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Area forecast discussion 
National Weather Service Burlington Vermont
1033 PM EDT Wednesday Sep 2 2015

Synopsis...
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 /until 11 am Thursday morning/...
as of 1023 PM EDT Wednesday...showers have continued to struggle
to cross the Saint Lawrence valley so I trended back the forecast
just a bit. Otherwise the current forecast is in good shape with
some light fog developing in northern New York. With light cirrus
is moving in ahead of the front I expect it will temper how dense
the fog gets as we likely wont clear out enough ahead of the front
to bottom out complete. Temperatures and dew points are in good shape
moving forward with no additional changes needed.

Previous discussion as of 613 PM EDT Wednesday... showers
associated with a prefrontal trough are slowly moving towards the
east-southeast just to the north and west of Ottawa. Based on latest laps
analysis the area still is quite primed for instability as the
ridge briefing breaks down this evening. The front is still well
west of the forecast region and isn't expected until much later
this evening. The current forecast has these showers covered with
mention of scattered showers with isolated thunderstorms across
northern New York and the Vermont Canada border. Expect as the
showers finally begin to move into the north country that the loss
of diurnal heating will decrease our overall chances for showers
and so isolated showers can be expected in the late overnight
hours. Temperatures and dewpoints are in good shape with no changes
needed.

Previous discussion 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
eastern Vermont.

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 /11 am Thursday morning 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
Adirondacks.

&&

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 /03z Thursday through Monday/...
through 00z Thursday...this was a tough forecast given the
unusually warm and moist pattern we are in. Some showers are
ahead of a prefrontal trough and are slowly advancing towards the
Saint Lawrence valley so I did go ahead and include vcsh for both
slk/mss. Just out ahead of the showers there is quite a but of
haze that has already brought both mss and slk to MVFR
visibilities. Overnight as the front moves closer to the area
expect increasing clouds aloft and near the surface. Upstream observation
have shown some IFR ceilings in the 400-800ft range as the front
moves through but I dont have quite the confidence in those
ceilings. I did bring down most sites tomorrow as the front
crosses the forecast area to MVFR 2000-3000ft. Fog/br is tough
right now because as the front moves in closer the clouds will
hinder development but with the warm moist airmass we may not need
temperatures to drop below crossover to develop some br/haze at
mss/slk/mpv. I did include IFR visibility as a tempo group in at
both mpv/slk and continued MVFR at mss. The weak front will move
through overnight drying out the area but not by very much and a
wind shift from variable light southerly to out of the north
tomorrow isn't expected until late morning.

There will still be some lingering moisture around tomorrow so as
we pick up diurnal heating in the morning the front could
reinvigorate and develop scattered to isolated showers and
thunderstorms mainly across central and southern Vermont. Given
timing stuck with just mention of vcsh tomorrow mainly through
14-21z.

Outlook 00z Thursday through Monday... mainly VFR. Early morning
vlifr/IFR ceilings and visibilities likely at mpv/slk, and
possible at mss.

&&

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

&&

$$
Synopsis...banacos
near term...banacos/deal
short term...banacos
long term...muccilli
aviation...deal

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