Area Forecast Discussion
Issued by NWS Albany, NY

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596
FXUS61 KALY 221425
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
925 AM EST Sun Jan 22 2017

.SYNOPSIS...
A storm system will gather strength in the southeast U.S today into
tonight, before emerging off the mid Atlantic coast by Monday. This
system looks to bring significant precipitation to much of the region
from Monday through Tuesday. Colder air will filter in tonight,
which will result in the potential for snow, sleet, freezing rain or
rain. The best chance for accumulating snow and ice will be from
around the Capital District northward. Gusty easterly wind will also
occur as the coastal storm continues to strengthen just south of New
York City Monday night into Tuesday. The storm will finally pull
away from the region Tuesday night.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 925 AM EST...One major change with this update was to add
slight chance pops to all zones except chance pops across
southern Vermont as showers have developed ahead of a cold
front dropping southeast from northern New York and northern New
England. Still some fog around but not as widespread nor
visibilities as low as earlier and the trend will be for gradual
improvement. Skies however, unlike Saturday, will remain cloudy
all day. Temperatures will still be mild, but not quite as warm
as yesterday due to more expected cloud cover. Highs ranging
from around 45-50 from the Capital District south, to around
40-45 north.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
Tonight, attention shifts to a strengthening low pressure system
across the southern Appalachians. The system is already closed off
at 500 mb, with an abundance of severe convection across the Gulf
Coast states. Very strong jet stream energy feeding into this
system. The upper level low/trough is forecast to gradually become
negatively tilted late tonight into Monday, and the associated
surface wave is expected to emerge off the mid Atlantic coast on
Monday. This is a sprawling and intense storm system, with a complex
evolution with regards to thermal profiles.

The key feature to focus on tonight, with be colder air drifting
southward from Quebec/northern New England as high pressure builds
in across that region. Ageostrophic wind component will become
northerly and aide in pushing low level cold air southward into our
area tonight. Mainly dry conditions expected, although some light
snow/rain/sleet cannot be ruled out as the aforementioned back-door
cold front slides southward across the area.

On Monday, the sprawling and almost vertically stacked low will be
lifting northward across the central Appalachians, with an easterly
fetch starting to strengthen considerably to the north and east of
the emerging coastal low. The system has noticeably slowed in terms
of latest 00Z suite of model guidance, with the system cut-off from
the main flow and the upper trough becoming negatively tilted. So
trends in the 00Z GFS/ECMWF/NAM continue to delay onset of
widespread precip until Monday afternoon/evening, moving in from
south to north and this is now reflected in the gridded forecast.
Surface temperatures will warm into the 30s, but will start to cool
once precip commences due to wet bulb effect with sub-freezing dry
wedge in place.

Looking at area forecast soundings from the NAM and GFS, the other
significant trend in the 00Z model guidance is for a colder
magnitude and depth of the low level sub-freezing layer that will
set up Monday into Monday night. So as the expected heaviest precip
moves in Monday night, primarily a mix of snow and sleet is expected
across much of the area, with rain mixed in from around the Capital
District southward. Much lower confidence forecast than normal for a
coastal storm in January due to the complex thermal profile. A warm
nose aloft will gradually move in towards Tuesday morning, which
will allow for more of a mix. This is when the best potential for
some freezing rain will occur, again mainly across the higher
terrain west and east of the Hudson Valley. The wintry mix will
gradually change back over to snow west of the Hudson Valley during
the day Tuesday, as temperatures aloft cool. Precip types could also
be dependent on precipitation rates, with more snow during times of
moderate to heavy precip rates.

Best chances for at least a plowable snowfall will be across the
higher terrain areas of the eastern Catskills, southern Adirondacks,
and southern Green Mountains of Vermont. Raised snow/sleet
accumulations slightly in the Capital District northward to the
Saratoga/Glens Falls area too based on the colder model trends.
Snowfall forecasts are subject to chance based on even subtle
changes in the storm track and evolution of the thermal profile.
Also keeping in mind the strong easterly flow aloft will likely
reduce overall precip amounts in the Hudson Valley, but it is
unclear how much of a factor downsloping will be given strong
dynamics with this system. Probabilistic data shows a large spread
for potential snowfall, with as little as a trace to an inch, with
several inches possible for the maximum potential outcome. The large
spread indicates a high level of uncertainty with this system.

Besides the complex and moderate to heavy precip, strong northeast
winds will be prevalent from mainly Monday afternoon through Monday
night. The strongest winds will be across the higher terrain of the
southern Green Mountains, Berkshires, Litchfield Hills and Taconics
and possibly the eastern Catskills. Will mention mainly 35-45 mph
gusts for now, with possible advisory level gusts of 45+ mph. It is
uncertain if stronger winds will mix down with an easterly flow
regime, so will mention potential for a possible wind advisory in
the HWO.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
In the mean, sharp troughing across the Northeast quarter of the
CONUS will drive the weather through the period.

The long term will be marked by a trend toward cooler temperatures
and weak disturbances. Temperatures will cool from current levels
(yesterday the mean temperature in Albany was 24 degrees above
normal). Temperatures will still be well above normal to start with
daily departures running 10-15 degrees above normal on Wednesday and
Thursday, cooling to 5 degrees above normal by Saturday.

No significant storms are on the horizon. The storm impacting us in
the short-term will be moving away Tuesday night. A clipper system
tracks north of the forecast area on Wednesday night bringing a
wintry mix of light precipitation mainly to higher elevations. In
the wake of this storm, cyclonic flow will prevail for the remainder
of the period. In this regime, light precipitation mainly snow and
again most likely in the higher elevations.

So, in summary expect cooling temperatures, but still above normal
for late January, and light wintry precipitation.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
TAFs are quite a challenge this morning. Conditions are
improving at KPSF and KGFL, but getting worse at KALB and KPOU.
Generally abundance of low level moisture in place this morning
should keep low clouds around through at least much of the
morning. Have followed the near term trends at all terminals in
keeping prevailing IFR conditions at KPOU and KALB and MVFR at
KPSF and KGFL. TAFs allow for bouncing in and out of IFR through
the morning with some slow improvement this afternoon. Needless
to say, current forecast is low confidence.

Outlook...

Monday Night: High Operational Impact. Breezy Definite RA...SN.
Tuesday: High Operational Impact. Breezy Definite RA...SLEET.
Tuesday Night: Moderate Operational Impact. Chance of SHSN...RA...SN.
Wednesday: Low Operational Impact. Slight Chance of RA...SN.
Wednesday Night: Moderate Operational Impact. Chance of RA.
Thursday: Moderate Operational Impact. Chance of RA...SN.

&&

.HYDROLOGY...
Daytime temperatures will be above normal today, although morning
lows are around or just above freezing for most areas. As a result,
some very minor snowmelt may occur in a few areas, but it will
likely have little impact on rivers and streams.

Widespread precipitation will occur from Monday through Tuesday, but
there are still questions regarding the exact precipitation type and
amounts. The latest MMEFS only shows potential for some minor tidal
flooding at Poughkeepsie. Otherwise, just within bank river rises
are expected to occur, as frozen precipitation will cut back on
runoff potential.

Gradual cooling will occur through the rest of the week, with
chances for rain and/or snow showers through Thursday, and snow
showers from Friday into next weekend.

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.
NY...None.
MA...None.
VT...None.

&&

$$
SYNOPSIS...JPV
NEAR TERM...11/JPV
SHORT TERM...JPV
LONG TERM...OKeefe
AVIATION...OKeefe
HYDROLOGY...JPV



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