Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
643 PM EST Sat Nov 28 2015
a slow clearing trend will develop across the north country
overnight as high pressure builds into the region.
However...additional low level moisture may continue to produce
clouds with temperatures holding slightly below normal for Sunday
into Monday. Our next weather system impacts our region on Tuesday
into Wednesday with some rain showers...that could start as a wintry
mix and end as a brief period of light snow.
Near term /until 6 am Sunday morning/...
as of 631 PM EST Saturday...forecast challenge tonight is amount
of clearing associated with building high pressure and
subsidence/dry air aloft. Late afternoon visible and infrared satellite
pics show little upstream clearing under surface ridge and latest
rap soundings support this thinking with very shallow moisture
between surface and 800mb. This moisture along with very weak
upslope flow and some cold air advection will lead to partly to
mostly cloudy skies overnight. There is clearing just across the
Canadian border and that should lead to some clearing in the St
Lawrence Valley. There are also small pockets of clearing
across parts of central Vermont that are adding to the mix. With all of
that temperatures will be tricky given the complex sky cover and
weak advection...but will go slightly above guidance. Thinking low teens
in the mountain valleys to middle 20s in the Champlain Valley. If
more clearing develops than anticipated temperatures will need to
be lowered by 3 to 5 degrees.
Short term /6 am Sunday morning through Monday night/...
as of 335 PM EST Saturday...on Sunday still plenty of
uncertainty on low clouds and potential impacts to temperatures
across our forecast area. Area soundings...especially the NAM
continues to show moisture between 2 and 3 kft between 12z and 21z
Sunday. Have noted weak secondary surge of low level cold air
advection...along with embedded 500 mb vorticity in the cyclonic northwest
flow aloft. Thinking these factors along with limited clearing on
upstream satellite pics will result in a mostly cloudy day across our
mountains and parts of the Champlain Valley. Some clearing is likely
in the lower CT River Valley...western Champlain Valley...and Saint
Lawrence valley. Prognosticated 925mb temperatures are between -2c south to -6c
north on Sunday...supporting highs only in the upper 20s mountain
towns to upper 30s valleys. Given the expected northerly winds and
clouds these temperatures will be several degrees below guidance. A
chilly night with clearing skies is expected on Sunday night...with
a strong thermal inversion. Coldest temperatures will be in the
deeper protected valleys with the warmest on the mountain summits.
Lows will range from the lower teens to lower 20s. A chilly but
mainly sunny day is expected on Monday. Prognosticated 925mb temperatures warm
several degrees along with expected sunshine. This should help to
warm temperatures back into the 30s to near 40f in most locations
after a chilly start. Another dry night expected on Monday
night...with a complex low level thermal profile likely. Developing
warm air advection after midnight will result in coolest
temperatures in the early evening hours with warming profiles after
midnight on southerly winds in the Champlain and Saint Lawrence
valleys. A strong thermal inversion is expected with warmest
temperatures across the mountain summits and coldest in the
protected valleys of the Northeast Kingdom. Lows will range from the
Lower/Middle teens Northeast Kingdom to middle/upper 20s Champlain
Valley/Saint Lawrence and mountain summits.
Long term /Tuesday through Saturday/...
as of 245 PM EST Saturday...dry conditions with increasing clouds
expected Tuesday morning as high pressure departs to the east.
Precipitation chances will be increasing Tuesday afternoon as warm
front associated with low pressure over the central Great Lakes
region lifts northeast towards forecast area. The day will start
off below freezing...but enough warming indicated by afternoon so
that precipitation should be mainly in form of rain...with just a
brief period of mixed precipitation possible at onset. Periods of rain
expected Tuesday night as low makes its way slowly east...and weak
secondary reflection indicated along New England coast. Expect maximum
temperatures Tuesday in the lower 40s...with lows Tuesday night in the
More showers Wednesday as upper low and surface cold/occluded front
make their eastward into forecast area during the day and then pass
east of the area Wednesday night into Thursday morning. Cooling
temperatures aloft Wednesday afternoon...so a mix or changeover to some
snow expected in the mountains. With passage of upper low later
Wednesday night...deep northwest flow and cold air advection
combined with sufficient low-middle level moisture will allow for any
showers to transition to mainly snow showers before tapering off.
Expect some minor snow accumulations over the higher terrain.
Any lingering snow showers will come to an end Thursday. Dry
conditions with some clearing will follow for late Thursday into
Thursday night. Disturbance in northwest flow aloft may bring some
clouds and slight chance for a few rain/snow showers Friday.
Large area of high pressure both at surface and aloft will then
build in for next weekend...with fair and dry conditions along
with warming temperatures.
Aviation /00z Sunday through Thursday/...
through 00z Monday...MVFR/IFR ceilings this evening till about
03z. Conditions are expected to gradually improve later on tonight as
low level cloud cover slowly erodes from NW-SW. Generally VFR
conditions expected after midnight and Sunday...although model
soundings indicate lingering low level moisture which may allow
for some patchy low clouds.
Winds will be light and variable overnight then becoming
northwesterly at 05-10 knots middle day Sunday.
Outlook 00z Monday through Thursday...
00z Monday through 18z Tuesday...VFR under high pressure. Weak
and dry frontal passage 18z Sunday to 00z Monday to bring some
clouds and MVFR possible at kslk.
18z Tuesday Onward...VFR conditions deteriorating to MVFR/IFR as low
pressure system brings rain to the region Tuesday afternoon into
Wednesday. Rain transitions to snow showers Wednesday night into
Thursday morning before ending.