-- Discussion containing changed information from previous version are highlighted. --
828
FXUS64 KMRX 142316
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
716 PM EDT Tue May 14 2024

...New AVIATION...

.SHORT TERM...
(This evening through Wednesday)
Issued at 330 PM EDT Tue May 14 2024

 Key Messages:

1. Strong to possibly severe storms from line of storms in western
TN and northern MS arriving this evening for the Southern Plateau
and southeast Tennessee. Marginal severe hail up to around 1 inch
and strong gusty winds to 50+ mph are possible. A very low threat of
tornadoes across southeast Tennessee this evening.

2. Wednesday Upper low shifts farther east but marginally severe
storms possible extreme northeast as upper low opens up and shifts
east of the Appalachians. Another relatively cool day with highs
mainly lower to mid 70s.

Discussion:

The nearly vertically stacked upper low and sfc low pressure center
slowly shifts east from near the Mississippi River and lower Ohio
Valley this afternoon to the Tennessee Valley late tonight. Then
east of the Appalchians by late Wednesday. An occluded front is
expected to move into the forecast area this evening with a warm
front moving across the southern part of the forecast area ahead of
this feature. The showers this afternoon have been weak with no
thunder. Temperatures have been in the 60s to lower 70s with little
sunshine. CAPE values have generally been around 500 J/kg with this
early convection. Breaks in the clouds were beginning to develop at
mid afternoon which with daytime heating will allow the atmosphere
to destabilize more ahead of the next round by early to mid evening.
CAPE values will generally exceed 1000 J/kg. The shear will be
strong enough to support organized multi-cluster storms. Mid-level
lapse rates around 6.5 deg C supportive of at least around 1 inch
hail. Marginal severe hail and damaging winds are the main threat
this evening either ahead of a line of showers and thunderstorms now
moving into southern middle Tennessee. A severe thunderstorm watch
cover the are to the west until 900 PM EDT. There is a low threat
for tornadoes as well this evening. The main question will be if
there is enough heating late this afternoon for strong storms to
develop ahead of the line or whether the line will hold together or
move into the area just when the sun is setting or weaken.

There will likely be some patchy fog after the rainfall ends late
tonight. Skies should remain mostly cloudy Wednesday as the slow
moving upper low reaches the southern Appalachian region Wednesday,
the center passes over the Kentucky, Virginia, and West Virginia
border area during the early to mid afternoon time. Another
shortwave associated with the upper low/trough will move through
the forecast area during the mid afternoon. Model soundings show
weak shear but increased lapse rates aloft and higher instability
over the central and northern parts of the CWA. A few strong
storms are possible with gusty winds and some hail could fall.
Skies will again be mostly cloudy with temperatures around 70
northeast to the upper 70s southwest where more sun may come out
away from the upper low/trough.

&&

.LONG TERM...
(Wednesday night through next Tuesday)
Issued at 330 PM EDT Tue May 14 2024

1. Showers and thunderstorms are likely Friday through much of
the weekend across the southern Appalachians.

2. Ridging builds in next week leading to temperatures climbing
above 80 across most of the Valley.

Discussion:

By Thursday evening the majority of the precipitation should be out
of the area with possibly some lingering showers across northeast TN,
southwest VA, and the upslope regions of the southern Appalachians.
We should be precipitation free most of Thursday and the sun will
try and poke through the lingering cloud deck, but it might not be
until the second half of Thursday. Combine this with the more
northerly flow and we`ll only see high temperatures climb a few
degrees between Wednesday to Thursday.

Friday through the weekend will bring another active period as a
more potent system looks to eject out of the central plains states
towards the eastern half of the U.S. Deterministic models continue
to struggle with how to handle this incoming system and how it
interacts with the Gulf ridge, leading to lower confidence. Some of
the longer range models have come into slightly better agreement on
the positioning of the low, with the greatest storm coverage across
the Tennessee Valley down to the Gulf Coast, but the severe
parameters in forecast soundings are still a bit all over the place.
Things are currently trending towards the boundary with strongest
storms staying closer to the Gulf, but hopefully we see multiple
to help increase confidence in storm strength over the weekend.

&&

.AVIATION...
-- Changed Discussion --
(00Z TAFS)
Issued at 710 PM EDT Tue May 14 2024

A line of showers and storms will move across the sites this
evening and into tonight while also gradually weakening. As such,
CHA is the most likely site to see the more notable aviation
impacts, especially with respect to temporary strong winds. At all
of the sites, the showers and storms are expected to drop
aviation conditions to MVFR and possibly later. After the rain
ends later this evening, there may be temporary VFR conditions
with potential for MVFR or lower at all sites due to fog and low
ceilings by the early morning hours. The low ceilings will
gradually lift through the day with additional rain chances later
in the day. However, this was left out of the TAFs due to timing
uncertainty and the length of them as it is.
-- End Changed Discussion --


&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             63  79  62  85 /  90  70  10   0
Knoxville McGhee Tyson Airport, TN  61  74  61  79 /  80  90  40  10
Oak Ridge, TN                       61  76  60  81 /  90  90  30   0
Tri Cities Airport, TN              58  72  58  76 /  60  90  50  30

&&

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

$$

SHORT TERM...TD
AVIATION...BW