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Area forecast discussion 
National Weather Service Burlington Vermont
747 am EDT Wednesday Jul 1 2015

Synopsis...
mostly cloudy skies with scattered showers and a few embedded
thunderstorms expected today as a trough of low pressure lifts
northeastward across the north country. A few stronger thunderstorms
are possible across Vermont this afternoon...and may produce gusty
winds and heavy downpours. As the low pressure area departs
northeastward across central Quebec tonight...a drier air mass will
move into the north country resulting in generally pleasant weather
conditions and low humidity for Thursday...Friday...and
Independence day.

&&

Near term /through tonight/...
as of 744 am EDT Wednesday...evolution of large convective mesoscale convective system
across southeastern New York and southern New England early this morning will likely
further limit out ability to destabilize this afternoon. Noting
the 06z NAM and btv-4km have lessened maximum cape values this
afternoon to 500-1000 j/kg across S-central Vermont with lower values
to the north and west. Forecast is largely unchanged...but
mesoscale trends are suggesting less potential threat of any severe
activity across Vermont this afternoon.

Previous discussion: amplified middle-level trough extending north-
south from southeastern Ontario across eastern Ohio/WV early this morning will
acquire slight negative tilt as it translates northeastward across New York late
this morning and across Vermont this afternoon. Moderately strong
height falls (by early July standards)...cyclonic flow and middle-
level differential vorticity advection will all contribute to
large- scale ascent and scattered to widespread shower activity.
It appears showers will be most widespread this afternoon...but
prevailing mostly cloudy conditions and cooling influence of
widespread showers make forecast maximum surface- based instability a
bit uncertain for the afternoon. Most of the numerical
guidance...including nam12/GFS/locally run btv-4km WRF indicate
SBCAPE values 1000-1500 j/kg across central and southern Vermont and
portions of the Champlain Valley...with generally 500-1000 j/kg
across northern New York. Southwesterly surface-6km shear is generally 25-30
kts...suggesting some storm organization if instability can
materialize as forecast. Would anticipate a few stronger
storms...mainly across Vermont...during the afternoon hours with gusty
winds and heavy downpours. Can/T completely rule out a severe
storm or two...with best potential central/S-central Vermont...but will
depend on development of surface based instability as best middle-
level forcing moves through central Vermont this afternoon. Storm Prediction Center 21z
calibrated sref probability of severe storms shows some low
potential across Vermont this afternoon (highest 18-21z) and initial 06z Storm Prediction Center
day 1 outlook carries 5% probability of severe hail/wind within 25
miles of a point. Will carry mention of sub-severe wind in the
grids and will continue to monitor mesoscale trends into the
daylight hours.

Highs today generally expected in the middle-upper 70s with dewpoints in
the 60-65f range. Gradient flow supports southerly winds 10-15 miles per hour
across most of the area late this morning through middle afternoon before
gradually diminishing this evening. Gusts 25-30 miles per hour possible this
afternoon.

Highest pop values generally this afternoon (70-90%)...and then
rapidly diminishing after 00z as middle-level trough axis shifts north
and east out of the area. Will see a westerly wind shift with a
modest accompanying cold front passing through 00-03z with temperatures
dropping back into the middle 50s for most areas. Should be enough low-
level flow and lingering clouds through at least the first half of
tonight to limit nocturnal fog development in most areas.

&&

Short term /Thursday through Friday/...
as of 317 am EDT Wednesday...deep-layer cyclone lifts out northeastward
across Quebec by daybreak Thursday. 00z GFS/NAM model soundings
indicate substantial low to middle-level drying in the wake of this
system in prevailing moderately strong westerly flow regime...and
should yield mostly sunny skies for the balance of the day. It
will feel pleasant with surface dewpoints falling into the middle 40s
by afternoon. Daytime mixing/insolational heating will result in
westerly surface winds of 8-14 miles per hour 15-23z. 850mb temperatures
around +8c and sunshine supports Valley High temperatures
generally in the middle 70s. No precipitation is expected.

