Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 200915

Area Forecast Discussion
National Weather Service Buffalo NY
415 AM EST Fri Jan 20 2017

A weakening trough will move from southwest to northeast across the
region today and produce a period of rain across Western and Central
NY this afternoon and evening, before weakening to scattered showers
across the North Country tonight. Plenty of low clouds, drizzle, and
patchy fog will persist behind this trough tonight through at least
the first half of the weekend. 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.


The drizzle has finally tapered off across most of the region early
this morning as the low level moisture field becomes more shallow
with time. Plenty of low clouds remain however, with areas of fog
mainly across the higher terrain as the stratus deck intersects the
hills. Short term mesoscale model guidance such as the HRRR have a
good handle on the current coverage of low stratus, and suggest it
will scatter out steadily from south to north this morning as
southerly flow increases just off the deck, both advecting out the
moisture and also increasing downslope flow into the lake plains,
further scouring out the low level moisture. This should bring an
end to the fog across higher terrain by mid morning across Western
NY, and midday for the Tug Hill.

Our attention then turns to a sharp mid level trough and weak
surface reflection across the Ohio Valley. This trough will move
steadily northeastward today and enter Western NY this afternoon,
before moving off to the North Country tonight. The trough will de-
amplify with time, allowing the associated DPVA to weaken with time,
and the low level jet also weakens with time. There will still be
enough forcing to support widespread rain as the trough moves into
the western Southern Tier by late morning or midday, but coverage
and intensity of rain will steadily diminish as the trough moves
northeast across the Finger Lakes and Central NY by late afternoon
and evening. By the time the trough reaches the North Country late
this evening and overnight, expect just a few scattered light
showers to be left.

Tonight plenty of low level moisture will be left behind in the wake
of the departing mid level trough. Relatively light and convergent
southwesterly flow will develop across Western NY, and combine with
frictional convergence off Lake Erie and upslope flow to produce
another round of drizzle, low clouds, and fog overnight. This is
likely to last through at least the first half of the weekend, more
on that in the short term section below.

Temperatures will run well above average, with highs in the low to
mid 40s in most locations today. Temperatures will remain in the
lower 40s tonight in most areas, with mid to upper 30s across the
North Country.


The weekend will be quite mild in temperature, but will still be
overall dismal with respect to cloud cover and lingering low-level
moisture producing areas of drizzle and fog at times.

On Saturday broad troughing will expand across the central plains
with deeper southwesterly flow developing into western NY. This will
continue to supply weak warm air advection and low-level moisture
into the forecast area with 850 mb temperatures rising to near +5C
in WNY but only near +1C in north Central NY. This will result in
high temperatures ranging from the low 50s in western NY to the low
40s in the North Country. Along with this warmer air, will be higher
dew points, pushing into the mid 40s across the very mild WNY. With
no real moisture aloft, and only subtle warm advective synoptic
forcing, this will continue to support low stratus with areas of
drizzle. The interaction of the higher dew points over the
relatively cold Lakes Erie and Ontario will also produce areas of
fog east and northeast of the lakes.

Saturday night temperatures will fall little, only into the mid 30s
in the North Country and the low to mid 40s in WNY due to trapped low-
level moisture and cloud cover. Patchy drizzle and some areas of fog
will persist into Sunday. Sunday will be nearly a carbon copy of
Saturday expect for temperatures running a couple of degrees cooler
as temperatures aloft start to fall slowly ahead of the approaching
large low pressure system for the start of the work week.


The focus remains on early next week as a large low pressure system
is set to churn up the east coast and bring unsettled weather to the
forecast area. There remains plenty of uncertainty with this system
with regard to the track and even precipitation type, however there
remains the potential for a portion of the forecast area to see
significant snow accumulations. With the 00Z model runs this
morning, the GFS has maintained fairly close where it ended up
yesterday after trending eastward. The ECMWF, which also trended
eastward yesterday, has actually trended back to the west with the
00Z run this morning. Despite the GFS maintaining the more eastern
track, more of its ensemble members are showing the potential for
significant snowfall into the eastern half of the forecast area.
This trend in the GEFS matches well with the 00Z EC trend back to
the west, as well as with the top matches from the CIPS analogs.
Speaking of the analogs, there weren`t a lot of great matches for
this storm, but a couple of the best matches brought significant
snows through central NY and eastern portions of the forecast area.
Long story short: we are not out of the woods on the potential for
significant snowfall across a portion of our forecast area, although
as of now it appears the best chance is probably from near the
Finger Lakes eastward into central NY. With respect to precipitation
type, despite the overall marginal airmass associated with this
storm system, it appears dynamically cooling and precipitation rates
in the deformation band (wherever it sets up) would be plenty to
support accumulating snow. West of that deformation band, any
snowfall amounts would drop off quite sharply.

A large pattern change appears to be on track in the wake of this
storm system. A large trough beginning to carve out across the CONUS
by midweek, with a leading wave pushing through the Great Lakes
across southern Ontario province by Wednesday into Thursday. This
will bring some rain and snow showers across the region, with some
lake and upslope enhancement. The real interesting time period comes
toward the end of the week as colder air floods into the region as
the large trough spins east of the Hudson Bay, which will start to
ramp up lake effect snows off of the lower Great Lakes. Global
models are in good agreement that a secondary colder shot of arctic
sourced air then surges into the region by the end of month with
continued (possibly significant) lake effect snows.


Low stratus will persist through early to mid morning across much of
the area, with IFR favored across higher terrain and MVFR at lower
elevations. The stratus will also intersect some of the higher hills
with fog across higher terrain.

The fog and low stratus will steadily erode later this morning from
south to north as southerly flow just off the deck increases, with
downslope winds helping to scour out the low level moisture. Rain
will arrive across the western Southern Tier by late morning or
midday as a mid level trough arrives. This area of rain will then
move northeast across the rest of Western and Central NY during the
afternoon and evening, weakening with time.

Expect a return to IFR during the afternoon across the higher
terrain of the western Southern Tier. MVFR/IFR conditions will then
become more widespread again tonight behind the departing mid level
trough, with abundant low level moisture supporting low stratus, fog,
and drizzle.


Saturday and Sunday...Areas of IFR/MVFR in low stratus, fog, and
Monday and Monday night...Areas of MVFR/IFR with rain changing to
wet snow.
Tuesday...Areas of MVFR/IFR with wet snow.


Winds and waves will remain relatively light at 15 knots or less
today through Saturday. A weak trough will cross the Lower Great
Lakes this afternoon and evening, followed by weak high pressure
late tonight and Saturday.

Northeast winds will begin to increase Sunday, and increase further
on Monday as low pressure deepens along the east coast and high
pressure builds east across Quebec.





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