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Area forecast discussion
National Weather Service Burlington Vermont
303 PM EDT sun Apr 30 2017

Synopsis...
persistent, cool northerly flow along with increasing clouds
will keep Max temperatures in the mid 40s across the north
country this afternoon. A large strengthening low pressure
system over the Ohio Valley region will lift a warm front
through New England bringing scattered showers through the rest
of the afternoon and into this evening. By late Monday night the
low pressure system will bring a cold front through with the
potential for some embedded thunderstorms and gusty winds
starting a period of unsettled weather through the mid week.
Another low pressure system looks to affect the region late in
the week.

&&

Near term /until 8 am Monday morning/...
as of 204 PM EDT Sunday...light rain and even sleet has been the
theme of the morning as ridging aloft continues ahead of an
advancing warm front. Clouds have been on the increase
throughout the morning and will continue this evening.
Persistent northerly flow has kept the north country cooler and
with the warm air advection not anticipated till this evening I
did go ahead and continue to drop the near term temperatures
along with today's Max temp forecast to the upper 40s.

The warm conveyor belt of the maturing cyclone is easily viewed
on latest GOES-16 satellite and is pushing warmer air and
moisture through the Great Lake and into Ontario/Quebec in
Canada. During the evening hours tonight expect the warm front
to finally lift north and get into that more moist environment
and become the forcing for showers generally along the
international border.

As the aforementioned warm air advection arrives late,
anticipate temps warming throughout the evening as we move
solidly into the warm sector. Our overnight "lows" will be
reached right at 0z and we should warm into the upper 40s to low
50s west of The Greens. East of The Greens and in the northern
Saint Lawrence valley expect temps to be much cooler given the
local wind flow. We stay locked into northeast flow at Massena
which will mean temps end up 5-10 degrees cooler than southern
Saint Lawrence County. East of The Greens the winds stay
easterly which will be advecting in the colder marine layer and
thus low 40s can be expected though the overnight hours.

&&

Short term /8 am Monday morning through Tuesday/...
as of 253 PM EDT Sunday...expect an active pattern through the
early week as a cold front will move through during the late
afternoon/evening hours on Monday. A deepening low pressure
system will be tracking well to the west of the north country on
Monday with strong warm air advection surging into the region.
With the warm front to our north and the cold front still well
to our west, expect most of the day on Monday to be warm and
quiet setting the calm before the storm.

The cold front will begin to track into the north country
during the overnight hours and its quite robust with strong
surface convergence and sharp thermal 925mb gradient associated
with the front. A strong 850-700mb low level jet will develop
and track up the Saint Lawrence resulting in moderately strong
0-6km shear and with marginal surface based cape expect some low
topped convection to develop. The cam models show this well and
so tomorrow night expect a convective fine line to develop and
track through the Saint Lawrence producing gusty winds and brief
heavy rain. I did go ahead and add in the mention of heavy
rain/gusty winds into the weather grids as thunderstorm threats
for tomorrow evening. The dynamics aren't as strong as the fine
line moves into the Champlain Valley and the rest of Vermont so
I only mentioned those storm attributes for the Saint Lawrence
valley.

Showers will continue into Tuesday as energy rounds the bottom
of the upper level trough and moisture stays in place. Expect
isolated to scattered showers with some terrain enhancement to
persist throughout the day. With the synoptic flow oriented
southwest to northeast expect channeled flow up the Saint
Lawrence with gusty winds 20-30mph possible during the
afternoon hours.

Temps will be tricky on Monday. The low level flow east of The
Greens stays mostly from the east and so the marine airmass will
dominate keeping temps in the upper 50s to low 60s. Similarly
over the northern Saint Lawrence valley the flow will stay
locked into northeast and so temps will be some 15-20 degrees
cooler in Massena than it will near Tupper Lake and Wanakena. In
the Champlain Valley, we'll be the benefactors of strong warm
air advection and we should see temps rise to upper 60s to low
70s Monday afternoon. Overnight the temps will fall behind the
cold front but only marginally as the flow will still be
southwesterly so anticipate lows in only falling to the 50s
overnight. With the showers and cloud cover on Tuesday our highs
are only expected to rise into the upper 50s to low 60s.

&&

Long term /Tuesday night through Sunday/...
as of 303 PM EDT Sunday...forecast remains on track for a
rather unsettled pattern through much of the extended forecast
period. Upper trough moving across eastern Canada Tuesday night
into Wednesday will have enough dynamic support to enhance
precipitation chances across the area...especially over the
mountains. Plenty of clouds will also exist and this will keep
highs on Wednesday in the upper 40s to upper 50s. Wednesday
night into Thursday looks to be about the only dry period in the
extended as upper trough moves far enough away from the area
and high pressure builds in. Should see some sunshine and high
temperatures getting into the upper 50s to lower 60s...which
will be right around seasonal normals. The pattern then changes
significantly with rather large upper trough taking shape over
the eastern third of the country. This feature will be slow to
move northeast right through the weekend and eventually closes
off over the northeast and eastern Canada by later in the
weekend. Expect quite a bit of clouds and precipitation during
this period as pronounced southerly flow gets established
Thursday night into Friday for the first surge of widespread
rain followed by stronger dynamic support enhancing
precipitation once again Saturday into Sunday. The clouds and
precipitation will limit temperatures from falling significantly
and thus looking at temperatures generally at or slightly below
seasonal normals. Looks like colder air does not move in until
we get on the backside of the upper low early next week.

&&

Aviation /19z Sunday through Friday/...
through 18z Monday...VFR conditions persist with north-northwest winds
generally 10 kts or less throughout the daylight hours.
Increasing clouds from the west will thicken and lower, bringing
with it some scattered rain showers before a brief window with
no showers is expected for all sites expect mss. The rain will
become reinvigorated this evening and anticipate -shra
developing for mss and slk this evening. MVFR conditions are
expected to accompany these showers with potential for IFR at
kmss after 06z.

North-northwest winds less than 10kts persists for all but kmss which will
be NE channeling down the St Lawrence Valley at 10-15kts. Some
gusts may also develop in the afternoon at kmss. After sunset,
expect winds to shift out of the south for all but kmss.

Greater confidence for showers and potential IFR/MVFR
conditions exists with activity for tonight, as models show the
boundary during the daylight hours is trending further north.

Outlook...

Monday night: VFR/MVFR. Breezy. Likely rain showers...tsra.
Tuesday: VFR. Windy with gusts to 30 kts. Chance rain showers.
Tuesday night: VFR. Chance rain showers.
Wednesday: VFR. Chance rain showers.
Wednesday night: VFR. No sig weather.
Thursday: VFR. No sig weather.
Thursday night: VFR. Likely rain.
Friday: VFR/MVFR. Definite rain.

&&

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

&&

$$
Synopsis...deal

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