Weak surface ridge builds into the region from the west Thursday
night and will be accompanied by 1000-500mb mean relative humidity values of 20-30
percent. All in all a quiet and mostly clear night with light and
variable winds controlled by local orographic effects. With moist
soil conditions...will likely see some patchy fog formation in the
favored valley locations 06-12z Friday. Good radiational cooling
will result in wide temperature range from the middle 40s across the
northern adirodnacks and Vermont/S Northeast Kingdom...to the low-middle 50s
in the Champlain Valley (warmest near lake champlain).

Continued pleasant weather conditions Friday/Friday evening with
maintenance of weak ridging surface and aloft and <30% mean
1000-500mb relative humidity values. 850mb temperatures moderate some to +10 to +12c and
should see valley highs in the upper 70s...but with continued low
dewpoints in the middle-upper 40s.

&&

Long term /Friday night through Tuesday/...
as of 340 am EDT Wednesday...latest trends have been for greater
uncertainty on chances for precipitation on Saturday and Sunday associated
with weak northern and southern stream systems.
Otherwise...excellent agreement with development of middle/upper level
ridge and surface high pressure for early next week...resulting in above
normal temperatures and dry conditions for Monday and most of Tuesday.
Have continue to mention schc to low chance probability of precipitation for Saturday
associated with very weak surface boundary and 500 mb vorticity in jet winds
aloft. Both GFS/European model (ecmwf) show weak ribbon of enhanced middle level
moisture impacting our northern zones...with very minimal
instability values. Have just mention showers with no thunder
at this time. Quantitative precipitation forecast will be very light and mainly confined to the northern
mountains on Saturday. Models disagree on Sunday...with latest 00z GFS
showing southern stream system coming close enough to provide our
region with light precipitation chances while European model (ecmwf) is mainly dry. GFS shows
better 850 to 500mb relative humidity fields...along with a deeper trough across
the northeast Continental U.S. On Sunday...resulting in some lift and weak
instability. Will keep forecast dry...but would not be surprised a few
showers/sprinkles develop during the afternoon hours on Sunday
from surface heating and weak instability. Any activity will quickly
weaken by sunset with temperatures mainly in the 70s for both Sat/sun and
lows in the 40s mountains valleys to near 60f cpv. Much warmer air
arrives Monday into Tuesday with prognosticated 850 mb temperatures near 15c by 18z
Tuesday...supporting highs in the middle 80s warmer valleys. Have
mention temperatures 3 to 5 degrees warmer than the superblend guidance
on Tuesday. Additional chances for showers/storms arrive late Tuesday
into Wednesday.

&&

Aviation /12z Wednesday through Sunday/...
through 12z Thursday...current radar shows a cluster of storms
with embedded lightning is impacting southern Vermont. These storms
will impact Rutland and mpv btn 12-15z with some lightning and
brief heavy rainfall and MVFR vis/cigs. Elsewhere...additional
showers with embedded IFR conditions are occuring over the
slv...and may impact mss through 15z. Expect a mix of VFR/MVFR this
morning with additional storms by early this afternoon. Some of the
stronger storms will be capable of brief gusty
winds...lightning...and heavy down pours...which will reduce visible
blw 3sm at times. Have used a tempo group between 16z and 19z to
cover thunderstorm potential this afternoon...with greatest
concentration of storms over our central/eastern taf
sites...btv/pbg/rut/mpv/slk. Slow clearing with VFR conditions
will develop by evening.

Outlook 12z Thursday through Monday... VFR with weak surface high
pressure...except for IFR in fog/br at mpv/slk between 06z and 12z Thursday
and again on Friday. Uncertainty on shower potential this
weekend...with latest trends showing the potential for additional
isolated showers Saturday and again on Sunday...with brief MVFR
ceilings possible at slk/mpv.

&&

Btv watches/warnings/advisories...
Vermont...none.
New York...none.

&&

$$
Synopsis...banacos
near term...banacos
short term...banacos
long term...Taber
aviation...Taber

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