Area Forecast Discussion
Issued by NWS Buffalo, NY

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802
FXUS61 KBUF 190157
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
857 PM EST Wed Jan 18 2017

.SYNOPSIS...
Low level moisture lingering across the region will maintain
cloudiness tonight through much of Thursday. A few periods of
drizzle are possible tonight, with some freezing drizzle possible
east of Lake Ontario through early Thursday morning. After
partial clearing late Thursday into Friday morning, there will be
a returning rain chance Friday night, then a cloudy but dry
weekend is expected.

&&

.NEAR TERM /THROUGH THURSDAY/...
There will continue to be lots of low level moisture trapped in
the boundary layer overnight. This will maintain cloud cover, and
result in areas of drizzle which will mainly be due to upsloping.
Outside of some higher clouds associated with a shortwave, cloud
tops are only about -6C which is not cold enough to support
dendritic snow growth. As a result, precipitation is mainly in
the form of drizzle situated ENE of the lakes or downwind of the
boundary layer flow.

The main forecast concern is the potential for freezing drizzle
since temperatures are generally in the mid 30s across the area
this evening. The persistent cloud cover should prevent
temperatures from dropping much at all overnight, with low
temperatures only a couple degrees cooler than current
temperatures.

Across most of Western New York, mesoscale guidance suggests
drizzle will taper off late this evening as slightly drier air
advects in from the west. During this time, temperatures should
remain just above freezing.

The forecast is more complex for the Eastern Lake Ontario region
with a shortwave forecast to pass just to the north tonight. This
will help enhance lift, but colder cloud tops may provide ample
seeding for drizzle to change over to snow showers for a period
overnight. Even so, it appears temperatures will be cold enough
for some freezing drizzle after this shortwave passes. As a
result, a winter weather advisory for freezing drizzle and very
light snow accumulations was issued for the Eastern Lake Ontario
region...mainly for higher terrain. Icing should only be a trace,
but even a trace of ice can make things very slick. Temperatures
are likely to remain just above freezing near the Lake Ontario
shoreline, with freezing drizzle mainly across higher terrain.
This is reflected in Mesonet obs, with these showing below
freezing temps only across higher terrain.

Expect Thursday to be a mainly dry day, with mostly cloudy skies. High
temperatures will reach the middle to upper 30s across the
Eastern Lake Ontario region and Saint Lawrence Valley with the
continued clouds cover with upper 30s to low 40s across Western
New York and the Western Southern Tier where cloud cover will be
less during the afternoon.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SUNDAY NIGHT/...
A sharp ridge extending back across the Great Lakes region from the
Carolinas will provide us with fair dry weather Thursday night. It
will remain `mild` by late January standards...as the mercury will
only settle to within a few degrees of freezing. At this level...
temperatures will be some 15 deg F above normal.

While fair weather will continue east of Lake Ontario on Friday...
it will become unsettled over the western counties. A negatively
tilted trough over the Ohio Valley will push north during the course
of the day...and as an attendant swath of moisture moves over the
region...showers will become somewhat widespread during the
afternoon. This will especially be the case over the Western
Southern Tier where likely pops have been raised to categorical.
High temperatures will be more typical of late March...ranging from
the mid and upper 40s over the west to around 40 east of Lake
Ontario.

The trough will shear out and weaken Friday night...as it will exit
across Lake Ontario to the Ottawa Valley. While showers associated
with this feature will gradually end in the process...skies will
remain shrouded under plenty of low cloud cover. Mins will
generally be in the mid to upper 30s.

A progressive shortwave ridge will amplify over the Lower Great
Lakes on Saturday. This will provide us with a fairly nice day for
outdoor activities...as H85 temps in the vcnty of 5c will support
afternoon high temperatures in the mid to upper 40s. There will
likely be some 50 degree readings sprinkled throughout the valleys
west of Ontario county.

Sunday will largely feature more uneventful weather across our
region...as the high amplitude ridge will gradually exit across New
England. Meanwhile...a deep closed low with highly anomalous heights
will churn its way across the Lower Mississippi Valley. This will
make Sunday a day of transition for our forecast area...as the
overlying pattern will be evolving into one that will guarantee very
wet weather for the start of the new work week.

