FXUS61 KBUF 170956

Area Forecast Discussion
National Weather Service Buffalo NY
556 AM EDT Wed Jul 17 2019

Showers and a few thunderstorms will continue off and on through
today, along with some heavier downpours as remnant tropical
moisture tracks across the area. Oppressive summer heat and
humidity will then build into the region Thursday through the
weekend with occasional showers and thunderstorms.


Initial round of showers and some embedded thunder passing across
Lake Ontario and the North Country early this morning. This
activity maximized on northern edge of the low level jet and mid
level short wave. Once this wave passes, we'll see a brief
decrease in coverage.

Expect coverage of showers and embedded thunderstorms to increase
once again by mid morning as shortwave axis associated with
the remnants of Barry comes into the region. Severe threat
continues to look limited with marginal instability and shear
profiles. Heavy rain remains the main concern. A tropical
airmass will reside across the area today with precipitable
water values of at least 2 inches with warm cloud depths close
to 12K feet. Certainly these ingredients would suggest the
potential for torrential downpours and extremely efficient
rainfall rates, especially when combined with increased forcing
for ascent associated with the shortwave energy. Isolated flash
flooding is certainly a possibility but difficult to pinpoint.
Certainly the evolution of any training activity will be closely
monitored through the day today, with the most vulnerable
locations being across the Southern Tier/southern Finger Lakes
due to terrain, and urban areas. A surface trough is also
expected to drop south through the area during the afternoon
enhancing the forcing.

Clouds and rain around today will keep temperatures well down from
what we saw Tuesday afternoon with highs only reaching the upper 70s
to lower 80s.

The best forcing will push away from the area tonight as the
shortwave shifts to the east coast and the surface trough pushes
south of the area. This will bring a downward trend to the showers
and embedded thunderstorms.


...Threat For Dangerously High Apparent Temperatures by Friday...

As the remnants of Barry move east, our focus this period will shift
to a significant increase in heat and humidity.

Thursday will be the start of an extended period of very warm
and sultry weather. As heights build in the wake of the now
exited tropical remnants, 850MB temperatures will climb into the
upper teens C. Given a fairly well mixed environment and the
return to at least partly sunny skies, afternoon temperatures
should have no problem reaching the mid to upper 80s across the
lower elevations, with a few 90 degree readings not out of the
question across the typically warmer spots. Dew points in the
upper 60s to lower 70s will allow heat index values to reach
into the low 90s across the lake plains and Genesee Valley, with
a few spots possibly nearing the mid 90s. This could warrant
Heat Advisories, which are issued when heat indices reach at
least 95 for a minimum of two hours. At this time, areas
possibly reaching heat index values of at least 95 do not look
to be too widespread. That said, a slight uptick in air
temperatures or dew points could easily move some areas up to
that 95 threshold. Otherwise, the sultry conditions should be
accompanied by mainly dry weather. Carried only slight chc PoPs
across portions of the interior Southern Tier and western Finger
Lakes region for Friday afternoon convection, with low chance
PoPs across the northcountry. Even in these areas though, weak
capping below 700MB and relatively dry air in the mid levels may
be enough to preclude much in the way of any convection.

As an impressive sub tropical ridge builds across the southern tier
of the country Thursday night and Friday, a 35 to 40kt jet extending
around the northern periphery of the 700MB portion of the ridge will
advect even warmer and more humid air across the Lower Great Lakes.
One can already see the potential that this airmass will have by
looking at the plethora of heat related flags that are in place
across the center of the country, extending east to the Ohio Valley.
850MB temperatures over our region are forecast to climb to around
20C Thursday night, and to 22C on Friday. Its one thing to see this
displayed by deterministic guidance, but even more impressive to see
it in a consensus ensemble forecast such as the SREF or GFS.

Temperatures Thursday night will only drop into the lower 70s across
the lower elevations, then as the core of the oppressively hot
airmass advects across the Lower Great Lakes, max temperatures can
be expected to reach the low to mid 90s for the majority of the
forecast area Friday afternoon. Readings will be several degrees
lower in the lake cooled air in the immediate Buffalo suburbs,
across the higher terrain and also in the Thousand Island region.
This heat, combined with dew points in the mid 70s, will support
stifling heat index values possibly as high as 105-107. Heat
Advisories can be expected for the entire region, with the risk for
Excessive Heat Warnings for some of the counties bordering the south
shore of Lake Ontario, as well as the typically warmer locations
across the western Finger Lakes region.

