Alert archive / Texas / Mesoscale Discussions in 2021
Mesoscale Discussion 656
The Storm Prediction Center issued this mesoscale discussion at May 17, 2021, 6:13 PM CDT for Dimmit County, La Salle County, Webb County, Texas. It was in force for 92 min.
The area
The outline as issued.
The facts
- Issued
- May 17, 2021, 6:13 PM CDT (23:13 UTC)
- Expired
- May 17, 2021, 7:45 PM CDT
- In force
- 92 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 60%
Counties Dimmit County, TX, La Salle County, TX, Webb County, TX
The radar
The Laughlin AFB radar (KDFX), 126 km from the middle of the area, began a volume at 23:17 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
Del Rio, TX (KDRT), launched 12:00Z, 11.2 hours before the alert went out and 163 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
- 2620 J/kg
- Mixed-layer CIN
- -127 J/kg
- Mixed-layer LCL
- 577 m above ground
- 0-6 km bulk shear
- 27 kt
- 0-1 km storm-relative helicity
- 85 m²/s²
- 0-3 km storm-relative helicity
- 181 m²/s²
- Significant tornado parameter
- 0.5
- Supercell composite
- 2.5
The text
As transmitted.
319
ACUS11 KWNS 172313
SWOMCD
SPC MCD 172313
TXZ000-180045-
Mesoscale Discussion 0656
NWS Storm Prediction Center Norman OK
0613 PM CDT Mon May 17 2021
Areas affected...South TX
Concerning...Severe potential...Watch possible
Valid 172313Z - 180045Z
Probability of Watch Issuance...60 percent
SUMMARY...Intense thunderstorm development is possible this evening
along an outflow boundary. A conditional threat for very large hail,
locally damaging wind, and a tornado or two will be present with any
supercell that develops.
DISCUSSION...At 23Z, convective initiation appears to be underway
across Dimmit County TX. This development is along a remnant outflow
boundary, with very hot conditions south of the boundary and very
warm/moist conditions noted north of the boundary. Extreme
instability (MLCAPE approaching 4000 J/kg) and sufficient effective
shear (35-45 kt) would support supercell development with any mature
convection in the area. Very large hail would be the primary initial
threat, though a tornado would also be possible, given the presence
of very large CAPE in the vicinity of the boundary, where low-level
shear is locally maximized. Watch issuance may be required soon.
..Dean/Grams.. 05/17/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CRP...EWX...
LAT...LON 28700042 28760006 28689932 28269877 27999875 27499953
27609968 27759978 27940011 28210034 28570048 28700042SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 16, 7:08 PM CDT | Severe Thunderstorm Watch | SPC | Cottle, Crosby, Dickens, Floyd, Garza, Hale and 8 more | 6 hr |
| May 16, 8:54 PM CDT | Mesoscale Discussion | SPC | Briscoe, Cottle, Foard, Hall, King, Knox and 1 more | 96 min |
| May 16, 9:38 PM CDT | Severe Thunderstorm Watch | SPC | Archer, Baylor, Clay, Foard, Hardeman, Haskell and 10 more | 4 hr |
| May 16, 10:46 PM CDT | Mesoscale Discussion | SPC | Baylor, Cottle, Dickens, Foard, Haskell, King and 3 more | 59 min |
| May 17, 1:09 AM CDT | Mesoscale Discussion | SPC | Archer, Baylor, Clay, Crosby, Dickens, Fisher and 17 more | 96 min |
| May 17, 9:18 AM CDT | Mesoscale Discussion | SPC | Jasper, Jefferson, Newton, Orange | 117 min |
| May 17, 12:47 PM CDT | Mesoscale Discussion | SPC | Austin, Bastrop, Bell, Blanco, Brazoria, Brazos and 29 more | 88 min |
| May 17, 1:39 PM CDT | Mesoscale Discussion | SPC | Dallam, Hartley, Oldham | 2 hr |
| May 17, 2:11 PM CDT | Mesoscale Discussion | SPC | Andrews, Bailey, Borden, Castro, Cochran, Crane and 20 more | 2 hr |
| May 17, 2:39 PM CDT | Severe Thunderstorm Watch | SPC | Armstrong, Carson, Collingsworth, Dallam, Donley, Gray and 10 more | 8 hr |
| May 17, 3:04 PM CDT | Tornado Watch | SPC | Andrews, Bailey, Borden, Briscoe, Castro, Cochran and 39 more | 8 hr |
| May 17, 4:44 PM CDT | Tornado Watch | SPC | Baylor, Childress, Cottle, Fisher, Foard, Hardeman and 10 more | 6 hr |
| May 17, 4:53 PM CDT | Mesoscale Discussion | SPC | Baylor, Callahan, Childress, Cottle, Fisher, Foard and 11 more | 97 min |
| May 17, 5:10 PM CDT | Mesoscale Discussion | SPC | Dallam, Hansford, Hartley, Hutchinson, Moore, Ochiltree and 3 more | 2 hr |
| May 17, 5:36 PM CDT | Mesoscale Discussion | SPC | Andrews, Armstrong, Bailey, Borden, Briscoe, Castro and 38 more | 84 min |
| May 17, 6:40 PM CDT | Severe Thunderstorm Watch | SPC | Dimmit, Frio, La Salle, Maverick, Webb, Zavala | 4 hr |
Nearby
Mesoscale Discussions in Texas, 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.