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  Monday August 20, 2018


NWS Area Forecast Discussion

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FXUS61 KBTV 181430

Area Forecast Discussion
National Weather Service Burlington VT
1030 AM EDT Sat Aug 18 2018

A departing cold front will result in some lingering showers through
this afternoon, then the weather turns quiet with near seasonal
temperatures tonight through Monday as high pressure dominates.
Moisture will be on the increase Tuesday, and showers will
develop Tuesday/Tuesday night as a warm front pushes through.
Cold front passage will occur Wednesday, prompting a return to
drier, slightly cooler weather to finish out the work week.


As of 1030 AM EDT Saturday...Small adjustments were made to
hourly temperature/dewpoint trends through late this afternoon
using a blend of our official forecast and most recent LAMP
output. This suggests a slight lowering of maximum temperatures
across eastern/southern VT by a degree or two as clouds will be
slower to exit there today. The rest of the forecast remains
right on track. As an interesting side note, latest GOES-R
visible imagery shows a thin veil of smoke from western
wildfires continues to sink southward across far southwestern QE
and southern ON. Vertical smoke integration progs suggest this
area will settle south and west over time this afternoon, so
while skies will trend partly to mostly sunny by days end across
northern counties, the sky will take on more of a hazy/milky
appearance, especially across the SLV where a bright sunset may
occur given particle scattering.

Previous discussion...Scattered showers will continue through
the morning hours as a frontal boundary pushes southeastward
through the forecast area. Current analysis places the front
over the northern Adirondacks in New York, extending
northeastward through the upper Champlain Valley and across the
International Border. Water vapor satellite imagery shows a
mid/upper level shortwave lifting northeastward out of the
eastern Great Lakes and towards northern New York. This wave
will provide enough lift today to keep some scattered to
isolated showers ongoing after the frontal passage, so have
continued with the idea of a slower end to the rain showers as
previous forecasters thinking. By early afternoon today,
expecting northern New York to be mainly dry, but some showers
could still be loitering in Vermont. By the evening hours, most
of the forecast area will be dry as deep northwesterly flow is
established after the passage of the upper trough axis. With the
arrival of the cooler air and lingering cloud cover,
temperatures today will be relatively cool, topping out in the
70s in most locations. The Saint Lawrence Valley will see the
warmest temperatures as the earlier timing of the frontal
passage will allow for the best solar heating. Clouds will
linger the longest in eastern Vermont, limiting daytime highs to
the upper 60s to low 70s.

Decrease in coverage of clouds tonight/deep subsidence from
ridging/high pressure moving in will lead to the potential for
the development of patchy fog in the early morning hours,
particularly in climatologically favored valley locations. Lows
tonight will generally be in the 50s to low 60s.

Sunday looks dry as high pressure crests over the area. The
ECMWF had previously shown fairly consistent run-to-run
development of a compact coastal low along a trailing shortwave
off the southern New England Coast Sunday, but was consistently
the only model indicating this scenario. The 18.00Z run has now
backed off, coming into better alignment with the GFS/NAM,
resulting in higher confidence in a dry day Sunday and a
subsequent reduction in PoPs with this forecast package. 925 mb
temperatures Sunday will be a couple degrees warmer than
Saturday, and with plenty of sunshine during the day leading to
a well mixed boundary layer, this will translate to high
temperatures returning to the upper 70s/low 80s, warmest in
valley locations.


As of 329 AM EDT Saturday...Dry weather is expected through the
period as weak upper ridging builds into the region and keeps a
weak upper trough from moving up into our area. Based on
thermal fields at 925/850 mb looking at high temperatures on
Monday generally in the upper 70s to lower 80s. Lows Sunday
night will be in the lower 50s to lower 60s.


As of 329 AM EDT Saturday...We will see a gradual pattern
change take place Monday night into Tuesday as upper trough
takes shape over the Upper Midwest and the flow aloft downstream
over our area becomes more southwest with time. Precipitation
will become more widespread over time ahead of the upper
trough...but the bulk of it will not move across our area until
Tuesday night through the first part of Wednesday. Kept the
forecast dry Monday night and for most of Tuesday with chances
increasing into the 60-80 percent range everywhere Tuesday
night. Instability is limited and any thunder threat will be due
to dynamic contributions...and thus have only mentioned a
chance of thunder Tuesday night as dynamics are not that strong.
If there is any concern it would be for heavy rain and we will
have to watch for this potential. Precipitation ends from west
to east during the day on Wednesday with trough moving across
the area...but another upper trough will start to take shape
over the Ohio Valley on Thursday and keep us in southwest flow
aloft. Not much moisture is anticipated with this system and
have kept the forecast on Thursday and Friday dry for now. Above
normal temperatures are expected on Tuesday ahead of the upper
trough with at or slightly below seasonal normals for high
temperatures on Wednesday and Thursday. We should return to
seasonal normals on Friday.


Through 12Z Sunday...Currently seeing widespread MVFR/IFR
conditions as a front pushes through the area, bringing
scattered showers with some low clouds and restricted
visibilities. Will see improvement in flight categories throughout
the morning as drier air moves in from the north behind the
departing frontal boundary. By 21Z, expecting VFR conditions to
predominate and last through 06Z. Between 06Z and 12Z, will see
some patchy fog develop, leading to reduced visibilities at KMPV
and KSLK.

Winds will be northerly through the forecast period, 5 to 10 mph
today and then becoming under 5 mph tonight.


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


Showers will dissipate from west to east today as a frontal
boundary moves through the forecast area. Localized heavy
rainfall is still possible over southern VT as PW values in this
area are still near 2.0 inches. The threat for heavy rainfall
will decrease through the morning hours as the passage of the
cold front marks the arrival of drier air from the the north.
Rainfall amounts from yesterday through this morning have
generally ranged from 0.25 to 0.5 inches, with isolated reports
of up to 1.00 inch. This is well below flash flood guidance,
however will continue to keep an eye out for isolated flash
flooding and/or sharp rises on smaller streams and rivers as
showers continue through the morning.




SHORT TERM...Evenson
LONG TERM...Evenson

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