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Area forecast discussion 
National Weather Service Albany New York
712 PM EST Wednesday Dec 17 2014

Synopsis...
the combination of low pressure strengthening off the northern New
England coast...and an upper level disturbance passing through
overnight...will keep skies mostly cloudy along with some rain and
snow showers. Snow showers will be most frequent across the southern
Adirondacks and southern Vermont. Thursday will be blustery...
although some breaks in the clouds will be possible south of the
capital region. Slightly colder air will seep into the region from
the north for Thursday night and Friday.

&&

Near term /until 6 am Thursday morning/...
as of 645 PM EST...radar echoes associated with the first shortwave
trough moving through the region have been weakening during the past
hour...so decided to keep probability of precipitation mainly in the chance range for this
evening with some likely probability of precipitation across some higher terrain areas.
Otherwise have only made some hourly temperature adjustments to reflect
current conditions...and also increased the cloud cover for tonight.



Previous discussion...
we will have to watch radar trends closely overnight...as the
latest rap13 and hrrr suggest that a middle level low center
associated a compact yet potent shortwave currently passing over
southern Michigan possibly closes off somewhere across southern
areas as it passes quickly east/southeast. This may allow for some
additional middle level forcing/deformation across central and
northern portions of the region...mainly after midnight. This
additional forcing could allow for some bursts of snow to
occur...initially across higher elevations...then even across some
valley areas...from around the capital region north to the Lake
George/Saratoga region. This could allow for higher
accums...perhaps into the 2-5 inch range for some higher
elevations of the Adirondacks...southern Vermont...and western Massachusetts.
Also...many valley areas between Albany and Lake George could
receive a quick coating...to just under an inch of snow later
tonight.

Otherwise...the occluded front has passed east and north of the
region. However...two shortwaves...one currently located across the
central New York state/PA border...and another over the southern Great
Lakes...will continue translating eastward overnight. The first one
will allow showers to persist through this evening...especially
across higher elevations of the eastern Catskills...Taconics...and
Berkshires. Some light rain showers or drizzle will occasionally
reach the valley areas as well through early tonight. Cloud tops are
relatively shallow...with cloud top temperatures generally in the -5 to -8
c range or slightly warmer. So...at least for now...there appears to
be minimal ice crystals in the clouds...with just perhaps some snow
grains across the higher elevations over the next 3 hours.

Later this evening...the first impulse will pass east of the
region...with the next one poised upstream. The combination of
enhanced low level moisture from the nearby lakes...and additional
middle level moisture rotating southeast to south from north of the
Great Lakes should allow for some seeder feeder processes...in
addition to overall cooling middle level temperatures...to allow for a
transition to mainly snow showers across higher terrain...with
rain showers or drizzle gradually mixing with...and possibly
changing to snow or snow grains in some valley areas after
midnight. Again...overall cloud top temperatures may not be quite cold
enough for dendritic snow crystals...so snow consistency may be
somewhat grainy in nature...and not conducive for significant
accums. At this time...it appears that 1-3 inches will be possible
across higher elevations across the southwest Adirondacks...as
well as across higher...west facing elevations across southern Vermont.
Some locally higher amts could occur for elevations above 1800 feet.
Also...portions of the Berkshires could get 1-2 inches late
tonight...with perhaps slightly higher amts for elevations above
1800 feet in eastern Berkshire Colorado.

It appears that low level directional wind shear will prevent true
single banded lake effect snow to occur...but still expect a
combination of synoptic...and orographic effects to produce the
overnight snow in higher elevations.

Winds will increase from the west to northwest overnight...with
some gusts possibly reaching 25-30 miles per hour by daybreak...especially in
favorable channeled west/east valleys...such as the Mohawk River
valley...as well as in the Berkshires.

The combination of clouds...and increasing wind should prevent
temperatures from falling as low as the mav MOS suggests...and in some
areas...it is possible that temperatures may only drop to near or even
slightly above freezing...especially within the immediate Mohawk River
valley/capital region and upper Hudson River valley. Have
therefore went with...or above the slightly warmer met MOS for
overnight mins.

&&

Short term /6 am Thursday morning through Thursday night/...
Thursday...aforementioned second shortwave impulse should move
generally east of the region in the morning. However...some
lingering upslope snow showers will likely persist across portions
of the SW Adirondacks...southern Vermont...and western Massachusetts. Additional
accums of an inch or two could occur within the more persistent
areas of snow showers. Elsewhere...the main story for Thursday should
be gusty winds...which may gust up to 35 miles per hour or slightly
higher...especially in portions of the Mohawk Valley/capital region and
Berkshires. Although most areas near and north of Interstate 90
should remain mostly cloudy to overcast...some breaks of sun will
be more likely to the south...with skies possibly becoming mostly
sunny at times across portions of the middle Hudson
Valley...Litchfield Colorado CT...and possibly extreme southeast Vermont. In these
areas...temperatures could warm into the 40s. Elsewhere...expect mainly
30s in valleys...and upper 20s/lower 30s across higher elevations.

