Area Forecast Discussion
Issued by NWS Burlington, VT-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KBTV 270816
Area Forecast Discussion
National Weather Service Burlington VT
416 AM EDT Thu Oct 27 2016
-- Changed Discussion --Rain mixed with wet snow across the mountains will develop from
southwest to northeast over the North Country today. A slushy inch
or so of wet snow is possible in the mountains...with up to 6 inches
at the summits. As low pressure tracks toward our region...gusty
southeast winds will develop along the western slopes and higher
terrain by this evening and continue overnight. Rain will taper off
by Friday afternoon before our next system arrives on Saturday.
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.NEAR TERM /THROUGH FRIDAY/...
-- Changed Discussion --As of 411 AM EDT Thursday...The forecast challenge is timing of precip
today...along with associated complex thermal profiles for
determining ptype. Water vapor shows potent short wave energy
across northern MI with good deep layer moisture advection over
the Ohio Valley/western NY. Current surface analysis shows 1014
mb low pres over northern Indiana with greatest 3 hr pres falls
toward western PA.
Warm air advection precip is already overspreading western/central
NY/PA at this time...with a mix of rain and snow depending upon
elevation and precip rate. BGM reported 1sm -sn with leading edge of
precip. Based on radar trends and following the 1000 to 500mb
greater than 70% rh line off the GFS/NAM precip enters our
southwest cwa by 15z...and quickly spreading into the Champlain
Valley by 18z...and northeast kingdom by 21z today.
Low level thermal profiles will be complex with some surface heating
in the morning...warming bl temps into the mid 30s to lower 40s
depending upon elevation. However...as precip falls into a dry
layer between 5000 and 15000 feet...expect some evaporational
cooling to occur resulting in a mixture of rain/snow initially
between 1000 and 2000 feet...with even a few wet snow flakes
possible in the valleys. Soundings show freezing levels dropping
between 1500 and 1800 feet during the higher precip rates late
this afternoon...supporting a quick slushy inch or so of wet snow
accumulation across the Dacks and Green Mountains. Depending upon
precip rates and timing...this could make for a hazardous late
afternoon/early evening commute across the higher terrain. An sps
maybe needed to highlight this scenario.
For tonight...initial band of warm air advect lift is located near
the international border by 06z...with additional forcing arriving
with potent short wave energy and strong upper level divergence
signature. This combined with a deepening and closing off 5h/7h
circulation moving from the Eastern Great Lakes into southern New
England will produce additional precip across our region overnight
into Friday. Models show good 1000 to 500mb rh with favorable 850 to
500mb q-vector forcing parameters from 06z to 18z Friday. Will
continue to mention pops near 100% overnight...before tapering off
from west to east on Friday. Given the track of surface low pres
into the gulf of Maine and closed 5h/7h circulation...thinking
additional moisture with area of rain and summit snow continues
for most of VT on Friday...including the Champlain Valley...as
strongly blocked flow develops.
Total qpf will range between 0.50 Saint Lawrence to 1.50 southern
Greens and eastern Dacks. Given developing 925mb to 850mb low level
jet of 40 to 50 knots from the southeast...expecting some impacts of
terrain on qpf fields. Highest amounts will be along the se
upslope regions from Ludlow/Killington to Stowe to Jay Peak...with
some shadowing in the Champlain Valley/Northeast Kingdom
initially. However...as wind shift to the northwest on
Friday...the northeast kingdom and western slopes/champlain valley
will see some additional qpf.
Snow levels become very tricky overnight into Friday as soundings
show warm layer developing between 5000 and 7000 feet associated
with southwest winds with cold pocket from 2500 to 3500 feet
associated with upslope cooling on southeast winds. By 15Z
Friday...cooling aloft occurs as winds change to the east then north
by early afternoon and progged 850mb temps drop below 0c. Current
thinking snow continues near the summits through early this
evening...then changes to a wintry mix with pockets of freezing rain
in the midslopes...before changing back to all snow by midday friday
at the summits and cold rain below 3000 feet. Once again snow
accumulations will be very elevation dependent with summits above
4000 feet seeing around 6 inches with several inches possible around
2000 feet and some minor ice accumulation in between. This should
have very limited impacts...given elevation.
