Forecast Discussion

Forecast Discussion for BUF NWS Office
FXUS61 KBUF 222028

Area Forecast Discussion
National Weather Service Buffalo NY
428 PM EDT Fri Oct 22 2021

A cool airmass will remain in place through the weekend, supporting
a few periods of lake effect rain showers east of Lakes Erie and
Ontario. Low pressure will then slowly move from the Ohio Valley
late Sunday to the eastern Great Lakes Monday and Tuesday, bringing
periods of rain to the entire region.


A poorly organized band of lake effect rain showers centered on the
Tug Hill, east of Lake Ontario will continue to weaken this
afternoon and end by early evening. Otherwise the rest of the area
will be mainly dry with plenty of clouds beneath an expansive post-
frontal stratocumulus deck. Temperatures will remain in the upper
40s to around 50 on the lake plains and mid 40s across higher

Tonight 850MB temps will continue to drop to the -2C to -4C range.
Despite the cold airmass, the lake response will be muted by dry air
and subsidence in the mid levels. Boundary layer flow will become
very weak tonight, allowing land breeze circulations to become
dominant. This will force bands of lake effect rain showers to
primarily reside over the lakes with very little inland penetration.
A few showers may clip the Lake Erie shore southwest of Buffalo at
times tonight. A few more showers may clip the Lake Ontario shore
from the Monroe County over to Oswego County late tonight and
Saturday morning. Otherwise the rest of the area will be mainly dry
tonight. Low temperatures will drop to near 40 on the lake plains
and mid 30s across the Southern Tier and North Country. Extensive
cloud cover should keep frost potential to a minimum.

Saturday will start with lake effect rain showers confined mainly
over Lake Erie and Lake Ontario as land breeze convergence zones
still dominate. A mid level shortwave and weak surface trough will
then cross the eastern Great Lakes in the afternoon. The synoptic
scale trough may produce a few scattered showers in the afternoon
across Western NY. Lake enhancement will bring a greater likelihood
of showers east of Lake Erie across the western Southern Tier,
possibly extending as far north as Buffalo for a few hours mid to
late afternoon. Meanwhile, mainly dry weather will prevail from
Rochester eastward to the eastern Lake Ontario region where drier
mid level air will remain. Highs will reach the lower 50s on the
lake plains and mid to upper 40s on the hills, which is 5 degrees
below normal for late October.


Saturday night into Sunday morning a deep cool cyclonic flow will
support a round of nuisance lake effect rain showers east of both
lakes...however these will be relatively brief and limited in scope
by both the rather short-lived nature of any deeper synoptic
moisture...with some shear another negative influence east of Lake
Ontario. Expect any Lake Erie-driven showers to come mainly during
the first half to two thirds of Saturday night...and the Lake
Ontario activity to be mainly between the second half of Saturday
night and early Sunday morning. Outside of the lake
will be mainly dry through Sunday morning...with just a few spotty
light showers accompanying the passage of a weak shortwave Saturday

During the balance of this period...our attention will turn back to
the synoptic scale as a sharpening baroclinic zone initially sets up
across the Ohio Valley Sunday...then pushes north into the Southern/
Lower Great Lakes Sunday night and Monday in response to a strong
shortwave/attendant area of low pressure rippling northeastward
along the resultant tight thermal gradient. Strong warm advective
lift/isentropic ascent along the baroclinic zone will combine with
plentiful moisture and favorable lower and upper level jet dynamics
(including an impressive coupled upper level jet structure and
strongly diffluent flow aloft) to bring a widespread soaking
rainfall to our region...with this beginning as early as late Sunday
afternoon/early Sunday evening across the Southern Tier...then
overspreading the rest of the area through the balance of the
period. Given all this...have continued the midnight shift`s trend
of raising PoPs... with these now bumped up into the categorical
range for both Sunday night and Monday. At this early
appears that we could be looking at a general inch to inch and a
half of rain across much of our area between Sunday night and
Monday...with somewhat lower amounts of a half inch to an inch
across the North Country.

With respect to temperatures...these will generally run near to a
little below average through the period. Expect lows in the mid 30s
to lower 40s Sunday night...highs in the upper 40s to mid 50s on
Sunday...and lows in the upper 30s to mid 40s Sunday night. On
Monday a tighter thermal gradient will likely be in place with our
region bisected by a slow moving surface frontal boundary...with
a rain-cooled northeasterly low level flow on the north side of the
front keeping highs confined to the mid 40s to lower 50s along and
north of the Thruway...while interior portions of the Finger Lakes
and Southern Tier should see readings reach the 55-60 range south of
the boundary.


Two Pacific systems will impact our region this period. The first,
with a surface low just to our southwest Monday Night will continue
the rain across our region...with low clouds and fog shrouding the
higher hilltops. Moist cyclonic flow aloft will maintain clouds
while rain becomes lighter through the night as the warm conveyor
belt and its lift slides towards eastern New York.

Under cold air advection Tuesday rain showers will continue over the
region and likely not until Tuesday Night when drier air follows the
departing upper level low will our region start to dry from west to

While a spot shower or two is possible early Wednesday across
eastern zones, a mid level ridge will pass over our region...with
this ridge separating the two Pacific systems. Dry weather is
expected under this ridge Wednesday and Wednesday Night.

The next Pacific low, this deeper both aloft and at the surface will
bring rain showers back into our region Thursday. As this upper
level low slowly passes across the Great Lakes Thursday and Friday,
periods of rain showers are likely for our region.

Cloud cover will likely keep our minimum temperatures from falling
below normal, while daytime highs will remain near to slightly above
normal this period.


A band of lake effect rain showers centered across the Tug Hill,
east of Lake Ontario will continue to gradually end late this
afternoon with any remaining MVFR VSBY ending. A cool airmass will
remain in place this afternoon through tonight, supporting fairly
widespread stratocumulus across the eastern Great Lakes. CIGS will
mainly be lower end VFR for lower elevations with areas of MVFR for
higher terrain this afternoon through tonight.

Saturday will start with just a few lake effect rain showers, mainly
over Lake Erie and Ontario. A trough will then cross the eastern
Great Lakes in the afternoon, bringing a better chance of rain
showers to Western NY, mainly from KBUF southward into the Southern
Tier where lake enhancement will develop. This will bring some VSBY
restriction in heavier showers and also bring a period of more
widespread MVFR CIGS. Elsewhere from KROC northeast towards KART,
mainly VFR will prevail through Saturday.


Saturday night and Sunday...VFR/MVFR with a chance of mainly lake
response showers.
Sunday night and Monday...Widespread IFR in rain.
Tuesday...MVFR/IFR with showers likely.
Wednesday...Mainly VFR with a chance of showers.


Northwest winds over Lake Ontario will continue to diminish this
afternoon with waves subsiding. A relatively weak pressure gradient
will then be in place tonight through Sunday with light winds. Low
pressure will then move into the Ohio Valley late Sunday before
moving into the eastern Great Lakes by late Monday. Northeast winds
will increase on Lakes Erie and Ontario as this system approaches,
likely bringing Small Craft Advisory conditions Sunday night through
Monday night.

A cold airmass and a few periods of lake effect showers will bring
the chance of waterspouts starting late tonight and extending
through Sunday on Lakes Erie and Ontario.





NEAR TERM...EAJ/Hitchcock
LONG TERM...Thomas

NWS BUF Office Area Forecast Discussion