Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 230620
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
220 AM EDT MON MAY 23 2016

.SYNOPSIS...
High pressure will move into the region overnight into Monday
with fair skies and above normal temperatures. Tuesday will see a
chance for showers for Vermont and northeast New York when an area
of low pressure lifts northeast along the New England coast. High
pressure will build into the region later in the week bringing
summer-like weather with warm temperatures and a chance for
afternoon showers and thunderstorms.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 201 AM EDT Monday...Fog will be the challenge of the evening
as latest 11-3.9 IR shows quite a few fog banks have developed
mainly along the river valley locations of Vermont that saw the
rain from yesterday. RAP forecast soundings capture the trapped
low level moisture and so I based most of the timing of the
mention of fog in the forecast off of RAP low level moisture. LAPS
surface analysis of dewpoint depressions (DD) shows 3 degrees or
less for nearly all of Vermont less than 1500 feet where as
northern New York is has DD`s of 4-7 degrees. This trapped
abundant low level moisture should keep patchy fog around through
5-6am before slowly eroding as surface heating begins and the fog
mixes out. Current forecast min Temps look right in line with the
obs trends so no changes we needed to the temp or winds forecast.

Previous discussion from 315 PM EDT Sunday...An odd pattern right
now with a 500 mb trough oriented NE to SW, and an upper low
closing off in the base of the trough and sagging southeast toward
the VA/NC coast by 12z Monday. Upper level flow is from the from
the northeast, and the few showers and thunderstorms that have
developed are tracking to the southwest. Lightning has mostly
skipped Vermont, occurring in NH and NY outside of the forecast
area in areas that have received more sunshine and instability
while Vermont had the morning clouds and sprinkles. Convection
will continue for a few more hours then taper off this evening. As
the upper low drops south away from the forecast area a narrow
ridge will topple over into the region from the west, and the
pattern will resemble a rex block through Monday. On Monday an
elongated narrow ridge of high pressure from the lower Mississippi
valley extends up across the Great Lakes into southern Quebec,
separating our southeast US closed low from the next trough of low
pressure moving across southern Canada.

Subsidence and some drying late tonight into Monday will allow for
wide temperature swings. With good radiation tonight temps to fall
into the 40s most areas to near 50 in the Champlain & St. Lawrence
Valleys. Some patchy light fog possible in the areas that saw some
rain during the day. Plenty of sunshine on Monday and 925 and 850
support high temps in the mid to upper 70s with full mixing of the
boundary layer. Light north winds during the day with surface ridge
axis positioned to the north of the area.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
As of 359 PM EDT Sunday...Forecast remains on track as the
vertically stacked low pressure system begins a slow northward
turn later Monday night, reaching an area east of NJ by daybreak
Tuesday. This should result in increasing mid-upper level cloud
cover and a low chance of showers across SE VT toward dawn on Tue.
Increasing clouds across VT will keep lows on the mild side,
generally in the lower 50s. May see some mid-upper 40s across nrn
NY and VT where clouds are thinner and less extensive.

The closed 500mb low tracks NNE across SE MA on Tuesday. System
is equivalent barotropic in nature, and likely will be associated
with bands of showers around the w/nw periphery rather than
broader zone of stratiform precipitation. PoPs 40-60 percent
highest across VT with precipitation amts 0.1-0.2, with lower
PoPs and lighter QPF across nrn NY further removed from the low
center. May see some locally heavier amts given PW values reaching
1.2" per GFS, and potential CAPE reaching 500-900 J/kg depending
on where breaks in the clouds occur which looks to be mainly on
the NW side of the upper circulation which is across VT. Some
model differences in exactly where the most instability will occur
as ECMWF and NAM a bit further east than GFS. In any event, a few
embedded thunderstorms will occur much like today. Deep layer NE
flow would result in slow W-SW storm motions if embedded
convection were to develop. Highs on Tuesday generally expected in
the low to mid 70s with 850 temps either side of 10C.

The upper low opens up and moves east Tuesday night with upper
level ridging moving in along with nighttime stabilization will
lead to some clearing and diminishing PoPs with lows mainly in
the 50s.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 359 PM EDT Sunday...A transition toward a warmer and more
humid overall weather pattern for the bulk of the extended
forecast period. Variability in the details of the GFS and ECMWF
makes daily details a bit uncertain. Still holding on to a low
chance of showers through Wed as a weak front and upper level trof
moves through with somewhat drier air following Wed Night. It
should remain dry Thursday but it looks like the front will return
as a weak warm front on Friday with a chance of showers and
thunderstorms, though GFS has convective bullseye affecting the
model output. Finally on Sat and Sun building heights reaching an
anomalous 588 dm and strengthening SW low-level flow should yield
a gradual increase in humidity with dewpoints getting into the
lower 60s by the upcoming Memorial Day weekend. With air mass
becoming more moist/unstable, PoPs continue generally 30-40% each
day. Highs generally continue above normal with highs in the 70s
to the lower 80s each day but if the current trends continue may
be even warmer by next weekend. low temps also showing a gradual
creep upward from the 50s to around 60 by the weekend.

&&

.AVIATION /06Z Monday THROUGH Friday/...
Through 06Z Monday...Clearing skies and trapped low level
moisture have enabled scattered areas of patchy fog to develop.
The residual moisture from the precip yesterday will continue to
aid in fog development especially at RUT and MPV. Both locations
have a well developed fog bank around the airport terminals and as
of 06z are 1/4SM with fog. Expect periods of IFR fog to be
possible for SLK/PBG/BTV as well through 10-11z this morning. MSS
should remain clear for most of the evening and the lack of precip
yesterday should preclude any visibility restrictions from fog
formation. Anticipate the low level moisture mixing out quickly
tomorrow and thus conditions should improve to VFR after 12z.
Winds will be light and variable overnight and then turn northerly
after 15z at 05-10 knots.

Outlook 06Z Tuesday through Friday...

06z Tue - 12z Thu: VFR with chance of afternoon showers Wednesday
with brief MVFR visibility restrictions.

12z Thursday - Friday: VFR/high pressure.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

$$
SYNOPSIS...Hanson
NEAR TERM...WGH/Hanson
SHORT TERM...Sisson
LONG TERM...Sisson
AVIATION...Deal



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