Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1011 am EDT Wednesday Jul 29 2015
hot temperatures are expected once again across the north country
with highs in the upper 80s to lower 90s. A few thunderstorms will
be possible over the higher terrain this afternoon...but a much
better chance for thunderstorms will come on Thursday as a cold
front moves across the region. Numerous thunderstorms are
expected to develop over the northern Adirondacks of New York by
midday on Thursday and move east through the afternoon. These
thunderstorms will also have the potential to be strong or severe
with strong and gusty winds...hail...and heavy downpours. Cooler
and drier weather returns on Friday as the cold front exits the
area Thursday night.
Near term /until 8 PM this evening/...
as of 958 am EDT Wednesday...ridging aloft and at the surface will
provide for another mostly sunny and hot day. Do have some thin cirrus
spilling over the top of the ridge but not enough to obscure the
sun. Will also have a cumulus-field develop this afternoon...mainly over
the terrain. Low level thermal fields are about 2c warmer than
yesterday...which should result in temperatures about 3 degrees
warmer than yesterday. This will yield highs in the upper 80s and
lower 90s area-wide. The heat combined with dew points in the
middle/upper 60s will produce heat index values of 91 to 97 degrees.
The heat/humidity will also lead to the development of between
500-1500 j/kg of MLCAPE. Most of the region should remain
capped...but the higher terrain may produce just enough lift to
trigger an isolated shower or thunderstorm or two. With only
limited wind shear (20-25 knots 0-6km)...a severe threat is not
Short term /8 PM this evening through Friday/...
as of 414 am EDT Wednesday...we are still looking at the threat
for strong to severe thunderstorms on Thursday across much of the
area. A sharp cold front will move into the Saint Lawrence valley
by midday. The moisture gradient associated with the front is
rather sharp...so this boundary will be a good source of lift as
it moves eastward Thursday afternoon. The atmosphere will
destabilize in advance of the front with with highs in the middle
80s to lower 90s and dew points will into the 60s. Still expecting
this to result in cape values in the 1000-1500 j/kg range. What
continues to stand out is the increasing deep layer shear over the
top of the cold front and instability axis to support the
development of organized storms which based on the strength of the
instability and shear...should become strong to severe. At this
time...thinking storms form over the northern Adirondacks and
quickly intensify with the Champlain Valley and remainder of
Vermont having the best chance to experience the strong to severe
storms. Will include the mention of gusty winds...hail...and heavy
downpours in the forecast. Narrow band of storms exits the area by
early evening and with cold front also exiting the area...cooler
and drier weather should move in for Thursday night and Friday
with highs on Friday closer to seasonal normals.
Long term /Friday night through Tuesday/...
as of 310 am EDT Wednesday...little overall change from previous
forecaster thinking in regards to the upcoming pattern for the
extended period with medium range global models remaining in good
agreement depicting a large-scale polar upper low taking residence
over hudsons Bay. This leaves the northeast in a persistent broad
upper trough with several pieces of weak shortwave energy moving
through the flow aloft. First piece moves through on Saturday and
this energy combined with daytime heating may trigger a few
showers and/or thunderstorms, though with the lack of any strong
forcing and limited deep layer moisture rainfall should be showery
in nature and on the light side. Best chances for showers/storms
during the period still look to be Monday and especially Tuesday
as a couple stronger shortwaves shift through the region as the
upper low digs slightly southward from James Bay into the Great
Lakes. This will allow a weak cold front to move across the area
as a better focus for precipitation. Temperatures through the
period will be near normal with highs in the middle 70s to lower 80s,
and lows in the middle 50s to lower 60s.
Aviation /14z Wednesday through Sunday/...
through 12z Thursday...VFR conditions will prevail through the
period with scattered-broken middle/high clouds drifting through the region.
Light winds early this morning become west-southwest (except
southeast at kpbg) at 5 to 10 knots through the day, going calm
again after 00z. Winds just off the surface pick up tonight ahead
of an approaching cold front which should inhibit any fog.
Outlook 12z Thursday through Sunday...
12z Thursday - 00z Fri: VFR with brief MVFR/IFR in showers/storms.
Isolated severe turbulence/winds/hail possible.
00z Friday - 12z Sat: mainly VFR. Chance MVFR/IFR fog.
12z Sat - 00z Mon: mainly VFR. Chance shra/tsra.