Area Forecast Discussion
Issued by NWS Burlington, VT-- Highlight Changed Discussion --
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FXUS61 KBTV 232333
Area Forecast Discussion
National Weather Service Burlington VT
633 PM EST Mon Jan 23 2017
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 339 PM EST Monday...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...latest trends have delayed
the arrival of precip until Midnight for southern sections and
quickly spreads to the international border by 3 or 4 AM. To keep
things simple we will not adjust advisory timing...but continue
to emphasis a later arrival to precip.
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
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
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 /00Z Tuesday THROUGH Saturday/...
-- Changed Discussion --Through 00z 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 moves in
overnight after 07Z. The forecast trend continues to show the
precip moving in late overnight between 03-06z in southern
Vermont and between 09-12z across central and northern Vermont
and across Northern New York. 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 00z Wednesday through Saturday...
00z 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
12z Thursday onwards: Generally VFR with on and off chances of
MVFR in periods of rain and snow showers.
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-- Changed Discussion --VT...Winter Weather Advisory until 10 PM EST Tuesday for VTZ001>012-
NY...Winter Weather Advisory until 10 PM EST Tuesday for NYZ026>031-
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