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  Tuesday August 20, 2019


NWS Area Forecast Discussion

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FXUS61 KBTV 180743

Area Forecast Discussion
National Weather Service Burlington VT
343 AM EDT Sun Aug 18 2019

Clouds with patchy fog this morning will give away to partly
sunny skies by mid morning with temperatures warming into the
80s by this afternoon. Once again a chance of showers and
thunderstorms will persist today, but areal coverage and
intensity will be less than on Saturday. Additional showers and
embedded storms are possible overnight into Monday, before a
mainly dry and warm day is expected on Tuesday. Much cooler and
drier air arrives toward the end of this upcoming week.


As of 323 AM EDT Sunday...Water vapor shows deep mid/upper level
dry layer acrs our cwa, however plenty of moisture trapped below
shallow subsidence inversion has resulted in areas of stratus
and fog across our cwa this morning. Expect these low clouds to
slowly burn off this morning, which may slow the rate of temp
rise for several hours.

Meanwhile, water vapor continues to show a complex mid/upper
level pattern across the Ohio Valley into NE CONUS, with
developing ridge aloft, while several pieces of short wave
energy tries to undercut the ridge. First piece of energy is
crntly over the central Great Lakes approaching western NY with
area of rain/embedded storms. This should slide by to our west
this morning/early aftn, but trailing vort lobe may produce a
few showers across our western cwa. Meanwhile, stronger short
wave energy is expected to lift from central NY into
central/southern VT btwn 00z and 06z this evening, with another
round of showers/storms. Soundings show instability parameters
are elevated with MU CAPE values of 800 to 1200 J/kg, mainly
across our southern CWA, while deep layer shear is in the 25 to
35 knot range. Thinking elevated convection is likely with
localized heavy rainfall possible, but given stable layer below
850mb, probably of winds mixing toward the sfc is minimal. Have
highest pops 40 to 60% toward 00z this evening across Essex
County NY into Southern VT, expanding northeast toward
central/eastern VT through 03z, before shifting east of our cwa
by 06z. Rainfall generally 0.10 to 0.25, but localized up to an
inch possible in the heavier convective elements. Temps will be
tricky today, as clouds will result in slow warming thru mid
morning, but expect breaks in the overcast to develop and temps
should warm into the upper 70s to mid 80s most locations. This
is supported by 925mb temps btwn 19c and 21c. Similar to
previous couple of nights, would not be surprised areas of
fog/br develop aft 06z, given saturated bl profiles and some
clearing behind departing short wave energy. Temps generally in
the 60s overnight with maybe a few values near 70f in the cpv
with some mugginess to the air mass.

Monday...Plenty of uncertainty with regards to thunderstorm
potential and timing of short wave energy and amount of
instability. ECMWF is later with arrival of short wave energy
near the international border and is most aggressive with cape
values approaching 2000 j/kg with favorable shear parameters
from approaching 850 to 700mb jet couplet. Meanwhile, nam/nam
nest is faster with s/w energy and passage of weak sfc
reflection, resulting in less instability and moisture profiles
and minimal threat for aftn/evening convection. Given
uncertainty in timing and potential magnitude will continue to
mention low chc pops for now from west to east across our cwa.
Progged 925mb temps warm another degree or two with values 20 to
22c, supporting highs mid/upper 80s cpv/lower ct river valley to
upper 70s/lower 80s mountain towns. Have noted in the high
resolution nam soundings, better mixing develops in the aftn,
which helps to mix drier air aloft toward the sfc and bl dwpts
drop into the low/mid 60s. This would help warm temps, while
mixing out the higher humidity values.


As of 301 PM EDT Saturday...Monday will be the warmest day of
the week as continued warm air advection allows 925mb temps to
climb to 22+ deg C, supporting surface temperatures in the mid
80s to near 90. Humidity will also be on the rise with dewpoints
rising into the upper 60s to near 70 as a warm front moves
through. Forecast soundings suggest afternoon mixing will reduce
dewpoints during peak heating hours, which will keep heat
indices somewhat in check...with heat indices in the upper 80s
to low 90s expected. Will have to watch the trends in cloud
cover with the warm front pushing through -if cloud cover is
more than expected we`d underachieve on afternoon highs. There
will be some showers and thunderstorms that pop up during the
afternoon hours amid the unstable air mass, mainly terrain
driven due to the lack of focused forcing. A cold front will
move through from the northwest to southwest early Monday
night, putting an end to any remaining showers as drier air is
ushered in from the northwest. The remainder of the night will
be dry with lows in the low to mid 60s.


As of 301 PM EDT Saturday...Forecast trending a little less
unsettled for the long term time range as the better instability
and moisture next week looks now to mainly stay to our south.
Most noticeable change to the forecast is to trend Tuesday drier
with rising confidence in high pressure building in at the
surface and subtle 500 mb height rises over the area. Although
925 mb temps won`t be quite as warm as Monday`s, solar heating
will offset the slightly cooler air and temperatures will again
rise into the mid 80s. Tuesday will, however, be noticeably
less humid than Monday given the drier air moving in from the
northwest. Wednesday and Wednesday night are still on track to
be rather wet as a cold front sweeps through, resulting in
showery conditions mid week. Once the front clears the area,
expect cooler and drier temperatures to return for the end of
the week with highs in the 70s and lows in the 50s.


Through 06Z Monday...Challenging early morning aviation forecast
with regards to low clouds and fog/br development. Crnt
conditions vary from lifr at slk/pbg to ifr for cigs at mpv to
vfr at btv/mss/rut. Thinking fog is most likely to prevail at
slk/mpv from 06z thru 12z or so, given saturated bl conditions
and crnt obs. Meanwhile, thinking intervals of ifr/lifr is
likely at pbg/mss and rut, given the recent rainfall and very
small temp/dwpt spread. At btv a period of mvfr with fog deck
nearby is possible around sunrise, but will continue to monitor
for potential clouds and associated impacts at all sites.
Otherwise, any ifr should lift by 12z with mainly vfr conditions
from 12z through 00z Monday, with some threat for showers/storms
aft 21z.


Monday: VFR. Chance SHRA, Chance TSRA.
Monday Night: VFR. Slight chance SHRA.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. Chance SHRA.
Wednesday: VFR. Chance SHRA, Chance TSRA.
Wednesday Night: VFR. Chance SHRA, Slight chance TSRA.
Thursday: Mainly VFR, with local IFR possible. Chance SHRA.





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