Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 231758
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1258 PM EST Fri Feb 23 2018

.SYNOPSIS...
An active period of weather is expected starting today lasting
through upcoming weekend with two systems providing the North
Country with a wintry mix to rain type of scenario. First system
impacts our region on this afternoon with the second on
Sunday...as the trend of above normal temperatures continue.
Minor ice accumulation will be seen in eastern and central
Vermont this afternoon and could produce a few slick spots
during the evening commute. The St Lawrence Valley will also see
some freezing rain this afternoon but will transition to rain by
late this afternoon. Gusty southeast downslope winds along the
Western Slopes are possible on Sunday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 936 AM EST Friday...Quick update to the morning forecast,
mainly to back off on precipitation chances for a couple of
hours and adjust for observed temperatures. In the deeper
valleys outside of the northern St. Lawrence temps are warming
into the lower 30s, while as expected the colder hollows of the
Adirondacks and eastern Vermont are holding below freezing. With
northeast flow at KMSS, the northern St. Lawrence Valley is
also holding onto sub-freezing temps. Precipitation looks to now
hold off closer to the noon hour across northern New York which
in the end supports a smaller window for mixed precipitation,
which is a good thing. Based on current temps though in Essex
County NY, felt there was enough confidence to be included in
the current advisory as mid slope to lower elevations should see
a brief period of a freezing rain/sleet mix before temps warm
above freezing through the column by early afternoon. Advisories
for eastern Vermont remain in place with no changes there.

Previous Discussion...As the precipitation moves into the area,
temperatures will warm rapidly as a warmer and wetter air mass
is advected into the area. HYSPLIT model trajectories from this
air mass date back to the Gulf of Mexico but has modified quite
as bit as it pushed across the eastern half of the US. With the
cold air already in place across the North Country, a quick warm
up poses quite the forecast challenge with precipitation type.
Thermal soundings show most of northern NY quickly transition
from from a snow and sleet mix to all rain by noon. However, the
northern St Lawrence Valley, especially Massena, will see a
different story as they will likely hold onto a northeasterly
wind at the surface. This will continue to replenish the cold
air at the surface while temperatures aloft continue to warm and
create a freezing rain/sleet thermal profile. A freezing rain
advisory has been issued for the northern Saint Lawrence Valley
from noon to 5 PM today but as soon as the winds shift to the
southwest late this afternoon, temperatures will quickly warm
into the 40s and the freezing rain concern will come to an end.

Another freezing rain concern will develop early this afternoon
from the Green Mountains eastward. A freezing rain advisory has
been issued from 1 PM to 10 PM from the Green Mountains east. The
main areas of concern will be low-lying valleys that have a
stronger low-level inversion as these locations will take
longer to scour out the cold air, thus leading to some light
freezing rain. The end time for freezing rain is a but trickier
over eastern Vermont as temperatures will cool slightly this
evening and freezing rain may last longer than in the Saint
Lawrence Valley. Rain chances will diminish through the evening
hours and also help bring an end to the freezing rain potential.

With all of this said, freezing rain amounts look like they
should be a tenth of an inch or less through the entire event so
only minimal impacts are expected. As usual, be careful and
cautious when traveling this afternoon and evening.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
As of 420 AM EST Friday...A weak NW flow follows on Saturday
and some of the higher terrain could see some light snow showers
or flurries by Saturday morning as colder air aloft moves in.
However, moisture is shallow and the profiles are very dry aloft
in the snow growth temperatures so it may be more of some light
rime or snow grains. Not expecting much more than a dusting of
snow accumulation. It will be mostly cloudy in the morning with
some breaks developing in the afternoon as High pressure over
Quebec and ridging aloft moves into the region. High
temperatures mainly in the upper 30s to mid 40s.

The ridge of high pressure holds for the first half of Saturday
night with partly cloudy skies and lows mainly in the 20s, perhaps
some upper teens in the far NEK where partly cloudy skies hang on
longer.  Meanwhile a rather strong and deepening low pressure system
(978mb) will track from CO through the western Great Lakes into
James Bay Canada through Sunday night. It`s associated occluded
frontal system and precipitation will move from southwest to
northeast into the North Country starting early Sunday with lowering
and thickening clouds in advance of strong warm advection.
Initially, it looks like it will be cold and dry enough for
evaporational cooling with an inch of snow or sleet on the leading
edge of the precipitation. We`ll be on the warm side of this system
as well as temperature profiles warm above freezing right up through
850 mb through the day so any mix/snow will change to rain from west
to east. Strong but short-lived lift and precipitable water up to
0.75" will yield QPF will be on the order of 0.25-0.50", with lower
amounts in the Champlain Valley. The winds should be stronger on
Sunday with a southerly low-level jet up to 65kt at 850 mb is
expected by midday and we see some SE downsloping developing. Right
now anticipate 20-30kts with gusts of 40-50kts possible along the
western slopes of the Greens and the northern slopes of the
Adirondacks. By Sunday afternoon, a dry slot develops in the St.
Lawrence valley where temps may shoot up into the mid to upper 40s
with a wind shift from E to SW. Elsewhere high temperatures will on
range from mid 30s east of the Greens and eastern Adirondacks to
around 40 in the Champlain Valley.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 420 AM EST Friday...Precipitation will be ending during
the first part of the overnight Sunday night. Then surface high
pressure will build into the region through Tuesday night. A
weak low passes to our North Tuesday, but not producing very
much for our area. Next chance for precipitation will come on
Wednesday and Wednesday night with another weak low crossing our
area. There should be a brief break in the precipitation on
Thursday. Thursday night and Friday will have a low pressure
approaching from the Great Lakes region bringing our next
widespread precipitation to the North Country. Temperatures will
remain above normal with highs generally in the upper 30s to
low 40s expected through the week.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Through 18Z Saturday...VFR conditions across the region this
afternoon will trend to a mix of IFR and MVFR as ceilings lower
mainly after 00Z for the overnight hours. A brief period of
mixed precipitation is possible this afternoon and early evening
before precipitation type changes to all rain and is scattered
through midnight, then isolated. Low clouds lift to VFR across
the area after 12Z Saturday with northwest winds becoming gusty
at 10-20kts.

Outlook...

Saturday Night: VFR. Chance SN.
Sunday: Mainly MVFR and IFR, with areas VFR possible. Windy with
gusts to 30 kt. Definite RA, Definite PL, Definite FZRA, Likely
SN.
Sunday Night: Mainly VFR, with local MVFR possible. Slight chance
SHRA.
Monday: Mainly VFR, with local IFR possible. NO SIG WX.
Monday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. Chance SHRA, Slight chance SHSN.

&&

.HYDROLOGY...
As of 410 AM EST Friday...Localized ice jams on the Great
Chazy, Missisquoi, Salmon, Winooski, and St Regis continue to
produce minor flooding. Additional precipitation today and
again on Sunday will have limited impacts on river levels with
no large scale warm ups anticipated.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory until 10 PM EST this evening for
     VTZ003-004-006>008-010-012.
NY...Winter Weather Advisory until 5 PM EST this afternoon for
     NYZ026-027-034.

&&

$$
SYNOPSIS...Clay
NEAR TERM...Clay/Lahiff/Sisson
SHORT TERM...Sisson
LONG TERM...Neiles
AVIATION...Lahiff
HYDROLOGY...Taber/Clay



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