462
FXUS64 KMRX 181722
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
122 PM EDT Sat May 18 2024

...New AVIATION...

.UPDATE...
Issued at 1026 AM EDT Sat May 18 2024

Forecast on track this morning with no updates. A few showers
persist across the area. Additional showers and storms are
expected to develop this afternoon as instability slowly
increases across the area.

&&

.SHORT TERM...
(Today and tonight)
Issued at 303 AM EDT Sat May 18 2024

Key Messages:

1. Scattered to numerous showers and thunderstorms can be expected
today, a few may become strong to severe.

2. Showers and thunderstorms will diminish tonight.

Discussion:

We start the period with considerable moisture lingering over the
area and a weak upper level trough to our west. This upper trough
will move east across the region during the period and will be
exiting to our east by late tonight. The better forcing with the
upper jet is forecast to stay to our south and east, but a period of
weak upper divergence is indicated this afternoon over our area.
Expect scattered to numerous showers and thunderstorms across the
area today, with the best coverage in the afternoon. Model data
generally suggests better instability developing than yesterday with
SBCAPES in the 750-1250 J/kg range likely across much of the area
this afternoon, but also generally shows relatively weak flow and
limited shear. The threat of strong to severe storms does not look
high. However, a few storms may become strong to severe with
damaging winds, large hail and locally heavy rain the primary
threats.  High temperatures today will be near to slightly below
seasonal normals.

The showers and thunderstorms will diminish tonight from west to
east as the trough axis shifts east. Low temperatures will
generally be a bit above normal.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 303 AM EDT Sat May 18 2024

Key Messages:

1. A lingering shower is possible on Sunday, most likely along the
mountains.

2. Drier and warmer on Monday and Tuesday.

3. Daily chances of showers and thunderstorms to resume Wednesday
onwards, with a warm and humid airmass in place.

Discussion:

Our weak trough is finally moving on, and Sunday as a result should
be mainly dry for much of the area. CAMs and global models, both
legacy and experimental, depict the best chances for a shower or two
to be along the spine of the mountains bordering with North
Carolina. This makes sense with the trough pulling away to the east,
and a surge of median aka drier PWATs entering in from the north
pushing any lingering moisture coupled with afternoon heating
isolated towards the mountains. After that, we get a break from the
storms as the upper ridge moves in and provides for rebounding
temperatures and much drier weather to start the workweek. An
isolated shower or thunderstorm is possible Monday and Tuesday
afternoon, but no washouts expected.

Beyond Tuesday the forecast enters into a low confidence stretch. It
seems likely based off of all available guidance that a broad upper
trough will be over south-central Canada, with a low moving
northwards over Lake Superior pivoting around the broader upper
level flow Wednesday morning. At the surface a cold front extending
from this low will push towards the Ohio River, but guidance is
showing persistence from yesterday on this front not making it to
the southern Appalachians. With the front washing out, flow aloft
switches to a more zonal pattern, but persistent southerly flow
brings increasing moisture and humidity into Tennessee. As a result,
the warm weather will likely continue into late week. Starting
Wednesday onwards we will have a daily low to medium (20 to 50
percent) chance for scattered showers and thunderstorms being fueled
in part by the southern moisture return, but as of now no organized
or significant signals for much beyond that.

&&

.AVIATION...
(18Z TAFS)
Issued at 104 PM EDT Sat May 18 2024

Isolated to scattered showers and storms expected through this
evening. VFR conditions through this evening expected except for
when/if any shower or storm passes over a terminal. Then, expect
MVFR conditions. MVFR conditions likely overnight, then VFR
returns by mid-morning. Also have a few hours of IFR in at TRI
around sunrise for CIGs.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             63  85  63  86 /  50  20   0  10
Knoxville McGhee Tyson Airport, TN  61  81  61  84 /  50  20   0  20
Oak Ridge, TN                       61  83  61  84 /  40  20   0  20
Tri Cities Airport, TN              60  78  56  81 /  40  30   0  10

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&

$$

SHORT TERM...
LONG TERM....Wellington
AVIATION...