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Area forecast discussion 
National Weather Service Albany New York
912 am EST Monday Dec 22 2014

Synopsis...
a weak upper level disturbance may allow for some very
light rain or snow today. An approaching warm front to the west will
allow for a wintry mix changing to rain for tonight into
tomorrow. On Wednesday...a storm will organize in the Tennessee
Valley and intensify rapidly as it moves north to the Ottawa Valley.
It will bring a period of locally heavy rain and strong winds
Wednesday into Wednesday night...before tapering to showers for
Christmas day.

&&

Near term /until 6 PM this evening/...
as of 912 am EST...our region is in a broad S-SW flow
aloft...thanks to a building ridge just off the eastern
Seaboard...and developing trough over the central portion of the
Continental U.S.. a subtle upper level disturbance is moving within the broad
SW flow at 500 hpa...allowing for some weak lift over our area.

Kenx radar shows very light and spotty reflectivity returns...but
observations and web cam imagery shows some very light snow is
occurring in the greater capital region and parts of the Hudson
Valley. Will allow low probability of precipitation for light snow for this morning and light
snow or snow/rain mix for this afternoon...as this may continue
within the broad southerly flow in place. Any accumulation will be
limited to just a coating...as snow won't be persistent or heavy
enough to produce much more than that.

Satellite imagery shows plenty of cloud cover in place...and with
the prospects for little to no sun again today...and light
winds...highs in the 30s.

Some additional spotty light mixed precipitation is possible into
the Catskills...middle Hudson Valley and northwest CT late this afternoon as
another upstream storm system approaches.

&&

Short term /6 PM this evening through Wednesday night/...
warm advection and boundary layer southerly flow very gradually
increases as the system in the southeastern U.S. Affects our
region tonight. The bulk of the moisture and dynamics...and
isentropic lift look to be in eastern New York and western New
England...where chances for mixed precipitation in the evening
become likely after midnight and through the morning.

Precipitation types look tricky...and depend on how much the
warming boundary layer can influence the surface temperatures...
which could rise slowly between midnight and sunrise in some
areas. So...any temperatures above freezing late in the afternoon
and evening...could wet bulb just below freezing through the
evening and into the early morning hours with the patchy light
precipitation...then...again some areas could see temperatures
rise a little back to or just above freezing toward daybreak. The
Hudson Valley from the capital district through the middle Hudson
Valley and into parts of northwest CT have the best chance to be at or
just above freezing when the steadier precipitation arrives around
and after midnight. The strong low level ridging in southeast Canada
should keep draining some anchoring of the colder air in at least
areas north of the Mohawk Valley into the southern Green
Mountains.

As for precipitation types...patchy light snow and rain late this
afternoon and evening...transitioning to a mix of snow and
sleet...with a chance of freezing rain...then toward daybreak...
some areas will see a mix of sleet and a continued chance for
freezing rain. With the uncertainties as to what areas will see
likely freezing rain...no advisories at this time. Since the onset
of any potential freezing rain should be well after dark...and
could affect the Tuesday morning commute...a more focused advisory
could be issued later today...once areas can be determined that
will have freezing rain likely or better...as opposed to the
current chances for freezing rain.

The freezing rain threat will be addressed in the hazardous
weather outlook until any headlines are issued. All interests
should be aware..though that some portion of eastern New York...southern
Vermont and northwest CT will see a mix of precipitation tonight and early
Tuesday morning. Any accumulations of snow should be an inch or
less and any ice accumulations should mainly be a trace...but
generally under a tenth of an inch.

Stronger warm advection is expected Tuesday to change any mix to
just a cold rain with highs in the 40s. Temperatures fall a few
degrees Tuesday evening but stay above freezing along with more
periods of rain. On Wednesday...even a little warmer with still
more periods of rain and highs in the middle 40s to lower 50s. There
are indications that the increasingly strong winds at the
boundary layer may not mix down to the surface except in the
highest elevations. The timing of the passage of the cold front is
in question...but the temperatures still look to be well above
freezing for Wednesday night.

