Scientific Forecaster Discussion
fxus61 kbtv 180538
Area forecast discussion
National Weather Service Burlington Vermont
1238 am EST Mon Nov 18 2019
a ridge of high pressure will remain in control tonight,
providing dry and tranquil conditions, but with early morning
lows not as cold as over the weekend. Low pressure approaching
southeastern New England will bring increasing morning clouds.
By Monday afternoon, intermittent periods of freezing rain will
develop across south-central Vermont, before overspreading
northern Vermont and New York by Monday evening. As colder air
moves in aloft, freezing rain is expected to transition to sleet
and snow during Tuesday morning, resulting in several inches of
snow accumulation. Icy and snow covered Road conditions are
expected to adversely affect travel late Monday through Tuesday
morning. Drier conditions are expected to return for Wednesday.
Near term /until 11 am this morning/...
as of 955 PM EST Sunday...going forecast remains in pretty good
shape, just needed to continue tweaks to temperatures and sky
cover. Deep hollows of northern Vermont and New York such as
Island Pond and Saranac Lake have really dropped off quickly
this evening. Current readings as of 945pm were 5 and 11,
respectively. Thinking temperatures should level off here in
the next couple hours as the marine stratus layer continues to
advect northward. Satellite imagery shows northern extent
creeping up towards Morrisville, however progress has been slow
across northern New York as it has struggled to make it into
the Adirondacks...thinking it'll somewhat similar for the
western slopes of The Greens as the mountains act as a natural
barrier. Eventually, low level clouds will overspread the area
as southeasterly moisture advection continues overnight. Areas
that do remain cloud free over the next several hours should see
temperatures continue to drop with lows generally in the teens
to low 20s.
Previous discussion...sunny skies across the north country this
afternoon have allowed for moderating temperatures, with 20z
readings generally in the low to mid 30s. Center of surface
anticyclone has drifted ewd into New Brunswick and the Canadian
maritime provinces, but ridge axis extends back swwd across
interior northern New England, and will maintain dry weather
overnight. Per GOES-16 imagery, have noted widespread stratus
associated with onshore flow across srn New Hampshire into extreme srn Vermont.
These clouds will gradually lift nwd into S-central VT, limiting
radiative cooling across Rutland/Windsor counties overnight.
Indicated lows in the teens across the northern two-thirds of
the forecast area, but holding in the lower 20s across Rutland
and Windsor counties.
For Monday, continue to monitor nwp trends involving northward
movement of deep-layer closed low off the Carolinas. Still some
model differences concerning overall timing and extent of
precipitation across Vermont and northern New York as the sfc low passes east
of the 40n 70w benchmark during the afternoon hours on Monday,
and eventually across Nova Scotia early Tuesday morning. Believe
we are largely on the western fringe of associated upward vertical velocity and
precipitation. Onshore flow results in substantial warm (above
freezing) layer 3-5kft. Thus, anticipate intermittent periods
of light freezing rain across S-central Vermont during Monday
afternoon. Eventually, potential intermittent periods of light
freezing rain lift nwd across central/nrn Vermont and nrn New York during
Monday evening. Ice amounts around 0.05-0.10" generally
expected, but may be slightly higher across the valleys of
central Vermont. Surface temperatures will generally be holding in
the upper 20s to lower 30s at the surface.
As we reach the pre-dawn hours on Tuesday, a 850-500mb trough
shifting newd from PA and S-central NY, will bring an additional
period of qg/synoptic forcing across nrn New York and Vermont for the
morning hours. Upward vertical velocity and dynamic cooling results in thermal profiles
more favorable for sleet and then snow, and may see a period of
moderate snow near the time of the Tuesday morning commute.
Snow exits/tapers off to snow showers by 18z Tuesday, but during
the morning, 2-3" of snowfall accumulation is generally
expected, with localized amts up to 4" possible.
With the combination of light ice accumulation and sleet/snow as
the event ends, anticipated adverse Road impacts are sufficient
enough to Post winter weather advisories. Went with a Winter
Weather Advisory 17z Mon thru 18z Tue for Rutland/Windsor/Orange
counties, where periods of freezing rain- will arrive first. For nrn Vermont
and Essex/Franklin/Clinton in NY, Winter Weather Advisory runs
from 23z Mon thru 18z Tue with the later time of onset. Across
St. Lawrence County, it appears any ice/snow will be limited,
thus have left out of the Winter Weather Advisory at the present
time. Once snow ends Tuesday afternoon, temperatures should
climb into the mid 30s for daytime highs.
Short term /11 am this morning through Tuesday night/...
as of 257 PM EST Sunday...should see quieter conditions for
Tuesday night, though cyclonic flow across the eastern Great
Lakes may maintain a few snow showers (30 pop) across St.
Lawrence/Franklin counties during the nighttime hours.
Elsewhere, skies should remain mostly cloudy. Lows Tuesday night
generally in the 24-28f range.
Long term /Wednesday through Sunday/...
as of 257 PM EST Sunday...forecast guidance has trended drier for
Wednesday. This is likely a result of northwesterly winds preventing
too much moisture to stream across the north country from Lake
Ontario. There could still be some potential for showers along
higher terrain as a backside vort of the upper trough lifts
Ridging begins to build in, but we remain on the eastern periphery
with northwest flow and some steepening pressure gradients, but
faster flow looks to remain aloft. There are some relatively high
lapse rates nearer the surface, with the GFS appearing to generate
lake effect showers off Lake Champlain and in the Northeast Kingdom.
For now, have mentioned 20% pops in the eastern Champlain Valley and
nek. With the deep layer ridge will come moderating temperatures.
Upper 30s and even some 40s look to make an appearance on Friday
ahead of the next system. The warm front looks to lift north of the
region overnight Thursday with the cold front pushing across late
Friday morning with mostly light precipitation. Temperatures will
cool behind the system, but not to the extremes we have seen as of
Aviation /06z Monday through Friday/...
through 00z Tuesday...an MVFR stratus deck continues to creep
across southern Vermont and portions of northern New York this
morning. Weak and blocked flow has kept the stratus from
advancing too far north and this looks like it should be the
trend over the next few hours with just kmpv and krut expected
to get in on the MVFR ceilings. Light southeasterly winds should
continue this morning with the surface winds shifting to the
north/northwest by Monday afternoon. The onset of precipitation
looks slower than it did previously with much of the
precipitation now not expected to start until after 00z. Have
included mention of -fzra and -pl at all taf sites except kmss.
It definitely looks like the onset of precipitation will be some
form of mixed freezing rain and sleet that will likely
transition to snow after 06z.
Tuesday: mainly MVFR, with local IFR possible. Definite sn,
slight chance shsn.
Tuesday night: mainly MVFR, with areas VFR possible. Slight
Wednesday: mainly MVFR, with areas VFR possible. Slight chance
Wednesday night: MVFR/IFR conditions possible. Slight chance
Thursday: MVFR/IFR conditions possible. Slight chance shra,
slight chance shsn.
Thursday night: mainly VFR, with areas MVFR and IFR possible.
Likely shsn, likely rain showers.
Friday: mainly MVFR, with local IFR possible. Chance shra, likely
Vermont...Winter Weather Advisory from 6 PM this evening to 1 PM EST
Tuesday for vtz001>009-016>018.
Winter Weather Advisory from noon today to 1 PM EST Tuesday
New York...Winter Weather Advisory from 6 PM this evening to 1 PM EST
Tuesday for nyz027-028-030-031-034-035.