Mesoscale Discussion 276

Issued

Mar 27, 2021, 8:41 AM EDT (12:41 UTC)

Expired

Mar 27, 2021, 10:45 AM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Nashville radar (KOHX), 94 km from the middle of the area, began a volume at 12:43 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

406 
ACUS11 KWNS 271241
SWOMCD
SPC MCD 271241 
VAZ000-TNZ000-KYZ000-271445-

Mesoscale Discussion 0276
NWS Storm Prediction Center Norman OK
0741 AM CDT Sat Mar 27 2021

Areas affected...Much of middle and eastern Tennessee into parts of
southeastern Kentucky and southwestern Virginia

Concerning...Severe potential...Watch possible 

Valid 271241Z - 271445Z

Probability of Watch Issuance...40 percent

SUMMARY...An evolving cluster of thunderstorms will continue
spreading across the Tennessee Valley toward the Cumberland Plateau
through 11 AM to Noon EDT, with some potential to organize further
and begin producing strong to perhaps occasionally severe wind
gusts.  It is not yet certain that a severe weather watch will be
needed, but trends will continue to be monitored for this
possibility.

DISCUSSION...Consolidation and upscale growth of vigorous
thunderstorm development continues across parts of the Mid South
into Tennessee Valley region.  This is being supported by
large-scale ascent associated with lower/mid tropospheric warm
advection, beneath a zone of enhanced divergence aloft, which is
forecast to continue spreading across the Tennessee Valley into the
Cumberland Plateau through 15-16Z.

This convection includes at least one area of increasing
organization, with a possible evolving broad mesoscale cyclonic
circulation near Nashville.  This still appears rooted above at
least a shallow near-surface, potentially cool/stable layer, but mid
60s+ F surface dew points have been surging toward the southern
Tennessee state border area the past few hours.  Although cloud
cover appears likely to slow boundary-layer insolation ahead of
activity, it is possible that thermal advection and moistening could
contribute to increasing boundary-layer instability as far north as
the Interstate 40 corridor of eastern Tennessee within the next few
hours.  If this occurs, a corridor with potential for strong to
severe wind gusts could begin to develop by mid to late morning, in
the presence of sheared, 30-50+ kt southwesterly to
west-southwesterly flow in the 850-500 mb layer.

..Kerr/Guyer.. 03/27/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MRX...JKL...LMK...OHX...HUN...

LAT...LON   35758667 36748557 37188336 35908335 35568479 35158683
            35158762 35758667

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.