Area Forecast Discussion
Issued by NWS Burlington, VT

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000
FXUS61 KBTV 240455
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1155 PM EST Mon Jan 23 2017

.SYNOPSIS...
A wintry mix of precipitation will overspread the North Country
after midnight tonight and become heavy at times during the
Tuesday Morning commute. An extremely hazardous Tuesday Morning
commute is anticipated with the icy roads and poor
visibilities. A plowable snow and sleet accumulation is
likely...along with some ice. Improving weather with above
normal temperatures return by Wednesday.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
As of 1033 PM EST Monday...Latest trends across e-central NY and
s-central VT show sleet as the predominant precipitation type.
With slow-moving closed mid-level circulation across the mid-
atlantic states, getting plenty of atlantic moisture and above
freezing temps aloft moving in on ely 850mb flow of 50-55kts per
RAP at 03Z across central New England. The 00Z NAM is in line
with observational trends, showing predominantly sleet across
much of our region as precipitation develops and intensifies
during the pre- dawn hours. It`s rare to get a predominantly
"sleet storm", but that appears to be the case given expected
thermal profiles, along with pockets of freezing rain during
Tuesday morning (especially central/ern VT). Impacts on the
morning commute will likely be significant, with moderate to
heavy sleet, with pockets of freezing rain expected resulting in
icy and hazardous roadways and sidewalks. All in all, no
significant changes needed to the forecast attm. Have adjusted
onset timing to be a bit quicker, with precipitation
(predominantly sleet) underway at SLK/RUT/LEB/VSF and spreading
nwd at 0330Z. Anticipate sleet into BTV by 05Z. Heaviest mixed
precipitation rates generally 08-14Z most locations.

Previous discussion...A complex and extremely difficult
forecast with regards to thermal profiles and associated precip
types. Complex thermal profiles have started with Whiteface down
to 19F and Mansfield at 21F...while BTV is 36F. We have taken a
conservative approach in the snow accumulation
department...with a general 2 to 6 inches of snow/sleet
expected...along with some ice accumulation...especially
eastern/central VT...including the Northeast Kingdom. We also
have to watch low level cold air bleeding down the CPV on north
winds...resulting in more freezing rain. Our thinking is
generally between one and two tenths of an inch of ice...with
some isolated higher amounts in central/eastern VT.

Winter weather advisory continues from 7 PM tonight until 10 PM
Tuesday for our entire forecast area. The most intense part of
the storm with the highest precip rates will occur right during
the Tuesday Morning commute (4 AM to 9 AM)...making for an
extremely hazardous morning commute.

Water vapor shows well defined closed cyclonic circulation over
central NC...with a tremendous feed of deep Atlantic moisture
advecting into the NE CONUS/Mid Atlantic. IR sat pic shows a classic
mature cyclone with well defined warm conveyor and strong upper
level divergence pattern with embedded dry slot over eastern NC.
This circulation will slowly move northeast with surface low pres
tracking from eastern NC to Cape Cod by 00z Weds. Overall models in
excellent agreement with tracking of surface low pres...along with
showing deeply negative mid/upper level trof lifting northeast...but
weakening through time. This weakening mid/upper level
feature...along with limited low level cold air advection will
minimize backside bonus snow potential on Tuesday Night.

NAM/GFS show band of very strong lift/fgen forcing with strong 700
to 500mb vorticity advection lifting from south to north across our
cwa between 2 AM and 10 AM tuesday. Helping to enhance deep layer
lift and low level moisture advection will be nose of 45 to 55 knot
easterly 850mb jet and anticyclonic curved 250mb jet over eastern
Canada.

Big question does this strong lift/upper vertical velocities
cool the column just enough to support snow or does the low level
easterly jet advect warm nose of 4 to 6C air into our region and
support a mix of sleet and freezing rain. Still plenty of
uncertainty with regards to low level thermal profiles with latest
12z GFS supporting a mostly snow event...while NAM/ECMWF is a mix of
sleet/freezing rain...while GEM is in the middle. For example the
NAM Bufkit at BTV at 10z shows 5C at 5000 feet associated with
southeast wind of 40 knots....while temps at 2000 feet are -6C with
low level north/northeast winds draining down the CPV.
Meanwhile...same time period GFS shows isothermal layer near 0C from
4500 to 7500 feet with -6C between 1500 and 3500 feet...supporting
more snow. Based on complexity of thermal profiles and
uncertainty...have gone conservative with snow and utilized a model
blend of NAM/BTV4km/GFS/ECWMF to determine precip type and
associated snow/ice amounts. This supports a mix of snow/sleet with
areas of freezing rain...thinking during the heaviest precip rates
mostly snow will occur...with some sleet. As warm layer becomes
better established on Tuesday and low level cold air bleeds down the
CPV/CT River Valley profiles support more of a freezing rain
threat...with more snow/sleet across Northern NY where warm nose is
limited. However...boundary layer temps are just marginally cold
enough...so ice accumulation is uncertain at this time...especially
CPV where temps today are in the mid/upper 30s. Given downslope
easterly flow...would not be surprised if temps warm into the
mid/upper 30s from Mt Holly to East Middlebury to Underhill to
support some rain on Tuesday Afternoon.

