Friday...MVFR/IFR in periods of light snow.
00z Fri-Onward...VFR with areas of MVFR/IFR in scattered to numerous