Area Forecast Discussion
Issued by NWS Burlington, VT-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KBTV 202335
Area Forecast Discussion
National Weather Service Burlington VT
735 PM EDT Sat Aug 20 2016
A few isolated showers and thunderstorms will continue to across
the Saint Lawrence Valley of New York this afternoon before
diminishing late this evening. Sunday, a low pressure will drag a
cold front across the region bringing widespread showers and
storms to the entire area...especially in the afternoon and night.
High pressure returns bringing cooler temperatures and drier
.NEAR TERM /THROUGH SUNDAY/...
As of 352 PM EDT Saturday...Isolated showers and thunderstorms
will continue across the St Lawrence valley this afternoon and
evening as instability remains significant through the daytime. As
the sun sets and nocturnal cooling starts to settle in,
instability will decrease and convective activity will diminish.
With the night starting mostly clear, few areas of patchy fog
especially where rain occurs will be possible early in the night.
A low level south to southwest jet will move into the region
overnight along with tightening pressure gradient head of
approaching low pressure system. Expect winds to mix with some
gusts developing late tonight/early Sunday morning, especially in
the St Lawrence Valley. With increasing clouds and winds, expect
temperatures to remain mild with morning lows ranging from around
60 to low 70s. Cooler areas will be in the Northeast Kingdom as
this area is more removed from clouds (spreading west to east) and
low level jet may not reach this area til sunrise.
Generally expect precip ahead of low and associated cold front to
hold off til about 12Z, before spreading west to east, reaching
the Champlain Valley around mid day. With PWATs 1.5-2 inches,
showers and thunderstorms could produce periods of moderate to
heavy rainfall. Strong deformation zone will move into the region
18z into the early evening, which will help provide focus for
showers/storms and heavier rainfall.
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 356 PM EDT Saturday...Short term period picks up 00z Monday
with band of rain forecast to be mainly in Vermont and surface cold
front entering the St. Lawrence Valley. Bulk of precip out of the
area by 06z Monday with lingering showers in Northeast Kingdom until
12z Monday. Winds turn northwesterly behind the cold front and
temperatures begin to fall. Best cooling in the northern NY portion
of the forecast area with lows into the 50s. Vermont will just be
feeling the effects of the cold front by the time we draw the line
for overnight lows at 12z Monday, so lows will be limited to upper
50s to lower 60s.
By 12z Monday the surface front moves off the New England coast.
Cold air advection makes itself felt on Monday with daytime temps
struggling to recover against 850 mb temps dropping 10 degrees in 12
hours from 03z-15z Monday. As noted by mid-shift forecast limited
sunshine as well with moisture trapped by a strong frontal inversion
resulting in considerable cloud cover through the daylight hours,
limiting overall insolational heating. Base of 500mb trough centers
over the Champlain Valley around 15z on Monday then moves quickly on
east. As a result Monday the coolest day of the week with highs
mostly in the 60s.
High pressure builds at the surface with rising heights and plenty
of sunshine in low RH air early in the week, and a broad 500 mb
ridge sets up along the eastern seaboard with warmer southwesterly
flow developing. A warming trend through midweek, and
temperatures rebound to the 70s Tuesday.
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 356 PM EDT Saturday...By Wednesday the surface and upper
ridge are forecast to be east of the area with trough over the
central US. Southerly boundary layer flow and southwesterly mid
and upper level flow returning moisture and reinforcing the warmer
air. Not terribly hot with highs in the 80s but dewpoints creep
back up into the 60s by the end of the week.
Thursday into Friday a southwest to northeast oriented cold front
slowly pushes eastward out of the Great Lakes. Gridded model
guidance for Probability of Precip performed poorly Thursday,
with our blend of models bringing high chance pops in Thursday
afternoon. This is well ahead of the arrival of the surface
boundary and upper dynamics, with the region still under the
influence of the nearby ridge. GFS BUFKIT soundings that far out
show no instability to support pre-frontal convection. As a
result scaled back Superblend POPs significantly through Thursday
night, blending in a healthy dose of straight MOS guidance to
bring POPs back down. Allowed pops to increase Thursday night to
Chance category by Friday morning and remain at chance during the
day Friday with the frontal passage. Still out pretty far to try
timing things on days 6 & 7, but expect it to be similar to
tomorrow`s cold front and move through pretty quickly.
Temperatures Friday a little cooler in the upper 70s/lower 80s
with clouds and rain, and generally in the 70s Saturday.
.AVIATION /23Z Saturday THROUGH Thursday/...
-- Changed Discussion --Through 00Z Monday...VFR through the overnight and a large part
of Sunday, trending VFR/MVFR 18-00z Monday. Skies should trend
mostly clear across the St. Lawrence Valley. Short- range and
LAMP guidance continues to show MPV getting some MVFR stratus, and
while that can happen on prevailing SSE/SE flow current satellite
reveals no such lower ceilings around. Started to trend more
optimistically with ceilings. Appears that winds will also be too
strong to support any fog development tonight despite otherwise
favorable conditions. South winds 6-10 kts tonight.
VFR with lowering ceilings west-to-east and gusty south winds for
Sunday. Ceilings to lower to VFR/MVFR with the front with a timing
from 18-00z. MVFR moderate showers/thunderstorms expected
primarily along the frontal zone. By 00z Mon, front should be near
the Champlain Valley. Winds south 10-12 kts gusts up to 25 kts.
NOTE: Rutland AWOS (RUT) is not operating. Because of the lack of
disseminated observations, we continue our suspension of
amendments for the RUT TAF. Once the communication problem has
been resolved, and we again get routine observations automatically
transmitted, we will lift that restriction.
Outlook 00Z Monday through Thursday...
00Z Monday through 12Z Monday...MVFR with any showers and
t-storms. 12Z Monday onward...VFR.
-- End Changed Discussion --
As of 320 PM EDT Saturday...Southerly winds are increasing this
afternoon (10 to 20 knots) and expected to continue to do so
through tonight. The winds will reach peak strength by Sunday
afternoon, with winds frequently reaching 30 knots, especially
across the open areas of the broad lake. Some gusts are expected
to approach 35 knots. Additionally, showers and a few
thunderstorms are expected to develop during the afternoon hours
on Sunday and continue into Sunday night. Those planning on
boating this weekend, especially Sunday, should pay close
attention to the forecast.