Area Forecast Discussion
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FXUS61 KPBZ 210144
Area Forecast Discussion
National Weather Service Pittsburgh PA
944 PM EDT Thu Oct 20 2016
Low pressure and a crossing cold front will generate more rain
through Friday. Much cooler weather will follow for the weekend.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Even the new 00z KPBZ raob indicated 1.42 in of precipitable
water, which is roughly 200 percent of normal. This is in an
environment of deep southwesterly moisture feed as indicated by
nearly saturated conditions from the surface up to about 500 mb
with strong southwesterly flow through the layer. This is embedded
in a deeper layer of shear and a strongly anti-cyclonically
curved upper jet over the region. As the mid and upper wave slowly
advanced eastward overnight and tilt turns from positive to
neutral and eventually negative, the environment will likely
remain conducive to heavy rainfall as low level flow right off the
deck will likely continue strong isentropic ascent into the slowly
SEward moving frontal boundary. All of this is only considering
the synoptic portion of the equation.
In the more mesoscale, several smaller vort maxima are advancing
northeastward in the deeply sheared environment ahead of the mid-
level wave. Each of these is harnessing a withering amount of
surface CAPE. Due to the slow-moving nature of the surface
boundary as well as mesoscale elements tracking up it, several
successive rounds of heavy rainfall will be possible as these
elements move northeastward in a friendly large scale environment
even as the threat for more significant convection wanes. The
previously issued flash flood watch remains in effect for this.
However, as convection tracks farther south and east into the area
and an increasing amount of the available surface-based
instability is used up, the severe thunderstorm watch has been
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Showers are expected to continue Friday as the surface low and
it`s associated cold front slowly slides east of the area. The
upper trough is progged to continue it`s slow approach Friday,
with the axis crossing Friday evening.
Cold advection in northwest flow, and the proximity of the upper
low/trough should keep shower chances continuing Saturday for
portions of the area. A few locations especially in the higher
terrain could see a few snow showers mix in at times. Building
high pressure and lowering inversion heights should result in
rapidly decreasing POPs by Saturday evening, with dry weather
continuing Sunday. Much cooler temperatures are expected, with
readings near or several degrees below the seasonal averages.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A fast moving shortwave is progged for an early week passage, with
most of the shower chances remaining north of PIT. Ridging is
progged thereafter through mid week before another trough advances
out of the Midwest by late week. Temperatures should average a few
degrees below seasonal levels through the period.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
All sites should gradually transition to IFR as low level moisture
increases and cold advection gradually begins. This will occur as
thunderstorm chances increasingly become confined to the SE
portions of the area. Guidance continues IFR conditions at all
sites through Friday, however there is a chance that as wind gusts
increase that a few sites may pop to MVFR for a time during the
.OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...
Periodic restrictions are expected into Sunday as an upper trough
crosses the area.
MD...Flash Flood Watch through Friday morning FOR MDZ001.
OH...Flash Flood Watch through Friday morning FOR OHZ039>041-
PA...Flash Flood Watch through Friday morning FOR PAZ007>009-
WV...Flash Flood Watch through Friday morning FOR WVZ001>004-012-