Area Forecast Discussion
Issued by NWS Burlington, VT-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KBTV 231926
Area Forecast Discussion
National Weather Service Burlington VT
326 PM EDT Fri Sep 23 2016
Any light showers, mainly across central and southern Vermont will
end by late afternoon. Clearing skies will develop from north to
south this afternoon and evening as high pressure moves in from
Canada. That high pressure system will persist over the North
Country through the weekend. Expect below normal temperatures on
Saturday and Sunday with highs only in the mid 50s to lower 60s.
No precipitation is expected...but the potential will exist for
frost in the northern adirondacks and northeast kingdom of
vermont, especially early Sunday and Monday mornings.
.NEAR TERM /THROUGH SATURDAY/...
As of 220 PM EDT Friday...thicker band of clouds, associated with
the mid level front slowly pushing southeast across the region.
Radar still showing a few light showers within this band, but as
model guidance had suggested, the overall coverage and intensity
has been steadily decreasing the last few hours. Still expect a
few to hang together this afternoon, so have maintained chance
level PoPs for south-central and southern VT. Up north along the
border, some sunshine has been breaking through, but with still
relatively moist low layers, shallow cumulus clouds quickly form
with daytime heating. However, the trend will be for drier air to
filter south, and then with sunset even those cumulus clouds will
fade away. Temperatures have been tricky, with southern sections
already seeing their highs, while across the far north, that
little bit of sunshine has allowed temperatures to poke up a
degree or two. In general, most everyone is in the 50s, and that
is where we`ll stay for the rest of the afternoon.
Overnight, high pressure will start to build in, but with the high
pressure centered well to our northwest, we`ll continue to have
northwest flow advect in cooler and drier air. Eventually the
entire region will clear out. Expect that to be early evening
across the north and by midnight in the south. A light northerly
breeze should continue most of the night, however some of the
protected hollows and river valleys should go calm and with the
recent rains and warm ground, I would think patchy fog should
develop fairly quickly, despite the drier air filtering in. It`s
conceiveable that the very coldest spots in the `Dacks and
Northeast Kingdom (Saranac Lake NY, Island Pond VT) some patchy
frost will also occur. Actually, that`s pretty normal for this
time of year. Based on trajectories, the airmass we`ll have
tomorrow morning was several hundred miles north of Montreal this
morning. Morning lows up in that part of Quebec were in the lower
40s. Thus, the idea of most of us seeing lower 40s for lows
(except 30s in higher elevations and colder spots and low 50s
right along Lake Champlain) still looks valid. I have made very
minimal changes to the low temperature forecast.
With the colder air moving in, we`ll probably start to see a
little bit of Lake Champlain effect clouds develop late tonight.
High pressure will continue to ridge southward over the area on
Saturday. Looking like a nearly wall-to-wall sunshiney day, with a
few patches of shallow daytime cumulus/strato-cumulus. With
temperatures aloft (925mb about 7C and 850mb near 2C), we are
looking at temperatures reaching only the lower 60s in the valleys
and staying in the 50s at higher elevations. This will give us a
rare day of below normal temperatures. Good boundary layer mixing
throughout the afternoon, so we`ll probably see some 15-20mph
gusts at times.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
-- Changed Discussion --As of 323 PM EDT Friday...Little change from previous couple of days
for the near term as we are still expecting the coldest night of
the early fall season to occur during this time period. Latest
guidance has trended slightly cooler for lows on Sunday night with
METSLK showing 19F and 38F at BTV. Synoptic pattern shows building
high pres from central Canada with dry northerly flow aloft.
