Severe Thunderstorm Warning 121, NWS Morristown, TN

Area Forecast Discussion
National Weather Service Morristown TN
721 PM EDT Thu May 8 2025

...New AVIATION...

.SHORT TERM...
(This evening through Friday)
Issued at 217 PM EDT Thu May 8 2025

Key Messages:

1. A fairly rare threat for large hail (golfball sized or perhaps
slightly bigger) exists across east TN this evening. Damaging
winds will also be possible but large hail is the primary
concern.

Discussion:

An upper low over far western Kentucky will shift east through the
afternoon and evening hours, sending a front towards our CWA and
sparking off fairly widespread showers and thunderstorms later
this afternoon and evening. Subsequently the primary concern for
the short term will be the chances for severe storms across the
forecast area later on today.

The environment will definitely be supportive of organized
convection, with effective shear values upwards of 35kt across
most of the forecast area this afternoon and evening. Shear is
mostly speed shear however as hodographs are relatively straight
due to unidirectional winds throughout the column basically,
favoring splitting cells. As such, I think the tornado threat is
fairly low, and would likely depend on there being some sort of
boundary interaction with any right splits that develop. The more
pressing concern by far is going to be hail. Forecast soundings
show thermal profiles that will support some large hail, golfball
size or larger, this afternoon and evening. Lapse rates are
relatively high at the moment and are forecast to remain so into
the late afternoon/early evening hours as additional upper level
support moves in. Couple this with 30-40 percent HREF
probabilities of CAPE values in excess of 2,000 J/kg into the
6-8PM EDT timeframe (and 70 percent or greater for +1,000 J/kg),
along with relatively low freezing levels and wet bulb zero
heights, and I think there's a good chance of seeing some large
hail in east TN later today. SPC maintained a 30% hatched area for
large hail in their updated Day 1 convective outlook and I think
this seems reasonable. Damaging winds are also a concern, but
should be slightly less a concern than hail. DCAPE values should
stay around or below 700 J/kg, which suggests the potential for
some strong winds but nothing exceptionally strong. That said,
some of these storms producing large hail will certainly be tall,
so when they collapse strong winds will be possible.

Current CAM guidance says storms should clear our area to the east
around midnight, with additional rainfall possible late tonight
into the early morning hours tomorrow as the trailing front moves
through. That should primarily be limited to the mountains I think
and PoPs reflect that overnight and tomorrow morning.

&&

.LONG TERM...
(Friday night through next Thursday)
Issued at 217 PM EDT Thu May 8 2025

Key Messages:

1. Friday night through Sunday, rain chances will be very limited
outside of the southern half of the area.

2. By early next week, more widespread rainfall is likely with
storms possible Tuesday and Wednesday.

Discussion:

Through the weekend...

In the upper levels, a cut-off low will be over Pennsylvania Friday
night moving into the Northeast by Saturday morning. At the surface,
high pressure over the Midwest will drift over the Great Lakes by
Sunday. A disturbance over the Gulf Coast is caused by a cut-off low
that is nearly stationary near LA. Most of that activity will stay
to our south through the weekend.

On Saturday and Sunday, showers will be isolated. POPs for this
weekend have come down compared to previous NBM runs. The extreme
southern half of the region will have the best chance for a shower
or sprinkle since it is closer to the Gulf disturbance but even
there only a 20% to 25% chance through the weekend.

Monday through Wednesday...

The cut-off low over the Lower Mississippi Valley slowly starts to
move northeast on Monday. The trough will be much closer to the
region by Tuesday although exact location does not have good model
agreement. With high pressure over the Atlantic, low level flow will
be southerly. Deep layer moisture advection is likely with the
trough pulling in Gulf moisture at higher levels also. Therefore,
widespread rain is expected Monday through Tuesday. The best chance
for storms will be Tuesday as instability increases with dew points
getting back into the 60s. With Pwat values expected to be around
1.3 inches early next week (near the 90th percentile for
climatology), we will have to keep an eye on flooding potential.

Temps will be near normal or slightly below normal with highs in the
70s and lows mainly in the 50s through Tuesday. A warming trend
starts by Wednesday.

&&

.AVIATION...
(00Z TAFS)
Issued at 634 PM EDT Thu May 8 2025

Scattered thunderstorms around early, and a few will be strong
with hail and/or strong gusty winds. Will try to time the best
chance for thunderstorms at each site with tempo groups that
include MVFR conditions, but of course a direct hit from a
thunderstorm may briefly bring conditions lower. Later tonight
there continues to be uncertainty about how much fog/low cloud
development will occur, and will include MVFR conditions all sites
for several hours late tonight/early Friday all sites. Will see
improvement back to all VFR later in the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             58  77  52  72 /  40  20  10  20
Knoxville McGhee Tyson Airport, TN  57  73  48  72 /  70  20   0  10
Oak Ridge, TN                       56  74  48  72 /  60  10   0  10
Tri Cities Airport, TN              56  70  42  71 /  70  40   0  10

&&

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

SHORT TERM...CD
LONG TERM....McD
AVIATION...

Hazardous Weather Outlook...UPDATED
National Weather Service Morristown TN
253 PM EDT Thu May 8 2025

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-091900-
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-
253 PM EDT Thu May 8 2025 /153 PM CDT Thu May 8 2025/

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

.DAY ONE...This Afternoon and Tonight

A few strong, to possibly several, strong to severe storms are
expected this afteroon and evening. Primary time for concern will
be from roughly 6 PM to 10 PM. The main threats with any of the
stronger storms will be hail up to golf ball size and damaging
wind gusts. The threat for tornadoes is very low.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

The probability of widespread hazardous weather is low

.SPOTTER INFORMATION STATEMENT...

Reports of severe weather, including hail and damaging winds, are
welcome this afternoon and evening.

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