Alert archive / Texas / Mesoscale Discussions in 2021
Mesoscale Discussion 683
The Storm Prediction Center issued this mesoscale discussion at May 18, 2021, 11:00 PM CDT for 6 counties in Texas. It was in force for 90 min.
The area
The outline as issued.
The facts
- Issued
- May 18, 2021, 11:00 PM CDT (04:00 UTC)
- Expired
- May 19, 2021, 12:30 AM CDT
- In force
- 90 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Dimmit County, TX, Duval County, TX, Jim Hogg County, TX, La Salle County, TX, Webb County, TX, Zapata County, TX
The radar
The Corpus Christi radar (KCRP), 177 km from the middle of the area, began a volume at 04:01 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
Corpus Christi, TX (KCRP), launched 00:00Z, 4.0 hours before the alert went out and 193 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
- 2386 J/kg
- Mixed-layer CIN
- -17 J/kg
- Mixed-layer LCL
- 721 m above ground
- 0-6 km bulk shear
- 22 kt
- 0-1 km storm-relative helicity
- 59 m²/s²
- 0-3 km storm-relative helicity
- 114 m²/s²
- Significant tornado parameter
- 0.8
- Supercell composite
- 6.4
The text
As transmitted.
767
ACUS11 KWNS 190401
SWOMCD
SPC MCD 190400
TXZ000-190530-
Mesoscale Discussion 0683
NWS Storm Prediction Center Norman OK
1100 PM CDT Tue May 18 2021
Areas affected...South TX
Concerning...Severe potential...Watch possible
Valid 190400Z - 190530Z
Probability of Watch Issuance...40 percent
SUMMARY...Convection developing near Laredo may develop into a
supercell or two, posing a severe threat into the early morning
hours.
DISCUSSION...At 0345Z, convection is gradually increasing in
coverage in and near Webb County TX, though storms thus far have
remained subsevere. The environment near and south of a nearly
stationary surface boundary remains conditionally favorable for
severe thunderstorms, with MLCAPE of 2000-3000 J/kg and effective
shear of 30-40 kt. While large-scale forcing is generally nebulous
across the region, moderately enhanced low-level southeasterly flow
may favor an increase in storm coverage near and north of the
boundary at some point late tonight into the early morning.
In the short term, a supercell or two may evolve out of ongoing
convection, posing a risk of large hail and perhaps localized strong
wind gusts. The potentially limited coverage of any such threat
makes the immediate need for watch issuance uncertain. A more
substantial increase in convection is forecast by several CAMs later
in the overnight period, though uncertainty remains as to when this
would occur.
..Dean/Grams.. 05/19/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CRP...EWX...BRO...
LAT...LON 28450028 28539897 28539877 28129860 27149823 26779854
26629916 26819946 27479993 27960014 28450028SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 18, 7:34 PM CDT | Tornado Watch | SPC | Austin, Bee, Brazoria, Chambers, Colorado, Fort Bend and 17 more | 6 hr |
| May 18, 8:00 PM CDT | Mesoscale Discussion | SPC | Cherokee, Gregg, Harrison, Marion, Nacogdoches, Panola and 4 more | 60 min |
| May 18, 8:54 PM CDT | Mesoscale Discussion | SPC | Austin, Fort Bend, Harris, Jackson, Montgomery, Waller and 1 more | 96 min |
| May 18, 10:39 PM CDT | Mesoscale Discussion | SPC | Hardin, Jasper, Jefferson, Newton, Orange, Tyler | 96 min |
| May 19, 3:32 AM CDT | Mesoscale Discussion | SPC | Brooks, Dimmit, Duval, Hidalgo, Jim Hogg, Jim Wells and 5 more | 118 min |
| May 19, 5:24 AM CDT | Severe Thunderstorm Watch | SPC | Brooks, Cameron, Duval, Hidalgo, Jim Hogg, Jim Wells and 8 more | 8 hr |
| May 19, 7:09 AM CDT | Mesoscale Discussion | SPC | Hidalgo, Jim Hogg, Starr | 96 min |
| May 19, 8:46 AM CDT | Mesoscale Discussion | SPC | Brooks, Cameron, Hidalgo, Kenedy, Willacy | 89 min |
| May 19, 2:10 PM CDT | Mesoscale Discussion | SPC | Callahan, Coke, Coleman, Concho, Crane, Crockett and 24 more | 3 hr |
| May 19, 6:06 PM CDT | Mesoscale Discussion | SPC | Crane, Crockett, Ector, Glasscock, Irion, Midland and 6 more | 84 min |
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.