Progged 850mb temps drop between 0c to -2c by 12z Sunday with
surface high pres axis across the Eastern Great Lakes. This would
suggest still some northerly gradient flow...which combined with
very warm lake temps...will produce some lake effect clouds and
keep temps near the lake slightly warmer. Thinking lows will range
from the upper 20s to mid 40s on Sunday morning...with areas of
frost in the colder sheltered valleys of the dacks and northeast
The upslope flow and leftover boundary layer moisture will
produce some fair wx cumulus clouds on Sunday...as temps warm into
the upper 40s mtns to near 60f valleys. A chilly night with clear
skies and light winds is anticipated for Sunday Night...with
widespread frost expected away from the Lake. Thinking lows will
range from the l/m 20s to near 40f...depending elevation and
closeness to the warm lake waters. Thinking even locations like
Williston...Milton and Highgate could experience some patchy frost
with a hard freeze likely for the Northeast Kingdom and Dacks.
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.LONG TERM /TUESDAY THROUGH FRIDAY/...
-- Changed Discussion --As of 323 PM EDT Friday...Guidance has trended toward a more progressive
mid/upper level flow across the northern CONUS for next
week...which places arrival of precip 12 hours earlier on Monday
Night/Tuesday time frame...but good news system lifts out quicker
for mid/late week. GFS has trended toward the ECMWF and NAM for an
earlier system arrival...so have increased pops to chance after
18z Monday for Saint Lawrence Valley. These pops quickly expand
east Monday Night into Tuesday associated with 50 to 70 knot flow
at 5h and developing low level jet of 35 to 45 knots. Thinking the
initial warm air advection surge will produce a period of
showers...with additional rain associated with surface boundary
and potent 5h vort on Tuesday. The dynamics look strong with good
deep layer moisture advecting ahead of digging mid/upper level
trof...so have increased pops to likely for Monday Night/Tuesday.
Initial guess on qpf looks to range between 0.25 and 0.75...which
is supported by pws around 1.5". Thinking highest pops and qpf
values will be in the mountains during this time period. After a
chilly start temps will warm into the mid 50s mountains to l/m 60s
warmer valleys on Monday with increasing clouds. A warmer night is
expected on Monday night associated with precip...clouds...and
southerly winds...mainly mid 40s to mid 50s...coldest northeast
Midweek...plenty of uncertainty with large scale synoptic
pattern...as models show very limited run to run continuity. Given
the complex and energized mid/upper level pattern....will continue
to mention some terrain focused pops/qpf for Weds...with a drying
trend for late Weds into Friday. Both GFS/ECMWF eventually show
mid/upper level trof being replaced by building heights and surface
high pres. This idea looks reasonable and supported by the latest
12z GFS ensemble data...with developing 1030mb high pressure across
the ne conus/mid Atlantic by late week. The combination of upslope
flow...lingering 850 to 700mb moisture...and weak low level cold air
advection with progged 850mb temps only btwn 0c and 2c...have cut
superblend numbers several degrees on weds. Thinking highs mainly
mid 50s to l/m 60s...with lows in the upper 30s to upper 40s. A
large swing in temps with cooler lows and slightly warmer highs can
be expected for Thursday into Friday with deep dry layer in place.
Overall...pattern will support near normal temps as we approach next
weekend....with dry conditions prevailing.
-- End Changed Discussion --
.AVIATION /20Z Friday THROUGH Wednesday/...
Through 18Z Saturday...Conditions run the gamut early this
afternoon. IFR all the way to VFR. All thanks to a frontal
boundary pushing slowly southeast across the region. Minimal
precipitation at this time, and though we`ll have a few more
showers in southern VT (mainly the RUT terminal), the
precipitation will not result in visibility restrictions. The
ceilings are the tough part of the forecast. As the front moves
south and the clouds start to dissipate, VFR conditions will
develop from north to south. I expect some TAF amendments will be
needed as Mother Nature decides to not follow our forecast
exactly. Overnight primarily VFR, but there could be some patchy
fog with MVFR/IFR developing. Think it`s primarily a MPV and SLK
situation, but there is some conflicting guidance for many other
locations in the region, so confidence is low on this aspect.
After any fog, Saturday will be VFR.
Outlook 18z Saturday through Wednesday...
18z Sat through 12z Tue: Mainly VFR. Overnight IFR with patchy fog
12z Tue onward: Potential MVFR with showers.