Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 190517

Area Forecast Discussion
National Weather Service Burlington VT
117 AM EDT Wed Oct 19 2016

A weak cold front with scattered showers will cross the area this
evening and tonight. The large scale pattern will become increasingly
unsettled across the North County by Thursday into Friday as we
transition into more seasonable cooler temperatures and showery
weather next weekend.


As of 1040 PM EDT Tuesday...Winds will remain moderately strong
until cold front pushes through...around 03-04Z for nrn NY and
04-06Z into the Champlain Valley. Looking for a W-NW wind shift
with the FROPA, and winds dropping off to 5-10 mph most areas. The
lake wind advisory for Lake Champlain has been cancelled. Scattered
showers continue to cross the region from W-E...with narrow band
of rain along the front extending from Chazy NY to Star Lake NY at
0245Z, moving east around 30kt. Rainfall amounts generally AOB
0.10" (a tenth was recorded at KMSS). Remaining quite warm across
wrn VT until FROPA...still 72F at BTV at 0245Z after a high of 81F
(25deg above climo avg high).

Previous discussion...This evening a weak cold front will
approach from the northwest with scattered showers developing
along an associated pre- frontal trough across northern NY
counties. Hires guidance shows two distinct bands moving through
one with the pre- frontal trough and then a second with the actual
front. However neither seems to be particularly heavy and so total
rainfall across the area will be on the lighter side. Given the
upstream conditions and some minor low level instability I did
continue to mention the chance for an isolated rumble of thunder
across the northern New York areas.

Once the front moves into the Champlain Valley the forcing weakens
and precip coverage should decline shortly after midnight as
front clears south. A weak ridge of higher pressure will begin
building in behind the front but the synoptic scale motion remains
from the southwest however, so there doesn`t seem as if there will
be a significant change in the atmospheric temperatures. Thus I
anticipate lows generally holding on the mild side in the 50s to
around 60.


As of 327 PM EDT Tuesday...Well advertised large scale synoptic system
will produce a long duration and widespread rainfall event across
our region starting Thursday morning and continuing into the
upcoming weekend. Initially the axis of heaviest rainfall will be
located over the Saint Lawrence Valley/Dacks on Thursday into
Thursday Night...before shifting into the Champlain Valley and
portions of VT on Friday.

Models in good agreement with potent 5h energy digging mid/upper
level trof across the Ohio Valley on Thursday...which is progged to
become negatively tilted and closed off. Meanwhile...a sharp
boundary will be draped across our region...with weak 5h short waves
moving along this boundary in the southwest flow aloft. Strong low
level moisture advection will occur as 925mb to 850mb south jet
increases between 35 and 45 knots...with nose of this feature
progged over northern NY thru 12z Friday. While right rear quad
of 140 knot jet at 250mb is lifting across southern
Canada...enhancing deep layer lift. The combination of nearly
stationary boundary with strong surface to 925mb convergence and
850 to 700mb fgen forcing...along with pwats surging between 1.25
and 1.75...thinking an axis of moderate to heavy rainfall is
likely Thursday afternoon into Friday. Based on moisture and
forcing profiles...1 to 3 inches of rainfall will be possible from
the Saint Lawrence Valley into the central/northern Dacks by 12z
Friday. Meanwhile...a general 0.25 to 0.75" will be expected
across northern VT...including the northern Champlain Valley
during this time period. Additional rainfall is likely for Friday
into Saturday.

Expecting a tricky temp forecast for Thursday/Thursday Night...based
on clouds/surface boundary and areas of precip. The combination of
northeast surface winds and plenty of clouds/precip...have cut
guidance by several degrees Saint Lawrence Valley and stayed close
elsewhere. Thinking with developing southeast downslope flow...some
warming will occur along the western slopes after the progged warm
front lifts north of region...but cooler air associated with
maritime influence is possible across eastern VT again. Bottom line
temps will range from the mid/upper 50s Saint Lawrence
Valley/Eastern VT to lower/mid 60s western slopes/champlain valley
on Thursday. Little change in thermal profiles expected Thursday
Night...with lows mainly in the upper 40s to mid 50s. Localized
gusts to 30 knots can be expected along the western slopes on
Thursday into Thursday Night...axis of strongest low level winds are
expected over northern NY.