Expecting a break in the heavier precip by mid-morning into early
afternoon...before next round of light to moderate mix
rain/sleet and freezing rain develops on late Tues
Afternoon/Evening...as closed system lifts northeast. Timing of
this secondary surge of precip could impact the evening commute
with another round of light wintry mix slowly changing back to
snow showers from west to east toward midnight...as profiles
cool.

Bottom line for snow/sleet accumulation is generally 2 to 6 inches
with some higher amounts possible Dacks/SLV and parts of the
southeast upslope region of the Green Mountains. Ice accumulations
of a trace to 0.10 of an inch CPV...with 1 to 2 tenths of an
inch possible across central/eastern VT...including the
Northeast Kingdom. The heavy wet snow/low ratios and freezing
rain will probably lead to some power outages.

Overall storm total qpf will range between 0.50 and 1.0 with highest
values along the se upslope regions of the Green Mountains from
Ludlow to Mansfield and another stripe along the eastern Dacks.
Expect some shadowing along the western slopes from near
Rutland/Danby to North Underhill and over the Northeast Kingdom.
Given winds expect terrain to impact qpf amounts for this system.
Qpf ranges from 0.25 to 0.75 across the western dacks/slv...as
moisture depth is less.

Wind threat is minimal and relatively small area along the western
slopes from Danby/Rutland to East Middlebury...with isolated gusts
to 30/35 mph possible. Mixing is limited as strongest winds occur
when precip rates are the strongest.

Temps cool into the mid/upper 20s to lower 30s tonight and warm
upper 20s to mid 30s...warmest along the western slopes.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
As of 332 PM EST Monday...By Wednesday morning aforementioned
low pressure will be over the Gulf of Maine and Nova Scotia,
with deep layer moisture rapidly shifting northeast of the BTV
CWA through the day. Could see some lingering snow showers
across the high peaks in the morning, but by mid-day weak
mid/upper level ridging briefly builds in so expect to see some
afternoon sun, especially across central and southern areas.
Highs will continue to run well above normal in the 30s.

Break in active weather is very short as another deep mid/upper
level trough over the central CONUS begins to shift eastward
Wednesday night, with surface low pressure over the Great Lakes
Wednesday shifting northeast in the Ottawa/St. Lawrence Valley.
Favorable southwesterly flow combined with increasing low/mid
level moisture will enhance precipitation potential downwind of
Lake Ontario and points northeastward into northern New York,
the northern Champlain Valley and north-central Vermont through
the night with boundary layer temps supporting mainly snow
except a rain/snow mix across southern portions of St. Lawrence
county. As the boundary layer warms further Thursday,
precipitation becomes more mixed area-wide until the low pulls
east of the area Thursday afternoon and cold air advection
develops on increasingly northwest flow. Overall not looking for
a lot of QPF through the period, so snow amounts will generally
be a dusting to perhaps 2 inches, and locally up to 2-4" across
the high peaks.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 332 PM EST Monday...Long term period for Thursday night
through the weekend highlights a broad upper trough across the
majority of the CONUS with no big systems on the horizon, rather
daily chances for light precipitation especially across the
high peaks. Temperatures return to more seasonal values though
still slightly above normal with highs mainly in the 20s and
lows in the teens which supports mainly snow as the dominant
ptype for anything that does fall. Best chances look to be
Thursday night through Sunday as we remain under cyclonic
northwesterly flow with light snow accumulating along the higher
peaks, followed by drier conditions for Sunday into Monday.

&&

.AVIATION /06Z Tuesday THROUGH Saturday/...
Through 06z Wednesday..VFR overall to start the period with
KRUT being the exception with MVFR ceilings. Conditions will
deteriorate rapidly to a mix of low MVFR/IFR as wintry precip is
now moving in. Expect a variety of precip types with a mix of
rain/snow/sleet and freezing rain possible. Additionally with
the icing layers just off the surface conditions could be dicey
with icing in the low levels of the atmosphere. An easterly low
level jet is expected to create gusty winds at RUT and also
cause issues with low level turbulence and wind shear due to the
speed differences from the ground to 2500-3000 feet agl. Winds
overall will also be northeasterly at 05-10 knots for most of
the period.

Outlook 06z Wednesday through Saturday...
06z Wednesday - 12z Wednesday: MVFR/IFR trending towards
VFR/MVFR as the wintry precip tapers off Tuesday evening.

12z Wednesday - 12z Thursday: VFR with skies becoming cloudy
late.

12z Thursday onwards: Generally VFR with on and off chances of
MVFR in periods of rain and snow showers.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory until 10 PM EST Tuesday for VTZ001>012-
     016>019.
NY...Winter Weather Advisory until 10 PM EST Tuesday for NYZ026>031-
     034-035-087.

&&

$$
SYNOPSIS...Taber
NEAR TERM...Banacos/Taber
SHORT TERM...Lahiff
LONG TERM...Lahiff
AVIATION...Deal/MV


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