Forecast Discussion

Forecast Discussion for BUF NWS Office
000
FXUS61 KBUF 201026
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
626 AM EDT Sat Jul 20 2019

.SYNOPSIS...
Oppressive summer heat and humidity will continue across the entire
area today. There will be several brief rounds of showers and
thunderstorms today through Monday, with plenty of rain free time as
well. A cold front will slowly cross the area Sunday night, bringing
an end to the heat and humidity.

&&

.NEAR TERM /THROUGH TONIGHT/...

Most of the region is dry early this morning, with scattered
showers and storms just upstream across southern Ontario and
Lake Erie. These showers and storms will approach Western NY by
mid morning as forcing from a weak, convectively generated
shortwave moves into the eastern Great Lakes.

Chances for showers and thunderstorms will continue today and
tonight, but timing and placement of the rain will be difficult at
best given the weakly forced and very unstable environment. The
forcing is mesoscale and convectively generated, born of upstream
convective clusters and inherently difficult to forecast by even
high resolution model guidance. A belt of 30-35 knot flow in the 850-
700mb layer will remain over the eastern Great Lakes through
tonight, with subtle variations in wind speed yielding mesoscale
moisture convergence at times.

In a general sense, expect one area of scattered showers and storms
to cross the area from west to east this morning through midday as a
weak convectively generated shortwave crosses the eastern Great
Lakes. By this afternoon this feature will be moving east of the
area, although additional scattered showers and storms may develop
along and inland of lake breeze boundaries. By late this afternoon
or this evening, the next convectively generated shortwave will be
moving across southern Ontario and approaching the area. Several
more convectively generated shortwaves will likely move east across
the area tonight as a weak frontal zone sags slowly southeast across
the area. This will support chances of showers and storms through
much of the night.

PWAT values remain at around 2 inches on average through tonight,
supporting torrential downpours with any storms that develop. There
may even be an isolated flash flood risk given the environment, if
any storms train along boundaries. A few storms may also become
severe, with isolated damaging wind the primary risk. A more
organized severe weather risk is not out of the question if a cold
pool driven MCS were to develop.

Oppressive heat and humidity will likely continue today. Expect
highs to reach the lower 90s at lower elevations away from the
immediate lakeshores. Surface dewpoints will continue to run in the
low to mid 70s, yielding a heat index in the upper 90s to lower 100s
in many locations. The highest heat index will be along a corridor
just south of Lake Ontario extending into the Genesee Valley and
western Finger Lakes, where a few hours of a 105 heat index is
probable. The one caveat, if showers and storms or more extensive
convective cloud debris cross the area during peak heating, this
would hold temperatures and the heat index down below warning
criteria. It will remain very muggy tonight, with dewpoints
remaining in the lower 70s.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Some relief from the heat will come on Sunday, however it`s the
reduction in humidity that will be the most noticeable, as the first
of two cold fronts slowly finishes pushing southward across the
area, then stalls out across northern PA by late in the day.
Humidity levels will lower from north to south across the region,
with the chances for showers and thunderstorms also lowering as we
progress through the day. By later Sunday afternoon, north-country
may be shower free, with showers and thunderstorms remaining likely
toward the NY/PA line closer to the stalled out frontal boundary.
One last warm day with highs in the lower to mid 80s.

A secondary cold front will slide south through the region Sunday
night, then like the first front, stall out somewhere to the
south/southeast of our area by early Monday. At the same time, the
upper level pattern will start to become much more amplified, as a
large longwave trough carves out across the eastern U.S. and a large
ridge builds across the west. Will keep the chance for some
showers/isolated storm in the forecast, with best chances again
across the Southern Tier closer to the boundary. As the upper level
trough continues to dig further south across the eastern half of the
country, an area of surface low pressure will form across the Ohio
Valley beneath the base of the upper trough along the stalled out
frontal boundary. The surface low will then deepen as it rides
northeast from the Ohio Valley to southwestern New England along the
now quasi-stationary front by late on Monday. The swath of
precipitation associated with this system continues to trend more to
the north and northwest. That said, after just the chance for a few
showers/storm Sunday night, have increased PoPs fairly substantially
for Monday as the low moves to the northeast, just southeast of our
area. To account for this have placed likely PoPs for
showers/isolated storms from the Southern Tier to the western Finger
Lakes, with chance PoPs across areas further north. Lows Sunday
night will be appreciably cooler than the previous few nights with
temps dropping back into the low to mid 60s. Monday`s temps will
continue this same trend, with highs much cooler in the lower to mid
70s.

Steadier precipitation will taper off from west to east Monday night
as the surface low moves toward the New England coast. Have
introduced a small chance of showers as we head into Tuesday as
well, mainly as increasing diurnal instability combines with
shortwave energy pivoting across the area through the main longwave
trough. Continued cooling of our airmass will result in fairly
comfortable conditions for the heart of Summer with overnight lows
dropping back into the mid 50s to lower 60s and highs on Tuesday
again in the lower to mid 70s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Dry weather is expected for Tuesday night through Wednesday night,
with a slight chance for a few showers on Thursday as a shortwave
passes over the area. The overall pattern will deamplify some toward
the end of the period, however will maintain a general trough over
the eastern half of the country.

Temperatures rebound a few degrees by Wednesday, however remain a
touch below normal with highs in the mid to upper 70s. A slight
warming trend will begin for Thursday and Friday when temperatures
will increase closer to normal, with highs in the upper 70s to
lower 80s.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...

Today and tonight there will be several chances for showers and
thunderstorms as weak/subtle forcing interacts with strong
instability. Model trends suggest one round of scattered showers
and thunderstorms may move across the area from morning through
midday, with another, greater chance of showers and
thunderstorms arriving late afternoon or early evening and
continuing through tonight as a frontal boundary moves southeast
across the area. Confidence in precise timing and placement of
the greater shower and thunderstorm chances is low in this type
of pattern. The majority of the time will still be VFR today and
tonight, but local/brief MVFR to IFR conditions will be found
in thunderstorms.

Outlook...

Monday...Mainly VFR with a chance of a few brief rounds of showers
and thunderstorms with associated local MVFR to IFR.
Tuesday and Wednesday...VFR conditions expected.

&&

.MARINE...
Southwest winds will average around 15 knots again today. This will
produce choppy conditions at times especially on Lake Erie, although
winds and waves will likely remain below Small Craft Advisory
levels.

There will be a chance of a few scattered thunderstorms at times
through the rest of the weekend. Any thunderstorm may produce
locally higher winds and waves.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Heat Advisory until 6 PM EDT this evening for NYZ007-008-
     010>012-019>021-085.
     Excessive Heat Warning until 6 PM EDT this evening for
     NYZ001>006-013-014.
MARINE...None.

&&

$$

SYNOPSIS...Hitchcock
NEAR TERM...Hitchcock
SHORT TERM...JM
LONG TERM...JM
AVIATION...Hitchcock
MARINE...Hitchcock

NWS BUF Office Area Forecast Discussion