Flood and Strong Wind in Tennessee, September 12 to 15, 2024

Area Forecast Discussion
National Weather Service Nashville TN
1221 AM CDT Thu Sep 12 2024

...New AVIATION...

.UPDATE...
Issued at 851 PM CDT Wed Sep 11 2024

Weather is quiet on this side of Francine this evening. The system
is making landfall in southern Louisiana and is expected to make
it to northern Mississippi by Thursday afternoon/evening. This
should be when we start to see impacts from the storm. Any tornado
threat still appears to be focused in our southern most counties
where weak instability will coincide with high 0-1km SRH late
Thursday night through early Friday morning.

As for the flooding potential...While there may be some pockets
of heavy downpours Thursday evening, the better heavy rainfall
threat will be when bands of rain start to take on a south to
north orientation late Thursday night into Friday morning. This
banding could produce a narrow swath of heavier rainfall that may
cause flooding issues. Some CAMs place the highest totals over
northern AL, some over western Middle TN, or further west across
the Tennessee River. So there's still quite a bit of
uncertainty...but areas west of I-65 and south of I-40 seem to be
in the most likely area to potentially experience flooding issues.
If current model runs are correct, what's left of Francine will meander
nearby and weaken as we move into the weekend...providing at
least the chance for more moderate and light rain Saturday and
Sunday for areas that desperately need it.

&&

.SHORT TERM...
(Rest of today through Friday)
Issued at 1046 AM CDT Wed Sep 11 2024

It is another quiet day across the area with temperatures in the
70s and climbing into the 80s. Temperatures are expected to climb
into the mid 80s to lower 90s this afternoon. Some high cloud
cover will start to filter into the area from south to north this
afternoon as the cirrus blowoff from Francine lifts northward.
Francine will make landfall later this evening along the Louisiana
coast and then lift northward along the Mississippi River. Models
have been pretty consistent with the path. Rain will enter our
area Thursday morning and lift north and continue into the
overnight hours. Some weak instability (200 J/kg) may move into
the southern part of the area after 00z Friday. Hodographs will be
backed with 0-1 SRH between 150-200 m2/s2. Given this, I am not
going to rule out a tornado in the Friday 00-09z time frame.
Instability values may actually increase as we move closer to 12z
Friday, but the wind fields begin to decrease. Bands of showers
and storms will continue on Friday.

By the time we get to Friday evening, ensemble guidance is showing
median rainfall totals of 2-3.5" in the west of the area and
dropping off the further east you go. The 95th percentile on the
12z HREF shows some values around 5" in the south. This should not
trigger widespread flooding especially given the recent dry
conditions and the current low levels of the rivers and
tributaries. The Hydrologic Ensemble Forecast System keeps our
rivers and streams, even the tributaries in the areas with the
highest rainfall amounts, below action stage which means runoff
should not be a major issue. For flooding to occur, high rainfall
rates over a sustained period will be needed. At this time, a
flood watch does not look necessary. We'll keep an eye on the CAMS
for signals of training over the next few runs.

As far as the wind with this system, easterly winds will increase
to 10-20 mph on Thursday with some gusts Thursday afternoon/
Thursday evening between 25-30 mph and perhaps a gust to 35 mph
which keeps us below our Wind Advisory criteria.

&&

.LONG TERM...
(Friday Night through next Wednesday)
Issued at 1046 AM CDT Wed Sep 11 2024

The remnants of Francine will weaken on Friday and become a more
nebulous area of low pressure this weekend. This will keep shower
and storms chances in the forecast but will be slightly more
scattered in nature especially on Sunday. Showers and storms will
be more isolated Monday and Tuesday. As far as temperatures, with
plenty of cloud cover around through the weekend, highs will be in
the 70s to around 80 degrees. Temperatures will warm into the mid
80s as we approach the middle of next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 1215 AM CDT Thu Sep 12 2024

VFR conditions currently prevail and will continue until the 12Z
to 15Z time frame. From here, conditions will deteriorate as the
remnants of a tropical system move into Middle TN. Rain, heavy at
times, will approach from the south mid-morning and continue
through the remainder of the TAF period. Expect at least MVFR
visibilities and ceilings in times of heavy downpours, and
conditions may even drop down to IFR at times. Southeasterly winds
will strengthen as well with gusts of 20 to 30 knots, especially
Thursday afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      79  67  82  68 /  70  80  90  90
Clarksville    81  64  78  66 /  70  90  90  90
Crossville     74  59  77  61 /  50  70  70  70
Columbia       75  64  78  65 /  90  80  80  80
Cookeville     76  62  80  65 /  50  70  70  70
Jamestown      77  60  79  62 /  30  70  70  60
Lawrenceburg   74  65  78  65 /  90  70  80  80
Murfreesboro   77  65  83  67 /  80  80  80  80
Waverly        77  62  78  64 /  80  90  90  80

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
None.
&&

UPDATE.......Whitehead
SHORT TERM...Reagan
LONG TERM....Reagan
AVIATION.....Clements