Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210738

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

A weak area of low pressure will move from the Ohio Valley to the
Mid Atlantic today and spread clouds and a few showers into much of
the region. This system will only slowly move off the east coast
Sunday with lingering clouds and a few spotty showers mainly inland
from the lakes. Dry weather and sunshine will then return early next
week as high pressure builds into the eastern Great Lakes. Summer
warmth and increased humidity is expected to arrive for the second
half of next week along with a few widely scattered showers and


Regional radars early this morning showing the leading edge of
returns moving into NE Ohio and NW PA, 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
through daybreak.

A mid level trough noted in water vapor imagery over the upper Ohio
Valley this morning will drift slowly east today, while an
associated surface low over the Ohio Valley will cross the central
Appalachians this afternoon and give way to secondary cyclogenesis
east of the Delmarva by this evening. Abundant mid level moisture
will continue to stream ahead of the mid level trough and across our
region today with solid cloud cover most of the day. An initial push
of warm advection and isentropic upglide supported by a modest 30
knot low level jet will reach the Southern Tier this morning, then
remain focused on that general area through the afternoon. Stronger
large scale ascent will also cross the Southern Tier from late
morning through the afternoon as a region of 700-300mb Q-vector
convergence ahead of the mid level trough moves into the area.
Otherwise for the rest of the area large scale forcing will be weak,
with a few periods of weak DPVA ahead of a few shortwaves moving out
ahead of the mid level trough and broad/weak isentropic upglide.

Given the expected layout of stronger forcing and deeper moisture,
have continued with the highest rain chances across the Southern
Tier. Farther north along the NYS Thruway corridor to the south shore
of Lake Ontario, kept scattered showers and chance POPS for the
afternoon with weaker forcing, very limited diurnal instability, and
unsaturated low levels. The Saint Lawrence valley will remain dry
farther removed from any forcing or deeper moisture.

Temperatures today will be closely tied to areal coverage of rain
and thicker cloud cover, with the Southern Tier remaining in the mid
to upper 50s while areas from the Niagara Frontier to Rochester and
Oswego county reach the mid to upper 60s. The Saint Lawrence valley
will be the warm spot this afternoon with lower 70s. Local onshore
flow will keep all the lakeshores cooler.

Tonight the mid level trough will slowly cross the lower Great
Lakes, while the coastal low matures and moves well offshore of the
southern New England coast. The mid level trough and remnant surface
inverted trough will keep the most widespread showers across the
Southern Tier, with scattered showers lingering from the Niagara
Frontier east across Rochester to the southern Tug Hill region. The
Saint Lawrence Valley will again remain dry. Expect lows in the
lower 50s on the lake plains and mid 40s across the interior
Southern Tier.


While there will be the potential for a few badly needed showers on
Sunday...this period will feature fair weather with day to day
warming. This trend towards more summery conditions will come
courtesy of a strengthening ridge found downstream from an
anomalously deep closed low over the Pacific Northwest. The ridge
will gradually push east from the nations mid-section...eventually
arriving over the Lower Great Lakes by Tuesday. The ridge will
finally displace a pool of H85-50 cool air that by this time will
have worn out its welcome over the Upper Ohio Valley.

Getting to the details...the most uncertainty (lowest confidence)
within this period will come right up front as the base of a
longwave trough will slowly cross the New York and Pennsylvania.
While the bulk of Sunday will be rainfree...relatively steep lapse
rates produced from the cooler mid level air with in the deep trough
(-20c @ H5 and -4c @ H7) will establish enough instability during the
midday and afternoon to support some widely separated convection.
The greatest instability and available moisture will be found along
the edges of our forecast area...that being across the Srn Tier and
Eastern Lake Ontario regions. Will leave chc pops in play for those
sites. Sunday afternoon temperatures will range from the mid 60s
across the Srn Tier where cloud cover will be the near
70 across the IAG Frontier and much of the North Country.

A mid level closed low within the longwave trough will develop off
North Carolina Sunday night. The ensuing weakening of the cyclonic
flow over the Lower Great Lakes will combine with a stabilizing moderating lapse rates due to warming in the mid
levels...and of course from the removal of diurnal heating. This
will encourage a night of fair weather across our region. Overnight
lows will once again be in the 40s.

Beautiful weather can be expected on ridging will nose
northeast from the Upper Great Lakes...extending across southern
Ontario To Quebec. Meanwhile the aforementioned closed low will be
anchored off the Mid Atlantic Coast. This will result in a
relatively short lived Rex Block...with our region finding itself
within the quadrant of nicest weather. The resulting sun filled
skies will be accompanied by warmer air H85 temps of 10c
will advect across our region from the Upper Great Lakes. This will
easily support afternoon temperatures in the low to mid 70s away
from the lakes and higher terrain.

After a gorgeous viewing of the full moon Monday night...general
ridging will be found over the Lower Great Lakes for Tuesday. This
should supply the region with more fair weather...although the much
talked about closed mid level circulation will be lurking just to
our east...slowly making its way up the Northeast coast. Cloud cover
on the western fringes of this feature could be as close as the
foothills of the Lewis County. As promised...the
day to day warming will continue. H85 temps are projected to climb
to arnd 12c. This will allow for most areas to reach into at least
the mid 70s...with 80 degrees not out of the question across the
Genesee Valley.

Speaking of max temps...will be aiming a little higher than most
guidance packages for Monday and Tuesday due to the abnormally dry


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.


A weak area of low pressure will move from the Ohio Valley to the
Mid Atlantic today before a coastal low redevelops off the coast
tonight and Sunday. Winds will remain light across Lakes Erie and
Ontario through the weekend, with high pressure bringing more light
winds through the first half of next week.


The Climate Prediction Center continues to highlight portions of
Western and North Central as being abnormally dry. The majority
of the region is averaging one to two inches below normal in
liquid equivalent precipitation since the start of this year...
with all of this departure taking place since the start of April. combination with an increasing sun angle (higher
insolation)...has resulted in the Genesee Valley...Finger Lakes
Region and much of the North Country being labeled as abnormally

This is an improvement from this time last year a
large portion of the region was considered abnormally dry with
moderate drought conditions found across the North Country...
Thousand Islands Region...and all of the lower plains of the St
Lawrence Valley.

The drier than normal Spring can be attributed to persistent
ridging over the western half of the country....which in turn has
supported longer stretches of high pressure over the Great Lakes
Region and the province of Ontario. Without a southerly feed of
moisture from the Gulf of Mexico...rainfall throughout our region
has been infrequent and generally inconsequential. This trend is
not expected to change until at least the second half of the
upcoming week.





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