Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
334 PM EDT Wednesday Sep 2 2015
an upper level disturbance and weak surface cold front will move
into the north country from Quebec and Ontario tonight. This system
will bring a period of mostly cloudy conditions overnight into
Thursday morning...along with a few rain showers and isolated
thunderstorms. Showers and isolated thunderstorms will increase in
coverage across south-central Vermont before exiting to our south
during early Thursday afternoon. Thereafter...a deep layer ridge
will return to the region. Temperatures will be closer to seasonal
averages on Friday with lower humidity...but the overall trend will
be toward very warm...moderately humid...and mainly clear conditions
for the Holiday weekend.
Near term /through Thursday/...
as of 331 PM EDT Wednesday...very warm afternoon in progress
across the north country with high temperatures generally reaching
the middle to upper 80s. Skies are mostly clear...and should remain
so through the early evening hours with just some passing cirrus
clouds...a few fair weather cumulus clouds...and a bit of haze
with dewpoints in the middle-upper 60s in most locations. Slightly
higher dewpoints are present in the St. Lawrence Valley...along
with some lingering areas of stratus clouds trapped beneath
relatively low subsidence inversion base (around 850mb). Winds
generally light and variable through this evening.
Visible satellite imagery reveals approaching weak cold front and
developing showers/thunderstorms across southwestern Quebec...well north and
west of Montreal. As upper ridge briefly weakens overnight...associated
shortwave trough and frontal boundary will shift southward reaching the St.
Lawrence Valley toward midnight...and shifting across northern Vermont
during the early morning hours Thursday. Passage of the boundary and
upper level shortwave is occurring during diurnal minimum in
convective instability. As such...most of the shower/isolated
thunderstorm activity will dissipate...and carried just a 20-30
pop overnight across northern New York into far northern Vermont associated with this
feature. Will see an increase in cloud cover...which will help
keep overnight lows quite mild...mainly in the low-middle 60s...with
a few upper 50s in the northern Adirondacks and far northestern Vermont. Arrival of
any significant cloud cover with the front may be late enough to
allow patchy fog formation east of the Green Mountains limited patchy
fog in the forecast to those favored areas across central and
Northwest-north wind shift and middle-level vorticity gradually push southward across Vermont
during the daylight hours Thursday. With daytime heating...will likely
see an expansion in the coverage of showers and a few thunderstorms
as frontal convergence reaches S-central Vermont...and ultimately exits
our forecast area during the afternoon hours. Have indicated areas
of 30-40 probability of precipitation across S-central Vermont during the middle-day period Thursday
before front exits. Behind the front...will see a slightly cooler
air mass with northerly winds around 10 miles per hour for the afternoon hours...along
with clearing conditions by early afternoon. Strong drop in precipitable water values
late in the day as well will be coincident with boundary layer
dewpoints falling into the upper 50s north and lower 60s south. High
temperatures several degrees cooler than anticipated highs
Wednesday...with Thursday seeing 80-85f most sections.
Short term /Thursday night through Friday night/...
as of 331 PM EDT Wednesday...deep-layer ridge becomes reestablished
across the north country with none probability of precipitation. Very quiet period...with
potential for some nocturnal fog 06-12z both Thursday night and
again Friday night...under mainly clear conditions. Daylight hours
Friday should be quite pleasant...with highs upper 70s to lower
80s under mostly sunny skies...and dewpoints back into the lower
50s. Low temperatures mainly in the 50s both Thursday and Friday
nights...but a few middle-upper 40s in the normally cooler spots of
Vermont/S Northeast Kingdom and within the valleys of the northern
Long term /Saturday through Wednesday/...
as of 235 PM EDT Wednesday...very warm and mostly sunny
conditions expected once again this weekend and into next week.
Upper level ridge parked overhead Saturday-Sunday will lead to
mostly sunny skies and well above normal temperatures. Highs
forecast 80-85 Saturday...increasing to 83-88 on Sunday with lows
generally upper 50s to middle 60s. Some fog development also likely
in the overnight/early morning hours in the favored river valleys.
The ridge will begin to slide southward Monday-Wednesday of next
week allowing for some westerly flow to return to the
region...with a possible weak system bringing the chance of a few
showers/thunderstorms on Tuesday. However partly-mostly sunny
skies and very warm temperatures will persist. Hottest
temperatures likely Monday with widespread 85-90 degree
temperatures (15-18 degrees above normal). Tuesday may be a couple of
degrees cooler with increased cloud cover and chances for showers.
Warmth persists into Wednesday ahead of a possible stronger system
late week with highs still 80-85. Lows upper 50s to middle 60s
through the period.
Aviation /20z Wednesday through Monday/...
through 18z Thursday...VFR expected through the remainder of today
with a few fair weather cumulus and scattered cirrus.
Tonight and into Thursday morning...clouds will increase along
with the chance of some showers along an approaching front. Will
just show vcsh for now due to isolated-scattered coverage. Lower
cloud deck associated with front currently located in Canada
expected to move southeastward and bring a period of MVFR (and
possibly IFR at slk) stratus Thursday morning. Fog/br development
will be hindered by increasing clouds but some still likely to
form at mpv and possibly slk. Winds generally westerly 5-7 knots
for this afternoon (except southeast at pbg with lake breeze)...become
light and locally variable tonight (except southeast at rut with drainage
wind)...before turning northerly on Thursday behind cold front.
Outlook 18z Thursday through Monday... mainly VFR. Early morning
vlifr/IFR likely at kmpv/kslk, and possible at kmss. Chance thunderstorms and rain
Thursday, mainly across central/southern Vermont.