Forecast Discussion

Forecast Discussion for BUF NWS Office
FXUS61 KBUF 041847

Area Forecast Discussion
National Weather Service Buffalo NY
247 PM EDT Tue Aug 4 2020

Unsettled weather will remain over the region through tonight as
weak disturbances pass through, while tropical system Isaias races
northeast across New England. High pressure will build across the
region late Wednesday with near normal temperatures and a dry
weather pattern through the end of the work week.


Regional radars show isolated to scattered showers across western NY
while widespread moderate to heavy rain to north of Isaias lifts
across eastern Finger Lakes and the North Country. Thus far some
areas east of Lake Ontario have seen over 0.75 inch thus far.

Main impact through the afternoon will be over portions of North
Country as moderate to at times heavy rain continues to lift across
the region as Tropical Storm Isaias lifts across southeast NY.
Appears most widespread and heaviest rain occurs east of Lake
Ontario between 3 PM and 6 PM. By early this evening, expect
rainfall totals of an inch to an inch and a half over portions of
the North Country, with localized amounts over 2 inches certainly
possible. These values still end up under 3 hr and 6 hr FFG, so at
this point looks like this moderate to heavy rain will just help put
a dent into the ongoing drought conditions seen in this region most
of the summer. Localized flooding potential not out of question

Farther west from Genesee valley to western NY, disorganized
isold to scattered showers continue to stream from ssw to nne
along inverted sfc trough across the region. Based on sfc wind
directions as light as they are, looks like the trough currently
extends from eastern Southern Tier nnw to between Buffalo and
Rochester. Though overall shear and instability is weak through
this afternoon, there is just enough of both to support isold
stronger storm especially those that form along any boundaries
(lake breezes and/or the primary sfc trough). Departure of
cirrus shield from broad upper jet and Isaias over southwest NYS
will only help instability build. Main hazard from any storms
will be brief heavy rains with ribbon of higher PWAT overhead
along sfc trough axis.

Tropical system quickly exits eastern Lake Ontario region between 6
PM and 8 PM. Eventually cold front sweeps across the region later
tonight. Shortwave moving through and lingering instability due to
cooler air crossing Lake Ontario will maintain the chance for a few
showers or an isolated thunderstorm southeast and east of Lake
Ontario through much of the night. Elsewhere, scattered showers will
diminish especially after midnight as the shortwave lifts through.

On Wednesday, primary upper low settles across Quebec through the
day. Cyclonic flow aloft will combine with some lingering moisture
in the wake of Isaias and even some lake enhancement to aid a
west/southwest upslope flow (H85 temps dip down into the upper
single digits C). This will produce a few showers east of Lake
Ontario during the first half of the day (most prevalent over the
terrain), with dry conditions elsewhere. By Wednesday afternoon, all
areas will trend drier as sfc high pressure builds in from the
southwest. High temps on Wednesday will be cool again with readings
mainly in the low to mid 70s. In fact, some areas across the
interior higher terrain may possibly only top out in the upper 60s.
These cooler temps along with dew points in the low to mid 50s and a
brisk westerly breeze will make it feel very refreshing outside.

Cool temps aloft persist on Wednesday night with H85 temps down to 7-
8c yielding delta t/s across the waters of 15c on Lake Ontario and
18c on Lake Erie. Large scale subsidence and drying does not leave
much synoptic moisture around, but given the over-water instability
think NAM idea of showing a few convergence bands (enhanced H9-H85
moisture plume) off Lake Ontario has merit. Put just a small chance
of showers in through late Wed night. Lows on Wednesday night will
be cool as we have seen in quite a while with readings over the
typical cool spots possibly into the upper 40s while elsewhere temps
will fall into the 50s.


High pressure will be across the eastern Great Lakes Thursday. A
cool, dry airmass will result in high temperatures reaching the
upper 70s to low 80s. While most of the region will be mostly sunny,
clouds will start to increase across the western Southern Tier as a
southerly flow transports moisture into the region.

An upper level trough will track across the Mid-West and Ohio Valley
Thursday night into Friday. Moisture will continue to move into New
York from the south and chances for showers will increase across the
western Southern Tier and Finger Lakes region Friday into Friday
night. The corridor of moisture will move east as the upper level
trough continues to approach the region Friday and Friday night and
the chance for showers will end Friday night. High temperatures will
reach the low 80s Friday and fall to the upper 50s to low 60s Friday


Aside from a diurnally driven shower or storm Saturday or Sunday
afternoon/early evening across the Finger Lakes and Southern Tier,
weak ridging should provide mainly dry weather for the majority of
the weekend. A moist southwesterly flow will develop on Monday and
continue into Tuesday as high pressure slides east of the area,
while an upper level trough over the upper Great Lakes approaches
the region. Increasing low level moisture and lowering heights aloft
combined with diurnal heating will bring the next better chance for
some showers and storms to start the work week.

Near normal temperatures to start the period will trend above
average by the weekend into the start of next week, along with a
noticeable uptick in humidity as we progress through the period.


Mix of MVFR to VFR conditions as scattered showers lift across
western NY to the Genesee Valley. These showers will be accompanied
by some thunder this afternoon. Meanwhile, widespread and
steady rain, potentially heavy at times, will continue at ART
as western fringe of Isaias lifts across the North Country.

Widespread rain over North Country will diminish this evening,
leaving scattered showers across the whole area through the night as
a cold front and upper disturbance lift across the region. MVFR to
VFR conditions, with localized IFR over the Southern Tier.


Wednesday...VFR, but showers possible east of Lake Ontario through
the morning.
Thursday through Sunday...VFR.


Light winds and negligible waves this afternoon before a cold front
crosses the lower Great Lakes tonight helping to increase winds from
the northwest, especially on Lake Ontario. A round of Small Craft
Advisories continue late tonight into Wednesday on Lake Ontario.

Waterspouts are possible through this evening with any stronger more
developed shower or thunderstorm over the waters. More waterspouts
will be possible behind the cold front later tonight through
Thursday with cooling temperatures. The period for best waterspout
potential would be later Wednesday into Thursday morning with cold
temperatures aloft and winds becoming light enough to favor
developing low-level convergence zones where waterspouts typically


MARINE...Small Craft Advisory from 2 AM to 5 PM EDT Wednesday for
         Small Craft Advisory from 2 AM to noon EDT Wednesday for
         Small Craft Advisory from 4 AM Wednesday to 2 AM EDT
         Thursday for LOZ044-045.




NWS BUF Office Area Forecast Discussion