As of 327 PM EDT Tuesday...Potent 5h vort will produce a strongly
negatively titled mid/upper level trof...which becomes closed off
and vertically stacked with deepening surface low pres by 12z
Saturday. The axis of heavy precip will shift from northern NY
into central/northern VT late Friday into Friday strong
cold front and upper level dynamics pass overhead. This should
produce additional rainfall across the Champlain Valley and
central/northern Vt of 0.50 to 1.0 thru 12z Saturday.

As system becomes vertically stacked and closed off from flow
aloft...a prolonged period of upslope precip is expected from
Saturday into early next week. How quickly system becomes closed off
and how fast it lifts to our northeast into the Canadian Maritimes
will determine how much deep Atlantic moisture can advect back into
our region. this moisture interacts with cold air
advecting on backside associated with brisk northwest winds...our
first accumulating mountain snowfall is anticipated by this weekend.

GFS is much more robust with deeper moisture...stronger upslope
forcing signature and associated heavier qpf fields...why 12z ECMWF
shows a shorter duration event with less qpf and forcing...will use
blend and mention likely pops over the weekend in the mountains.
Additional qpf will be between 0.25 to 0.75 with isolated higher
amounts near the summits. Between the synoptic and mesoscale events
from Thursday through Sunday...expecting total qpf of 1 to 3 inches
across the region with localized higher amounts possible. Given the
very dry conditions and long duration event not anticipating any
hydro related issues.

Snow levels start near summit levels on Friday Night...but as 850mb
temps drops below 0c by 06z Saturday and near 2000 feet by 12z
Saturday...expect snow levels near 2000 feet by 12z Saturday.
These temps profiles support accumulating snow with several inches
likely above 2000 feet by 15z Saturday. Favorable upslope winds
and moisture continue on Saturday into Sunday with progged 850mb
and 925mb temps near 0C...supporting additional accumulating
mountain snow. Thinking a few wet snow flakes are possible in the
valley floor on Saturday Night...but no accumulation. Given setup
and thermal profiles thinking 6 to 10 inches is possible near
summits above 3500 feet from Mt Mansfield to Jay Peak and over the
Northern Dacks...with 3 to 6 inches in midslope areas...and
dusting to 3 inches between 1500 and 2000 by Sunday. These early
season mountain snow accumulations are always tricky and complex
so stay tuned. Unlike earlier potential events this year...this
system will have favorable moisture in the snow growth region and
better cold air advection on back side.

Otherwise...below normal temps are expected this weekend with highs
mainly in the 30s mountains to 40s valleys with lows mainly in the
20s to mid/upper 30s depending upon location. A cold and raw weekend
is expected...especially with brisk northwest winds. Temps and
conditions slowly improve by early next week as trof lifts.


.AVIATION /06Z Wednesday THROUGH Sunday/...
Through 06z Thursday...BKN/OVC VFR cigs expected through 12Z with
cold front and scattered showers exiting south and east. Only
carried showers at KMPV/KRUT early, otherwise dry weather
expected. Only exception to VFR will occur at KSLK where MVFR cigs
will be likely through 12Z. After 12Z skies gradually trend
scattered, then SKC by 00Z. Winds veering to west/northwest from 5
to 10 kts today, trending light and variable by 00Z.

Outlook 06z Thursday through Sunday...

06z Thursday through 00z Friday: VFR under weak high pressure.

00z Friday through Sunday: MVFR/IFR as frontal zone and developing
low pressure bring widespread showers/rainfall to the area through
much of the period. Gusty north winds will be developing on Sunday
as well.




NEAR TERM...Banacos/Deal
AVIATION...JMG/Evenson is the U.S. government's official web portal to all federal, state and local government web resources and services.