Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 201057

Area Forecast Discussion
National Weather Service Buffalo NY
657 AM EDT Sat May 20 2017

While high pressure will bring sunny skies to the North Country and
the Lake Ontario shoreline today, cloudiness will dominate the
southern half of the forecast area, closer to a stalled frontal
boundary. This boundary will lift north as a warm front tonight into
Sunday, with showers expected from late Sunday into Monday ahead of
a cold front that will cross the area Monday. Another disturbance
and associated frontal boundary is expected to bring another round
of showers Wednesday.


The upper level pattern this morning consists of a strongly amplified
ridge extending from the southeastern U.S. coast to northern
Manitoba, or just upstream of our area, while upstream of that
feature, an upper low can be found spinning over the central Plains.
At the surface, anticyclonic northeasterly flow around a high
centered near James Bay is advecting cool and dry air into the North
Country, where clear skies are noted this morning. Meanwhile, mid-
level clouds continue to be found across western and central New
York, closer to a stalled frontal boundary extending across the Ohio
valley and the central Appalachians.

Clouds will linger across much of western New York and the Southern
Tier throughout the day, courtesy of warm advection aloft. This band
of cloud cover is not expected to extend much north of the Thruway
however, as high pressure, subsidence, and drier air to the north
will exert its influence from the North Country to the southern
shores of Lake Ontario. Temperatures will remain on the cool side of
average, thanks to persistent northeasterly flow, with highs ranging
from the mid 50s along the Lake Ontario shore, with lower 60s
inland. The North Country will be the warmest portion of the
forecast area today, in spite of being in the cooler air aloft, due
to an abundance of sunshine.

Clouds will spread north and eastwards tonight, as the upper level
ridge shifts to the east, opening up the lower Great Lakes to more
southerly flow aloft, and thus stronger warm advection and greater
moisture aloft. While showers associated with the approaching low
pressure system will be moving into the western and central Lake
Erie basin overnight, they should hold off long enough to guarantee
a dry night for all but the extreme westernmost portions of the
forecast area. In addition, strengthening southeasterly flow will
generate downsloping winds off the Chautauqua Ridge later tonight,
with local gusts to 30 mph possible. This will also make the Lake
Erie shoreline the warmest portion of the forecast area overnight,
with lows in the mid 50s, with mid to upper 40s found from the
Genesee valley east.


Our weather Sunday and Monday will be controlled by a slowly
deepening storm system tracking from the Upper Midwest states
northeast across the Great Lakes to the tip of James Bay. A warm
front associated with this system is first expected to shift
eastward across western and central NY from Sunday morning into the
afternoon. This front will bring a first round of scattered to
widespread showers across the region Sunday. Temperatures and
humidity levels will then briefly surge in the warm sector behind
the eastward shifting warm front. Gusty winds are also expected
Sunday up about 30mph as the passing low tightens up the pressure
gradient over the eastern Great Lakes. Afternoon high temps will be
capable of climbing 10 degrees above todays readings.

A cold front will then quickly cross western and central NY Sunday
evening/night with another widespread area of showers and perhaps a
few isolated thunderstorms. PWATs climbing to as high as one and one-
half of an inch which is 2SD above normal will lead to another
soaking rainfall...with as much as a half to three-quarters of an
inch of rain. Otherwise, severe storm threat looks minimal given
weak instability and shear. Weak surface high pressure over the mid-
Mississippi valley will then build in behind the cold front Tuesday
with mainly dry weather...though a few showers cannot be totally
ruled out across western counties as the next system approaches
later in the day.

The temperature forecast on Sunday which is expected to be above
normal could be tricky as 850 mb temps surge to between +10C and
+15C at the same time that cloud and shower coverage expands west-
east. Expecting highs mostly in the low to mid 70s but again such a
forecast could be a bit optimistic if the clouds and showers arrive
faster than current expectations. Mild temperatures expected Sunday
night within the warm sector with lows only slipping into the lower
to mid 50s. Cool air advection in the wake of the cold front will
keep highs Monday limited to the low to mid 60s before warm air
advection and dry conditions ahead of our next storm system allow
readings to climb back into the upper 60s to lower 70s on Tuesday.


Unsettled weather will continue for mid to late next week due to re-
amplification of midlevel troughing over the Great Lakes and
Northeast. Another surface low will form over the Southern
Appalachians Wednesday connected by a cold front to a low over
eastern Quebec. Showers and thunderstorms will be possible along
this front as it crosses into a potentially unstable airmass over
western and central NY. Shower potential looks to persist into
Thursday and Friday with slowly diminishing POPs as the low departs
into Quebec. Near to slightly above normal temperatures Tuesday
night and Wednesday will slip back to a little below average for the
remainder of the period with highs only expected to reach the low
60s Thursday and mid 60s on Friday.


Much of the forecast area remains under VFR cigs, as mid-level
clouds continue to cross the region, courtesy of a passing upper
level shortwave. VFR cigs will persist across much of the forecast
area today - even as mid-level clouds associated with the wave move
off to the east, they will be replaced with increasing clouds from
the southwest due to increasing warm advection aloft ahead of an
approaching warm front. The one exception will be across the North
Country and along the Lake Ontario shoreline, where skies will
remain clear through much of the day.

Clouds will shift to the northeast tonight in response to increasing
warm advection and southerly flow aloft. This will push VFR cigs
across KROC this evening and into the North Country by Sunday
morning. Also, a strengthening low level jet combined with low-level
inversion will result in spotty areas of low level wind shear across
the Southern Tier late tonight.


Sunday through early Monday morning...MVFR. Showers likely with a
chance of thunderstorms.
Later Monday and Tuesday...Mainly VFR.
Wednesday...VFR/MVFR with showers likely.


Northeasterly flow around a high centered just southeast of James
Bay will freshen this afternoon, as the gradient tightens between
this high and low pressure tracking from the Great Plains towards
the western Great Lakes. This should be just strong enough to
generate small-craft advisory winds along the southwestern end of
Lake Ontario this afternoon, before winds drop back off this evening
as flow veers to the east.

Winds will veer to the southeast Sunday ahead of an approaching cold
front before veering to the west and freshening behind a cold front,
expected to cross the lakes Monday. Conditions may approach advisory
conditions Monday afternoon on the east end of Lake Erie, but
otherwise, conditons are expected to remain sub-advisory level
into the middle of the coming week.


MARINE...Small Craft Advisory until 6 PM EDT this evening for LOZ042.
         Small Craft Advisory until 6 PM EDT this evening for



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