Flash Flooding and Heavy Rain in Tennessee, August 16 to 17, 2018

Area Forecast Discussion
National Weather Service Nashville TN
610 AM CDT Thu Aug 16 2018

.UPDATE...
FOR 12Z AVIATION DISCUSSION.

&&

.DISCUSSION...

Scattered thunderstorms occurred around Clarksville over the past
hour, and more showers and thunderstorms over western Tennessee
were poised to push into other parts of western Middle Tennessee
later this morning.

At 3 am, it was mostly cloudy over the western half of the Mid-
State, while mostly clear conditions lingered over the east.
Temperatures were in the lower and middle 70s.

Showers and thunderstorms will become likely today over about the
northwestern half of Middle Tennessee, with scattered storms
expected further east. If the latest HRRR pans out, we may need to
expand our area of likely PoPs a little further to the east.
However, either way, our western areas will still stand the
greatest chance for rain today, with MOS PoPs for our extreme
eastern areas barely getting to 20% today.

As an upper level shortwave shears to our north over the next 12
to 24 hrs, it will drag a band of deep atmospheric moisture
down across all of the Mid- State by tonight, with scattered to
numerous showers and thunderstorms lingering through the nighttime
hours.

On Friday and Friday night, another shearing shortwave rolls in,
keeping us shrouded in clouds, along with scattered to numerous
showers and thunderstorms.

SPC continues to keep us in a marginal risk for severe storms
today and tomorrow, with an expectation of the potential for gusty
straight line winds from a few of the storms, along with heavy
downpours.

The chance of rain decreases gradually from the north Saturday and
Saturday night, as band of deep moisture sags slowly to the
south. As upper level ridging briefly builds over our area on
Sunday, expect that part of the weekend to end up more like a
typical summer day, with partly cloudy skies and scattered mainly
afternoon and evening thunderstorms.

A shortwave drops out of the Upper Midwest and Middle Mississippi
Valley on Monday, increasing our chance for thunderstorms once
again. By Monday afternoon, scattered to numerous showers and
storms will, once again, be in progress over our area. There are
some model discrepancies regarding the progressive nature of this
shortwave Monday night into Tuesday, with the GFS showing a more
highly sheared and slower movement and the ECMWF sweeping it
eastward a bit faster. For now, will keep likely PoPs running for
Monday night, with the expectation that they may need to be
eventually lowered, if the faster ECMWF pans out.

By mid to late next week, models build an amplified upper trough
over the eastern United States, putting us in a not-so-hot
northwest flow--thermally speaking. Despite lots of sunshine
expected by Wednesday and Thursday, daytime highs should only top
out in the 80s. Highs at BNA both of those days are forecast to be
87 degrees. So, maybe a wee taste of fall, if we're lucky.

&&

.AVIATION...
12Z TAF DISCUSSION.

BNA/MQY/CKV/CSV...An area of showers with embedded thunderstorms
is propagating slowly into Middle Tennessee this morning. The
cells have formed right along an upper trough. The HRRR shows this
activity weakening as it pushes deeper into Middle Tennessee and
the shortwave flattens out. So we'll probably see some activity
this morning and into the early afternoon at CKV, maybe a little
later at BNA & MQY. Showers won't likely affect the Cumberland
Plateau until after 00Z.

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

DISCUSSION......19
AVIATION........08

Hazardous Weather Outlook
National Weather Service Nashville TN
501 AM CDT Thu Aug 16 2018

TNZ005>011-023>034-056>066-075-077>080-093>095-171015-
Stewart-Montgomery-Robertson-Sumner-Macon-Clay-Pickett-Houston-
Humphreys-Dickson-Cheatham-Davidson-Wilson-Trousdale-Smith-
Jackson-Putnam-Overton-Fentress-Perry-Hickman-Lewis-Williamson-
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501 AM CDT Thu Aug 16 2018

This Hazardous Weather Outlook is for portions of Middle
Tennessee.

.DAY ONE...Today and Tonight

Look for storms to begin developing across Middle Tennessee today.
Some of the storms will become strong to severe, with damaging
straight-line winds the primary threat.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

There is a marginal risk of severe storms again on Friday.
Damaging straight-line winds and large hail are the primary
threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed today and tomorrow.