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Area forecast discussion 
National Weather Service Albany New York
940 am EST Friday Dec 19 2014

Synopsis...
the area of low pressure that has been dominating our weather
recently will finally move northeastward away from the region today.
High pressure will build in from the west and will move over the
region over the weekend with mainly fair weather expected.

&&

Near term /until 6 PM this evening/...
as of 940 am EST...mostly cloudy skies persist across the
region...although some breaks in the clouds were developing across
the upper Hudson River valley. Some very weak radar
returns...suggesting flurries/snow grains...continue across
portions of the Schoharie valley/helderbergs and eastern
Catskills...with a few flurries occasionally extending into
portions of the capital region and Berkshires.

Breaks in the clouds may indeed expand southward within the Hudson
Valley this afternoon...as some subsidence in the wake of the
shortwave trough passing southward across the region this
morning combines with some downsloping off the Adirondacks. May
need to reduce cloud coverage with next update pending trends in
visible satellite/surface observation.

The flurries/snow grains will gradually sink southward through the
day...as low level winds veer more into the north behind the
passage of a weak reinforcing cold frontal boundary. Some weak low
level cold advection should prevent temperatures from rising
much...although if enough breaks in the clouds can develop/expand
southward...maximum temperatures could rebound by at least 3-5 degrees from
current levels in some valley areas. For now...still expecting
mainly Lower/Middle 30s in valleys from Albany north and west...and 35-40 to
the south...with mainly 20s across higher elevations.

&&

Short term /6 PM this evening through Sunday night/...
ridging builds in at the surface and aloft. The low level flow
shifts to the north and we lose moisture from Lake Ontario. Will
have decreasing cloud cover and diminishing winds setting the stage
for a cold night with temperatures dropping mainly into the lower
teens to lower 20s.

Expecting sunshine on Saturday with ridging dominating our weather.
Unfortunately cloud cover will be back on the increase Saturday
night and remain high Sunday as the upper ridge weakens and a weak
short wave trough approaches and crosses the region Sunday. Have
a slight chance for very light snow and rain in the forecast for
Sunday for areas mainly to the east of the Hudson River valley as
low level moisture off the ocean increases as the short wave moves
through. Seasonable temperatures are expected both Saturday and
Sunday. Sunday night heights rise aloft as ridging reestablishes
itself resulting in the surface high strengthening some. Cloud
cover is expected to decrease.

&&

Long term /Monday through Thursday/...
an active weather pattern is setting up for the long term period.

At 500 hpa...strong ridging will be developing just off the eastern
Seaboard...while a deep trough begins to develop and strengthen over
the central portion of the US. This will place our region in a broad
SW flow aloft...allowing milder air to work its way into our area. A
weak disturbance within the southern stream will be moving up the
middle Atlantic coast and off into the Atlantic for late Monday through
Tuesday. The models Don/T show a lot of quantitative precipitation forecast in our area with this
system...as forcing will remain weak and mainly south of the area.
Still...with an onshore flow...it/S possible for a period of light
snow or rain/snow mix for late Monday into Monday night...which will
transition into a light rain everywhere by Tuesday morning. Any snow
accumulation will be very minor...and generally confined to the
higher elevations. Both the surface and aloft temperatures look to warm up at
the same time...so p-type should transition from just snow to rain.
However...if surface temperatures were to remain colder for a longer period of
time...there could be a brief period of freezing rain as well. Temperatures
look to be in the 30s on Monday...and then hold steady or slightly
rise for Monday night into Tuesday.

The bigger weather impact will occur for Wednesday /Christmas
eve/...as the deepening trough takes on negative tilt...and surface
low pressure rapidly develops along an occluded/S fronts triple
point. This low looks to lift from the middle Atlantic towards upstate
New York and then back northwestward towards Ontario for Wednesday into Wednesday
night. The models are showing this system to become quite
deep...perhaps even lower than 980 hpa by Wednesday night. As a
result...we can expect a period of rain showers everywhere ahead of
the low and associated frontal boundary...along with gusty
winds...especially for the high terrain areas. Rain could be heavy just
ahead of the boundary...as there is the potential for a narrow cold
frontal rain band to develop. With a strong southerly flow ahead of
this system...temperatures will be very warm for late December...with temperatures
into the 40s to low 50s. We will have to monitor for locally heavy
rain potential...as well as gusty winds...and will continue to
headline this storm in our severe weather potential statement statement.

Colder air will work into the region behind the storm for late
Wednesday night into Thursday...but by that point most of the precipitation
will be done. There may be some lingering rain or snow showers
across far northern areas for late Wednesday night into Christmas day.
Temperatures look seasonable for Christmas day with highs in the 30s to
near 40...although gusty west to northwest winds will be in place
behind the storm.

&&

Aviation /15z Friday through Tuesday/...
an upper level trough is located just east of the region over
eastern New England. Cyclonic flow around this system is keeping
plenty of moisture and clouds in place with broken-overcast ceilings at around
3500-4500 feet for the valley terminals...and around 2500 feet at
kpsf...where some upslope flow is causing some lower clouds in the
Berkshires.

These low clouds look to remain in place through much of the day.
Ceilings may even lower to high end MVFR conditions around 3 kft for a
period in the morning hours. However...they should remain above IFR
thresholds...and no precipitation should occur today. There may be a brief
return to VFR ceilings for the valley sites in the afternoon...but lingering
low level moisture will allow for ceilings to lower back down to MVFR
levels for tonight.

West-northwest winds of around 10 kts will continue through much of the day
today...with a few higher gusts possible...mainly at kalb/kpsf.
Winds will lower to around 5 kts for tonight.

Outlook...

Saturday through Sunday night: no operational impact. No sig weather.
Monday: low operational impact. Slight chance of rain...sn.
Monday night: moderate operational impact. Chance of rain...sn.
Tuesday: moderate operational impact. Chance of rain.

&&

Hydrology...
no hydrologic issues anticipated into early next week as any
precipitation expected will be light. However...a widespread
rainfall is expected Wednesday/Christmas evening as a large low
pressure system moves across the region. Rainfall amounts are
highly uncertain 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...iaa
near term...iaa/kl
short term...iaa
long term...frugis
aviation...frugis
hydrology...iaa

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