Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1243 PM EST sun Nov 29 2015
high pressure will continue building in across the north country
through Sunday with calm and quiet weather expected through the
rest of the weekend and to start the work week. By middle week expect
the next weather system to bring a chance of wintry mix switching
to rain and then ending with a period of light snow. Temperatures
through the forecast are expected to continue to be at or slightly
above seasonable normals for the end of November into early
Near term /until 10 PM this evening/...
as of 1229 PM EST Sunday...clouds continue to increase across
central and northern Vermont as well as parts of northern New York
along a secondary cold front. Have noted a few light snow showers
being reported upstream in Montreal and now Newport Vermont. So I have
bumped probability of precipitation up slightly over the mountains and will mention a few
flurries or a period of very light snow this afternoon. No
accumulation is expected...given the lack of deep layer moisture.
Temperatures will hold steady with the clouds and developing cold
air advection over northern New York into central Vermont...with some
additional warming in the sunshine over southern Vermont. Highs will
range from the lower 20s mountains to near 40f vsf. All covered
well in forecast.
Once again the battle with low clouds continues across parts of
our forecast area this morning. Current visible satellite picture shows
mostly cloudy skies over the northern dacks and parts of the
central and northern Green Mountains with clearing over the Saint
Lawrence valley and parts of central and southeast Vermont early this
morning. Best chance of seeing sunshine today will be southern
Saint Lawrence County and parts of southern Vermont. A secondary
cold front just north of our region will continue to slowly sag
south today...with increasing clouds and low level moisture
expected to impact most of the northern Saint Lawrence valley into
the Champlain Valley and portions of northern Vermont. A few light
flurries are possible in the mountains. Otherwise temperatures
will be highly depend upon the clouds...with warmest values south
and coldest temperatures north and in the mountains. Overall many
of the concepts are covered well in current forecast with only
minor changes to capture latest trends and conditions.
Changes with this update to the forecast mainly include
increasing to a slight chance for some orographic snow to develop
this evening. 700mb flow remains northwest and as the moisture
increases overnight some light orographic snow could develop.
Nothing of any significant amount but especially given the blocked
flow and a saturated layer between 950mb and 850mb is possible for
snow to fall on the western slopes of both the Adirondacks and The
Greens between 00-06z this evening. Snow...if it does fall would
only be likely above 1500 feet and really only on the northwest side
of the mountains. The rest of the forecast remains largely
unchanged as current observational trends are holding consistent
with the forecast.
Previous discussion as of 350 am EST Sunday...cloud cover will
continue to be the tricky portion of the forecast today. The only
available moisture is a thin layer of saturated air between
1000-900mb with forecast models continuing to point to this
starting to erode right around day break. However, a second
increase in low level moisture will begin to push into the north
country in the early afternoon and will see clouds build back in
behind the eroding cloud cover from this morning. Based on latest
hires guidance and forecast soundings I cleared out much of
southern Vermont in the afternoon whereas along the international
border with New York Vermont and Canada expect clouds to increase
to overcast conditions by middle afternoon.
The moderate cold air advection below a weak subsidence inversion
will keep temperatures on the cooler side today with the typical
colder locations in the Northeast Kingdom and over the Adirondacks
only warming into the upper 20s with the Champlain and Saint
Lawrence valley warming to the middle 30s. Light to moderate
northerly flow will continue to drive boundary layer temperatures down
though the afternoon and evening so as we turn towards the
overnight lows the forecast 925mb temperatures will be around -7c to
-10c. Colder temperatures aloft with spotty cloud cover over will lead to
a large range of overnight temperatures. Areas that clear out
including the Northeast Kingdom will likely radiate out to the low
teens or even near single digits whereas the cloud cover should
prevent temperature completely bottoming out elsewhere. Expect
temperatures in the Northeast Kingdom to drop to the low teens with the
Champlain and Saint Lawrence valleys cooling to the upper teens.
Short term /10 PM this evening through Tuesday/...
as of 322 am EST Sunday...a ridge of high pressure will be over
the region through early Tuesday...with fair and dry weather
expected. On Tuesday...a warm front will move northeast from the
Middle Atlantic States. European model (ecmwf) and GFS models in good agreement on
holding off rain showers until Tuesday afternoon across the
region...as a ridge of high pressure at the surface and aloft will
be over the north country Tuesday morning. Temperatures will be
mainly in the lower 40s by the time the rain showers make it into
the north country during Tuesday afternoon.
Long term /Tuesday night through Saturday/...
as of 322 am EST Sunday...models show a wet Tuesday night across
the north country with rain showers expected. Have gone with
likely or categorical probability of precipitation for Tuesday night. Cold front to move
through the region late Tuesday night. Expecting rain shower
activity to linger into Wednesday. An upper trough will swing east
from the Great Lakes on Wednesday along with colder air aloft.
Expecting rain shower activity to change to snow showers over the
higher elevations of the Adirondacks and Green Mountains by
Wednesday afternoon...as colder air aloft moves into the region.
Expecting any residual rain shower activity Wednesday night to mix
with or change to snow showers in valley locations as the upper
trough moves through the region. Forecast area expected to remain
under cyclonic flow on Thursday from a deepening low pressure area
over the Canadian Maritimes on Thursday. Have slight to low chance
probability of precipitation for snow showers on Thursday...mainly over the higher
elevations of the Adirondacks and Green Mountains.
A ridge of high pressure will build into the region Thursday night
with fair and dry weather expected. GFS model showing an upper
trough moving southeast from Canada on Friday. Have gone with
slight chance probability of precipitation for snow showers over the higher elevations of
the Adirondacks and Green Mountain on Friday. A ridge of high
pressure will then build into the region Friday night and remain
through Saturday...with fair and dry weather expected.
Aviation /18z Sunday through Friday/...
through 18z Monday...VFR/MVFR ceilings expected for the rest of
today into this evening as low level moisture persists across the
north country. A period of MVFR ceilings expected this afternoon
into early tonight as moisture associated with cold front pushes
south across forecast area. As front pushes further south
overnight expect a return to VFR conditions with skies clearing
after midnight. Skies will remain clear during the day on Monday.
West winds will become northwest and then north at 5-10 knots this
afternoon/evening. Light and variable winds overnight will become
southerly 5-10 knots during Monday.
Outlook 18z Monday through Friday...
18z Monday through 18z Tuesday...VFR under high pressure.
18z Tuesday through 18z Thursday...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.
18z Thursday Onward...mainly VFR.