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Area forecast discussion
National Weather Service Burlington Vermont
1014 am EDT Mon Sep 23 2019

Synopsis...
a low pressure system moving through the Great Lakes will bring
periods of showers and perhaps some rumbles of thunder to the north
country today along with gusty winds. Somewhat drier weather is
expected tonight, before conditions take a turn for the worse on
Tuesday with scattered showers redeveloping and much cooler
temperatures expected as low pressure moves overhead. Dry weather
and seasonable temperatures return Wednesday under brief high
pressure, with showers returning for Thursday.

&&

Near term /through Tuesday/...
as of 951 am EDT Monday...no changes were needed with this
update. The first round of showers associated with the
prefrontal trough are crossing the region at this hour and
should exit to our east by this afternoon. Still anticipate a
second batch of showers and possible thunderstorms to move
through this afternoon ahead of the front. Note that Storm Prediction Center has
placed portions of our area, mainly the Adirondacks eastward
into central VT, in a marginal risk for severe thunderstorms
today. Given the jet dynamics, can't totally rule out a strong
wind gust or two out of any stronger convection today, but the
best shear and any severe chances looks to be just to our
south. Have left any enhanced wording out of the forecast as
chances of marginally-severe winds are low.

Previous discussion...for today, showers will be developing
ahead of the occlusion around daybreak across the St. Lawrence
Valley and shift across northern New York into Vermont during
the mid-day hours. Behind this initial batch of precip, there
will be a brief break during the early afternoon before the
surface boundary moves through the region reinvigorating showers
from late afternoon through midnight. Additionally during the
afternoon, surface instability increases to around 400-600 j/kg
which may help to develop some rumbles of thunder, but don't
think we'll see any cgs. Finally, surface winds will remain
gusty from the south/southwest, strongest across northern New
York this morning in the 20-30 mph range, with 10-20 mph
elsewhere. Highs will continue to be mild for early fall, and
run only slightly cooler than yesterday in the mid 70s to low
80s.

Occlusion/cold front moves through the forecast area this evening
with a strong mid-level dry slot shifting in behind it helping to
reduce coverage of precipitation for the first half of the night. As
the dry slot shifts east of the area after midnight, the core of the
upper low begins to shift in, first redeveloping scattered showers
across the Adirondacks early Tuesday morning, then across the entire
forecast area during the day as low/mid level lapse rates steepen
and the low centers overhead. It will certainly feel more like fall
after the past couple days of Summer-like temperatures, with
somewhat mild lows in the 50s tonight, followed by highs only in the
60s for Tuesday.

&&

Short term /Tuesday night through Wednesday/...
as of 354 am EDT Monday...fallish, upper low lifting east-northeast allowing a
shortwave ridge to move in on Wednesday. Any remaining shower
activity early Tuesday evening will be exiting with gradual clearing
Wednesday with nek being the latest. Highs will be at or above (aoa)
seasonable levels in the 60s/70.

&&

Long term /Wednesday night through Sunday/...
as of 354 am EDT Monday...after a week of ridging the active pattern
that began Monday-Tuesday will continue for the rest of this period
with a disturbance basically every other day. It's been dry lately
and although we'll be getting a chance of rainfall, the amounts
during this period are nothing that great. Meanwhile temperatures
will largely stay at or above seasonable levels for the period.

Wednesday night...upper level ridge already departing with SW flow
ahead of northern stream shortwave and surface cold front that will
approach Thursday. Whatever convective feedback issues on the GFS
calling for very strong lift and precipitable waters have disappeared. There will
be some decent lift but much is lifting north-northeast across Canadian border
and unfavorable timing may limit any chance of T-storms.

This system departs with southeast Continental U.S. Ridge attempting to build into the
northeast but New York/Vermont should stay in northern periphery and more
zonal flow thus allowing influence from northern stream or ridge
runners.

Friday looks dry with surface high pressure nosing across the area
with temperatures in the 60s to l70s. A weak disturbance along the
periphery of the ridge threatens Saturday.

Currently, timing differences doesn't allow US to elaborate an
all day threat or just in the afternoon. The GFS appears more
aggressive in a southerly push across the area with the
northern stream then the other medium range models. Given the
semi- permanent nature of this southeast Continental U.S. Ridge, i'm leaning
toward a less progressive, thus milder solution.

By Sunday...the above disturbance should be out of the region for
mainly dry conditions.

&&

Aviation /14z Monday through Friday/...
through 12z Tuesday...VFR with areas of MVFR across northern New
York is expected through the daylight hours as a surface front
approaches bringing periods of showers and gusty winds from the
south/southwest. The front shifts through the region later this
afternoon through midnight with some restrictions in vsby to
MVFR through midnight, before ceilings lower area-wide to MVFR
and potentially IFR after 06z. Gusty winds in the 15-25kt range
abate after 22z.

Outlook...

Tuesday: mainly VFR, with areas MVFR possible. Chance rain showers.
Tuesday night: mainly VFR, with local IFR possible. Slight chance
rain showers.
Wednesday: mainly VFR, with local IFR possible. No sig weather.
Wednesday night: VFR. Chance rain showers.
Thursday: VFR. Chance rain showers.
Thursday night: mainly VFR, with local MVFR possible. Chance
rain showers.
Friday: mainly VFR, with local MVFR possible. No sig weather.

&&

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

&&

$$
Synopsis...lahiff

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