Severe Thunderstorm Warning 31, NWS Nashville, TN

Area Forecast Discussion
National Weather Service Nashville TN
847 PM CDT Sun Mar 30 2025

...New MESOSCALE UPDATE...

.KEY MESSAGES...
Updated at 840 PM CDT Sun Mar 30 2025

- Severe thunderstorms are a threat tonight into early Monday
  morning with a level 3 out of 5 risk across the area. Damaging
  winds, large hail, and tornadoes are all possible. The greatest
  risk for tornadoes and large hail is west of I-65.

- Flooding and severe thunderstorms will be possible mid to late
  week with a series of weather systems to impact the area. The
  flooding could become significant by late week with some areas
  possibly exceeding 5 inches of rainfall through the week.

&&

.MESOSCALE UPDATE FOR TORNADO WATCH 78...
Issued at 840 PM CDT Sun Mar 30 2025

The 00Z sounding from OHX does still show good instability with
sufficient mid-level lapse rates for strong updrafts, but a cap
has developed around 800 mb. At this time, there is still
enough surface heating to overcome the cap, but any appreciable
surface cooling could act as an inhibitor should the cap remain in
place. The surface based LI is -4 and the 0-3 km helicity is 238,
which isn't astronomical, but still enough to allow for tornado
production. At this time, existing storms are getting very close
to the northwest corner of Middle Tennessee. There is an axis of
higher CAPE values just ahead of the existing line of storms,
with values ~2,000 J/kg in this region. Also, there is a bullseye
of 400-500 helicity values around the Linden/Hohenwald/Waynesboro
area, so this is one spot worth watching.

&&

.SHORT TERM...
(Rest of today through Monday)
Issued at 1155 AM CDT Sun Mar 30 2025

Obviously our main concern is the potential for severe weather
tonight, but first a few words about today. Some pieces of
shortwave energy are producing scattered showers. Through the
afternoon, most of the showers will move off to our east, but
there will be weak but sufficient lift and enough instability for
a few (20 to 30 percent coverage) showers or thunderstorms to
bubble up as temperatures warm well into the 70s. Areas west of
I-65 will see cape values climb into the 1500-2000 range by mid
afternoon as deep layer shear values approach 40kt. So, we cannot
rule out a brief severe storm west of I-65 this afternoon, but the
threat will become much greater tonight.

For this evening, stronger shortwave energy will approach along
with a surface cold front. In a wide zone out ahead of the front,
deep south to southwest flow will keep moisture flowing up into
the region with dew points in the upper 50s to lower 60s, and
pockets of mid 60s. This will result in widespread capes of
1000-2000 J/kg. Deep layer shear will reach 40-50KT and low level
helicity values will be mostly in the 100-200 range. CAMs show
some locally enhanced SRH values as the storms move into our
western counties late this evening, and that is certainly
concerning for tornado potential in our far west.

The greatest cape and lapse rate values will be in place out to
our west this afternoon and early evening, and that is where the
greater threat for discrete supercells with large hail and strong
tornadoes will be located within the zone of strong forcing. That
"all modes" potential will still exist as the forcing and storms
move into our far western counties, but starting around that
time, things will begin a transition toward QLCS or line segments
with damaging winds being the dominant mode along with some
embedded tornadoes. Bottom line, this is a complex balance of
shear and instability with all hazards possible, so everybody
should be weather aware and have multiple ways to receive
warnings. Take warnings seriously and move to your safe place as
quickly as possible if warnings are issued.

The latest timing estimates show our northwest counties under
greatest impact from 9 PM to midnight, Nashville and other areas
along I-65 from 11 PM to 2 AM, and Plateau mainly from 2 AM to 6
AM. These times are just to offer a general idea of the greatest
severe risk. Multiple clusters or lines of storms will be
possible, so check our social media or other reliable sources for
the latest timing updates and details graphics for your location.

There could be some local ponding in heavy downpours, but
thankfully we do not expect widespread flooding tonight. Rainfall
amounts are expected to be mostly 1 to 1.5 inch.

The line of convection is expected to clear the area early Monday
morning with quieter weather then settling in for Monday afternoon.
The trough axis will work through during the late morning and
afternoon and may bring a few pop up showers but they will be low
impact. After seeing highs in the 70s today we will see them fall
back into the 60s for Monday. We will start to get some clearing
Monday night and it will be on the chilly side with lows in the
upper 30s to lower 40s.

&&

.LONG TERM...
(Tuesday through next Sunday)
Issued at 1155 AM CDT Sun Mar 30 2025

Quiet weather will stay in place on Tuesday as a short wave ridge
moves overhead and a surface high sits to our north. The quiet
weather won't stick around for long though as we will move into a
rainy and stormy period of weather from Wednesday through the
weekend. A trough will track out of the Rockies Wednesday with a
surface low developing over the Plains. This will push a cold
front into the western part of the area Wednesday evening into
Wednesday night. Once again parameters look favorable for severe
weather and is something to keep an eye on. The threat would
mainly be from around I-65 west.

The cold front will then stall over the region as it bumps up
against a strong ridge centered off the east coast of Florida.
Deep southwest flow along the periphery of the ridge will bring a
series of systems along the stalled boundary resulting in
multiple episodes of rain and storms. Flooding is a growing
concern with parts of the area expected to receive more than 6
inches of rainfall and at least a low chance for more than 8
inches of rain over our northwest counties! Thankfully the severe
storm threat will diminish after Wednesday, but some strong
storms with gusty winds and enhanced downpours could bubble up
from time to time.

&&

.AVIATION...
(00Z TAFS)
Issued at 643 PM CDT Sun Mar 30 2025

It's going to be an active night for convection across Middle
Tennessee. Severe storms are ongoing over extreme southeast MO and
eastern AR, and are due to arrive in Middle Tennessee beginning
around 02Z with slow eastward progress throughout the late evening
and overnight. We have used the 22Z HRRR for timing of the
expected storms. There hasn't been a great deal of change with the
forecast, so there is reasonably good confidence in the timing of
the TEMPO groups in the 00Z TAFs. Since all of our terminals are
under an enhanced risk of severe storms, have included higher wind
gusts within the TEMPO period. There is also a hail probability,
but not enough of a probability to warrant mention in the TAFs.
Once the storms depart, expect low ceilings to fill in behind the
surface boundary for much of the day on Monday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Nashville      56  66  42  71 /  90  50   0   0
Clarksville    51  61  40  68 /  90  10   0   0
Crossville     58  67  37  68 /  90  80  10   0
Columbia       55  67  40  71 /  90  60   0   0
Cookeville     56  65  39  69 /  90  70   0   0
Jamestown      56  66  37  68 /  90  70  10   0
Lawrenceburg   57  68  40  71 /  90  70   0   0
Murfreesboro   55  68  39  73 /  90  60   0   0
Waverly        51  63  39  70 /  90  20   0   0

&&

.OHX WATCHES/WARNINGS/ADVISORIES...
TORNADO WATCH 78.
&&

SHORT TERM...13
LONG TERM....13
AVIATION.....Rose