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  Friday May 14, 2021

 

NWS Area Forecast Discussion


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FXUS61 KBTV 111815
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
215 PM EDT Tue May 11 2021

.SYNOPSIS...
An unsettled and cool weather pattern continues across the
forecast area today with scattered showers developing and
temperatures mainly in the 50s. Additional showers are possible
over Vermont on Wednesday, before a drying trend develops for
Thursday into Friday. Temperatures will be warming back into the
60s by Thursday with lows mainly in the in the mid 30s to mid
40s.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 215 PM EDT Tuesday...A special weather statement is in
effect for continued showers with embedded pea-size or smaller
hail/graupel across the region through at least 5 PM as cold
upper level trough axis gradually swings through the region.
Cloud tops have trended colder with steep lapse rates from the
surface through at least 10,000 feet, with surface-based CAPE of
around 250 Joules per kilogram estimated as of 1 PM. Low
relative humidity near the ground has promoted high cloud bases
(around 3000 feet) and very limited thunderstorm chances, but
with the low freezing level and cold cloud tops, we should
continue to see more hail reports through the day. Low wind
shear (about 15 knots in cloud layer) will continue to prevent
any strong winds or severe hail. Tweaked temperatures and
precipitation forecast slightly, but no big changes needed at
this time.

10 AM Update...Scattered showers in the vicinity of the Green
Mountains and Northern Vermont Piedmont have developed, with
brief light rain associated with these being observed as they
scoot eastward at about 25 MPH. Some showers also have formed
over parts of northern New York, so overall with this update I
have added a larger area of shower chances for this morning as
the expected scattered shower idea has developed ahead of
schedule. Still expect areal coverage to further increase this
afternoon, with no further changes needed to the forecast.

Previous Discussion...
Water vapor shows our next closed 5h/7h circulation just north
of Lake Superior with elongated 5h vort approaching the northern
Great Lakes. This energy and associated 7h ribbon of enhanced
moisture wl approach our northern cwa by 18z this aftn.
Expecting the areal coverage of widely scattered showers to
increase, especially near the International Border and expanding
southward by 00z. Based on steepening sfc to 3 km lapse rates
and moisture btwn 800-700mb, expecting high based cumulus cloud
field to develop btwn 15-18z today, which wl limit additional
heating/instability during the aftn hours. This idea results in
minimal CAPE values of 100 to 200 j/kg when best s/w dynamics
arrive, so while the thunder chances are not zero, the coverage
wl be minimal<10% and have not mention in fcst attm. Also, while
thermodynamic profiles are cold enough to support some
hail/graupel, uncertain exists if updrafts wl be strong enough
to produce this threat. The best forcing from 5h vort and axis
of deepest moisture arrives btwn 22z-03z acrs our northern cwa,
therefore have the highest pops of 45 to 60%, along with the
highest qpf values of 0.10 to 0.20 acrs the northern Dacks/Green
mtns. Temps today wl be cool with clouds developing and progged
925mb temp only in the 3-6C range, supporting upper 40s SLK/NEK
to mid/upper 50s elsewhere. Tonight, areal coverage of precip
decreases aft 06z with some low clouds possible, as modest llvl
caa continues on northwest 925mb to 850mb flow of 25 to 30
knots. The combination of pres gradient and clouds, should limit
frost formation acrs our fa with lows in the lower 30s to lower
40s. Weds...mid/upper lvl trof prevails with additional s/w
energy dropping acrs central/eastern VT, including the NEK btwn
15z-18z. This energy, along with 850 to 500mb RH > 80% supports
the idea of additional showers, mainly over VT. Have continued
with chc pops (35 to 45%) on Weds, as temps warm back into the
50s to near 60F.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 356 AM EDT Tuesday...For Wednesday night, quiet conditions
expected with deeper moisture departing eastwards. Anticipate a cool
night under northwest flow with lows in the 30s to near 40. During
the day, weather conditions will feel quite pleasant. Building
heights and increased atmospheric thicknesses should yield pleasant
temperatures amidst northwesterly flow. Anticipate highs to reach
the low to mid 60s. Late in the evening, a density boundary will
propagate southwards from Canadian surface high descending across
Hudson Bay in Canada. Some showers will develop with diurnally
driven instability across Quebec Province and shift southeastwards.
Depending on the strength of the incoming upper ridge, portions of
our forecast area could be affected, or the focus could shift east
towards New Hampshire and Maine. Thus, the most likely chances for
precipitation will be displayed for the Northeast Kingdom around 8
PM Friday, and slight chances will exist across the remainder of our
northern tier.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 356 AM EDT Tuesday...We are definitely transitioning towards
summer based on the weaker jet stream, along with the chances for
diurnally driven convection just about every day in the extended.
Synoptic models are depicting some convection on Friday; however,
the upper ridge will be shifting directly overhead. Thus, this
forecast will depict a slight chance for much of the region, but
better odds over the high terrain. Saturday looks a bit better for
afternoon showers, mainly since there will be warmer afternoon
temperatures in the lower 70s and an upper trough that will wash out
across the eastern US. Then on Sunday, a remnant surface trough will
shift across the region with some weak warm advection. There will be
more CAPE available, approaching 500 J/kg, but rising heights may
put a damper on convective development.

Heading into the new week, synoptic models diverge on forecasting
the speed and strength of two northern stream shortwaves. Monday
will likely be relatively dry as the upper ridge looks to be at peak
strength over the North Country, suppressing convection over the
area. How the middle of next week will play out will depend on
whether the upper ridge maintains strength or begins to break down
as these shortwaves translate eastwards. Ensemble prediction systems
offer no clear path for precipitation chances, but it seems likely
that temperatures will warm above seasonal normals.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Through 18Z Wednesday...Widely scattered showers may impact all
terminals during the TAF period, with better chances at MSS and
SLK in the 23Z to 03Z period with briefly reduced visibilities.
However, VFR conditions are expected through that time aside
from a briefly lowering cloud base to around 2500 feet. Deep
mixing will continue to support wind gusts mainly in the 17 to
22 knot range out of the west through about 03Z. After that
time, a modest frontal boundary will drop southward mainly
serving to lighten winds and allow for lowering ceilings. MVFR
conditions are expected for a few to several hours overnight
hours, although IFR ceilings are favored at SLK before stratus
lifts after 13Z. Mainly VFR conditions northwest winds promoting
some gusts upwards of 20 knots at MPV and PBG for the 12Z to 18Z
period, with additional vicinity showers mainly over MPV and
points north and east.


Outlook...

Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. Slight chance SHRA.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. Chance SHRA.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. Chance SHRA.

&&

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

&&

$$
SYNOPSIS...Kutikoff/Taber
NEAR TERM...Taber
SHORT TERM...Haynes
LONG TERM...Haynes
AVIATION...Kutikoff


 
 
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