FXUS64 KOHX 260906

Area Forecast Discussion
National Weather Service Nashville TN
406 AM CDT Wed Sep 26 2018


While the larger batch of showers and thunderstorms earlier
tonight have moved off the Cumberland Plateau, widely scattered
showers continue to stream into Middle TN at forecast time. With a
frontal boundary not too far off to our northwest, precipitation
coverage is expected to increase throughout the day. While enough
shear for severe or even strong storms is not expected, rainfall
amounts, on the other hand, are becoming a greater concern. The
NAM's persistently high QPF values with the frontal passage give
me pause until I remember that its spatial placement has been good
over the last few days, but the QPF has been overdone. For this
reason, I'm going to focus highest Middle TN PoPs over the
southern and eastern halves of the area, tapering things off over
the northwest as the front starts to push in later this morning.
The front lingers into the evening hours across the south, so I'm
going to carry higher PoPs past 00Z, but we should have full
frontal passage through the mid-state before midnight.
Unfortunately, that doesn't preclude our southern and eastern
counties from seeing additional rain throughout the night and into
the morning hours on Thursday.

Even though I'm not biting on the NAM's outlier QPF values, I do
still think there's a better than average chance of 1 to 3 inches
through Thursday afternoon, with the bulk of that coming today.
The biggest concern continues to be the counties closest to the
Alabama state line. Excessive rainfall over the last couple of
days have saturated the grounds in these counties and again, while
there shouldn't be enough shear for severe storms, wind profiles
later today suggest the potential for backbuilding storms. This
means there is a decent chance that some see more than the 1 to 3
inches. For these reasons, we're going to go ahead and issue and
Flash Flood Watch for our southern tier of counties until 7 pm
this evening. Models seem to want to taper things off into the
evening, at least reducing rain rates, but there is a small chance
that this Watch will need to be extended into the evening hours.

Consensus from global models and their ensembles on Saturday is to
keep rain chances minimal at best, mainly across our southern
counties. Latest GFS/EURO solutions would lean toward a dry forecast
entirely on Saturday, but will allow for a little more run-to-run
consistency before removing PoPs entirely. Sunday will also remain
mostly dry area wide, with the exception again being extreme
southern counties kept under slight chance PoPs. An impulse of
energy rotating around the western side of high pressure over the SE
U.S., along with increased moisture and southerly flow, will be
enough to spark afternoon showers and thunderstorms on Monday.
Heavier precip may set up across western/Middle Tennessee Monday
afternoon, but the GFS/EURO solutions with regard to mid-level
energy/placement vary enough to keep likely PoPs confined to the
west-southwest portion of the CWA for now. Tuesday, a lower chance
for PM showers/t-storms returns. By Wednesday-Thursday morning, a
cold front will begin to take shape over the Midwest and be the
focus for showers and thunderstorms as it propagates east. The 00z
GFS/EURO runs differ significantly from Day 7 and beyond in terms of
timing this front, so have only introduced chance PoPs across the NW
late Wednesday/early Thursday. This timing will likely need
adjusting as we move closer to the middle of next week.

With regard to temperatures, northerly flow at the surface on
Saturday will become southerly on Sunday. Even with a north wind,
reduced cloud cover should still allow for a warm up into the upper
70s/near 80 degF on Saturday. 500mb height rises will help to warm
temperatures into the low-mid 80s Sunday and into the beginning of
the work week. Low temperatures Sunday morning will still be chilly,
dipping into the mid-upper 50s. Otherwise, morning lows in the low-
mid 60s Monday thru Thursday can be expected. Much of the weekend
appears favorable for any outdoor plans!



CKV/BNA/MQY/CSV...Consistency with the terminal forecast
continues thru 27/06Z. Several amendments possible thru 27/06Z.
Continue to expect only some VCSH potentially for CKV/BNA/MQY thru
26/08Z. As sfc front approaches mid state after 26/06Z and then
sags slowly sewd into cntrl portions of mid state by 26/18Z,
another round of shwrs/tstms is likely to occur. As sfc front is
expected to push well southeast of mid state region by 27/00Z,
look for some drier air to work into at least northwestern parts
of mid state region. However, with a continuance of southwesterly
flow aloft anticipated, look for the potential of shwrs to hang
around all terminals expect CKV thru 27/00Z. Potentially VCSH
possible CSV thru 27/06Z. Current VFR ceilings will degrade to
generally low end MVFR/IFR ceilings and stay that way thru much of
the valid TAF period. Exception to this will be CKV which may see
a return to VFR ceilings by 26/21Z. Sly sfc winds will veer
slowly to the N as sfc front progresses thru the mid state region
by 27/00Z.


Nashville 74 61 74 62 78 / 60 20 20 10 10
Clarksville 72 56 72 55 77 / 30 10 10 10 10
Crossville 70 61 70 61 73 / 100 60 60 40 20
Columbia 73 61 74 61 78 / 80 20 20 10 20
Lawrenceburg 73 61 74 61 79 / 100 30 30 20 20
Waverly 73 57 72 56 78 / 40 20 20 10 10



Flash Flood Watch from 7 AM CDT this morning through this
evening for Bedford-Coffee-Giles-Grundy-Lawrence-Lewis-Marshall-
Maury-Van Buren-Warren-Wayne.



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