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  Monday November 18, 2019

 

NWS Area Forecast Discussion


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273
FXUS61 KBTV 181435
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
935 AM EST Mon Nov 18 2019

.SYNOPSIS...
Freezing rain will move into southern and eastern Vermont this
afternoon with a mix of freezing rain and sleet moving into western
Vermont and northern New York during the evening and overnight
hours. This mix of precipitation will change over to snow prior to
sunrise on Tuesday and will gradually taper off during the afternoon
hours on Tuesday. Quieter weather is expected on Wednesday and
Thursday but another storm system will move into the region on
Friday. This system will likely bring a mix of rain and snow to the
North Country.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 927 AM EST Monday...Overall forecast remains on track
this morning. Cloud cover is creeping across the whole region
and over the Adirondacks now. Warm air advecting over the cold
air near the surface will keep conditions cloudy with periods of
drizzle/freezing drizzle possible late morning/early afternoon.
Otherwise, mainly minor tweaks to the previous forecast based on
the discussion below.

Previous Discussion...Temperatures overnight have been 10
to 15 degrees warmer than yesterday morning as warm air advection
coupled with increasing cloud cover stifling our cooling.
Clouds cover will continue to work into the region this morning
but weak and blocked flow has kept the clouds on the windward
(southern and western) slopes of the Adirondack and Green
Mountains. The coastal low developing well off the coast of
North Carolina and Virgina has tracked further east than the
guidance showed this time yesterday. The observed pressure falls
from the few buoys and coastal sites show the low will likely
continue to track to the northeast through the remaining
morning hours which should take this low well east of the
benchmark. This will likely yield very little precip working
into the North Country through the morning and afternoon hours
as the main moisture axis will be shunted eastward. Some wrap-
around precipitation will be possible across eastern Vermont
during the mid to late afternoon hours which looks like it
should fall as freezing rain. The big question across southern
and eastern Vermont this afternoon will be the degree of heating
at the surface. Any fluctuations a degree or two warmer than
the current forecast would likely yield a transition from
freezing rain to just a cold rain but the northerly flow
developing this morning should help replenish the cold air and
negate the latent heat release from the falling freezing rain.

Heading into the evening and overnight hours, things begin to get
even more interesting. A negatively tilted 850-500 mb trough will
move across the North Country with strong synoptic forcing and upper
level diffluence. The combination of these features will allow
precipitation to overspread the North Country between 8 and 11 PM.
Much of this precipitation will start off as freezing rain with
warmer air overrunning a below freezing surface. The thermal profiles
remain the most challenging aspect of the forecast as the placement
and timing of the upper level trough will impact the degree of cold
air advection and the ultimate transition from freezing rain to an
hour or two of sleet and eventually over to snow. Freezing rain
amounts are slightly less for the Champlain Valley given the
latest data with less than a tenth of an inch expected but up to
two tenths of an inch is still possible for southern and
eastern Vermont. It should be noted that the 06Z NAM has come
into very good agreement with the 00Z GFS and 00Z ECMWF in
regards to the precipitation tonight which begins to increase
our confidence in a mixed precipitation event happening through
the overnight hours.

It looks like most places will transition to snow before the
morning commute on Tuesday but the possibility of an icy layer
on the roadways with falling wet (8:1 to 10:1 ratio) snow will
create some very slick surfaces. Snowfall will taper off from
southwest to northeast throughout the day on Tuesday before
ending in northeastern Vermont by late afternoon. Overall
snowfall accumulations look to range from 1-3 inches with some
local amounts near 4 inches across the northern Green Mountains.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
As of 410 AM EST Monday...Tuesday night and Wednesday will be
relatively quiet in relation to the near term. A negatively tilted
upper level trough will pass to our South during these 2 periods.
Will be tough to rule out some light snow showers with the upper
trough and associated vorticity advection nearby. Temperatures will
warm a bit, but still remain below seasonal normals. Mainly cloudy
conditions are anticipated.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 410 AM EST Monday...Wednesday night and Thursday will trend
drier with surface and upper level ridging building over the north
country. Headed into Thursday night, a low pressure system will lift
northeastward from the Great Lakes into Quebec. Will have chance for
rain showers with this feature on Friday, though nothing very
significant with best forcing remaining closer to parent low well to
our North. Better chance for precipitation in our area will come on
Friday night as surface cold front crosses the area and we`ll have
better forcing with the surface feature. At this time looks like
precipitation would start out as rain and then change to snow or
snow showers with cold air advection behind the surface front.
Pretty decent upper level trough and shortwave energy also passing
through on Friday night. Showers will end during Saturday morning.
The rest of Saturday heading into Saturday night would mainly be dry
with some weak surface ridging. Headed into Sunday a weak clipper
type low crossing the North Country will bring another chance for
light snow showers. Surface and upper level ridging will return once
again for Monday and Tuesday. Very changeable patterns in the
extended portion of the forecast will keep the weather active.

&&

.AVIATION /15Z 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 across KSLK and KMSS. Light southeasterly winds
should continue this morning with the surface winds shifting to
the north/northwest by this afternoon. The onset of precipitation
is 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.


Outlook...

Tuesday: MVFR/IFR conditions possible. Chance SN, Chance RA.
Tuesday Night: Mainly MVFR, with areas VFR possible. NO SIG WX.
Wednesday: Mainly MVFR, with local IFR possible. Slight chance
SHSN.
Wednesday Night: Mainly VFR, with local IFR possible. Slight
chance SHSN.
Thursday: Mainly VFR, with local IFR possible. Slight chance
SHRA.
Thursday Night: Mainly VFR, with areas MVFR possible. Likely
SHRA, Chance SHSN.
Friday: Mainly MVFR, with areas IFR possible. Likely SHRA, Chance
SHSN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory from 6 PM this evening to 1 PM EST
     Tuesday for VTZ001>009-016>018.
     Winter Weather Advisory until 1 PM EST Tuesday for VTZ010>012-
     019.
NY...Winter Weather Advisory from 6 PM this evening to 1 PM EST
     Tuesday for NYZ027-028-030-031-034-035.

&&

$$
SYNOPSIS...Clay
NEAR TERM...Clay/Haynes
SHORT TERM...Neiles
LONG TERM...Neiles
AVIATION...Clay



 
 
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