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Area forecast discussion 
National Weather Service Burlington Vermont
656 PM EST sun Dec 21 2014

Synopsis...
as a low pressure system moves east of the area this
evening...light snow will come to an end with clouds lingering
over the entire area tonight. Dry weather is expected on
Monday...but a south to southeast low level flow Monday night into
Tuesday will bring moisture into the region and a light wintry mix
of precipitation will be possible. Eventually the precipitation
changes to all rain Tuesday night with widespread rain on
Christmas evening along with windy conditions.

&&

Near term /until 7 am Monday morning/...
as of 656 PM EST Sunday...other than a few flurries here and
there...variably cloudy skies expected along with seasonably cold
temperatures. Some breaks possible here and there overnight...especially
in the St Lawrence Valley per satellite trends and 1 km above ground level rap relative humidity
forecasts. Minor adjustments to sky/temperatures to account for current
trends...but mainly noise level adjustments with current forecast
in good shape. Prior discussion follows. Have a great evening.

Prior discussion from 339 EST Sunday...
light snow associated with a small upper level low pressure
system is gradually coming to an end across south central Vermont
this afternoon with just cloudy skies expected overnight. The
clouds will keep overnight lows in the teens to lower 20s.

&&

Short term /7 am Monday morning through Wednesday/...
as of 339 PM EST Sunday...quiet weather is expected on Monday
with high pressure over the area and slightly warmer temperatures
with highs in the middle 20s to lower 30s. The main concern in the
short term will take place Monday night into Tuesday as low level
flow turns more to the south and southeast. This will bring
Atlantic moisture into the region. At the same time...the flow
aloft becomes more south and southwest with warm air advection
taking place. This will set up a thermal profile conducive to
mixed precipitation. Precipitation amounts will be light...but
nevertheless some light freezing rain is expected especially over
the southern portions of the area. Eventually the precipitation
becomes all rain Tuesday night with steadier rain and wind still
not expected until Wednesday.

&&

Long term /Wednesday night through Sunday/...
as of 357 PM EST Sunday...latest guidance still supports the idea
of rainy and possibly windy conditions on Christmas evening day into
the morning hours of Christmas day.

Wednesday morning the precipitation chance increases quickly as
the upper level trough deepens over the Midwest. A pulse of energy
will slide up the trough and then lift over the northeast bringing
categorical chances for rainfall on Christmas evening. The
strengthening southwest flow will be shifting more towards
southerly flow ahead of the trough. That will continue the
moisture advection into the low levels which will aid in the
development of a persistent rain event on Wednesday. The long term
guidance has continued the trend of weakening the 850mb jet over
the region and develop the system as more of a strong open wave
instead of a closed low. This will still provide for chances of
30-40 miles per hour gusts but without the eastern component the chances of
strong downslope wind gusts are weakening. The biggest area of
concern for localized high winds continues to be over the higher
terrain and perhaps along the western slopes of The Greens and the
Adirondacks.

As far as quantitative precipitation forecast amounts for this system...we still expect total
amounts to range from 1 to 2 inches across much of the region.
Amounts will vary a bit due shadowing in some areas and orographic
enhancement in others. Highest totals likely along south facing
slopes of southern greens and Adirondacks...with lighter amounts over
northwest Vermont and far northern New York. The guidance has been
fairly consistent that southern Vermont and the coastal areas of
New England would see more rainfall for this event. Flooding still
continues to remain a potential issue with this system. With
temperatures on Wednesday expected to reach into the upper 40s and lower
50s...and little drop off Wednesday night...the combination of
rain and mild temperatures will result in significant snowmelt. The
snowmelt combined with the 1-2 inches of rain could cause some
localized flooding in areas of poor drainage and in small streams.
Right now river gauges are showing river levels are quite low...so
while some minor flooding will be possible we don't expect
significant river flooding issues.

Rain continues early on Christmas day...then some drying expected with
passage of cold front during the morning. Lingering showers will
continue during the afternoon...and will transition to snow
showers over the higher terrain as colder air returns. Temperatures in
valleys remain mild though for much of the day with readings in
the 40s.

Drier conditions expected for Thursday night and Friday...with
just some lingering mountain snow showers. Shortwave trough brings
a weak chance of snow/rain showers to the entire region Saturday.
Temperatures Friday and Saturday are expected to remain above
normal with highs each day in the middle 30s to around 40.

&&

Aviation /00z Monday through Friday/...
through 00z Tuesday...general idea of MVFR to IFR conditions due
to low ceilings and occasional mist. Very light winds (under 10
knots) and saturated relative humidity conditions through a deep depth of the
atmosphere will favor periods of mist at most of the terminals
overnight. While ceilings will predominantly be MVFR through most
of the period...IFR ceilings will also exist but be most favored
at mss overnight. Any mist will burn off into Monday morning as
weak inversion dissipates but still expect there to be plenty of
MVFR ceilings around. Precipitation then approaches from the south
late in the taf period with vcsh indicated at rut. Any
precipitation that should initially fall would be in the form of
light snow, but be more likely after 00z elsewhere.

Outlook 00z Tuesday through Thursday...

00z Tuesday-12z Wednesday...periods of MVFR in light mixed precipitation.

12z Wednesday-18z Thursday...periods of MVFR/IFR in rain. Gusty winds possible.

18z Thursday-00z Friday...mostly VFR with MVFR possible in scattered
rain/snow showers.

&&

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

&&

$$
Synopsis...evenson
near term...jmg/evenson
short term...evenson
long term...deal
aviation...loconto/deal

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