Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
134 am EDT Thursday Jul 30 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 this morning/...
as of 1014 PM EDT Wednesday...isolated thunderstorms across the
Champlain Valley and across northern LaMoille County during the late
afternoon/early evening - driven by very warm planetary boundary layer temperatures and
ororgaphic forcing - have dissipated with onset of diurnal cooling
cycle. With shortwave ridging in place through the overnight
period...looking for mostly clear and muggy conditions. Will see
scattered middle- upper level clouds from the west towards daybreak
associated with upstream frontal system. Otherwise...with
southerly low-level 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 (warmest in the Champlain valley). 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.
Noting 20-25 kts at slk around 900mb level by 06z...so should be
just enough turbulent mixing to mitigate nocturnal fog potential
in the valleys within the northern Adirondack region.
Short term /8 am this 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 Wednesday/...
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 /06z Thursday through Monday/...
through 06z Friday...other than patchy MVFR/br visibilities at
kslk and kpbg VFR conditions expected through 12z. After 12z
frontal boundary pushes through the area with showers/storms
possible from west to east in the 14-20z time frame. A few storms
may trend strong to locally severe with turbulence/wind from
kpbg/kbtv and points east. Brief IFR visibility/MVFR ceilings possible
with this activity. Showers/storms to clear eastern terminals by
21z. Winds light through 12z, then southerly from 6-12 kts and
occasionally gusty from 12z Onward, trending light once again by
Outlook 06z Friday through Monday...
06z Friday - 12z Sat: mainly VFR. Chance MVFR/IFR fog mainly at
12z Sat onward: mainly VFR. Chance shra/tsra.