238
FXUS64 KOHX 270703
AFDOHX

Area Forecast Discussion
National Weather Service Nashville TN
203 AM CDT Fri Sep 27 2024

...New SHORT TERM, LONG TERM...

.SHORT TERM...
(Today through Saturday)
Issued at 142 AM CDT Fri Sep 27 2024

Already, the center of TC Helene has made it into southern
Georgia, and the initial band of showers has spread almost
entirely across Middle Tennessee. At the same time, we are largely
devoid of any thunder; this is entirely a rain event thus far, and
will likely stay that way, except for perhaps an occasional
isolated thunderstorm or two. The most recent ACARS sounding
(0635Z) shows a nearly saturated column with precipitable water
of 1.64", which is near the 90th percentile for this date.
Instability parameters are at a minimum, and the 700-500 mb lapse
rate is just 5.2 C/km. So this is definitely a tropical
environment. Latest model projections bring the center of the low
into NE Tennessee by 15Z, with the low center then turning
northwestward into KY, then curving back toward TN, and ending up
near Land-between-the-Lakes by 06Z Saturday. So surface winds are
going be all over the place based on the movement of the low.
However, we do expect to reach no more than Wind Advisory criteria
throughout this event, and winds will diminish considerably on
Saturday as the surface low continues to fill. Storm total QPF
values resulting from TC Helene continue to fall into the 2" to 5"
range. So we will continue with the Flood Watch given these high
rainfall amounts.

&&

.LONG TERM...
(Saturday Night through next Friday)
Issued at 142 AM CDT Fri Sep 27 2024

The surface and upper low show little additional movement until
Sunday night or Monday, when the system finally starts to pull
off to the north or northeast. By then, it will have weakened
considerably. So we will continue with lower PoPs on Sunday and
even into Monday while still under the influence of tropical
moisture. As the remnants of this tropical system continue to
pull away from Middle Tennessee, a cold front will sweep through
the mid state late Monday and Monday night, returning us to drier
conditions and also giving us slightly cooler weather for a couple
of days. But high temperatures will return to the low 80s for
much of the region by the end of next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 1229 AM CDT Fri Sep 27 2024

Hurricane "Helene" has come ashore now and will be tracking
through Georgia. She was a cat 4 hurricane upon landfall and will
gradually weaken into a tropical storm as she reaches Northern Ga
toward sunrise. Following this she is expected to turn
northwestward and reach our Cumberland Plateau area, as a
weakening depression tomorrow afternoon. This all spells a
continuous bout of rain through the period. Helene is being aided
by a strong upper level low to our west. This is allowing a
divergent pattern aloft to further fuel Helene and keep her going.
Furthermore, any dry air intrusion which can act to weaken the
system at a quicker rate, has been cut off.

In addition to the rain fall of course, will be the increasing
wind speeds. As the depression moves into the area, wind speeds
will pick up in the morning and increase into the afternoon, with
highest gusts across our Plateau. Moreover, a decisive wind shift
will commence once the system slowly moves further west. Gusts as
high as 40 knots will be rather common place across the Plateau
area, with slightly lower wind impacts as you move west.

As for IFR conditions, look for IFR conditions to prevail
throughout the duration of the taf period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      73  63  69  63 / 100  90  90  60
Clarksville    72  62  68  62 / 100 100  90  70
Crossville     70  58  65  57 / 100  70  80  50
Columbia       69  61  68  61 / 100  90  80  50
Cookeville     70  60  65  60 / 100  80  80  60
Jamestown      71  59  66  59 / 100  80  80  70
Lawrenceburg   68  60  67  61 /  90  80  80  40
Murfreesboro   72  62  68  62 / 100  80  90  50
Waverly        71  59  67  61 / 100 100  90  60

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Saturday morning for Bedford-Cannon-Cheatham-
Clay-Coffee-Cumberland-Davidson-De Kalb-Dickson-Fentress-Giles-
Grundy-Hickman-Houston-Humphreys-Jackson-Lawrence-Lewis-Macon-
Marshall-Maury-Montgomery-Overton-Perry-Pickett-Putnam-Robertson-
Rutherford-Smith-Stewart-Sumner-Trousdale-Van Buren-Warren-Wayne-
White-Williamson-Wilson.

Wind Advisory until 7 AM CDT Saturday for Bedford-Cannon-
Cheatham-Clay-Coffee-Cumberland-Davidson-De Kalb-Dickson-
Fentress-Giles-Grundy-Hickman-Houston-Humphreys-Jackson-Lawrence-
Lewis-Macon-Marshall-Maury-Montgomery-Overton-Perry-Pickett-
Putnam-Robertson-Rutherford-Smith-Stewart-Sumner-Trousdale-Van
Buren-Warren-Wayne-White-Williamson-Wilson.

&&

$$

SHORT TERM...Rose
LONG TERM....Rose
AVIATION.....21