Winter Storm Warning 1, NWS Burlington, VT

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
436 PM EST Tue Jan 8 2019

.SYNOPSIS...
Periods of light mixed precipitation will redevelop across
northern New York and Vermont this evening into the overnight,
as low pressure tracks eastward from western New York across
central New England. Temperatures will be warm enough for plain
rain in the lower valleys of western Vermont, and across the St.
Lawrence Valley. However, an intermittent mix of sleet and
freezing rain is expected in spots across the northern
Adirondacks and far northeastern New York, and also for areas of
Vermont east of the Greens, where temperatures will remain below
freezing. As low pressure deepens across Maine on Wednesday,
colder air will return to the North Country on northwesterly
winds, with frequent snow showers developing, especially across
the northern Adirondacks and Green Mountains. Mountain snow
showers will continue through Thursday before tapering off
Thursday night. Temperatures will trend much colder for Thursday
night, Friday and through the weekend. Wind chills are expected
to be well below zero for Thursday night into early Friday.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 435 PM EST Tuesday...Winter Weather Advisories in effect
6pm tonight through 7am Wednesday for mixed wintry precipitation
potential. Additional advisories may be required to cover
transition to snow during the day Wednesday, and significant
snow potential across the northern Mountains as flow becomes NW
on Wednesday thru Wednesday night.

Interesting setup tonight and through the near-term period.
Upstream shortwave troughs are associated with 120kt jet exit
region focusing strong divergence across wrn NY. Have noted
strong cloud top cooling across the eastern Great Lakes, and
development of sub-synoptic surface low near KROC. We've also
been monitoring embedded convective elements with cloud-to-
ground lightning across swrn NY/wrn PA into nern OH throughout
the day.

Anticipate first upstream area of precipitation moving back
into nrn NY and VT by 23Z, and lasting through 06Z or so.
Thermal profiles support widespread sleet and freezing rain
across the nrn Adirondacks and all of central and eastern VT.
Temperatures are particularly concerning east of the Green Mtns,
with 2-m readings and pavement temperatures currently in the
mid 20s and not likely to change much. Thinking icy roads may
become a significant problem overnight, especially central/ern
VT. Ice accumulation generally expected around 0.1", but locally
higher ice amts possible depending on amount of sleet that
mixes in. The immediate St. Lawrence and Champlain Valley should
be warm enough for plain rain early tonight. On the western
slopes of the Greens, may see a few pockets of freezing rain,
and this will need to be monitored as well.

Synoptic low deepens as it moves just to our south tonight and
into Wednesday morning across Maine. We'll see strong dynamic
cooling and a changeover to snow by daybreak Wednesday areawide.
Best synoptic snowfall potential is across ern VT, but will see
a transition to orographic forcing as well as low-level winds
turn northwesterly. Anticipate periods of snow areawide on
Wednesday, becoming increasingly orographic in nature later in
the day and through Wednesday night. Through Wednesday night,
should see snow accumulations of 2-5" across most of the
forecast area, and locally 6-10" along the western slopes of the
Green Mountains. Morning commute could be challenging across
the region with slow travel conditions as precipitation changes
to snow. Will likely need additional winter wx advisories beyond
the mixed precipitation period expected tonight, to address
snow-covered travel potential during the daylight hrs Wednesday.

Temperatures quasi-steady tonight. Temperatures on Wednesday
generally in the low-mid 30s early in the day, and likely begin
to fall during the afternoon. Lows Wednesday night mainly low-
mid 20s across VT, and teens across nrn NY.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 250 PM EST Tuesday...The upper level trough will finally begin
to make some eastward progression on Thursday which will help weaken
upper level forcing and force much of the lingering moisture out of
the region. This will lead to a steady decline in areal coverage and
intensity of lingering upslope snow showers. Much, if not all, of
the snow showers will mainly dissipate by sunrise on Friday. As the
trough slides eastward, a strong push of arctic air will quickly
descend across the North Country. Instead of seeing the typical
warming diurnal curve Thursday afternoon, temperatures will continue
to plummet as strong cold air advection filters in across the region
associated with aforementioned arctic air mass.

