Severe Thunderstorm Warning 155, NWS Morristown, TN

Area Forecast Discussion
National Weather Service Morristown TN
938 PM EDT Tue May 20 2025

...New UPDATE...

.UPDATE...
Issued at 926 PM EDT Tue May 20 2025

Ongoing severe weather event across western portions of our area
which is progressing eastward, and the environment remains
favorable for all severe hazards including damaging winds, large
hail, and tornadoes. Latest RAP indicates SBCAPE values are
around 1000-2000 J/kg, while 0-6 km shear is near 55 kts and 0-1
km shear is in the 20 to 30 kts range. We have seen line segments
and supercells, and this will likely continue in the short term
although the severe threat may gradually become more isolated as
the activity moves east over the next few hours, especially over
northeastern portions of our area, as instability is expected to
gradually weaken. No changes needed to the forecast at this point.

&&

.SHORT TERM...
(This evening through Wednesday)
Issued at 338 PM EDT Tue May 20 2025

Key Messages:

1. The threat for strong to severe storms with all hazards will
continue through the early overnight hours. Continue to have
multiple ways to receive watch and warning information.

2. Localized flash flooding threat may develop in flood prone
location that see repeated strong to severe storms.

3. Severe threats will gradually diminish a few hours after
midnight. Cooler and breezy conditions are expected Wednesday.

As of 300PM ET a nearly stationary warm front remains draped across
central and eastern KY as cold front approaches the Mid-Mississippi
river valley. The parent low churns near the tri-state border of
IA/MO/IL. On-going convection aided by an outflow boundary, 1000-
1500 J/kg MLCAPE, and 50kts EBShear, has warranted a tornado watch
for Scott/Morgan counties northeast into southwest Virginia through
8PM ET in closer proximity of enhanced moisture convergence and low-
level shear on southern side of the aforementioned warm front. The
main focus point for this tornado threat will be embedded supercell
structures within the line which will be capable of damaging
straight line winds itself. Hail threat can of course accompany any
rotating storm.

Additional convection is expected to develop later this evening into
the early overnight hours along and ahead of the cold front. This
will bring another round of expected strong to severe storms.
However, there will be some uncertainty on the northern side of I-40
and how well we destabilize after the on-going activity moves
through the region. Some of the higher resolution guidance has
started to hint at more pronounced bowing segments along and south
of I-40 where the environment will be less tainted. Nonetheless,
severe weather is likely with continued strong wind shear, marginal
CAPE, and a strong strong swly LLJ near 40-45kts. Most likely timing
will be between 8PM - 2AM ET. Some showers and storms will linger a
bit longer but the widespread severe threat will diminish rather
quickly around 3am or so. Breezy winds and cooler conditions will
develop in a post frontal air mass Wednesday.

&&

.LONG TERM...
(Wednesday night through next Tuesday)
Issued at 338 PM EDT Tue May 20 2025

Key Messages:

1. Scattered showers and thunderstorms early in the period.

2. Cooler and mostly dry weather for Friday into Saturday.

3. Rain chances increase for Sunday through Tuesday.

Discussion:

We start the  period with a broad upper trough over the eastern
CONUS.  While models are struggling with the details and timing,
there is general agreement one or more short waves moving through
the northwest flow aloft will bring scattered showers and possibly
thunderstorms to our area in the Wednesday night/Thursday/Thursday
night time frame.  Freezing levels will be on the low side and model
mid level lapse rates are steep, so if enough moisture and
instability are present (which is still questionable), at least
small hail will be possible with any thunderstorms.

Surface high pressure will build in for Friday into Saturday, and
both days look mostly dry and cool, with temperatures Friday looking
to be around 10 degrees below normal and Saturday just a bit higher.

The upper levels will be transitioning to more zonal flow for Sunday
and Monday, and by Tuesday a strong short wave will be digging in to
our west Tuesday.  We will see moisture returning and more coverage
of showers and thunderstorms for the Sunday through Tuesday period.
High temperatures are forecast to be a little warmer, but
still generally near to below normal all three days.

&&

.AVIATION...
(00Z TAFS)
Issued at 721 PM EDT Tue May 20 2025

Showers and thunderstorms will move through early in the period.
Strong gusty winds and hail will be possible with a stronger
storm, and will include gusty winds as well as lower vsby and cigs
with a prob30 group all sites when the highest probability of
these stronger storms is expected. There may be a period of MVFR
level cigs around sunrise at TYS and especially TRI for a few
hours, so will include in a tempo group at TYS and prevailing at
TRI. Should see all VFR later in the period, along with gusty west
and southwest winds.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             67  81  60  80 /  80   0  10  20
Knoxville McGhee Tyson Airport, TN  66  78  58  75 /  90  10  10  40
Oak Ridge, TN                       65  78  57  75 /  80  10  10  30
Tri Cities Airport, TN              62  76  53  71 /  90  20  10  40

&&

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

SHORT TERM...
AVIATION...

Hazardous Weather Outlook
National Weather Service Morristown TN
343 PM EDT Tue May 20 2025

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-211945-
Cherokee-Clay-Scott TN-Campbell-Claiborne-Hancock-Hawkins-
Sullivan-Johnson-Morgan-Anderson-Union-Grainger-Hamblen-
Northwest Cocke-Cocke Smoky Mountains-Northwest Greene-
Southeast Greene-Washington TN-Unicoi-Northwest Carter-
Southeast Carter-Roane-Loudon-Knox-Jefferson-Northwest Blount-
Blount Smoky Mountains-North Sevier-Sevier Smoky Mountains-
Sequatchie-Bledsoe-Rhea-Meigs-McMinn-Northwest Monroe-
Southeast Monroe-Marion-Hamilton-Bradley-West Polk-East Polk-Lee-
Wise-Scott VA-Russell-Washington VA-
343 PM EDT Tue May 20 2025 /243 PM CDT Tue May 20 2025/

This Hazardous Weather Outlook is for portions of southwest North
Carolina...east Tennessee and southwest Virginia.

.DAY ONE...This Afternoon and Tonight

Severe thunderstorms are expected to continue this afternoon and
into the overnight hours ahead of a cold front. Damaging winds
will be the primary risk, but there will be a chance of large hail
and tornadoes with the strongest storms.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

The probability of widespread hazardous weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not needed at this time.

Preliminary Local Storm Report
National Weather Service Morristown TN
947 PM EDT Tue May 20 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0945 PM     Tstm Wnd Dmg     Oneida                  36.50N 84.51W
05/20/2025                   Scott              TN   Public

            Several trees down.

&&

dh

Preliminary Local Storm Report
National Weather Service Morristown TN
948 PM EDT Tue May 20 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0940 PM     Tstm Wnd Dmg     1 WSW Oneida            36.50N 84.53W
05/20/2025                   Scott              TN   911 Call Center

            Trees reported down in Scott County.

&&

NAW

Preliminary Local Storm Report
National Weather Service Morristown TN
951 PM EDT Tue May 20 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0951 PM     Tstm Wnd Dmg     3 W Oak Ridge           35.96N 84.35W
05/20/2025                   Roane              TN   Public

            Trees down.

&&

dh

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