Thursday nt-Friday nt...a surface trough is expected to gradually settle
southward late Thursday nt into Friday...with a slightly colder...shallow
air mass in its wake. As the trough passes...it could allow for a
brief resurgence in snow showers/flurries...mainly across higher
elevations late Thursday nt. As winds shift more into the northwest to north in
the wake of the trough...any lake enhanced snow showers should
shift into the central New York state...perhaps occasionally grazing the
Catskills. Elsewhere...the potential for clearing skies will
increase in at least valley areas during Friday...with mainly
clear skies anticipated for Friday nt. Temperature Thursday nt should fall into
the 20s in most areas...with some teens possible across the
southern Adirondacks. Friday should be chilly...with maximum temperatures mainly
reaching the Lower/Middle 30s in valley areas...except near 40 across
the middle Hudson Valley and southern Litchfield Colorado CT...with mainly
20s to lower 30s expected across higher elevations. Friday nt should
be colder...with most min temperatures falling into the Lower/Middle 20s in
valleys...and teens across higher terrain.

&&

Long term /Friday through Wednesday/...
Saturday still looks dry with seasonably chilly temperatures. After
that...it looks as if we will be dealing with a mainly weak southern
stream disturbance...but then a potentially much stronger "phased"
system as head to Christmas evening.

The only day that we might see any some sunshine would be
Saturday...otherwise plenty of clouds will persist. Either way look
for highs from the upper 20s northwest to look to middle 30s south.

By Sunday...we will be dealing with an easterly flow from high
pressure anchored in extreme eastern Canada...as well as some sort
of weak wave developing well south in the jetstream. Also...there
might be an even weaker wave in the northern branch of the jetstream
that might interact with the southern one to develop some sort of
inverted trough late Sunday into Monday. This feature...combined
with an easterly flow...could trigger enough lift to produce what
looks to be nuisance type precipitation...mountain snow and a valley
rain/snow mix Sunday into Monday. Again...this is not going to be a
big storm but it could produce some slippery roads...especially
Sunday night and higher elevations. The timing of this possible
event is still uncertain so for now we have included slight chances
Saturday night...and low chances Sunday into Sunday night and slight
chances
Monday.

Highs Sunday will generally be in the 30s...above freezing in the
valleys. Lows Sunday night will be around 30 in most places. Highs
Monday again in the 30s.

By late Monday...the European and GFS forecast models are
forecasting a much stronger trough associated with the northern
branch to dig in the nation/S middle section. This trough is forecast
to interact with southern stream energy to produce what could be a
powerful storm as we head into late Tuesday and Wednesday.

The track of this storm looks to be along or near the Appalachian
Mountains...well to the west of the Hudson Valley. It would impact
our region mainly on Christmas evening. A storm with this track would
likely bring mostly rain...perhaps a little wintry mix on the front
side. As it moves up to our northwest...it would pull air in cold
enough to perhaps switch leftover rain showers into snow showers by
Christmas evening night.

This storm might bring some strong wind to the higher terrain
Wednesday...as it looks similar to the setup of the great
appalachian storm of 1950 as well as the "cleveland bomb" of 1978.
Heavy rain might trigger some Hydro issues as we still have a bit of
snow to melt in the mountains.

Being nearly a week away a lot of the synoptic setup could
change...but this storm definitely bears watching.

Highs on Wednesday look to be mainly in the 40s...dropping to below
freezing by late Christmas evening night.

&&

Aviation /00z Thursday through Monday/...
as a couple of shortwave troughs rotate across the region tonight and
early Thursday...widespread cloudiness will persist at the
kgfl/kalb/kpou/kpsf taf sites. On Thursday...after the second short
wave trough has passed through...clouds will slowly decrease.

For tonight...expect MVFR to VFR conditions at the kgfl/kalb sites...
with mainly VFR conditions at kpou. At kpsf...upslope flow combined
with the short wave troughs will produce MVFR to occasional IFR
conditions. On Thursday...expect kgfl/kalb/kpou to have a broken/overcast
VFR cloud deck...while kpsf is mainly MVFR due to the upslope flow.

Surface winds will be westerly tonight at 8 to 12 kts with some
gusts up to 20 kts...especially at kalb/kpsf. On Thursday the wind
speeds will increase to 10 to 15 kts with gusts of 18 to 25 kts.
Late in the day the speed will diminish.

Outlook...

Thursday night: no operational impact. No sig weather.
Friday: no operational impact. No sig weather.
Friday night: no operational impact. No sig weather.
Saturday: no operational impact. No sig weather.
Saturday night: moderate operational impact. Chance of shsn.
Sunday: moderate operational impact. Chance of shsn.
Sunday night: moderate operational impact. Chance of shsn.
Monday: moderate operational impact. Chance of rain showers...shsn.

&&

Hydrology...
no hydrologic concerns through the remainder of the week.

Additional light rain or snow showers will continue into tonight.
Basin average precipitation amounts will be light...generally less than a
quarter of an inch. Only very minor rises are expected on rivers
and streams...with most river flows expected to remain fairly
steady.

Some additional light mountain snow showers are possible Thursday
into Friday...but these very be fairly limited and won't have any
impact on area waterways. Temperatures look to be a little colder
for thurs/Fri...which will limit the amount of snow melt that
occurs. Mainly dry weather is expected for the weekend...with just
a low chance for some light snow.

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. 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...gjm/kl
near term...gjm/kl
short term...kl
long term...hwjiv
aviation...gjm
hydrology...kl

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