Mesoscale Discussion 1879

Issued

Oct 21, 2021, 2:50 PM CDT (19:50 UTC)

Expired

Oct 21, 2021, 5:15 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

The Knoxville radar (KMRX), 136 km from the middle of the area, began a volume at 19:52 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.

088 
ACUS11 KWNS 211951
SWOMCD
SPC MCD 211950 
VAZ000-TNZ000-KYZ000-GAZ000-ALZ000-212215-

Mesoscale Discussion 1879
NWS Storm Prediction Center Norman OK
0250 PM CDT Thu Oct 21 2021

Areas affected...Portions of central/eastern KY...middle/eastern
TN...far southwestern VA...northern AL...and far northwestern GA

Concerning...Severe potential...Watch unlikely 

Valid 211950Z - 212215Z

Probability of Watch Issuance...20 percent

SUMMARY...An isolated wind damage threat with strong storms may
persist through the afternoon. Watch issuance is unlikely.

DISCUSSION...Low-topped convection with occasional embedded
lightning continues to gradually increase in coverage along/ahead of
a cold front from central/eastern KY across the TN Valley. Broken
cloud cover and poor mid-level lapse rates are limiting instability,
with around 500-1000 J/kg of MLCAPE present per latest mesoanalysis
estimates. Area VWPs show low-level winds veered to a generally
west-southwesterly component, which is limiting convergence along
the front. Even so, these winds do quickly strengthen with height in
the 0-3 km layer owing to the presence of a mid/upper-level trough
over the OH Valley. About 30-40 kt of effective bulk shear should
support some updraft organization, with both cells and small
clusters possible. As filtered diurnal heating continues through the
remainder of the afternoon, modest steepening of low-level lapse
rates may support efficient momentum transfer within convective
downdrafts. Isolated strong to damaging winds of 40-60 mph should be
the main threat with the developing convection for at least the next
few hours. Regardless, the overall severe risk should be tempered by
the marginal thermodynamic environment, and watch issuance appears
unlikely at this time.

..Gleason/Bunting.. 10/21/2021

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

ATTN...WFO...RLX...MRX...JKL...FFC...ILN...LMK...OHX...BMX...
HUN...

LAT...LON   34308582 34058699 33948813 34898807 35828666 36348585
            36918504 37298437 37668412 38538379 38298284 37588232
            37048222 36378271 35628374 34638512 34308582

Mesoscale Discussions in Tennessee, 2021Mesoscale Discussions in Kentucky, 2021Mesoscale Discussions in Alabama, 2021Every mesoscale discussion in 2021

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.