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  Thursday September 20, 2018


NWS Area Forecast Discussion

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FXUS61 KBTV 181121

Area Forecast Discussion
National Weather Service Burlington VT
721 AM EDT Tue Sep 18 2018

Steady rains come to an end across southern Vermont this
morning, followed by a few showers this afternoon and early
evening as a strong cold front pushes south through the area.
Behind this front, variable clouds and cooler, more seasonable
weather is expected by tonight onward into Thursday. A brief
warmup is expected by Friday before another strong front brings
more cool weather for the upcoming weekend.


As of 721 AM EDT Tuesday...The forecast remains in good shape
and no changes were needed as of 700 am. Have a great day.

Prior discussion...
Changeable weather is on tap for today and is not without its
challenges, especially in terms of temperatures and cloud cover.
Current analysis places steady light to moderate rainfall
across eastern NY state into MA and the southern portions of
VT/NH associated with remnant moisture from once Hurricane
Florence. Expect this rainfall to continue across these areas
through mid- morning before tapering off by late morning. Little
to no precipitation is expected along and north of a
Ticonderoga, NY to Newberry, VT line this morning, with just
high clouds the rule. Total rainfall in Rutland/Windsor counties
from this event to generally range from 0.25 to 0.75 inches
with localized totals near 1 inch.

We`re also watching a strong cold front across southern ON/QE this
morning, which will drop southward into northern counties by early
this afternoon, and into southern VT by late afternoon/early
evening. In actuality there are two fronts - one in ON approaching
from the northwest, and another backdoor-type boundary surging
southwest from QE. This morning`s hi-res CAM output show these
features and their associated wind shifts quite nicely. In terms of
sensible weather the low to mid level flow will actually trend
northwesterly later this morning behind Florence`s remnants and in
advance of the front(s). This will allow an overall weakening of
boundary layer convergence and with limited instability only
scattered light showers are expected as these fronts pass. A number
of spots across the north may miss these showers altogether and
remain dry. High temperatures are a bit tricky as well given morning
rainfall and clouds south, and the frontal passage in the north by
early afternoon. Felt a blended solution of available bias-corrected
guidance and our running forecast was a best approach showing highs
ranging through the 70s to around 80.

Lingering showers then end over time this evening as cooler air
filters south/southwest into the area and variable clouds prevail
under a fairly sharp frontal inversion. Some patchy drizzle may be
possible in the higher terrain as low level moisture will be
abundant. Did lean away from the NAM MOS guidance in regard to
temperatures as it continues to suffer from a pronounced cold bias.
Overall, lows tonight should range from the upper 40s to mid 50s
north and mid to upper 50s south.

Variable cloudy skies then continue into Wednesday, though will tend
to erode by afternoon as mixing processes deepen and the
aforementioned inversion weakens. Some patchy morning drizzle may
linger along the eastern slopes of the Greens. Once again have
discounted cool NAM MOS guidance for temperatures, opting instead
for a blended solution incorporating at least some bias-corrected
data which offers readings from the mid 60s to lower 70s.


As of 324 AM EDT Tuesday...Cooler air will continue to filter down
from the north Wednesday night as high pressure crests
overhead. Bufkit forecast soundings indicating a stout
subsidence inversion between 750mb and 850 mb, trapping moisture
beneath. Low-level winds will become easterly through the
night, advecting in some higher moisture maritime air east of
the Green Mountains. Under this setup, expecting to see a
continuation of stratus clouds through the night in eastern
Vermont. Should still see some low clouds in northern New
York/Champlain Valley, but less moisture in the low-levels won`t
favor as widespread coverage. Low temperatures will be highly
dependent on cloud cover. Western portions of the forecast area
should see the coolest lows, while eastern portions will be more
moderated by cloud cover. Expect lows in the upper 40s to low
50s in Vermont, and upper 30s to upper 40s in northern New York.

Low-level flow Thursday will become increasingly southerly as a
warm front advances northeastward towards the forecast area.
High clouds will spread in from the west, thickening and
lowering throughout the day. At this point, it looks like
precipitation associated with the warm front will hold off until
Thursday evening, so have kept PoPs below 30% most of the day.
Rain showers should start Thursday evening in northern New York,
while Vermont will stay dry until Thursday night. Highs
Thursday will be in the mid 60s to low 70s.


As of 324 AM EDT Tuesday...A low pressure system tracking
northeastward from the Great Lakes Region through central Quebec
will control our weather Thursday night through the first part
of the weekend. The system`s warm front will spread some rain
through the forecast area Thursday night. Best upper-forcing at
this point will remain well to our north, but a large area of
synoptic-scale ascent over the northeastern US within the warm
air advection regime should allow most areas to see some
measurable precipitation.

By Friday morning, the forecast area will be solidly within the
warm sector of the cyclone, and a fairly warm, but windy, day
can be expected. 925 mb temperatures will shoot up to 20C.
Should see pretty good cloud cover through the day which will
limit solar heating, but the warm nature of the air mass will
support surface temperatures in the upper 70s. A 50+ kt
southwesterly low-level jet will be present within the warm
sector of the cyclone. As the boundary layer becomes
increasingly well mixed through the day, many areas will see
gusts in excess of 25 mph. Strongest winds will be in the Saint
Lawrence Valley and over higher elevations of the northern
Adirondacks/Green Mountains.

A cold front will sweep through Friday night/Saturday morning,
triggering some additional showers and an abrupt transition to
cooler, fall-like weather. High temperatures over the weekend
will only top out in the low to mid 60s. Nights will be cool and
crisp, with lows in the upper 30s to upper 40s.


Through 12Z Wednesday...Changeable conditions over the next 24
hours with a mix of VFR/MVFR. Steadier rains now departing
southern counties with any lingering -ra/-shras to end at KRUT
by 13Z. Some patchy MVFR at KSLK/KRUT currently, otherwise
mainly VFR/light winds through 15Z. Thereafter, two separate
cold fronts drop south into the area by this afternoon/evening
with scattered light shower activity expected. Scattered nature
of activity warrants only VCSH in the forecast at this point.
Winds shift from light south/southwesterly to northerly 6 to 12
knots behind the boundaries with cigs lowering to MVFR stratus
at northern terminals by later this afternoon and this evening.
Some patchy -dz also possible at favored locations.


Wednesday: Mainly VFR, with local MVFR possible. NO SIG WX.
Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. Chance SHRA.
Thursday Night: Mainly MVFR, with areas VFR possible. Likely
Friday: Mainly MVFR, with areas VFR possible. Likely SHRA, Slight
chance TSRA.
Friday Night: Mainly VFR, with areas MVFR possible. Chance SHRA.
Saturday: Mainly VFR, with areas MVFR possible. Slight chance





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