Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 210854

Area Forecast Discussion
National Weather Service Burlington VT
454 AM EDT Wed Aug 21 2019

Numerous showers and embedded thunderstorms return to the North
Country today. A few stronger afternoon thunderstorms are
expected with gusty winds, locally heavy rainfall, and frequent
lightning. A cold front will follow late tonight into Thursday
morning, bringing a few additional light rain showers. Canadian
high pressure building into the region will ultimately bring
noticeably cooler and drier conditions, with high temperatures
generally in the 70s Friday through next Monday.


As of 444 AM EDT Wednesday...Unsettled weather returns to the
North Country today with a few strong to severe thunderstorms
and a localized threat of flash flooding.

Early this morning, we continue to monitor the evolution of
convectively induced mid-level vorticity max across nern Ohio
and Lake Erie. Meanwhile, a developing sfc-850mb warm front and
strong surge of higher dewpoints/higher PW values is beginning
to develop newd in advance of the vort across s-central NY into
the Catskills. 850mb flow increasing to 25-30kt will aid in
moisture advection into nern NY and VT late this morning through
the afternoon hours. Overall, large-scale forcing will become
quite favorable for precipitation in the form of numerous
showers across our region late this morning through this
afternoon. However, the ongoing early AM arrival of mid- level
clouds and potential shower activity suggest that the surface-
based instability may remain limited, and may mitigate a more
significant severe thunderstorm threat. At this point, it
appears best juxtaposition of low-level moisture and mid-level
forcing will line up across the Adirondacks ewd across
central/s-central VT. With instability limited, the greater
threat may be localized flash flooding, especially if training
thunderstorms develop...which appears increasingly possible
given forcing along elongated east-west thermal/moisture
boundary across our southern zones. Also have noted warm cloud
depths near 12kft, so rainfall should be efficient with expected
convection. Have indicated average rainfall amounts of 0.50" to
1", but localized totals in excess of 2" are indicated in 06z
run of the NAM3km.

Could see a strong cell or two further north, but have lowered
daytime highs by several degrees (mainly 75-80F highs), and PBL
won`t be quite as favorable for severe activity with marginal
surface heating. Localized flash flood and severe weather trends
will need to be monitored through the afternoon hours.

Best synoptic support passes east of the region by 22Z or so,
and a trailing cold front will bring just a few additional rain
showers for the overnight hours into early Thursday morning.
Low temperatures tonight generally in the low-mid 60s. PBL flow
will shift into the west for Thursday, with 2-m dewpoints
falling back into the 50s by early to mid afternoon hours.
Included just 20-30 PoPs for rain showers, mainly across the
Adirondacks and Green Mtns, but should see partly sunny
conditions on balance across most of the forecast area.
Afternoon highs on Thursday will range from the low to mid 70s
for the Adirondacks and St. Lawrence Valley, to 75-81F from the
Champlain Valley ewd across central/ern VT.


As of 253 AM EDT Wednesday...Upper level trough and associated cold
pool will move through the area between 15-18z on Friday bringing an
increase in cloudiness and a slight chance for showers across the
far northern parts of the NEK. Very minimal elevated CAPE shown in
model soundings (barely even reaching 0 C in some locations) so
not expecting any thunder with these showers despite dry
adiabatic low level lapse rates. Winds remains generally out of
the west ahead of this shortwave passage so have kept
temperatures very near Superblend/MOS guidance with highs in the
mid/upper 60s to low 70s. Winds turn out of the NW behind this
front which will bring below normal overnight lows in the low
40s to mid 50s across the area.


As of 253 AM EDT Wednesday...No major changes to overall synoptic
pattern and therefore forecast for the extended with high pressure
in control through early next week. Highly amplified pattern builds
in towards the end of the weekend with large scale ridging and
subsidence across New England. Slightly below to near normal
temperatures expected Saturday/Sunday under mostly sunny skies. With
heights rising behind departing shortwave have offered a dry
forecast despite some guidance showing precipitation. After this,
model uncertainty increases after Sunday with differences in the
long wave pattern and quickness of large scale trough for midweek
next week.


Through 12Z Thursday...VFR conditions are expected through 13Z
with increasing mid to upper level cloudiness from SW-NE. After
13Z, combination of developing warm front across s-central NY
and approaching shortwave trough from the ern Great Lakes will
bring increasingly numerous showers and embedded thunderstorms
to the North Country TAF locations. During the 15-22Z period,
should see generally overcast conditions with a mix of VFR to
MVFR ceilings. Brief IFR intervals are also possible in any
heavier convective showers or thunderstorms. A few stronger
cells will contain gusty winds and brief heavy rainfall. Winds
will increase from the S-SW at 10-12kt, with gusts to 20 kt
possible at times at BTV. Should generally see a return to VFR
conditions tonight, though fog development is possible at
SLK/MPV 05-12Z Thursday.


Thursday: VFR. Slight chance SHRA.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: Mainly VFR, with local MVFR possible. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.




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