Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210512

Area Forecast Discussion
National Weather Service Buffalo NY
112 AM EDT SAT MAY 21 2016

High clouds will increase tonight ahead of a low pressure
system that will pass to our south on Saturday. This system will
bring showers to the Southern Tier, with a chance of showers
elsewhere Saturday. Another round of showers will be possible Sunday
as the low lingers along the Eastern Seaboard before high pressure
returns with fair weather and increasingly warm temperatures
expected next week.


Regional radars early this morning showing the leading edge of
returns moving into NE Ohio, but much of this is not reaching the
ground as of yet with a dry layer in the low levels to overcome.
Expect the leading edge of scattered showers to reach the western
Southern Tier around 12Z. Extensive mid/high clouds will continue to
thicken across the region from southwest to northeast overnight.

The combination of a warmer airmass and thicker high clouds aloft
will yield warmer temperatures tonight as compared to the relatively
cool readings from last night with most areas only bottoming out in
the upper 40s to lower 50s, and even mid 50s across portions of
Western NY.

After a fine stretch of weather over the last few days...things will
turn more unsettled on Saturday as the upper level trough axis moves
overhead and a broad mid-level and surface low passes to our south
across the Ohio valley. The combination of DPVA aloft and theta-e
advection in the lower levels along with some limited component
diurnal instability/lake-breeze convergence will produce scattered
showers across much of the forecast area as we move through the day
on Saturday with the highest chances across the Southern Tier,
closest to the 850mb theta-e ridge axis and deepest moisture. Areas
north of the thruway should remain largely dry...albeit cloudy as
mid/high clouds will remain in place across the region. The
increased cloud cover will have a significant damping effect on
temperatures with highs expected to range from the upper 60s in the
North Country, where cloud cover will be thinnest, to the mid 50s in
the cloudier and wetter Southern Tier.


A mid level trough will advance very slowly east Saturday night and
Sunday with the associated coastal low maturing and moving slowly up
the East Coast. This will leave a general decreasing trend in cloud
cover and precipitation chances across our area Saturday night, with
any showers on Sunday confined to the Finger Lakes and Eastern Lake
Ontario region. There will be a clearing trend from west to east,
but it looks like the clearing will hold off until Sunday evening
and night. Even though the flow becomes northerly behind the
departing mid level trough, the upstream air will actually be
warmer, so we can expect high temperatures on Sunday to be in the
lower 70s along the lake plains south of Lake Ontario and across the
North Country, but in the mid to upper 60s where clouds will linger

Sunday night and Monday the mid level closed low will further
consolidate along the east coast. A building mid level ridge and
subsidence just west of the closed low will bring a return to
sunshine by Monday with highs warming back into the mid 70s as 850mb
temps reach +10C. The airmass remains fairly dry, so expect good
radiational cooling Sunday night with lows generally within a few
degrees of 50 on the lake plains and mid 40s in some of the cooler
valleys and Tug Hill region. Overnight low temperatures will be a
couple degrees warmer Monday night. Tuesday will be warm and dry
across the entire forecast area with ridging aloft and surface high
pressure taking control. 850mb temps range from +10C to near +13C,
yielding afternoon high temperatures in the lower to mid 70s with
abundant sunshine and light westerly winds. The weather will start to
feel more like late Spring as Tuesday night`s low temperatures don`t
dip much below the lower to mid 50s.


Wednesday through Thursday, the closed low finally moves out to sea,
allowing a more zonal flow to develop across the Great Lakes region.
The deep layer southwesterly flow will transport even warmer and more
humid air into our region, with a real taste of summer on the way
for the second half of next week. Expect highs to reach into the
lower 80s in many areas by Wednesday and Thursday away from the
immediate lakeshores, a little less warm on Friday. Dewpoints will
climb to around 60, which will yield better instability, with
several weak shortwaves possibly supporting a few scattered showers
and storms from Wednesday night through Friday. The summer-like
warmth, humidity, and thunderstorm chances will likely last through
next weekend.


A weak surface low over the Ohio Valley will drift east to the Mid
Atlantic region by this evening. A shield of extensive mid level
clouds will continue to stream northeast across the area through the
remainder of the overnight and Saturday morning. A few scattered
showers may reach the western Southern Tier near KJHW by around 12z.
Through the day Saturday, moisture will continue to deepen and lower
with scattered showers spreading as far north as Lake Ontario, with
somewhat more widespread showers from late morning through afternoon
across the western Southern Tier. Most of the rain will remain light
with VSBY mainly VFR. CIGS will also remain VFR in most locations as
the low levels remain unsaturated, with the exception of the higher
terrain of the Southern Tier where some MVFR will develop this

A weak mid level trough will very slowly cross the region tonight.
This will maintain scattered showers in many areas this evening with
more widespread showers across the Southern Tier. Overnight expect a
slow diminishing trend in showers from northwest to southeast. The
low levels will remain largely unsaturated with VFR CIGS and VSBY in
most areas, with some MVFR CIGS lingering across the higher terrain
of the Southern Tier.


Sunday...Mainly VFR with a chance of showers eastern areas.
Monday through Wednesday...VFR.


High pressure will remain across the Eastern Great Lakes region into
tonight. While an area of low pressure will pass to our south on
Saturday and transition into a coastal low by Sunday, its effects on
the Great Lakes should be negligible with generally light winds and
waves prevailing well into next week, as high pressure returns to
the region.





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