Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 210445
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1145 PM CDT Sun Aug 20 2017

.UPDATE...
Issued at 1145 PM CDT Sun Aug 20 2017

Updated for 06Z aviation forecast discussion.

&&

.SHORT TERM...(Tonight through Tuesday night)
Issued at 318 PM CDT Sun Aug 20 2017

Widespread convection continues over our western 4 counties in
southeast Missouri as of 20Z. Torrential rainfall and lightning
are the main concerns, but some very localize strong outflow winds
will be possible. The storms are trying to move east, but figure
the overall development will be to the southeast through the Boot
Heel and into northwest Tennessee through the remainder of the
afternoon. Not sure if it will make it east of the Mississippi
River in southern Illinois, but the river counties of Kentucky may
be impacted. There is considerably drier air over northwest
Tennessee, so a weakening trend is likely as it gets east of
Mississippi River.

Farther northeast along the old outflow, an isolated storm will
be possible, but they have been struggling to develop thus far
despite temperatures in the lower 90s and dewpoints in the mid to
upper 70s. Low-level winds are veered to the southwest ahead of
the outflow in Illinois, so the convergence may be negligible up
there.

The dry air over Kentucky and portions of southern Illinois has
helped keep heat indices in check, while clouds and outflow have
provided relief from 100-105 indices over southeast Missouri and
southern Illinois. No plans to issue a Heat Advisory at this time.

We should be dry throughout the area tonight. With mostly clear
skies and nearly calm winds, more patchy fog will be possible.

The 12Z models continue to bring a cold front through the area
late Tuesday into Tuesday evening. The GFS actually brings a
decent amount of QPF southward through the area late Monday night
into Tuesday morning, which would likely hold down the convective
potential for the afternoon and evening. The NAM does not have the
early morning QPF, and indicates the potential for some vigorous
convection in the late afternoon and evening. If the NAM solution
is right some strong to severe storms would be possible.

...Eclipse Forecast...

The 12Z models are emphasizing Iowa for MCS activity tonight, but
it will be moving east and is forecast to die out over northern
Illinois and northern Missouri Monday morning. This should keep
anvil blow off to our north. We continue to play a general diurnal
scenario with plentiful cu development, but the eclipse may limit
this some. There continues to be some signal for convective
development around midday, mainly in the Ozark Foothills. This
activity may eventually spread eastward a bit into southwest
Illinois most likely after the total eclipse around 21Z.
Elsewhere, the area should be dry.

Heat indices will be similar to today`s levels with some
modulation by the eclipse. The worst conditions will likely be
right after the eclipse. We will continue with the Special Weather
Statement for the heat. If we hear of significant numbers of heat
issues from this afternoon, we may need to go ahead and issue a
Heat Advisory for tomorrow, but for now we have not heard of any
such issues.

.LONG TERM...(Wednesday through Sunday)
Issued at 318 PM CDT Sun Aug 20 2017

A pronounced difference in air masses will become apparent as we
transition into mid-week. Following the passage of a cold front,
lower temps and dew points will arrive on Wednesday. Highs on
Wednesday will be in the lower 80s as dew points fall to around 60
in the afternoon. Some post-frontal showers may linger into
Wednesday morning, mainly in the Tennessee and Arkansas border
counties. Otherwise, skies will become mostly sunny.

An unusually strong surface high for August will move slowly east
across the Great Lakes region Thursday through Saturday. This high
will suppress the summer heat well to the south of our region. The
models continue to indicate 850 mb temps will fall to around 11C
both Thursday and Friday. The extreme dryness of the air mass will
yield clear, cool nights and sunny, pleasant afternoons. Overnight
lows will be mainly in the upper 50s, with daytime highs around 80.

The 500 mb longwave trough position will remain anchored over the
eastern USA next weekend. As the first shortwave trough ejects
northeast out of New England, the next shortwave will move southeast
into the upper Mississippi Valley on Sunday. Ahead of this
shortwave, there will be a slow increase in warmth and moisture as
low level winds become south. This will lead to a slight chance of
showers and storms Sunday in parts of our region. Highs will
moderate a bit Sunday, reaching mainly into the middle 80s.

&&

.AVIATION...
Issued at 1145 PM CDT Sun Aug 20 2017

Winds will be calm or near calm tonight, so we could see a repeat
of this morning`s fog, with the worst conditions at KCGI and
KPAH. Some isolated to scattered convection will be possible over
southeast Missouri by late morning Monday, but most of it should
be to the west and northwest of KCGI. Otherwise, some diurnal cu
will form that should stay few to scattered. Cu will dissipate
after around 00Z and some high level clouds will be possible
during the evening hours.

&&

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

$$



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