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Area forecast discussion
National Weather Service Burlington Vermont
453 am EDT Wed Jul 17 2019

Synopsis...
an active period of weather is expected across the north country
through Saturday. Showers are expected this morning with heavy
downpours possible over southern areas. A cold front drops south
from Canada and heavy downpours from showers or storms will be
possible this afternoon over northern areas. The cold front
pushes south tonight and drier weather is expected for Thursday
and Thursday night. Hot and humid conditions are expected on
Friday and Saturday. There could be some late afternoon and
evening thunderstorms on Friday. The best chance for
thunderstorms...some of which could be strong or severe...looks
to be Saturday afternoon and night.

&&

Near term /through Thursday/...
as of 453 am EDT Wednesday...first surge of moisture associated
with tropical system Barry is now moving into our area...mainly
across the southern sections. Flow aloft will be west to
southwest this morning and thus expect additional showers...some
with heavy downpours...to move across most of the area.
Precipitation shield is not continuous upstream but would expect
additional showers or isolated storms to move in across the
same areas getting the precipitation this morning. This could
enhance the potential for localized flooding given the high
moisture content...but not expecting widespread flooding. One
interesting trend is this afternoon the flow aloft becomes more
west and northwest which helps to bring down a cold front from
Canada. Thus northern areas that are not receiving much in the
way of precipitation this morning could see bursts of heavy
downpours from showers and storms ahead of the southward moving
front this afternoon. With precipitable water values around 2
inches the potential for localized flooding will exist later
this afternoon and into the early evening hours. With plenty of
clouds and precipitation over the area today high temperatures
will generally be in the 70s to around 80.

The front moves south of the area by about midnight and this
will help to bring precipitation to an end from north to south
during the first half of the night. Lows will generally be in
the mid 50s to lower 60s. Thursday looks to be a day of
transition with weak high pressure over the area and limited
forcing to inhibit convection. Thus most of the area should stay
dry with a return to south-southwest flow later in the day which
could develop a shower or two over parts of northern New York.
Highs on Thursday will be in the upper 70s to lower 80s.

&&

Short term /Thursday night through Friday/...
as of 453 am EDT Wednesday...dry weather is expected Thursday
night with lows in the 60s to around 70. Continued south to
southwest flow will allow for the return of higher dew points
Thursday night and this will continue into Friday. The idea of
hot and humid conditions for Friday looks real good with
noticeably warmer 925 and 850 millibar temperatures moving into
the region. Highs should be in the mid 80s to lower 90s and dew
points reach the 70 degree mark in the afternoon. The larger
valleys will be looking at heat index values in the lower to mid
90s and 85 to 90 in the mountains. These conditions will
increase the risk for heat related illnesses. Instability will
develop over the region in these conditions...but forcing will
be limited and ridging aloft will help to cap the atmosphere.
Cannot rule out the possibility of some late day convection
given cape values in the 1000-2000 j/kg range...but activity
should be isolated and with deep layer shear on the weak
side...any storms would be pulse in nature. Saturday appears to
be the day where storms are more likely and the threat of strong
to severe convection will exist as well. See long term
discussion for more details.

&&

Long term /Friday night through Tuesday/...
as of 453 am EDT Wednesday...latest suite of guidance offers
little changes to prior forecast thinking regarding the
likelihood of oppressive heat and humidity for the end of the
week/beginning of weekend. With warm and muggy conditions
expected Friday, and little relief from limited convection,
temperatures Friday night under generally light southwesterly
flow will keep nighttime temperatures from falling to
comfortable levels. St. Lawrence and Champlain Valley locations
will see lows only dropping into the mid 70s with upper 60s to
low 70s elsewhere. These warm nighttime temperatures will help
prime US for increased heat on Saturday as 925 mb temperatures
warm a degree or so from Friday. At the moment I am hedging on
the conservative side of guidance for Max temperatures given
signals for convection across our area on Saturday, however heat
headlines are looking increasingly necessary regardless,
especially across the Champlain and St Lawrence valleys. Current
heat index values are between 95-104, with a few locations
across Addison County likely to exceed these.

Both 00z GFS/Canadian and to a lesser extent 00z Euro (although 12z
Euro supported previous consensus) suggest active weather for
Saturday afternoon. Ingredients are coming together which indicate
the potential for strong/possibly severe thunderstorms: height
falls, shortwave energy, better wind shear, ample moisture and heat,
and a surface boundary are all present across the north country. The
presence of an eml only enhances the possibility for storms. In
contrast to latest guidance for Friday convection, cap on Saturday
is much weaker, and low level lapse rates are impressive given such
warm temperatures. With unidirectional 0-6 km shear ~30-35 kt expect
squall line/bowing segments as main storm Mode with primary threat
damaging wind gusts.

Sunday should bring relief from the stifling heat and humidity
however still expect temperatures to be above normal in the mid to
upper 80s, albeit with dew points in the 60s (not 70s). Chances for
precipitation remain Sunday as well as we are still under somewhat
zonal flow ahead of amplifying trough to the west. The well
advertised pattern change for next week continues to look likely
with broad upper level trough stationed over New England through
much of next week. Temperatures will return to near to slightly
below normal with chances for precipitation throughout the
period.

&&

Aviation /09z Wednesday through Sunday/...
through 06z Thursday...a mix of MVFR/VFR through the taf period
as remnants of Barry begin to move into the north country.
Deck of high clouds will begin to lower through the night with
ceilings becoming MVFR by 12z. Rain showers and potentially
some thunderstorms will develop after 10z. Expecting mostly
MVFR visibilities in these showers, however locally IFR may be
possible in heavier showers/thunderstorms with best chances at
krut and kmpv terminals. Winds during this time frame will be
generally out of the south between 5-10 knots. A cold front
sags south from Canada towards 22z bringing with it improved
conditions on northwesterly/northerly winds between 5-8 kts.

Outlook...

Thursday: VFR. Slight chance rain showers.
Thursday night: VFR. Slight chance rain showers.
Friday: VFR. Chance shra, chance thunderstorms and rain.
Friday night: VFR. Chance shra, chance thunderstorms and rain.
Saturday: mainly VFR, with local MVFR possible. Chance shra,
chance thunderstorms and rain.
Saturday night: mainly VFR, with local MVFR possible. Chance
shra, chance thunderstorms and rain.
Sunday: VFR. Chance rain showers.

&&

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

&&

$$

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