-- Discussion containing changed information from previous version are highlighted. --
648
FXUS64 KMRX 080535
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
135 AM EDT Wed May 8 2024

...New AVIATION...

.UPDATE...
Issued at 1125 PM EDT Tue May 7 2024

Forecast is on track tonight, so no significant changes were made.
Tomorrow is shaping up to be a significant weather day, with several
rounds of thunderstorms possible throughout the day and into the
night. Should the thunderstorms around daybreak materialize and
move into the East Tennessee valley, the flood threat will
increase ahead of the expected MCS Wednesday night. Questions
about storm coverage, initiation times, and overall timing still
abound, but the environment is supportive of severe weather. The
most important message is to stay weather aware and tuned in to
weather reports.

&&

.SHORT TERM...
(This evening through Wednesday night)
Issued at 326 PM EDT Tue May 7 2024

Key Messages:

1. Scattered to numerous showers and thunderstorms will be around
this afternoon and tonight, some of which could be strong to severe
with damaging winds and large hail as the main threats. A low-end
tornado threat exists as well mainly across northern portions of the
area.

2. A much higher severe weather risk exists from later Wednesday
afternoon through Wednesday night. Damaging winds and hail are the
main concerns, but there is also a fairly notable tornado risk in
comparison to most events in our area, especially north and west of
Knoxville.

3. Repeated showers and storms could lead to flash flooding anytime
from this afternoon through Wednesday night.

Discussion:

We start the period in a broad warm sector with an upper level
northern jet edging eastward across the Ohio Valley and a southern
jet pushing east across the Gulf States. MLCAPE values are
approaching or exceeding 1500 J/kg across most of the area and a
strengthening and increasingly veered wind profile is bringing deep
layer/effective shear values to around 40 kts. Thunderstorms that
develop this afternoon into tonight may become severe, with damaging
winds and hail the primary threats. There is also a very low risk of
a tornado mainly across the north where the better shear will exist
in the lower levels.

For Wednesday into Wednesday night the complicated jet structure
makes the upper forcing difficult to pin down at this time, and
mutes confidence in the details of how the timing of the convection
will play out. However, it appears we may see two periods of upper
divergence moving across the area associated with the jet, one in
the afternoon/early evening and another during the night. Any
ongoing weaker convection in the morning may slow the
destabilization early in the day, but MLCAPES look likely to
approach or exceed 2000 J/kg by late afternoon and by late
afternoon/early Wed night the veering wind profile shows effective
shear approaching 50kts and 0-1km shear of 20 to 30kts across much
of the area. Given the expected wind profile, instability, and very
impressive mid-level lapse rates (7.0 C/km lapse rates and 700+ J/kg
of -10 to -30 C CAPE), there is a threat for all severe weather
hazards across the area with damaging winds, large hail, and
tornados possible. The tornado threat looks highest over our
northwestern areas, but does exist area wide.

While the CAMS are still are not in great agreement on how the
convection plays out, they are coming into somewhat better alignment
and it currently looks like there will be an earlier round of storms
with the greatest threat across the Plateau and north during the
late afternoon/early evening, then another round area wide
overnight. Some of the guidance suggests there will be a weak
surface boundary across portions of the northern Plateau and north
which could help to focus the convection during the late
afternoon/early evening and also may be a focus for the tornado
threat at least early on.

In addition to the other threats, repeated rounds of rainfall will
continue the concern for the possibility of flash flooding,
especially given the recent rains the past few days.

&&

.LONG TERM...
(Thursday through next Tuesday)
Issued at 326 PM EDT Tue May 7 2024

Key Message:

1. Several chances for showers, mostly light, through the period
with much cooler temperatures through Sunday. No severe weather
anticipated beyond Thursday morning.

Discussion.

We begin the long term period with showers and storms still ongoing
across the area. The severe threat should be greatly diminished
compared to the Wednesday night period. However, a few storms may
still be strong to severe as the Thursday period begins. Showers and
storms then exit to our east from late morning through mid afternoon
as drier air begins to move into the region. The main threat with
these lingering showers and storms still appears to be centered
around flash flooding.

Friday through Sunday, pops are back in the forecast as several
shortwaves swing through the longwave trough that will be in place
across our area. Temperatures will be much cooler as we will be in a
northwest flow pattern, with temps 5 to 10 degrees below normal.

Monday and Tuesday, we return to a more zonal pattern and
temperatures begin to climb back into the upper 70s and low 80s.
Pops remain in the forecast as a few disturbances are progged to zip
through the zonal flow.

&&

.AVIATION...
-- Changed Discussion --
(06Z TAFS)
Issued at 129 AM EDT Wed May 8 2024

Overall, fairly quiet aviation conditions are expected through the
remainder of the night and into the early morning hours. The main
impact beyond the early morning through Wednesday night will be
multiple rounds of thunderstorms, many of which could likely
become severe from the afternoon onward. There is still some
uncertainty as to when these storms will be in the area at the
terminals with a potential break in activity during the early to
mid afternoon. It is also likely that CHA will see the least
activity during the day with an uptick by later in the evening.
Within any storms, a rapid reduction in conditions are expected,
not to mention that all severe hazards are on the table.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             86  69  84  61 /  70  70  80  40
Knoxville McGhee Tyson Airport, TN  83  67  80  58 /  70  80  80  40
Oak Ridge, TN                       82  66  82  58 /  70  70  80  30
Tri Cities Airport, TN              81  63  76  56 /  60  60  90  40
-- End Changed Discussion --

&&

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

$$

SHORT TERM...Wellington
AVIATION...BW