Scientific Forecaster Discussion
fxus61 kbtv 171407
Area forecast discussion
National Weather Service Burlington Vermont
1007 am EDT Sat Aug 17 2019
scattered showers and thunderstorms will redevelop across the
region this afternoon, with some strong storms possible
containing gusty winds, heavy rainfall, and frequent cloud to
ground lightning. The warm and muggy conditions will continue
with highs in the mid 70s to lower 80s today. The chances for
precipitation will decrease on Sunday, but temperatures will
warm into the upper 70s to mid 80s. More unsettled weather is
anticipated for early this upcoming week, before cooler and
drier air arrives toward the middle of the week.
Near term /through Sunday/...
as of 1002 am EDT Saturday...forecast remains on track with
partly sunny conditions leading to surface-based destabilization
and potential strong thunderstorms this afternoon across nrn New York
into Vermont. Water vapor shows upstream 700-500mb shortwave trough
crossing Lake Huron into sern Ontario at 14z. We continue to
monitor ongoing showers and embedded thunderstorms across Lake
Ontario and far wrn New York late this morning...as this area of
large-scale forcing and upward vertical velocity will interact with developing
instability across the north country beginning early this
afternoon. Continue to expect enough sunny breaks for sfc- based
cape values in the 1000 to 1800 j/kg range, especially portions
of the central/southern cpv. Areal coverage of convection
should increase after 17z as dynamics arrive with S/W energy.
Only other change was to mention patchy fog areawide on Saturday
night/Sunday morning with soundings indicating plenty of
leftover bl moisture and lighter wind profiles.
Previous discussion below:
active overnight with areas of scattered showers and storms
impacting parts of our cwa associated with potent 5h vort
lifting across our fa. This activity should continue to impact
mainly central/eastern Vermont thru the next 1 to 3 hours, before
moving eastward. Main impacts have been brief heavy down pours
and cloud to ground lightning.
The challenge today will be how much clearing/instability can
develop along with the potential for strong storms. As we have
witness all convective season, not all ingredients coming
together for widespread/organized severe storms, but expecting
some strong convective elements with maybe a severe storm or
The main uncertainty is how much instability can develop, as
soundings show some lingering leftover low to mid level moisture
behind departing short wave this morning. This will limit sfc
heating this morning, while mid/upper level debris clouds advect
toward our cwa this aftn in moderate southwest flow aloft. These
different cloud layers will impact sfc heating/instability.
However, water vapor does show a potent 5h vort and associated
mid/upper level height falls across the central Great Lakes,
which will impact our cwa aft 18z today. This energy will
interact with moderate instability parameters and modest mid
level lapse rates to produce scattered to numerous
showers/storms. Href shows cape values in the 1000 to 1800 j/kg
range with highest values in the cpv, while 0 to 6 km shear is
in the 35 to 40 knot range. These ingredients combined with
height falls associated with vort should be enough to produce
strong storms, with a few isolated severe possible. Soundings
show steep sfc to 3km lapse rates with good mixing profile and
dcape values in the 500 to 800 j/kg range. Thinking as typical
the primary concern would be localized damaging thunderstorm
wind gusts up to 60 mph in the stronger convective elements.
Also, with dynamics and pws in the 1.50 to 1.75 range, localized
heavy rainfall is likely in the strongest storms, but storm
motions of 20 to 25 knots should limit flash flood threat. Have
mention gusty winds/heavy rainfall in grids, which matches well
with Storm Prediction Center marginal risk for day 1 outlook. Highs ranging from the
mid 70s to lower 80s, given clouds and threat for storms.
Tonight, areal coverage/intensity of convection will decrease
after sunset with areas of fog/br likely in the deeper river
valleys, especially locations that receive rainfall today. Temps
mainly in the 60s overnight with some values near 70f cpv.
Sunday...weak short wave ridge builds into our cwa, which
combined with limited forcing will reduce the chances for
showers/storms. In addition, pws drop behind departing S/W
energy tonight in the 1.20 to 1.40 range for Sunday, indicating
some dry air aloft across our cwa. However, still cannot
completely rule out a trrn driven shower/storm, with leftover
boundary draped across our cwa and some afternoon instability.
