Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
300 PM EDT Wednesday Jul 29 2015
after another very warm day across the north
country...temperatures will remain mild tonight with lows from the
60s to lower 70s. A few thunderstorms will be possible over the
higher terrain this afternoon and evening...but more widespread
thunderstorms are expected on Thursday as a cold front moves
across the region. These thunderstorms will have the potential to
become strong to severe with gusty winds...hail...and heavy
downpours. Cooler weather returns on Friday as the cold front
exits the area Thursday night.
Near term /until 8 am Thursday morning/...
as of 244 PM EDT Wednesday...500-1500 j/kg of cape has led to the
development of some scattered cumulus and a few isolated
showers/thunderstorms this afternoon where enough lift was
generated to break the cap. This has occurred mainly across the
higher terrain and over portions of southern Canada. With minimal
shear (20-25 knots 0-6km)...no severe threat is anticipated.
Activity will wane as the sun sets and instability lessens. For
the rest of tonight...partly to mostly clear skies are expected
for much of the time...with an increase in clouds from the west
towards morning ahead of an approaching frontal system. May even
see a few showers approach Saint Lawrence County as sunrise nears.
With southerly flow gradually increasing and 925 mb temperatures
holding in the 22-24c range...temperatures will be quite
mild...with lows for much of the area in the 60s and lower 70s.
Some patchy fog possible across the valleys of eastern
Vermont...but coverage is expected to be less than previous nights
due to increased wind field.
Short term /8 am Thursday morning through Friday night/...
as of 244 PM EDT Wednesday...initial front/dew point boundary
will cross the region from west to east during the day Thursday
bringing a quick period of showers/thunderstorms. Current timing
looks to be 12-16z across the Adirondacks/Saint Lawrence valley of
New York...16-19z in the Champlain Valley...and 18-22z across
central and eastern Vermont. Greatest threat for any severe
weather will be from the Champlain Valley eastward into
Vermont...and especially points south and east of there. For much
of northern New York...frontal passage will likely be too early
for severe. Current models indicating roughly 500-1500 j/kg of
MLCAPE developing by 18z from the Champlain eastward...with 0-6km
shear of about 30-40 knots. While a widespread severe event is not
anticipated...this should be enough for some thunderstorm
organization with a scattered severe threat. Wind shear is mostly
Uni-directional from the southwest and parallel to the front...so
primary concern will be damaging winds from bowing segments. With
the early onset of convection...an official heat wave is not
forecast at btv...with highs for much of the region in the 80s.
Parts of southeast Vermont may be able to squeeze out another 90
Southwest flow continues across the region Thursday night as the
upper trough lags behind and eventually crosses early Friday
morning. Thus the cooler air will take its time moving in...and we
should be looking at lows in the 60s for most...except some 50s in
the normally cooler spots of the Adirondacks and Northeast
By Friday...westerly flow takes hold with mostly sunny
skies...however the next vorticity in cyclonic flow will already be
approaching northern New York by evening as a large closed low
takes hold across Hudson Bay. This will bring with it another
chance for showers/thunderstorms across northern New York...mainly
the Saint Lawrence valley. Wind field will actually still be quite
strong...so a gusty thunderstorm is possible. High temperatures
will be cooler...closer to the climatological normals...mainly
75-85f. The chances for a few showers linger into Friday night
across the north country.
Long term /Saturday through Tuesday/...
as of 259 PM EDT Wednesday...cyclonic northwest flow across eastern noam
will influence our weather through the period. In this pattern
temperatures will largely be seasonable with no expected heat.
Middle-level disturbance rotating in the base of eastern noam trough
will bring about chance/scattered -shra/-tsra Friday night through Sat. We/re still in
flow but more stable and weaker energy thus chances still there sun
but less so. Another sharper shortwave and surface cold front
approach Monday night/Tuesday with a better chance of rain showers/thunderstorms and rain then slight
height building as trough axis shifts NE should bring about drier
conditions middle week.
Again...temperatures will largely be seasonable through this period.
Aviation /19z Wednesday through Monday/...
through 18z Thursday...VFR conditions will prevail through the
period with scattered-broken middle/high clouds drifting through the region.
Southwest (except southeast at kpbg/krut) 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 at kslk but still possible at kmpv.
Showers/thunderstorms developing along/ahead cold front in northern New York
between 14-17z and after 17z in Vermont.
Outlook 12z Thursday through Sunday...
18z 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.