874
FXUS63 KPAH 212331
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
631 PM CDT Mon Aug 21 2017

.UPDATE...
Issued at 631 PM CDT Mon Aug 21 2017

Updated for 00Z aviation forecast discussion.

&&

.SHORT TERM...(Tonight through Wednesday night)
Issued at 219 PM CDT Mon Aug 21 2017

Agitated cu field has been stymied by the Eclipse, but may still
re-agitate with dew points hovering in the upper 70s/near 80F and
sunshine returning. Latest short res modeling, however, does
downplay active convection, so we`ll likely shave off to slight
chance mentions, if/where warranted.

Otherwise, our eyes turn to the sharp cold frontal boundary
currently draped across Iowa into Nebraska, where there is a 20F
(or close to it) temp and dew point drop behind it. This front
approaches the PAH FA tonight and early tmrw, and pretty much
makes its passage over the course of the afternoon and evening
hours. During this peak heating time, it will encounter still high
dew points with projected surface based Cape in excess of 3K
J/kg. As the jet drives the front thru, deepening shear profiles
favor linear storms/damaging wind potential along the Ohio river
valley, with the slight risk zone extending southward and westward
to almost Paducah, and a marginal risk elsewhere.

The front has made nearly complete passage by 06Z Wed or
thereabouts, with pcpn dying with it. Cooler/drier air then works
in with the help of a large area of surface high pressure, whose
center is over NE/IA/MO/KS area. By 12Z Wed, dew points have
dropped into the 50s in our north, and these will drop on down
across the remainder of the FA thru/by 06Z Thursday.

One more day of humid Highs from the mid 80s north (more
convective cloud debris) to around 90F south is expected tmrw.
Combined with dew points, heat indices will top out in the 90s,
with triple digits hovering just off to our south. Air temps drop
to low end 80s for Wed highs, and Lows do something similar with
one more muggy 70s tonight, transitioning thru the 60s tmrw, and
falling back into the 50s by Wed night.

.LONG TERM...(Thursday through Monday)
Issued at 219 PM CDT Mon Aug 21 2017

Surface High pressure prevails over the Ohio valley through much
of the extended forecast, as an upper Low pinwheels reinforcing
cool/dry shots of air across the Great Lakes and it filters
down/across the Ohio valley. We have reasonably strong confidence
this will be enough of the case thru the remainder of the
week/into the weekend, to preclude any audible mention of Pops,
though some rimfire is possible deeper in the forecast period just
off to our south and west.

Come day 7 next Monday, models return surface plume of moisture
into mid-upr end 60s across portions southern and western FA as
mean upper ridge across western-central U.S. amplifies its
influence into/across the Mississippi river valley and our
Heartland. This will result in a return to near normal
temps/humidity along with some low chance introductory Pops by the
time we start off the next workweek.

&&

.AVIATION...
Issued at 631 PM CDT Mon Aug 21 2017

Isolated convection could impact the sites over the next hour or
so. Therefore, opted for a VCTS for the first hour of the
forecast and see if we can get the storms to dissipate by then.
Gusty winds will be a factor in and around storms. Afterwards,
quiet conditions should prevail. Later on, an incoming frontal
boundary will allow for low level moisture to increase and our
best chance for showers and storms will be late Tuesday morning
through early afternoon. Timing will likely be adjusted as the
progression of the front is fine tuned.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$