Area Forecast Discussion
Issued by NWS Albany, NY

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FXUS61 KALY 200914
AFDALY

Area Forecast Discussion
National Weather Service Albany NY
414 AM EST Fri Jan 20 2017

.SYNOPSIS...
A weak disturbance will bring some light precipitation to the
area late today and tonight, mainly as rain. However across
portions of the southern Adirondacks into the Lake George region
and in parts of southern Vermont there is chance of freezing
rain. Fair weather returns for much of the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Inversion and moisture layer supporting the cloud cover is very
apparent in area 00Z soundings. Satellite trends show holes in
clouds in central and eastern New England closing as cloud cover
remains persistent. Extensive clouds in NY and CT not showing
signs of mixing out either. High clouds along the leading edge
of the approaching weakening system are slow to advance. The
southern and western edge of the cloud cover seems to be mixing
out along the leading edge of the high clouds approaching the
NY/PA/NJ border. Some of that clearing could occur over our
region later this morning or afternoon as the high clouds
continue to advance.

Winds will be light, so mixing will be limited. Temperatures
still have a good chance to get at least into the lower 40s, but
mid to upper 40s southern areas and upper 30s northern areas.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/...
Weakening upper energy tracking northeast out of the TN/OH
valley and Appalachians will affect our area tonight with good
coverage of precipitation advancing into the eastern Catskills
to mid Hudson Valley. As the precipitation builds north and east
it should steadily shrink in coverage so that the Mohawk Valley
to Capital District and Berkshires to NW CT will see just
chances and some areas of the southern Adirondacks and Lake
George area small to slight chances.

Temperatures slowly cooling tonight will support some possible
mixed precipitation north of the Mohawk Valley into southern VT.
Lows tonight in the 30s but near or just below freezing in the
southern Adirondacks, Lake George area and southern VT. If newer
data, guidance and trends show better coverage of mixed
precipitation in northern areas, a winter weather advisory may
be needed for pockets of possible freezing rain. Will mention
possibility in HWO.

Precipitation exits around daybreak and with steady west
boundary layer flow, there could be breaks in the clouds with
intervals of clouds and sun. So, dry weather and highs Saturday
potentially well into the 40s, with around 50 to lower 50s
southern areas.

Upper low begins it initial approach to our region from the
northern Gulf coast states and SE US Sunday and Sunday night.
Coverage of clouds, especially mid and high clouds, should
increase through Sunday and Sunday night. Winds will be lighter
and highs Sunday are expected to be well into the 40s but around
40 northern areas.

Northern stream upper energy dropping southeast through eastern
Canada is expected to increase the downstream upper confluence,
supporting a strengthening surface high pressure in southern and
southeastern Canada. This low level ridging is expected to push
colder and drier low level air south into our region Sunday
night as the southern stream upper energy and strengthening
warm/moisture advection pushes north. These opposing forces will
contribute to enhanced frontogenesis and forcing that will
affect precipitation type as precipitation spreads across our
region through Sunday night.

During the onset of the precipitation, it should be mostly rain,
except a mix in northern areas. As colder air drains southward
and low level temperatures trend toward wet bulb temperatures
as intensity of precipitation increases, mixed precipitation is
expected to build south across much of the region. Based on
thermal profiles, it looks like mainly a rain/snow/sleet mix but
will have to keep an eye for areas of freezing rain as we get
closer to the event.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
The main concern in the long term will be a sprawling storm
system that is forecast to move onshore along the west coast
Saturday, and then quickly track eastward across the southern
U.S. before starting to track northeast into the Appalachians by
Monday. Model guidance in fairly good agreement depicting a 500
mb cut-off low in the Carolinas/Virginia vicinity on Monday,
with a strong easterly fetch to the north of the system bringing
Atlantic moisture into our region. Good diffluence to the north
and east of the main cut-off will likely result in a
significant precipitation event across much of the region
through Tuesday, as the system tracks near or along the New
England coast.

The models are in fairly good agreement with the main synoptic
features, but differ in details of exact storm track, timing, QPF,
and thermal profiles. There is high enough confidence to mention
likely to categorical pops from Monday through Tuesday. The thermal
profiles and resulting precip types will have a big impact on
eventual snow, sleet and/or ice accumulations. Models trending
towards a deepening colder column on Monday, as colder air drifts
southward due to a northerly ageostrophic flow from high pressure
settling into the Canadian Maritimes. Used the GFS for top-down
procedure to determine precip types, with a myriad of mainly snow,
sleet and rain.

As is typical for these large cut-off lows, the best chance for
accumulating snow will be across the higher terrain west and east of
the Hudson Valley, although some accumulations are possible in the
Hudson Valley too, especially Monday into Monday night. The WPC
probabilistic snowfall outlook for this time frame shows a 50-70
percent chance of at least 0.25" liquid equivalent of snow/sleet in
the higher terrain with 30-50 percent in the valleys. So will
continue to mention chances for wintry precip in the HWO, although
it is too soon to mention specific amounts.

The system will finally pull away from the region late Tuesday into
Tuesday night, as a short-wave ridge builds in from the west.
However, the next system will be quickly approaching from the Great
Lakes region in the fast flow pattern bringing a chance for
snow/rain showers Wednesday into Thursday. Colder air will gradually
work in later next week with each passing trough. Temperatures will
start out above normal, but should trend colder by the end of the
week.

&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
A ridge of high pressure over the region both at the surface and
aloft will lead to dry conditions overnight and through much of
the day. However, low level moisture is trapped beneath a
strengthening inversion aloft, so clouds are expected to remain
in place through the period.

Will trend towards a more pessimistic ceiling forecast due to
widespread cigs currently in place and not much opportunity for
mixing over the next 24 hours. Cigs will be mainly in the MVFR
range well into the morning, with slight improvement to VFR
levels later this morning into the afternoon. Cigs expected to
lower again after dark, as a weakening upper level disturbance
approaches from the mid Atlantic region. Will mention VCSH at
KALB/KPSF/KGFL this evening, with prevailing -SHRA developing at
KPOU. Again, conditions are expected to be mainly MVFR from
around 00Z-06Z Saturday.

Winds will be light and variable overnight, becoming southeast
around 3-6 kt during the day.

Outlook...

Friday Night: Moderate Operational Impact. Chance of RA.
Saturday: Low Operational Impact. Slight Chance of DZ.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: Moderate Operational Impact. Chance of RA.
Sunday Night: Moderate Operational Impact. Chance of RA...SN.
Monday: High Operational Impact. Likely RA...SN.
Monday Night: High Operational Impact. Likely RA...SN.
Tuesday: Moderate Operational Impact. Chance of RA...SN.

&&

.HYDROLOGY...
Some light precipitation is possible this evening into Saturday
morning, but QPF amounts will be a tenth of an inch or less.
Daytime temperatures will be above normal through the weekend,
although overnight lows will fall 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 looks to occur early next week, but
there are still questions regarding the exact precipitation
type and amounts. The latest MMEFS do not show any flooding on
area rivers and streams, although some river rises are likely to
occur.

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...NAS
NEAR TERM...NAS
SHORT TERM...NAS
LONG TERM...JPV
AVIATION...JPV
HYDROLOGY...NAS



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