Alert archive / Texas / Mesoscale Discussions in 2021
Mesoscale Discussion 673
The Storm Prediction Center issued this mesoscale discussion at May 18, 2021, 2:30 PM CDT for 4 states. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- May 18, 2021, 2:30 PM CDT (19:30 UTC)
- Expired
- May 18, 2021, 4:30 PM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 34 counties
Clark County, AR, Columbia County, AR, Hempstead County, AR, Howard County, AR, Lafayette County, AR, Little River County, AR, Miller County, AR, Montgomery County, AR, Nevada County, AR, Pike County, AR, Polk County, AR, Sevier County, AR, Bossier Parish, LA, Caddo Parish, LA, Choctaw County, OK, McCurtain County, OK, Bowie County, TX, Camp County, TX, Cass County, TX, Cherokee County, TX, Franklin County, TX, Gregg County, TX, Harrison County, TX, Hopkins County, TX, Lamar County, TX, Marion County, TX, Morris County, TX, Panola County, TX, Red River County, TX, Rusk County, TX, Smith County, TX, Titus County, TX, Upshur County, TX, Wood County, TX
The radar
The Shreveport radar (KSHV), 112 km from the middle of the area, began a volume at 19:30 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 12:00Z, 7.5 hours before the alert went out and 115 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
- 56 J/kg
- Mixed-layer CIN
- -268 J/kg
- Mixed-layer LCL
- 968 m above ground
- 0-6 km bulk shear
- 16 kt
- 0-1 km storm-relative helicity
- 41 m²/s²
- 0-3 km storm-relative helicity
- 37 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
403
ACUS11 KWNS 181930
SWOMCD
SPC MCD 181930
ARZ000-LAZ000-TXZ000-OKZ000-182130-
Mesoscale Discussion 0673
NWS Storm Prediction Center Norman OK
0230 PM CDT Tue May 18 2021
Areas affected...Portions of northeast TX into southeastern
OK...southwestern AR...and northwestern LA
Concerning...Severe potential...Watch possible
Valid 181930Z - 182130Z
Probability of Watch Issuance...40 percent
SUMMARY...A strong to damaging wind threat may gradually increase
this afternoon. Isolated severe hail could also occur. Watch
issuance is possible.
DISCUSSION...A band of convection has persisted early this afternoon
from north-central into northeast TX and far southeastern OK. Ascent
associated with a subtle mid-level vorticity maximum and modest
low-level warm advection are probably aiding these storms. Gradual
destabilization of the boundary layer should continue downstream of
this activity across the ArkLaTex region through the remainder of
the afternoon, with the development of MLCAPE around 1000-1500 J/kg
probable. Mid-level flow is expected to fairly modest across this
region through the rest of the day (generally 20-30 kt), and the
lack of stronger effective bulk shear may limit overall storm
organization and intensity to some extent. Still, the ongoing
activity should eventually encounter a more unstable airmass with
eastward extent as convective inhibition continues to weaken this
afternoon. A small cluster similar to the current radar depiction
would pose mainly a strong to damaging wind threat, although
isolated, marginally severe hail may also occur with stronger
embedded updrafts. Other storms may form along an outflow boundary
farther south based on recent visible satellite and radar imagery.
It remains unclear whether any of these storms will strengthen
enough to justify watch issuance, but observational trends will be
closely monitored.
..Gleason/Guyer.. 05/18/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LZK...SHV...TSA...FWD...
