334
FXUS64 KMRX 041036
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
636 AM EDT Sat May 4 2024

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 313 AM EDT Sat May 4 2024

Key Messages:

1. Numerous showers and thunderstorms expected this afternoon,
mainly across eastern mountain and foothill areas near the TN/NC
line.

2. Drier tonight with more isolated convection due to shortwave
ridging, but this is expected to be short lived as another trough
moves east across the Lower Mississippi Valley.

Discussion:

Weak troughing across the region will continue to result in
southerly flow and periods of showers and thunderstorms. The most
widespread coverage is expected during the afternoon hours when
instability is at its peak. The greatest coverage is also expected
east of the trough axis which will place highest PoPs near our far
eastern counties across the mountains near the TN/NC state line
through southwest Virginia. Some locally heavy rain rates will be
possible with PW values near the 90th percentile, but overall, the
flash flood risk is very low.

Shortwave ridging arrives tonight as the trough axis shifts east
and another shortwave troughing moves into the Lower Mississippi
Valley. Temperatures remain near normal today and tonight.

&&

.LONG TERM...
(Sunday through Saturday)
Issued at 313 AM EDT Sat May 4 2024

Key Messages:

1. Scattered to numerous showers and storms are expected each day
through at least Thursday with more organized convection possible
Wednesday to Thursday.

2. Temperatures will be generally above normal through Thursday.

Sunday through Tuesday

At the start of the period, fairly weak flow will be in place aloft
with a shortwave ejecting out of the Southern Plains. Warm
conditions and abundant moisture will be present across much of the
southeast. During the day, the shortwave will continue to progress
eastward with downstream ridging allowing for warmer conditions
across the region. Surface heating will lead to development of
showers and storms, especially across the higher elevations in the
afternoon hours. The overall environment will consist of minimal
shear and fairly low-end instability, i.e. MLCAPE of near or above
500 J/kg.

Sunday night into Monday morning, the aforementioned shortwave will
approach the area from the west and begin to flatten, which will be
sufficient for more widespread showers and storms. Based on the
timing, instability will remain fairly limited as surface heating
will be capped by convection and cloud cover early in the day. On
Tuesday, ridging will return and will lead to warmer conditions once
again. A strengthening upper jet will be noted to the northwest and
will be slowly progressing eastward. This will help to increase the
flow throughout the layer and promote a more veered wind profile.
Current data suggests MLCAPE at or above 1,000 J/kg with more
notable deep-layer shear, which would support better organization to
convection than in previous days.

Wednesday through Friday

By Wednesday, the aforementioned northern jet will remain across the
same area with a southern jet strengthening to in excess of 100 kts.
A surface frontal boundary will also be located across the Plains.
This will provide a broader divergent pattern aloft and 850mb flow
possibly reaching 40 kts by the evening and into Thursday while the
frontal boundary approaches from the northwest. Models are
suggesting a potential MCS moving into the area from late Wednesday
into Thursday morning, which would be supported by the overall
pattern. In any case, convection during this timeframe would likely
be even more organized than on Tuesday. This timeframe will
definitely be something to watch as confidence increases, but low
probability HWO wording will be maintained for to encompass this
event and repeated convection earlier in the period. By Friday, the
front is likely to move through the area, which, combined with
height falls, will promote cooler conditions.

&&

.AVIATION...
(12Z TAFS)
Issued at 634 AM EDT Sat May 4 2024

An area of showers and a few thunderstorms will impact the TYS
terminal over the next few hours. Chances of showers and
thunderstorms will be highest at TRI this afternoon with at least
vcts at all sites. Temporary IFR conditions will be possible
within heavier rain showers or thunderstorms. After 0z, convection
is expected to decrease in areal coverage. Winds today will be
generally light with gusty winds in the vicinity of thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             80  65  85  66 /  60  40  40  50
Knoxville McGhee Tyson Airport, TN  77  62  82  64 /  70  40  50  40
Oak Ridge, TN                       78  62  83  64 /  70  40  50  40
Tri Cities Airport, TN              75  60  79  60 /  90  60  60  40

&&

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

$$

SHORT TERM...JB
LONG TERM....BW
AVIATION...JB