The change to unsettled conditions will begin Sunday night...as a
deep feed of Atlantic moisture will stream across our area ahead of
the deep closed low over the Deep South. The forecast track of the
lumbering stacked storm system is further east than previous
guidance packages...as the general track is now favoring a track up
the east side of the Appalachians rather than the continental side.
While this is not expected to change the pops much in the following
periods...it could significantly affect the type of pcpn. That being
said...the weekend will end with some rain overspreading the western
counties during the course of Sunday night. Pops for the overnight
will range from slight chc east of Lake Ontario...to likely across
the Western Southern Tier.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
While there is very high confidence that the weather will be very
unsettled for the bulk of this period...the various guidance
packages have introduced some uncertainty as to the precipitation
type. In a nut shell...there has been a trend by the ensemble
packages to track the stacked storm system up along the east side of
the Appalachians rather than the west side. This has led to a
`colder` solution...which for some ensemble members...translates
into at least the chance for some snow...if not accumulating snow.
Have tried to stay the course with continuity and the somewhat
rainier solution to avoid `flip flopping`...but have added the
mention of snow as a means of half stepping until there is increased
run to run model consistency. As for some details...

The mature storm system will drift to the Mid Atlantic region on
Monday. This will establish a deep easterly flow (40-50 kts) of
Atlantic moisture over our region where a strongly coupled H25 jet
and enhanced upslope will provide lift for increasingly widespread
rain. This pcpn could be moderate to heavy at times with some areas
possibly receiving a half to one inch of rain. High temps will be in
the mid 40s for most areas.

The rain will continue across the region Monday night into
Tuesday...as the storm system will track north-northeast across New
England. This is when things could get interesting. Because of the
more eastward track...colder air will be able to work in behind the
parent low. As mentioned...the air could be cold enough to allow for
a transition to wet snow...especially across the higher terrain. In
a worst case scenario...the snow would change over at a point where
significant accumulations could occur. While this has the lowest
chance for verifying at this point...there is a clear trend towards
the event being colder. Have thus added at least the mention for
some snow.

Drier air will then work its way across our region later Tuesday
night and Wednesday...finally bringing an end to the pcpn event.

The more eastward track will also lower the risk for a downslope
wind event off the Chautauqua Ridge. The low level jet on Monday is
not forecast to be quite as strong as originally expected and the
flow is now forecast to be more easterly...so this will considerably
lower the high wind potential.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
There continues to be lots of low moisture trapped int he boundary
layer, with the majority of TAF sites IFR or lower early this
evening. There is also patchy drizzle due to upsloping. Looking
upstream, a very slow improvement in conditions is expected
overnight but even so expect most sites to remain IFR through
tonight.

Forecast soundings show drier air thinning out moisture early
Thursday as high pressure ridges in from Ohio. Timing the
improvement is tricky, but expect a partial clearing to spread
into the Western Southern Tier Thursday afternoon with cigs
lifting into the MVFR category and eventually scattering out late
in the day.

Outlook...

Thursday night...VFR/MVFR.
Friday...Mainly VFR. Friday night and Saturday...MVFR to IFR with
a chance of rain.
Sunday...MVFR ceilings.
Monday...MVFR to IFR ceilings with scattered showers. Windy.

&&

.MARINE...
A tightening pressure gradient between departing low pressure and
approaching high pressure will increase the winds on the lakes,
requiring small craft advisories for the nearshore waters of Lake
Erie and the south shore nearshore waters of Lake Ontario into
tonight. Winds will lessen on Thursday as the center of the high
pressure moves across the lakes. Lighter winds are expected into the
weekend.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory until 7 AM EST Thursday for NYZ006>008.
MARINE...Small Craft Advisory until 7 AM EST Thursday for LEZ040-041.
         Small Craft Advisory until 7 AM EST Thursday for
         LOZ043-044.

&&

$$

SYNOPSIS...APFFEL/WCH
NEAR TERM...APFFEL/WCH
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...APFFEL
MARINE...APFFEL/WCH



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