LAT...LON 33479568 34109572 34659499 34669419 34519346 34209303
33559304 33009323 32489365 31919447 31839484 31859536
32339532 32609543 33079555 33479568SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 18, 3:51 PM CDT | Severe Thunderstorm Watch | SPC | Clark, Garland, Hempstead, Hot Spring, Howard, Lafayette and 11 more | 5 hr |
| May 18, 5:39 PM CDT | Mesoscale Discussion | SPC | Clark, Conway, Crawford, Faulkner, Franklin, Garland and 20 more | 2 hr |
| May 18, 3:10 AM CDT | Mesoscale Discussion | SPC | Jefferson, Lafourche, Orleans, Saint Charles, Saint John the Baptist, Saint Tammany and 1 more | 95 min |
| May 17, 7:04 PM CDT | Mesoscale Discussion | SPC | Cotton, Jefferson, Stephens, Tillman | 86 min |
| May 17, 7:23 PM CDT | Mesoscale Discussion | SPC | Beaver, Cimarron, Texas | 2 hr |
| May 17, 9:28 PM CDT | Mesoscale Discussion | SPC | Beaver, Beckham, Cimarron, Ellis, Roger Mills, Texas | 2 hr |
| May 17, 7:32 PM CDT | Tornado Watch | SPC | Brown, Callahan, Coke, Coleman, Concho, McCulloch and 4 more | 3 hr |
| May 17, 7:37 PM CDT | Mesoscale Discussion | SPC | Callahan, Coke, Coleman, Glasscock, Howard, Jones and 6 more | 83 min |
| May 17, 8:04 PM CDT | Severe Thunderstorm Watch | SPC | Archer, Clay, Comanche, Eastland, Erath, Hamilton and 11 more | 5 hr |
| May 17, 8:34 PM CDT | Mesoscale Discussion | SPC | Atascosa, Dimmit, Frio, La Salle, McMullen, Maverick and 2 more | 116 min |
| May 17, 9:44 PM CDT | Mesoscale Discussion | SPC | Armstrong, Borden, Briscoe, Childress, Collingsworth, Cottle and 15 more | 91 min |
| May 17, 10:23 PM CDT | Mesoscale Discussion | SPC | Archer, Brown, Callahan, Clay, Coke, Coleman and 16 more | 97 min |
| May 17, 10:35 PM CDT | Mesoscale Discussion | SPC | Andrews, Borden, Brewster, Crane, Crockett, Dawson and 13 more | 85 min |
| May 17, 10:58 PM CDT | Severe Thunderstorm Watch | SPC | Andrews, Borden, Brown, Coke, Coleman, Concho and 22 more | 7 hr |
| May 17, 11:37 PM CDT | Mesoscale Discussion | SPC | Bosque, Brown, Comanche, Denton, Eastland, Erath and 9 more | 83 min |
| May 18, 1:02 AM CDT | Mesoscale Discussion | SPC | Brooks, Duval, Jim Hogg | 58 min |
| May 18, 1:29 AM CDT | Mesoscale Discussion | SPC | Coke, Concho, Crane, Crockett, Ector, Glasscock and 13 more | 91 min |
| May 18, 5:07 AM CDT | Mesoscale Discussion | SPC | Coke, Concho, Irion, Reagan, Runnels, Schleicher and 2 more | 53 min |
| May 18, 1:18 PM CDT | Mesoscale Discussion | SPC | Atascosa, Austin, Bastrop, Bexar, Brazos, Burleson and 28 more | 117 min |
| May 18, 1:57 PM CDT | Mesoscale Discussion | SPC | Bailey, Castro, Deaf Smith, Parmer, Randall, Swisher | 3 hr |
| May 18, 2:29 PM CDT | Tornado Watch | SPC | Anderson, Atascosa, Austin, Bastrop, Bexar, Blanco and 30 more | 7 hr |
| May 18, 3:52 PM CDT | Mesoscale Discussion | SPC | Bastrop, Caldwell, Colorado, Fayette, Gonzales, Guadalupe and 2 more | 83 min |
| May 18, 5:10 PM CDT | Mesoscale Discussion | SPC | La Salle, McMullen, Webb | 95 min |
| May 18, 6:07 PM CDT | Mesoscale Discussion | SPC | Armstrong, Borden, Briscoe, Carson, Castro, Cochran and 17 more | 113 min |
| May 18, 6:13 PM CDT | Mesoscale Discussion | SPC | Austin, Brazos, Burleson, Colorado, DeWitt, Fayette and 14 more | 92 min |
Nearby
Mesoscale Discussions in Texas, 2021Mesoscale Discussions in Arkansas, 2021Mesoscale Discussions in Louisiana, 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.