Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS64 KMRX 241106 AAA
AFDMRX

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
706 AM EDT Tue May 24 2022

.UPDATE...
FOR 12Z AVIATION.

&&

.SHORT TERM (Today and tonight)...

Key Messages:

1. Mostly cloudy today as a moist air mass lingers across the
area.

2. A shortwave trough will spread north across the area tonight,
bringing a chance of showers and thunderstorms from late afternoon
through tonight.

Discussion:

A cold front has settled south of our area, across SC/central
GA/central AL, and surface high pressure over the Great Lakes
extends across the TN Valley. However, abundant low level
moisture is creating a widespread deck of low cloud cover that
will persist through much of the morning. Partial scattering of
this cloud deck is expected during the late morning and early
afternoon. Later this afternoon, mainly around or after 20Z, rain
chances will rise in southern sections as a midlevel shoftwave
trough lifts north across AL/GA, pushing the front to our south
northward. Scattered showers and thunderstorms will be forecast
in the late afternoon and evening hours, with PoPs spreading
northward through the night. No severe threat is expected with
these storms as CAPE remains quite weak in this moist air mass,
although a few storms could potentially produce locally heavy
rainfall.

DGS

.LONG TERM (Wednesday through Monday)...

Key Messages:

1. A moist pattern continues Wednesday through Friday, with an
approaching trough/cold front enhancing rain chances especially
Thursday into Friday morning, during which time some strong to
severe storms and locally heavy rain are possible.

2. Cooler temperatures Friday and Saturday with lingering showers.
Warming temperatures to above normal by Sunday and Monday as high
pressure move in from the west.

Discussion:

A warm front will be lifting north through the area to begin
Wednesday, which will provide focus for a few isolated to scattered
showers and storms. Still going with lower POPs across the central
TN Valley and southward compared to the NBM as these areas will be
within the warm sector. The big question is where does the warm
front settle during the afternoon hours. Previously, it looked like
the front would be just north of northeast TN/southwest VA. Now
models are hinting that the front may end up residing across these
areas during the afternoon hours. If this occurs, expect this to be
an area of focus for showers and storms. For this reason, am going
slightly higher with POPs across this area compared to the NBM. A
few strong storms are possible as soundings show 2000 J/kg of SBCAPE
during the afternoon hours. Little to no shear is present so gusty
winds and hail are the main threats.

Our Thursday system has changed somewhat and now more uncertainty
exists. Previously, models were in fair agreement that the center of
low pressure would track northeast through the Ohio River Valley and
its associated cold front would move through at some point on
Thursday. Now models are beginning to show that the low will become
cutoff from the upper flow, thus slowing it`s eastward progression.
Though this is the new trend, models still vary quite a bit on
timing of the front. The NAM is now within range and is by far the
slowest of the models. A NAM solution means our best chances for
rain/storms would occur Thursday night as opposed to during the day.
I haven`t completely bought into the NAM just yet since it`s the
outlier but we will definitely keep an eye on future model runs. If
other models continue to trend toward the NAM, POPs on Thursday will
end up being much lower than what are currently forecast and the
highest POPs would shift to Thursday night/Friday morning.
Regardless of when the cold front moves in, whether during the day
or overnight, the potential for severe weather still exists. Both
GFS and NAM soundings show moderate shear within the lower levels
which would mean the risk of an isolated tornado is possible. Won`t
go into further specifics due to the high uncertainty on
timing/instability. Also, 30 to 40 mph wind gusts are expected
across the higher terrain of the east TN mountains as the cold front
nears and the 850 mb jet increases to 40 kts. Bottom line, stay
tuned to further developments and know that severe weather is
possible with Thursday`s system regardless of timing.

Friday looks wetter now because of the cutoff low. The low pressure
center will slowly meander across the forecast area through the day
with on and off showers and a few isolated thunderstorms expected
through the day. Showers will even linger into Friday night across
northeast TN and southwest VA. Keeping Saturday dry for now but may
eventually end up with some slight chance POPs if the low keep
slowing down. Sunday looks dry as high pressure builds into the area
from the west.

SR


&&

.AVIATION...
12Z TAF DISCUSSION.

Low clouds will gradually rise and scatter through the
morning at CHA, and in the early afternoon at TYS and TRI. Rain
chances will start to increase at CHA in the late afternoon, and
spread north through the evening. Will over this with a PROB30
with MVFR vis/cigs for now. CHA will have a chance of TS as well.

DGS

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             79  66  83  67  78 /  40  40  50  70  90
Knoxville McGhee Tyson Airport, TN  81  64  86  68  80 /  20  40  50  50  80
Oak Ridge, TN                       81  65  85  65  79 /  20  40  50  60  80
Tri Cities Airport, TN              78  60  83  63  79 /  10  20  50  40  60

&&

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

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.