Areal coverage will be limited and have kept pops in the 20 to
30% range. Progged 925mb temps range btwn 20-22c, should support
highs upper 70s mountains to M/u 80s warmest valleys. Some
mixing of drier air aloft is possible per soundings on Sunday
aftn, so humidity levels will drop.
Short term /Sunday night through Monday night/...
a warm front boundary will move north of the area overnight Sunday
into Monday ahead of an approaching front for Monday night.
Scattered rain showers are possible during the overnight hours with
a slight chance for thunderstorms due to some weak elevated
instability. Increasing humidity, southerly flow and clouds will
keep nighttime temperatures above average across the area with lows
in the upper 60s to low 70s. Temperatures Monday warm into the mid
to upper 80s with humid and muggy conditions during the day as
dewpoints climb into the mid 60s.
Thunderstorms will be possible late Monday afternoon into the
evening as the aforementioned front moves across the area. A few
things area working against widespread activity... 1) questionable
available instability as there will be a lot of junky clouds around
Monday morning/early afternoon associated with any overnight rains.
If we are able to clear some areas out there will be plenty of cape
to work with (~1000-1500 j/kg). 2) surface boundary is lifting
northward as it passes over area, rather than digging south so best
dynamical forcing will be north of the area. And lastly, 3) amount
of available moisture along frontal boundary is rather meager. All
in all to say, there certainly is the potential for thunderstorms,
possible strong/severe given potential available instability and
decent shear ~30 but areal coverage and certainty regarding
intensity is just too difficult to say at this point. Based off
current progs, primary threats with any storms that do develop will
be damaging winds and small hail, along with locally heavy
Long term /Tuesday through Friday/...
period of active weather continues for the long term as several
shortwave impulses will pass through the region through middle of
next week. Tuesday will bring warm temperatures once again but with
lesser humidity values as westerly flow increases across the area. A
shortwave moving through the fast flow aloft will pass just south of
the area with just a chance for pops across our far southern
zones...much of the area will stay dry Tuesday. After Tuesday upper
level pattern shifts from zonal to a more amplified pattern as a
deepening upper level trough develops across the Midwest.
Precipitation chances appropriately increase ahead of this feature
for Wednesday as broad southwesterly flow advects high precipitable water air into
New England. Chances for thunderstorms exist Wednesday with
shortwave forcing, moisture and cape ~1000 j/kg. Relief from the
heat and humidity will arrive Thursday with temperatures in the mid
to upper 70s. A reinforcing shot of cool air will push through
Friday on northwesterly flow aloft.
Aviation /14z Saturday through Wednesday/...
through 12z Sunday...well it was a challenging night in aviation
as anticipated with flight categories ranging from VFR to vlifr.
Crntly fog with vlifr continues at slk, but has lifted at mss,
while IFR cigs prevail at mpv. Thinking fog lifts shortly aft
12z at slk, while IFR cigs linger until 15z at mpv. All sites
should eventually become VFR by 15z today with additional
threat for showers/storms developing by 17z. Periods of MVFR
cigs/vis likely with brief windows of IFR vis possible in the
heavier convective elements. Areas of fog with LIFR/vlifr
conditions likely at slk/mpv by 06z tonight with fog/br possible
at most other taf sites btwn 07z-12z Sunday morning, with the
combination of plenty of bl moisture and light winds.
Sunday: VFR. Chance shra, chance thunderstorms and rain.
Sunday night: mainly VFR, with local MVFR possible. Chance shra,
slight chance thunderstorms and rain.
Monday: mainly VFR, with local MVFR possible. Chance shra, chance
thunderstorms and rain.
Monday night: VFR. Slight chance rain showers.
Tuesday: VFR. Chance shra, slight chance thunderstorms and rain.
Tuesday night: VFR. Chance shra, slight chance thunderstorms and rain.
Wednesday: mainly VFR, with local MVFR possible. Chance shra,
chance thunderstorms and rain.