Area Forecast Discussion
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FXUS61 KPBZ 210127 AAB

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
927 PM EDT Sat Jul 20 2019

Warm, humid conditions will continue through the weekend with
afternoon/evening storm chances. Frontal passage will bring rain
throughout the day Monday, followed by cooler, drier weather for
much of next week.


A very moist, moderately unstable airmass is engulfing the Ohio
Valley this evening beneath very weak mid-level flow. The 00Z KPBZ
RAOB indicates steep low- and mid-level lapse rates and deep moisture
surmounted by a dry layer. This combination supports the substantial
DCAPE evident in mesoanalysis. As a result, the atmosphere is
conditionally primed for downbursts in any vigorous thunderstorms
that can form.

Three areas of convective development are evident this evening.

-one area is along a diffuse residual outflow boundary in west-
 central PA. Isolated storms have developed in this zone from PIT-
 BTP-IDI-LBE. A couple storms have been briefly intense, but mostly
 are reported to have produced torrential rain.

-a second area is along a lake breeze from near CLE-YNG. Storms here
 have had greater longevity as they move ewd along and north of I-80.
 These storms also have produced very strong wind.

-the third area is the more-organized MCS exiting ern MI and poised
 to cross Lake Erie. The outflow appears to be undercutting the
 storms with swd extent, so it is unclear how its future will fare as
 the storms cross the cooler lake. It is possible the outflow could
 interact favorably with storms along the lake breeze to lead to
 upscale growth, or it could interact destructively and kill ongoing

So, PoPs have been adjusted a bit to reflect higher values now that
storms are no longer a conditional threat. But increasing uncertainty
in storm evolution/tenacity late tonight does not warrant categorical
PoPs at this time.

If widespread storms develop in the I-80 corridor, flash flooding is
a likelihood owing to upwards of 4-5 inches of rain observed last


Relief from the heat is in sight as models are in agreement with the
breakdown of the central-/eastern-CONUS ridge and the establishment
of an amplified western-CONUS ridge with strong troughing across the

A cold front is expected to advance swd and stall somewhere in the
vicinity of the I-90 corridor on Sunday morning as cyclogenesis
occurs upstream over the Plains. While the quasi-stationary front
should act as a focus for convection on Sunday, scattered convection
across the CWA is likely with diurnal destabilization.

Although humidity and heat will be similar to the last two days, it
does not appear that they will combine favorably to produce the
oppressive apparent temperature observed during the last two days. In
addition, rapid increase in cloud cover and early afternoon convective
development producing cold outflow will hinder the diurnal cycle. At
this time, it does not appear that a Heat Advisory will be needed
for tomorrow.

Coverage in showers/storms will pick up overnight Sunday through
Monday as the aforementioned trough deepens across the Great Lakes
and divergence associated with the right-entrance region of an
upper-level jet spreads across the Ohio Valley. The cold front will
then push through the region late Monday as the trough axis and
low/mid-level low exit northeastward.


Strong cold air advection behind the front will make for seasonal or
even slightly below seasonal temperatures for the area through much
of next week. Highs will be in the mid 70s to low 80s with lows in
the mid 50s to low 60s. Temperatures will rebound this weekend as
southerly flow returns as high pressure slides east off the Atlantic
and as a trough digs across the central CONUS.

Global model consensus places the trough and frontal system across
PBZ CWA on Sunday, leading to a rather wet day across the area. From
there, with just minor differences, global models suggest a less-
amplified /more-flat wave pattern across North America, leading to a
moderation in temperatures to near or just above seasonal values.


A residual outflow boundary and lake breeze have focused isolated-
scattered tstm development this evening ahead of an MCS advancing out
of MI. VCTS was carried at PIT, AGC, LBE, FKL and DUJ given the
ongoing storms.

The MCS crossing Lake Erie offers greater uncertainty, as it is
unclear how long it will last and whether it will interact favorably
or destructively with convection along a lake breeze inland from Lake
Erie`s shore. The current expectation is that there will be at least
some impact near KFKL/KDUJ as this line approaches late this evening.
Models indicate that it will dissipate late tonight near FKL-DUJ.

Storms are expected to regenerate by late morning Sun along the
remnant outflow /quasi-stationary frontal boundary. A modestly-
organized squall line appears possible that could affect most
terminals during the afternoon.

Widespread restrictions will be possible Sunday evening into Monday
with the approach and passage of a cold front.





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