-- Discussion containing changed information from previous version are highlighted. --
676
FXUS64 KMRX 061108
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
708 AM EDT Mon May 6 2024

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 333 AM EDT Mon May 6 2024

Key Messages:

1. Scattered showers and thunderstorms today with an upper-level
shortwave across the area.

2. Drier tonight as shortwave ridging builds in across the region
and a stronger system approaches from the west.

Discussion:

Model guidance and WV satellite imagery this morning shows
shortwave troughing across the Mid-Mississippi Valley, and this
unsettled weather will move eastward through the day. By this
afternoon, the upper-level trough is forecast to be over our
region with widespread scattered shower and thunderstorm activity.
There is a low probability of some stronger thunderstorms this
afternoon as the RAP shows MLCAPE around 2000 J/Kg; however,
limited bulk shear will limit overall storm organization and
mitigate the severe weather risk.

By tonight, shortwave ridging builds in from the west with drier
and clearing conditions. Fog will be possible if cloud cover can
significantly clear out as guidance suggests.

&&

.LONG TERM...
(Tuesday through Monday)
Issued at 333 AM EDT Mon May 6 2024

Key Messages:

1. Scattered to numerous showers and storms are likely Tuesday into
Tuesday night with a few strong to severe storms possible. Damaging
winds and hail will be the main threats.

2. More organized storms are increasingly likely Wednesday evening
into Wednesday night with all modes of severe weather possible.
Localized flooding will remain of concern to Thursday due to
repeated storms.

3. Much cooler conditions return by Friday through the weekend with
more limited rain chances.

Tuesday through Thursday

At the start of the period, an upper trough will be centered across
the Northern Plains with a downstream jet extending to the upper
Mississippi River Valley. A surface cold front will be located just
west of Missouri/Arkansas. Across the southeastern U.S. up through
the Ohio River Valley, a broad warm sector will be in place, along
with deep moisture indicated by PWAT values of near 1.4 inches, i.e.
above the 90th percentile. During the day on Tuesday, some height
falls are expected across the area as the upper-level features shift
slightly eastward. Diurnal heating and large-scale ascent will be
sufficient for scattered to numerous convection, especially in the
afternoon through the evening hours. During the day, most sources
suggest MLCAPE to peak in excess of 1,000 J/kg with deep-layer shear
reaching 30 to 35 kts. As this is the first run of the CAMs, a great
degree of uncertainty still exists with the timing and coverage of
convection. However, this overall environment is supportive of
better organization than all recent days. During the overnight
hours, low-level winds and shear will increase, but this will also
be when low-level instability decreases. A lot of the current model
sources are suggesting more development overnight. As such, the main
concerns will be damaging winds and hail, which is emphasized by mid-
level lapse rates near 6 C/km and more organized storm structures.
The abundant moisture and repeated rainfall will also keep the
localized flooding threat.

By Wednesday morning, a near 100-kt upper jet will extend into the
southern Mississippi River Valley, which will enhance upper
divergence via an indirect vertical circulation. Depending on the
evolution of convection from the previous night, activity may
continue through the morning. However, as the day goes on, dynamics
will continue increase with the aforementioned cold front
approaching from the west and 850mb flow exceeding 40 kts. Timing
differences still exist, but most sources indicate convection to be
ongoing to our west by the evening before moving in overnight. With
respect to instability, the main question will be how much activity
is ongoing through the day. With less activity, MLCAPE could be in
excess of 1,500 J/kg with deep-layer shear above 40 kts and 0-1km
shear of over 25 kts. In this scenario, all modes of severe weather
would be of concern, notably above and beyond that of Tuesday. We
are still at a temporal scale where CAMs will not reach into this
event, but concern continues to increase for a more notable severe
weather event Wednesday night into Thursday morning. This is further
emphasized by the CIPS Analogs and ensemble probabilities of over 50
percent for Supercell Composite Parameter of over 5, especially
along the Cumberland Plateau and southern Valley. By the day on
Thursday, the cold front will likely reach the area with activity
likely continuing through the day.

Friday through Sunday

By Friday, deep troughing will be over the area with much cooler
conditions following the passage of the frontal boundary ahead of
surface high pressure to the west. Still, weak ascent and remaining
moisture will be sufficient for lower but continued PoPs. Large-
scale troughing will persist into Saturday with high pressure
arriving from the west but weakening in the process. This will make
for cooler and drier conditions. Additional troughing into Sunday
will keep cooler temperatures in place with low-end PoPs based on
potential development of a weak system to our south.

&&

.AVIATION...
-- Changed Discussion --
(12Z TAFS)
Issued at 706 AM EDT Mon May 6 2024

Showers and thunderstorms will impact terminals this morning.
Model guidance is having a difficult time resolving the current
convective activity, but timing on this complex of convection has
it impacting CHA around 12-13z and TYS around 15z. If this
activity holds together, it would impact TRI around 17z. Numerous
showers and thunderstorms will result in periods of poor flight
conditions throughout the day; exact timing is uncertain this
afternoon, but additional scattered thunderstorms are expected
later today. As this upper-level disturbance shifts eastward
tonight, probability of thunderstorms will decrease by 12z
Tuesday.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             83  66  86  68 /  60  30  50  60
Knoxville McGhee Tyson Airport, TN  80  63  82  66 /  90  70  60  70
Oak Ridge, TN                       79  63  83  66 /  90  60  70  60
Tri Cities Airport, TN              76  60  81  63 /  80  80  60  50
-- End Changed Discussion --

&&

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

$$

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