After a mainly dry Thursday night, precip chances will increase some
toward early Friday morning. Appears there is the possibility for a
convectively enhanced shortwave/MCS to potentially ride southeast
along a weak warm frontal boundary that will near western NY Friday
morning. Convection looks fairly impressive over the Upper Great
Lakes earlier Thursday night, however it appears as though it will
be in a much weakened state by the time it reaches our region Friday
morning. That said, it would give parts of the region a chance for a
little rain during the morning. Otherwise after a mainly dry midday,
there will be a another chance for showers and thunderstorms along
and inland of any lake breeze boundaries, with a bit better chance
for convection across the northcountry as a weak shortwave moves
across northern NYS.

Any convection late Friday would die off during the evening hours
for areas south of Lake Ontario. However, low chance PoPs will
remain in place across the northcountry through the overnight, as
yet another piece of shortwave energy moving east along the northern
periphery of the upper ridge, passes just north of Lake Ontario.
Friday night will see the potential for just about the entire area
to see lows only drop into the lower and middle 70s, combine this
with dew points only a tick or two lower than the air temperatures,
and you have what is going to be a very uncomfortable night for
sleeping without the A/C.


...Continued Oppressive Heat and Humidity for the Weekend...

An impressive 592-595dm sub tropical ridge extending across the
southern half of the country will remain our dominant weather
feature as we open this forecast period. Anomalously high H85
temperatures of 20 to 22c will continue to pour across our region
around the 'top' of this hemispheric sized anticyclone...and this
will keep dangerously high heat and humidity in place throughout our
forecast area on Saturday. Max temps will be in the lower 90s for
all but the lake shadowed areas immediately downwind of Lakes Erie
and Ontario and across some of the higher terrain...with heat
indices/apparent temps likely exceeding 100 again for the counties
lining the south shore of Lake Ontario...including the bulk of
Livingston co. This would support continued Heat Advisories and
possible Excessive Heat Warnings.

While it will still be quite warm and uncomfortable on Sunday...the
good news is that Saturday should be the last day of the potentially
dangerous heat. A cold front is forecast to drop south across our
region Saturday night and/or Sunday...so at this time...our concern
will once again shift...this time from oppressive heat to the risk
for severe weather. This boundary will likely become the focus for a
an eastward propagating MCS. As has been discussed at length now,
the pattern developing is textbook for a tongue of steep mid level
lapse rates (EML plume) to work from the Plains and Upper Great
Lakes into our region. HYSPLIT trajectory forecasts advect the mid
and upper portions of this unstable airmass into our region for the
weekend. This can also be seen in BUFKIT sounding profiles and plan
view H500-700 lapse rate forecasts that suggest fairly steep 700-500
mb lapse rates of 7.5 to 8.5 deg c/km to be present across our
forecast area. Why is this significant? The EML, in combination with
the aforementioned weak frontal boundary hanging around our area,
and steep mid-level lapse rates, will provide the potential for
strong to severe convection. Don't forget there also could be the
potential for an MCS. In fact, a study done by Ekster and Banacos
found that on severe weather days when an EML was present over 80
percent of those days contained numerous high end severe weather
reports. The target for this severe weather potential is now
Saturday night or early Sunday morning.

As the front slowly pushes across and to the south of our region
Sunday afternoon and night...it is projected to stall over
Pennsylvania. This would leave much of our forecast area prone to
additional showers and thunderstorms.

A reinforcing/secondary cool front is then forecast to push through
the region later Monday. This should finally usher in a cooler
and drier airmass across the region for Tuesday.


Tropical airmass in place across the area. Initial mid level wave
generating an area of convection will impact areas from KART to
KRME through 10z. Secondary wave, remnants of Barry, will cross
the region later today resulting in clusters of showers and
embedded thunderstorms. Visibility restrictions to at least MVFR
will likely occur with most of the showers and thunderstorms.
Should see ceilings fall to higher IFR or low MVFR in the
afternoon at IAG, BUF and ROC as passage of sfc trough/lake
breeze off Ontario shifts winds to northerly in the afternoon.


Tonight...IFR/MVFR. A chance of showers and thunderstorms early in
the evening at JHW.
Friday through Sunday...Mainly VFR with a chance of showers and


A warm southwesterly flow will be present across the lakes through
the end of the week. While winds may occasionally reach 15 knots,
especially on Friday, waves will likely remain around 2 feet or less
on the waters.

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





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