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  Tuesday August 20, 2019

 

NWS Area Forecast Discussion


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767
FXUS61 KBTV 190510
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
110 AM EDT Mon Aug 19 2019

.SYNOPSIS...
A very warm and humid air mass will persist across the North
Country through Monday. A few showers and thunderstorms are
possible this evening, mainly across south-central Vermont. A
weak cold front approaching from the west Monday afternoon will
bring additional isolated to scattered showers and thunderstorms
to northern New York and Vermont Monday afternoon. High temperatures
on Monday will reach 85 to 90 degrees across valley locations.
Temperatures and humidity levels drop slightly on Tuesday, but
much cooler and drier air won`t arrive until Thursday.

&&

.NEAR TERM /UNTIL 2 PM THIS AFTERNOON/...
As of 102 AM EDT Monday...Have made some adjustments to pops
tonight into Monday based on radar trends and matched hourly obs
into grids. Radar shows initial isolated to scattered shower
activity exiting the NEK as of 05z, so have decreased pops
across most of VT. Meanwhile, a line of showers with embedded
storms continues across the central Great Lakes and approaching
the Buffalo area early this morning. Have utilized pop from
model reflectivity to highlight this band of showers/storms as
it moves from west to east across our cwa btwn 09z and 15z
today. Also, based on quick movement and large area of
subsidence building behind convective complex, thinking most of
Monday after morning showers/storms will be dry and have updated
pops to reflect this thinking. Otherwise, rest of fcst in good
shape with some patchy fog possible in climo favored areas
overnight.

Prior discussion...
Will be monitoring two potential periods of convective
precipitation during the near-term forecast period. Warm and
humid air mass in place (2-m dewpoints in the mid 60s) could
support a few strong thunderstorms this evening in association
with 700mb shortwave trough crossing w-central NY and nrn PA
this afternoon. Convective storms through 1830Z have been
limited to s-central NY into PA, but both the NAM-3km WRF and
BTV-4kmWRF indicate some additional northward convective
development is possible, with the greatest threat across
s-central VT between 23-03Z this evening. Included 30-40 PoPs
from Essex County NY ewd across Rutland/Windsor counties this
evening to account for this scenario. If isold convective storms
can develop northward, SBCAPE around 1000 J/kg and modest sfc-
6km shear (20-25 kt) could lead to a few strong convective wind
gusts this evening. We will continue to monitor. Otherwise,
continued southerly gradient flow combined with humid conditions
will make for a warm night. Overnight low temperatures are
generally expected to range from 65-72F, with the warmest
temperatures in the Champlain Valley. Some patchy fog is likely
as well, mainly across the valleys of central/ern VT and within
the northern Adirondack region. If rainfall occurs across
s-central VT, there will be increased potential for fog
development later tonight in that region as well.

On Monday, modest 700-500mb vort axis translates enewd across
nrn NY into VT during the daylight hours per 12Z GFS. This
modest feature combined with +16 to +17C at 850mb (thermal
ridge axis) could lead to some additional shower and
thunderstorm development during the daylight hours on Monday.
SBCAPE values should be higher than today, with valley high
temperatures in the 85-90F range contributing to SBCAPE values
reaching 1500-2000 J/kg. Absence of any significant height
falls and only weak upper support leaves overall intensity of
convective threat in question, as does modest sfc-6km shear in
20-25 kt range. Can`t rule out a few strong to severe storms,
but won`t include any enhanced wording with this forecast
package. Max PoPs reach 40-50 percent for Monday afternoon
associated with potential tstm activity. Also, it appears heat
index values will remain just below Advisory criteria, likely
peaking in the lower 90s in most locations. Highest heat index
values may touch 95F in the upper CT river valley, aided by 2-m
dewpoints near 70F.

Drier conditions expected Monday night with weak nwly wind shift
and lower deep-layer RH values settling sewd across the region.
Should set up additional nocturnal fog and some slightly cooler
low temperatures. Have indicated lows in the low-mid 60s across
VT, except upper 50s in the Northeast Kingdom. Across the
northern Adirondacks and St. Lawrence Valley, lows mainly in the
mid-upper 50s for Monday night.

&&

.SHORT TERM /2 PM THIS AFTERNOON THROUGH TUESDAY NIGHT/...
As of 303 PM EDT Sunday...Picture perfect late summer weather
expected for Tuesday with high pressure settling across the region.
Drier air will work southward from Canada behind Monday/Monday
night`s frontal passage. Thus expect plenty of sunshine, lower
dewpoints, and highs in the upper 70s to mid 80s. The dry weather
will continue into Tuesday night, though moisture will begin to
spread northward overnight as the flow turns to the southwest ahead
of a potent upper trough approaching from the west. A few showers
may move into southern Rutland and Windsor Counties late, but
overall expect any precipitation to hold off until Wednesday. Lows
will be in the upper 50s to mid 60s.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 303 PM EDT Sunday...Wednesday and Wednesday night are the focus
of the long term as a vigorous upper trough is expected to bring a
round of showers and thunderstorms to the region. However, still
uncertainty as to how things will play out since, as is usually the
case, parameters are not all quite optimally lined up. Moisture will
surge into the North Country during the day Wednesday, though how
much is in question. The GFS continues to show the highest PWATs
remaining to our south with a frontal boundary across coastal New
England, while the NAM indicate 1.5-1.75 inch PWATs streaming into
areas from the Champlain Valley eastward. This has implications on
instability, as does the 700-850mb warm layer indicated by the GFS.
In spite of increasing moisture, there does look to be quite a bit
of dry air to overcome aloft Wednesday afternoon as well. A
prefrontal trough will precede the cold front, which won`t arrive
until after peak daytime heating. However, this is a very dynamic
system, and 0-6km shear will be around 30kt. Have therefore gone
with likely PoPs for Wednesday evening, but subsequent shifts will
need to monitor for severe potential. Wednesday will be hot and
muggy as well with highs in the lower to mid 80s in many spots. The
front will push through Wednesday night, and precipitation will wind
down as a result. It`ll be one last uncomfortable sleeping night
with lows remaining in the 60s.

For Thursday onward...pleasant weather expected with high pressure
building across the region. The upper low will pivot across southern
Quebec Thursday-Friday, so a few showers will be possible,
particularly in the northern mountains. However, dry weather takes
hold through the end of the week. Conditions will be much more
comfortable as dewpoints will drop back into the 40s and 50s. Highs
will be seasonable, mainly in the 70s, though Friday could be a bit
cooler in spots as the upper low spins just north of the
international border. Overnight temperatures will be in the upper
40s to mid 50s.

&&

.AVIATION /05Z MONDAY THROUGH FRIDAY/...
Through 06Z Tuesday...Changeable conditions anticipated this
morning with a window of fog/br and associated ifr possible at
slk/mpv. In addition, line of showers/embedded storms will
impact our western taf sites btwn 09z-12z this morning with a
period of mvfr vis/cigs. IFR in fog/br most likely at slk
through 09z, however expecting conditions to improve as
clouds/precip and mixing develops with approaching line of
showers. Meanwhile, at mpv thinking fog/br develops btwn 06-07z
associated with window of clearing skies and light winds, before
lifting around sunrise. Elsewhere, mainly vfr conditions prevail
with approaching showers toward sunrise. Expect south/southwest
winds to increase behind showers at 10 to 15 knots with
localized gusts up to 20 knots at slk/mss and btv.

Outlook...

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

&&

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

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos/Taber
SHORT TERM...Hastings
LONG TERM...Hastings
AVIATION...Taber



 
 
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