Area Forecast Discussion
Issued by NWS Buffalo, NY

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257
FXUS61 KBUF 221733
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
133 PM EDT Wed Mar 22 2017

.SYNOPSIS...
High pressure will move from the upper Great Lakes, across the
forecast area overnight, and then east of the region on Thursday.
One last very cold night will come tonight before a moderating
temperature trend Thursday into the weekend. A frontal boundary will
then set up across the region this weekend, with several
disturbances moving along the front, which will bring an extended
period of wet weather Friday through early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
Sprawling arctic high pressure will continue to build in across the
Great Lakes late this afternoon through tonight. Already limited
lake effect south of Lake Ontario will diminish to patchy flurries
late this afternoon, and end this evening with strong subsidence and
a very dry airmass in place. The high pressure system will move over
the forecast area overnight setting us up for optimal radiational
cooling with light to calm winds and mostly clear skies. Locations
with lingering snowpack, like the North Country and interior
portions of the western Southern Tier will see low temperature
plummet overnight, with lows bottoming out in the single digits to
near zero. Meanwhile, lake plains locations, those with limited snow
pack and urban areas will temperatures mainly in the low to mid
teens.

The large high pressure system will slide to our east on Thursday,
with some limited return flow developing by mid-day and the
afternoon. This will allow for some moderation in temperatures as
the core of the cold airmass exits the region. High temperatures
will run a fair bit warmer than Wednesday, as temperatures reach the
low 30s in the North Country to near 40 in western NY. It will be a
fair weather day with mostly sunny skies, a very dry airmass in
place, and light winds.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
The progressive pattern that we have experienced the past week or so
will become somewhat blocked up as we push into the weekend. This
can be a good thing if you are parked under the heart of a ridge...
but if not...then you could be in for an extended period of
unsettled weather. In this particular case...our region will
unfortunately be on the northern fringes of a ridge that will become
pinched between a deep closed low over far eastern Quebec and a slow
moving stacked low over the Upper Mississippi Valley. The lack of
shear found in the lower levels within this synoptic pattern will
then encourage a strengthening surface boundary to become aligned
with the flow...stalling over/near our forecast area in the process.
The result will be a prolonged period of unsettled weather with the
potential for rainfall in excess of an inch and a half. Luckily...
this rain will fall over several days so the risk for any hydro
problems will be minimized. Digging into the details...

Thursday night...a broad ridge over the Mississippi Valley will
push east to the Ohio Valley and Great Lakes. Ahead of this
feature...a tightening baroclinic zone will become established
from Wisconsin and Lower Michigan to Lake Erie. The associated
isentropic lift along this elevated boundary will generate some
showers...with some of that activity spreading across our far
western counties. Any light pcpn will fall as a mix of light
rain or wet snow showers. Given the strength of the warm
advection...temps after midnight will actually start to
rise...climbing back above freezing for counties near Lake Erie.

Conditions will further deteriorate on Friday...as the strengthening
baroclinic zone will evolve into a fairly pronounced warm frontal
boundary. This feature will push north across our forecast area
during the course of the day and serve as a focus of lift for the
wealth of moisture being pumped into the region from a 40kt low
level jet. The pcpn could initially start as a bit of wet snow...but
will quickly transition to just rain. The 60 mile wide band of pcpn
will push north during the course of the midday and afternoon...with
the axis of rain aligning with Lake Ontario and the North Country by
late in the day. This means that the Srn Tier will could be far
enough into the warm sector for the bulk of the pcpn to end...or at
the least considerably taper off. Max temperatures on Friday will
range from the low to mid 50s over the Southern Tier to the lower
40s north and east of the Tug Hill.

Friday night...while a mid level ridge will remain pinched in place
over the Lower Great Lakes...the conspicuous sfc frontal boundary
stretched the length of Lake Ontario will slowly be pushed south by
a strong area of high pressure near James Bay. The associated swath
of steadier rain will settle south to the counties lining the south
shore of Lake Ontario with an increasing chance for rain also across
the Finger Lakes and Genesee Valley. Colder air pushing south in the
wake of the slow moving boundary could support some mixed wintry
precipitation after midnight for the Eastern Lake Ontario region.

The pronounced frontal boundary will continue to push south to the
Pennsylvania-Maryland during the day Saturday...while a tight H925-
85 thermal gradient will support fairly strong frontogenetic forcing
over much of our forecast area. This will keep widespread rain over
the western counties...while there could actually be some
improvement over the North Country. Have backed off the pops for
much of Jefferson and Lewis counties while increasing pops to
categorical across the Srn Tier. There will continue to be a fairly
large temperature gradient over the region with daytime highs
ranging from just the upper 30s in the Thousand Islands region
to the low to mid 50s right along the Pennsylvania a border.

As the slow moving stacked low drifts closer to the Lower Great
Lakes saturday night...the boundary will stall and eventually be
pushed back towards the north. This will spread the rain back
towards Lake Ontario...with a wintry mix once again possible over
the North Country.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
Unfortunately...there is high confidence that the wet...unsettled
weather will remain in place across western and north central New
York during this period.

The persistent stacked storm system over the mid west will gradually
`open up` and drift across the Lower Great Lakes later Sunday into
Monday. While the baroclinic zone responsible for much of the
previous days pcpn will be shoved out of the region...significant
hgt falls and the introduction of mid level energy will fuel
additional rainfall.

Our region will experience a very brief lull in the inclement
weather Monday night in the wake of what will then be a passing mid
level trough. Will only have chc pops in place for rain and wet snow
showers...although the majority of the night could very well be pcpn
free.

On Tuesday...while the medium range ensembles are not in agreement
as to the strength of the next shortwave...they generally agree that
another disturbance will drop southeast across the Lower Great
Lakes. This will generate a renewed round of shower activity.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
High pressure will build across the region through tonight and will
move to our east on Thursday. This will bring a long stretch of fair
weather and VFR conditions and light winds to the area.

Outlook...

Friday...Deterioration to MVFR/IFR with mixed rain and
snow developing...then changing over to all rain.
Saturday thru Monday...MVFR/IFR with rain likely.

&&

.MARINE...
Northwest winds will maintain small craft advisories on Lake Ontario
late this afternoon. High pressure will build towards the lakes
tonight, allowing for winds and waves to subside, with SCA lingering
longest along the SE Lake Ontario shoreline.

This high pressure will then build across the region Thursday while
bringing a return to light winds and negligible waves.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 2 AM EDT Thursday for LOZ043-044.
         Small Craft Advisory until 5 PM EDT this afternoon for
         LOZ042-045.

&&

$$

SYNOPSIS...CHURCH
NEAR TERM...CHURCH
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...CHURCH
MARINE...CHURCH



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