-- Discussion containing changed information from previous version are highlighted. --
835
FXUS64 KMRX 262253
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
653 PM EDT Sun May 26 2024

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 648 PM EDT Sun May 26 2024

Quick update of the forecast as storms had moved out of most of
the area so lowered rain chances for the rest of the evening
before next round moves in and dropped Severe Watch except for
counties in the eastern foothills and Appalachians in Tennessee.
-- End Changed Discussion --

&&

.SHORT TERM...
(This evening through Monday)
Issued at 354 PM EDT Sun May 26 2024

Key Messages:

1. Showers and thunderstorms still moving east into Virginia late
this afternoon and then upstream convection may move into the area
early this evening and could shift farther south, although
confidence is increasing on timing, the coverage and intensity of
storms and how far south is still somewhat uncertain.

2. High confidence that a line of strong to severe storms will move
through the region late tonight/early Monday morning.

3. Localized flooding will be possible in places where soils are
more saturated from recent rains. Especially the northern plateau
eastward into northeast Tennessee and southwest Virginia.

Discussion:

Late this afternoon the threat of severe storms continues through
the afternoon and evening. Models are still indicating a very
favorable environment for severe storms from Middle into East TN. A
very unstable airmass continues over the central and southern valley
with storms starting to develop. NAM soundings show steep lapse
rates and ML CAPE around 2500 J/KG. High effective shear will
support supercells. Low LCL heights and 0-1 Km shear high enough to
help tornado formation. These storms will move across the southern
sections late in the afternoon to mid evening and then decrease.

There is still good confidence in more storms moving through late
tonight as the cold front and trough approach the region. CAMs are
in good agreement on a squall line moving through around 2 AM to 7
AM. CAPE will be lower at this time less than 1K in most areas but
shear will be favorable around 50 to 60 knots. The main threat will
be damaging straight-line winds but a few isolated tornadoes cannot
be ruled out with favorable 0-1 km shear (30 knots) and 0-1 km
helicity (200 to 300).

Rain amounts will generally be 1 to 2 inches for most locations.
The line of storms will be moving fairly quickly but will likely
have high rain rates. Flooding potential will be higher in places
where storms have moved through this afternoon/evening and places
that have had heavy rain recently. Overall, flooding threat is
higher than earlier because of todays severe storms and
additional rainfall.

By late Monday morning the front will be moving through the region
as the line of storms from overnight should be moving east of the
Appalachians. Moving into the afternoon/evening hours we will likely
see another round of thunderstorms along shortwave energy traversing
the south side of the low pressure system over the Great Lakes.
Storms Monday are expected to be weaker and more isolated in
coverage, with the greatest chances to see storms being north of
Interstate 40. If the sky is able to clear out earlier in the day
after tonight`s line the atmosphere could destabilize enough that
some of the stronger storms will be capable of producing strong
winds gusts and hail during the afternoon/evening. Once the sun
begins to set Monday evening the better synoptic forcing and diurnal
convection should quickly end.

&&

.LONG TERM...
(Monday night through next Sunday)
Issued at 334 PM EDT Sun May 26 2024

Key Messages:

1. A few more showers and storms exiting the area Monday evening.

2. Drier and cooler weather to begin Tuesday through the end of the
week. A warming trend starting next weekend. Also an increasing
chance of showers and thunderstorms.

Discussion:

For the rest of the work week we`ll generally see a trend of cooler
weather, a few degrees below seasonal normals as we sit at the base
of the trough which will help keep light westerly to northwesterly
winds over the region. We also could see some light showers along
the spine of the Appalachians with the northwest flow, but generally
most of the eastern Tennessee Valley should remain dry Tuesday
through Friday.

Rain chances return over the weekend as a low tries to move through
the eastern United States. PoP chances will remain lower at this
time due to uncertainty with how far east the system is able to
progress before taking a more northward course towards the Great
Lakes Region. The ridging that will build in to fight against this
system will also likely increase temperatures to above seasonal
normals by Saturday/Sunday.

&&

.AVIATION...
(18Z TAFS)
Issued at 127 PM EDT Sun May 26 2024

Confidence is higher with timing of showers and storms across
northeast TN and coverage so have some vicinity thunder for TRI
and TYS early evening. Included Tempo for TRI for a few hours but
not sure for TYS. The best chance for widespread thunder will
still be late tonight/early Monday morning when a line of storms
moves through. Some of these storms still may be strong to
severe. Lower ceilings and visibilities will have all sites except
MVFR except TRI in the morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             69  87  63  86 /  80  50   0   0
Knoxville McGhee Tyson Airport, TN  68  82  61  81 /  90  60  10   0
Oak Ridge, TN                       67  82  60  82 /  90  60  10   0
Tri Cities Airport, TN              64  80  59  77 /  70  70  10  10

&&

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

$$

SHORT TERM...TD
LONG TERM....TD
AVIATION...TD