Alert archive / Tennessee / Mesoscale Discussions in 2021
Mesoscale Discussion 277
The Storm Prediction Center issued this mesoscale discussion at Mar 27, 2021, 11:00 AM EDT for Bell County, Harlan County, Kentucky; 18 counties in Tennessee; 4 counties in Virginia. It was in force for 90 min.
The area
The outline as issued.
The facts
- Issued
- Mar 27, 2021, 11:00 AM EDT (15:00 UTC)
- Expired
- Mar 27, 2021, 12:30 PM EDT
- In force
- 90 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 24 counties
Bell County, KY, Harlan County, KY, Anderson County, TN, Blount County, TN, Campbell County, TN, Claiborne County, TN, Cocke County, TN, Grainger County, TN, Greene County, TN, Hamblen County, TN, Hancock County, TN, Hawkins County, TN, Jefferson County, TN, Knox County, TN, Loudon County, TN, Roane County, TN, Sevier County, TN, Sullivan County, TN, Union County, TN, Washington County, TN, City of Bristol, VA, City of Norton, VA, Lee County, VA, Scott County, VA
The radar
The Knoxville radar (KMRX), 6 km from the middle of the area, began a volume at 14:59 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.
The nearest sounding before it
Nashville Metro, TN (KBNA), launched 12:00Z, 3.0 hours before the alert went out and 283 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 710 m above ground
- 0-6 km bulk shear
- 45 kt
- 0-1 km storm-relative helicity
- 347 m²/s²
- 0-3 km storm-relative helicity
- 316 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
063
ACUS11 KWNS 271501
SWOMCD
SPC MCD 271500
VAZ000-TNZ000-KYZ000-271630-
Mesoscale Discussion 0277
NWS Storm Prediction Center Norman OK
1000 AM CDT Sat Mar 27 2021
Areas affected...Portions of eastern TN...far southeastern KY...and
extreme southwestern VA
Concerning...Severe potential...Watch unlikely
Valid 271500Z - 271630Z
Probability of Watch Issuance...20 percent
SUMMARY...Mainly an isolated, marginally severe hail threat
continues in the short term. Watch issuance is unlikely this
morning.
DISCUSSION...Multiple reports of 0.5-1.5 inch diameter hail have
occurred over the past few hours across middle/eastern TN into
southeastern KY. This activity is being largely driven a 25-35 kt
southwesterly low-level jet and related warm advection. Most of
these storms are occurring to the north of a surface warm front
where generally 500-1000 J/kg of MUCAPE is present. Isolated
instances of marginally severe hail should remain the primary severe
threat across eastern TN and vicinity this morning, as strong
deep-layer shear continues to support storm organization. A strong
wind gust or two cannot be completely ruled out as the warm front
develops very slowly northward, but the majority of convection
should remain elevated. Current expectations are for these elevated
storms with associated hail threat to remain fairly isolated for the
next couple of hours as they develop east-northeastward. Watch
issuance this morning appears unlikely, but the overall severe
threat across eastern TN will likely increase this afternoon
along/south of the warm front.
..Gleason/Thompson.. 03/27/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MRX...JKL...
LAT...LON 35638361 35488418 35588480 36268452 36638414 36978354
36998274 36738209 36398195 36058275 35638361SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Mar 27, 8:41 AM EDT | Mesoscale Discussion | SPC | Bell, Clinton, Knox, Leslie, McCreary, Wayne and 1 more | 2 hr |
| Mar 27, 3:05 AM EDT | Mesoscale Discussion | SPC | Bedford, Cannon, Chester, Coffee, Decatur, Fayette and 18 more | 115 min |
| Mar 27, 12:55 PM EDT | Mesoscale Discussion | SPC | Bedford, Bledsoe, Bradley, Cannon, Carroll, Chester and 39 more | 3 hr |
| Mar 27, 2:51 PM EDT | Tornado Watch | SPC | Bedford, Benton, Carroll, Chester, Coffee, Crockett and 24 more | 7 hr |
| Mar 27, 4:42 PM EDT | Mesoscale Discussion | SPC | Chester, Crockett, Decatur, Fayette, Hardeman, Hardin and 12 more | 93 min |
| Mar 27, 7:42 PM EDT | Mesoscale Discussion | SPC | Crockett, Fayette, Haywood, Lauderdale, Shelby, Tipton | 2 hr |
| Mar 27, 2:03 PM EDT | Severe Thunderstorm Watch | SPC | Carroll, Floyd, Franklin, Halifax, Henry, Patrick and 3 more | 6 hr |
| Mar 27, 4:49 PM EDT | Mesoscale Discussion | SPC | Halifax, Mecklenburg | 56 min |
Nearby
Mesoscale Discussions in Tennessee, 2021Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in Kentucky, 2021Every mesoscale discussion in 2021
Sources
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.