&&

Long term /Thursday through Sunday/...
the period starts out on Christmas morning with a cold front
attached to a deepening low pressure system racing eastward across
our region. There is good model consensus that the low will track
well to our north and west...deepening into a near 970 mb cyclone by
late in the day as it tracks into Quebec. Showers will accompany the
front as it clears the entire area during the morning...although
additional rain transitioning to snow showers are expected mainly
across the higher terrain of the Adirondacks the rest of Christmas
day. High temperatures will spike during the late morning or early
afternoon...then fall through the rest of the day. Early highs will
be in the upper 40s to lower 50s from the Hudson Valley eastward.
Temperatures will fall into the 30s and 40s during the afternoon.

The main concern across the entire area will be the potential
for strong gusty westerly winds in wake of the cold front passage
during the day Thursday. With the deepening low and cold advection
setting up...relatively deep mixing should be able to tap into the
50-60 kts core of winds aloft. There will be some slight
modification due to friction...but a windy day is expected with the
possibility for advisory or even warning level wind gusts. This far
out there is still some uncertainty with regards to the strength of
winds aloft and mixing heights...but there is enough confidence to
continue mention in the severe weather potential statement.

While it will still be breezy Thursday night...the potential for
strong winds will diminish as mixing decreases and the flow regime
becomes increasingly anticyclonic. Other than a few leftover snow
showers across the western Adirondacks...dry conditions will prevail
with temperatures cooling to at or below freezing across the region. Dry
weather will continue Friday into Friday night...as a ridge builds
along the eastern Seaboard. Temperatures will remain above normal...with
milder air quickly returning.

An area of low pressure is then forecast to track eastward across
southeast Canada Saturday into Saturday night...dragging a cold
front through our region. With limited moisture...just a few
rain/snow showers will be possible across the higher terrain.

Then much more uncertainty builds for Sunday...as there are vastly
differing model solutions yielding the potential for tranquil
weather /GFS/ or a possible fast-moving southern stream system
bringing widespread rain and/or snow /ECMWF/ to the region. Due to
low confidence...will mention chance probability of precipitation at this time and continue
to monitor model trends.

&&

Aviation /14z Monday through Friday/...
high pressure remaining anchored across the Canadian Maritimes
will keep a persistent low level easterly flow in place across the
region through the upcoming 24 period. A strong inversion in place
will allow for widespread ceilings mainly in MVFR range to continue as
well. Moisture associated with a weak disturbance south of Long
Island will continue to result in some -shsn limited to kalb. Some
IFR ceilings will be possible at kpsf for a few hours after sunrise.

A weak area of low pressure is forecast to track northward along
the eastern Seaboard tonight into Tuesday morning...which will
result in gradually increasing chances for either -ra/sn/pl/fzra
depending on the location. Best chance for -fzra will be at
kgfl/kpsf...with mainly -ra mixed with some -pl at kalb/kpou.

Winds will remain light...from the northeast-east up to 5 kts
through 12z Tuesday.

Outlook...

Tuesday night: high operational impact. Likely rain.
Wednesday: high operational impact. Definite rain.
Wednesday night: high operational impact. Definite rain.
Christmas day: moderate operational impact. Windy. Chance of rain showers.
Thursday night: low operational impact. Breezy. No sig weather.
Friday to saturday: no operational impact. No sig weather.

&&

Hydrology...
no hydrologic issues are anticipated through Tuesday night. A
widespread rainfall is expected Wednesday into Wednesday night as
a large low pressure system moves across the region. Rainfall
amounts of 1 to 2 inches are likely along with significant
snowmelt which raises the potential for minor flooding and
significant within bank rises of larger Stem rivers. Mmefs
guidance suggests the best chances for minor flooding would be
from the Hudson Valley through western New England. It is too
early to issue any flood watches...however will mention in the severe weather potential statement
at this time.

For details on specific area rivers and lakes...including observed
and forecast river stages and lake elevations...please visit the
advanced hydrologic prediction service /ahps/ graphs on our website.

&&

Aly watches/warnings/advisories...
CT...none.
New York...none.
Massachusetts...none.
Vermont...none.

&&

$$
Synopsis...frugis/NAS
near term...frugis/NAS
short term...NAS
long term...jpv
aviation...jpv
hydrology...NAS

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