Still anticipating breezy to gusty southeast winds along the western
slopes from near Rutland to East Middlebury to Nashville tonight.
The strongest winds will occur between 7 PM and 2 AM associated with
925mb to 850mb jet of 40 to 50 knots. Thinking localized surface
wind gusts to 35 knots is possible with a few isolated power outages
Temperatures mainly in the mid 30s to mid 40s today...fall back only
into the lower 30s to lower 40s overnight...with similar profiles
expected on Friday. Hourly temps will drop several degrees when
precip starts today and during higher precip rates...have tried
to show this detail in grids.
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.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 316 AM EDT Thursday...Brief ridging at the surface and
aloft builds in over the North Country for the first half of
Friday night before heights begin to fall again ahead of weak low
pressure which will pass north of the Canadian border on Saturday.
Overnight temp forecast will be tricky as winds slacken in the
wake of an exiting system to our east, but pick up again markedly
after midnight from the southwest. Not expecting a whole lot of
clearing, so think mins will be mild and slightly above freezing.
Timing of lows I think will fall early across the St. Lawrence and
Champlain Valleys before warming slowly through the night with
increasing winds, but elsewhere likely follow the normal diurnal
Weak low passes north of the border on Saturday and while low/mid
level moisture is abundant with this system, overall forcing is
rather weak so even though we continue to highlight likely PoPs
for showers, QPF will be light with temps pushing well above
seasonal normals into the upper 40s east to mid 50s west. By
nightfall, the deepest low level moisture begins to shift east as
the low tracks off into the Canadian maritimes and thus
precipitation will gradually taper to nil by Sunday morning as
high pressure building eastward into the Great Lakes approaches.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 316 AM EDT Thursday...The extended period looks to be
fairly dry with a fast zonal flow aloft Sunday trending towards
ridging for Monday and Monday night. A strong low developing out
of the northern plains Monday afternoon tracks north of Lake
Superior Monday night to the tip of James Bay by Tuesday night
pushing a dry warm front through the area. We remain mainly dry
all the way through Wednesday with temps warming well into the 50s
for Tuesday and Wednesday in increasing south/southwesterly flow.
.AVIATION /08Z Thursday THROUGH Monday/...
Through 06z Friday...Several impacts to aviation expected over the
next 24 hours associated with approaching storm system. Vfr
conditions will prevail through 15z Thursday...with precip and
mvfr cigs developing at MSS/SLK/RUT by 18z...with a period of wet
snow providing intervals of ifr vis at slk. The precip overspreads
PBG/BTV and MPV by 20z with mvfr cigs and potential brief period
of ifr vis at MPV in -sn. Expecting mainly a cold rain by 00z at
all taf sites with mvfr cigs...some ifr cigs are possible at MSS
associated with northeast flow and MPV/SLK. Next concern is
developing low level jet of 45 to 55 knots at 5000 feet lifting
from southwest to northeast across our taf sites between 00z and
06z. This will create areas of turbulence and enhanced low level
wind shear...especially when this jet interacts with the higher
terrain. A few surface gusts between 30 and 35 knots can be
expected at RUT between 00z-06z Friday with gusts up to 30 knots
possible at BTV.
Outlook 06z Friday through Monday...
Precip will be slowly ending from southwest to northeast by 12z
Friday with lingering upslope focused precip impacting mpv/slk.
Profiles support mostly rain. As winds shift to the northwest on
Friday morning...intervals of ifr cigs are possible at
BTV/RUT/MPV/SLK...given the amounts of low level moisture
available. A warm front feature lifting across our taf sites on
Saturday morning will shift the winds to the southwest with some
scattered showers possible...especially mss/slk. Expecting mainly
vfr conditions with intervals of mvfr cigs possible across
northern NY taf sites on Saturday. Gusty southwest up to 35 knots
are possible at MSS with 30 knots expected at SLK/BTV on Saturday.
Another wind shift to the west/northwest will occur Sat Night into
Sunday with additional scattered showers. Drier conditions with vfr
flight conditions for Sunday afternoon into Monday.