Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210530

Area Forecast Discussion
National Weather Service Buffalo NY
1230 AM EST Sat Jan 21 2017

Plenty of low clouds, drizzle, and patchy fog will linger late
tonight through much of the weekend, though temperatures will be
unseasonably mild. An area of low pressure is then forecast to move
northward along the east coast early next week. This system may tap
into just enough cold air to allow rain to change to wet snow later
Monday through Tuesday.


A surface trough continues to push northeastward across the region
overnight. Weakening forcing ahead of the trough will only support a
few scattered light showers across the eastern Lake Ontario region

Though the trough and associated precipitation will pass, moisture
will remain abundant in the lower levels. Dewpoints rising into the
mid 40s across Lake Erie and surrounding areas with similar surface
temperatures and light winds will promote areas of fog through the
night, especially near Lake Erie where a light wind and additional
lake moisture will bring areas of dense fog along the shoreline.
Additional dense fog will be found across the higher terrain of the
Southern Tier, and hills of Southern Erie, Wyoming and Livingston
counties. The abundant low level moisture will also support areas
of drizzle, especially east of the lakes and across higher terrain.

The gloomy weather will linger through the day on Saturday,
particularly across the Lake Ontario plains, as low level flow
becomes northeasterly and upslope. The one consolation though will
be that it will be exceptionally mild, with highs in the lower 50s
across many areas. The North Country will not be in quite as warm an
airmass however, and temperatures there should remain in the lower


Ridging aloft will keep a subsidence inversion in place at about
900mb where models continue to show this inversion will keep
moisture trapped just off the surface. Expect overcast to mostly
cloudy skies with low clouds Saturday night through Sunday with some
weak lift leaving a slight chance for some drizzle. Temps bottoming
out in the mid 30s across the north county with low 40s across and
west of the Finger Lakes will warm about 10 degrees for Sunday with
most areas topping out in the mid to upper 40s. A few 50s can be
found toward the Lake Erie shoreline where an easterly winds will
downslope to the lake shore.

Sunday night through Monday night will be focused on a strengthening
storm system that looks to roughly track from the Gulf Coast states
up along the Southern Appalachians Sunday night then across the Mid-
Atlantic to off the New Jersey coast Monday and Monday night as the
parent upper trough becomes negatively tilted along the east coast.
A 50-70kt southeasterly low level jet ahead of this system will
advect deep Atlantic moisture north and northwestward ahead of the
700mb low center which will bring in a widespread swath of
precipitation Sunday night and Monday into western and central NY.
Temps during this period will run above freezing surface and aloft
with the main p-type being plain rain. Cooler profiles are found
across the North County were some rain, wet snow and potentially
sleet will likely bring a wintry mix. Later Monday into Monday night
guidance indicates that dynamic cooling will cool profiles to below
freezing which will likely change p-type over to a mix of rain and
snow then wet snow by Monday night. Any accumulations through Monday
will be confined to the higher terrain of the Southern Tier, Bristol
Hills and across the Tug where the latest forecast allows for an
inch or two of snow. QPF forecasts are still quite uncertain for
Monday night and beyond but could lead to more accumulating snow.
There still is a potenial for significant snows as several of the
analogs for this event show 72-hour snow totals above the warning
threshold although the mean of the top 15 analogs only includes
warning level snows east of the lakes with below warning threshold
snows elsewhere. Stay tuned.


Latest model guidance remains in fairly good agreement depicting a
mid level cut off low in the eastern Pennsylvania/New Jersey
vicinity early Tuesday, lifting across eastern New York during
the day. Bulk of the associated heavier precipitation should fall
to the east of the area, as main area of forcing is aligned to
the north and east of the of the main cut off. Nonetheless, steady
precipitation should be found as far west as the north Country
aided by a favorable upslope mechanism.

The models are in fairly good agreement with the main synoptic
features, but differ in details of exact storm track, timing,
precipitation amounts, and thermal profiles. The thermal profiles
and resulting precipitation types will have a big impact on eventual
snow accumulations. Models trending towards a deepening colder
column on Tuesday, as colder air drifts southward due to a northerly
flow from high pressure settling into the Canadian Maritimes. Used
the ECMWF for top-down procedure to determine precipitation types,
with a myriad of mainly snow, some sleet and rain. Expect the best
chance for accumulating snow will be across the higher terrain of
the North Country, potentially significant. Therefore will continue
to mention chances for wintry precipitation in the Hazardous Weather
Outlook product, although it is much too soon to mention any
specific amounts.

The system will pull away from the region Tuesday night, as a short-
wave ridge builds in from the west. However, the next system will
quickly approach from the upper Midwest/western Great Lakes
region in the fast flow pattern bringing increasing chances for
snow/rain showers Wednesday into Thursday. Colder air will
gradually work in later next week with better chances for snow,
and possibly some lake effect snow by the very end of the period.
Temperatures will start out above normal, but should trend colder
by the end of the week.


Abundant low level moisture in the wake of a weakening trough will
continue to support widespread IFR in low stratus, fog, and drizzle
across Western NY overnight into Saturday morning. MVFR conditions
farther east from KROC to KART will deteriorate to IFR overnight as
the deep low level moisture spreads east.

Flight conditions will then remain IFR for a good portion of the TAF
cycle, with only brief improvements to MVFR Saturday afternoon and
early evening. A passing ridge of high pressure will maintain not
only the cloudy, low clouds through the day Saturday, but continue
the light wind flow across all five TAF sites.


Saturday Night and Sunday...Areas of IFR/MVFR in low stratus, fog,
and drizzle.
Monday and Monday night...Areas of MVFR/IFR with rain changing to
wet snow.
Tuesday...Areas of MVFR/IFR with wet snow.
Wednesday...VFR/MVFR with a chance of rain and snow.


Light winds will remain in place across the lakes through the first
half of the weekend. However, northeasterly winds will freshen on
Sunday as a large and deepening low pressure system tracks from the
southern Plains to the Piedmont. This will bring small craft
advisory conditions  to the western half of Lake Ontario by Sunday
evening. These conditions should last at least through Monday night
before winds back to the northwest as the low morphs into a coastal
low that moves up the Northeast corridor through Tuesday.





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