Looking at the surface and lower levels of the atmosphere on
Thursday, a mature low pressure system centered off the coast of
over New Brunswick will begin to weaken and drift to the northeast
while surface high pressure tries to build across Vermont and
northern New York. This will yield a strong gradient across the
North Country which will allow for strong and gusty northwesterly
winds ranging from 15 to 30 mph. As temperatures drop near and below
zero Thursday night into Friday morning and while winds continue to
blow at 10 to 20 mph, we will see wind chills approach 15 to 30
degrees below zero across much of the region. If this trend
continues, a wind chill advisory may be needed in the coming days.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 250 PM EST Tuesday...The extended period starting on Friday and
continuing through Monday will be highlighted by below normal
temperatures and drier weather. Following the passage of the
upper level trough on Thursday, the jet stream will sink south
of the North Country into southern New York which will allow
very cold arctic air to settle into the region. Models are
currently progging 850 mb temps 20 degrees below zero or colder
with this push of arctic air. With such a cold air mass
overhead, temperatures on Friday will likely not be able to
rebound into the double digits. Some clearing of skies will be
seen Friday night into Saturday which will allow temperatures
across the entire forecast to drop below zero for overnight
lows. Luckily, surface high pressure will move overhead on
Friday and keep winds light and variable during the overnight
hours and prevent wind chills from being an issue.

A similar trend will be seen on Saturday but temperatures will
likely be a degree or two above those seen on Friday as the air mass
begins to moderate and some sun is able to peek through the clouds.
A pretty impressive shortwave will track through the forecast area
on Monday but the lack of moisture with the jet stream to our south
will likely prevent any precipitation developing as it moves
through, However, this feature will be ahead of an amplifying upper
level trough that will be sliding eastward toward New England Monday
night and Tuesday. As this happens, we will see temperatures aloft
begin to warm which will translate to a warming trend at the
surface. However, temperatures will still remain below seasonal
normals through Tuesday even with the aforementioned warming trend.
As terms as the next chance of precipitation, a weak disturbance on
Tuesday may be able to coincide with just enough moisture to squeak
out a few snow showers but amounts would be very minor.

&&

.AVIATION /22Z TUESDAY THROUGH SUNDAY/...
Through 18z Wednesday...Looking at a prevailing MVFR overcast
most sections with HIR TRRN OBSCD within stratus deck. Localized
swly orographic conditions producing an IFR overcast layer at
SLK, which should persist thru 00Z this evening. Next areas of
precipitation over western NY moves newd and arrives around 23Z,
with periods of mixed wintry precipitation through the
overnight hours. Based on S-SW winds and temperature trends,
should see mainly plain rain at MSS/BTV/RUT this evening and
most of the overnight period. However, periods of sleet/freezing
rain are a possibility at SLK/PBG, and especially MPV. May see
moderate impact to aviation ground ops at MPV with up to 0.10"
ice accumulation possible. Colder air returns toward daybreak
Wednesday with developing NW winds 10-12kts with gusts to 20kts.
Should see more widespread IFR conditions developing for
Wednesday morning, with 1-2SM in periods of snow and ceilings
falling below 1000ft.

Outlook...

Wednesday Night: Mainly MVFR and IFR, with local VFR possible.
Likely SHSN.
Thursday: MVFR. Chance SHSN.
Thursday Night: Mainly VFR, with local MVFR possible. Chance
SHSN.
Friday: VFR. Slight chance SHSN.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. Slight chance SHSN.
Sunday: VFR. Slight chance SHSN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory until 7 AM EST Wednesday for VTZ003-
     004-006>008-010-012-019.
NY...Winter Weather Advisory until 7 AM EST Wednesday for NYZ030-
     031-034.

&&

SYNOPSIS...Banacos
NEAR TERM...Banacos
SHORT TERM...Clay
LONG TERM...Clay
AVIATION...Banacos

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