Alert archive / Texas / Mesoscale Discussions in 2021
Mesoscale Discussion 466
The Storm Prediction Center issued this mesoscale discussion at Apr 29, 2021, 1:09 AM CDT for 12 counties in Arkansas; 7 counties in Oklahoma; 28 counties in Texas. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 29, 2021, 1:09 AM CDT (06:09 UTC)
- Expired
- Apr 29, 2021, 3:15 AM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 121
All 47 counties
Hempstead County, AR, Howard County, AR, Little River County, AR, Logan County, AR, Miller County, AR, Montgomery County, AR, Pike County, AR, Polk County, AR, Scott County, AR, Sebastian County, AR, Sevier County, AR, Yell County, AR, Atoka County, OK, Bryan County, OK, Choctaw County, OK, Latimer County, OK, LeFlore County, OK, McCurtain County, OK, Pushmataha County, OK, Bowie County, TX, Camp County, TX, Cass County, TX, Collin County, TX, Dallas County, TX, Delta County, TX, Ellis County, TX, Fannin County, TX, Franklin County, TX, Gregg County, TX, Harrison County, TX, Henderson County, TX, Hill County, TX, Hopkins County, TX, Hunt County, TX, Kaufman County, TX, Lamar County, TX, Marion County, TX, Morris County, TX, Navarro County, TX, Rains County, TX, Red River County, TX, Rockwall County, TX, Smith County, TX, Titus County, TX, Upshur County, TX, Van Zandt County, TX, Wood County, TX
The radar
The Shreveport radar (KSHV), 175 km from the middle of the area, began a volume at 06:12 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Shreveport, LA (KSHV), launched 00:00Z, 6.2 hours before the alert went out and 179 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
- 976 J/kg
- Mixed-layer CIN
- -47 J/kg
- Mixed-layer LCL
- 1188 m above ground
- 0-6 km bulk shear
- 43 kt
- 0-1 km storm-relative helicity
- 169 m²/s²
- 0-3 km storm-relative helicity
- 258 m²/s²
- Significant tornado parameter
- 0.8
- Supercell composite
- 5.0
The text
As transmitted.
032
ACUS11 KWNS 290610
SWOMCD
SPC MCD 290609
ARZ000-LAZ000-TXZ000-OKZ000-290815-
Mesoscale Discussion 0466
NWS Storm Prediction Center Norman OK
0109 AM CDT Thu Apr 29 2021
Areas affected...northeast Texas into southwest Arkansas
Concerning...Tornado Watch 121...
Valid 290609Z - 290815Z
The severe weather threat for Tornado Watch 121 continues.
SUMMARY...The threat for severe weather continues over eastern parts
of watch 121, and may persist toward the Arklatex area, and a new
watch may be needed.
DISCUSSION...Numerous thunderstorms currently extend from northern
AR into southeast AR and into north TX, along and ahead of the
outflow-composite cold front. Surface analysis shows upper 60s to
lower 70s F dewpoints over northeast TX and into southwest AR,
contributing to around 1500 J/kg MLCAPE. Deep-layer shear remains
favorable for organized storms as well, with 50-60 kt. In addition,
effective SRH remains substantial with 300 m2/s2 over much of the
area. The favorable shear may sustain storms over the next several
hours, despite a minor warm layer near 700 mb.
Various strong storms along the front may yet become severe as they
evolve ahead of the cold front. Though storm mode is mixed, at least
brief supercells are possible, with tornado threat. Given that the
threat may persist beyond the typical 2-hour watch extension period,
a new watch may be considered.
..Jewell.. 04/29/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LZK...SHV...TSA...FWD...OUN...
LAT...LON 32079517 31849679 31999721 32399731 32979679 33989632
34359614 34859556 35299482 35389378 35199331 34959312
34329317 32949375 32229460 32079517SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 28, 7:55 PM CDT | Tornado Watch | SPC | Clark, Cleburne, Conway, Crawford, Faulkner, Franklin and 18 more | 6 hr |
| Apr 28, 9:19 PM CDT | Mesoscale Discussion | SPC | Crawford, Franklin, Howard, Little River, Logan, Montgomery and 5 more | 116 min |
| Apr 28, 10:22 PM CDT | Mesoscale Discussion | SPC | Cleburne, Conway, Craighead, Crittenden, Cross, Faulkner and 22 more | 113 min |
| Apr 29, 2:01 AM CDT | Tornado Watch | SPC | Clark, Conway, Faulkner, Garland, Hempstead, Hot Spring and 17 more | 6 hr |
| Apr 29, 3:14 AM CDT | Mesoscale Discussion | SPC | Clay, Craighead, Greene | 3 hr |
| Apr 28, 7:01 PM CDT | Mesoscale Discussion | SPC | Bastrop, Bexar, Caldwell, Comal, Gonzales, Guadalupe and 4 more | 89 min |
| Apr 28, 7:31 PM CDT | Mesoscale Discussion | SPC | Callahan, Coleman, Collin, Comanche, Cooke, Dallas and 24 more | 119 min |
| Apr 28, 9:13 PM CDT | Mesoscale Discussion | SPC | Bastrop, Bexar, Caldwell, Colorado, Comal, Fayette and 4 more | 92 min |
| Apr 28, 10:22 PM CDT | Tornado Watch | SPC | Atascosa, Bandera, Bastrop, Bexar, Blanco, Burnet and 27 more | 7 hr |
| Apr 28, 11:03 PM CDT | Mesoscale Discussion | SPC | Atascosa, Bandera, Bastrop, Bell, Bexar, Blanco and 37 more | 117 min |
Nearby
Mesoscale Discussions in Texas, 2021Mesoscale Discussions in Arkansas, 2021Mesoscale Discussions in Oklahoma, 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.