Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 648
The Storm Prediction Center issued this mesoscale discussion at May 17, 2021, 9:18 AM CDT for 13 parishes in Louisiana; 4 counties in Texas. It was in force for 117 min.
The area
The outline as issued.
The facts
- Issued
- May 17, 2021, 9:18 AM CDT (14:18 UTC)
- Expired
- May 17, 2021, 11:15 AM CDT
- In force
- 117 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Acadia Parish, LA, Allen Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, Evangeline Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Rapides Parish, LA, Saint Landry Parish, LA, Vermilion Parish, LA, Vernon Parish, LA, Jasper County, TX, Jefferson County, TX, Newton County, TX, Orange County, TX
The radar
The Lake Charles radar (KLCH), 33 km from the middle of the area, began a volume at 14:18 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
Lake Charles Mun, LA (KLCH), launched 12:00Z, 2.3 hours before the alert went out and 33 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
- 626 J/kg
- Mixed-layer CIN
- -14 J/kg
- Mixed-layer LCL
- 699 m above ground
- 0-6 km bulk shear
- 32 kt
- 0-1 km storm-relative helicity
- 207 m²/s²
- 0-3 km storm-relative helicity
- 314 m²/s²
- Significant tornado parameter
- 0.7
- Supercell composite
- 10.3
The text
As transmitted.
668
ACUS11 KWNS 171419
SWOMCD
SPC MCD 171418
LAZ000-TXZ000-171615-
Mesoscale Discussion 0648
NWS Storm Prediction Center Norman OK
0918 AM CDT Mon May 17 2021
Areas affected...Far Southeast TX...Southwest LA
Concerning...Severe potential...Watch unlikely
Valid 171418Z - 171615Z
Probability of Watch Issuance...20 percent
SUMMARY...A tornado or two is possible across southeast TX and
southwest LA over the next few hours.
DISCUSSION...Widespread showers and thunderstorms are ongoing across
the region. Overall buoyancy is limited by this widespread
convection, and most updrafts have been relatively transient and
short-lived. However, occasional updrafts have been able to
persist/deepen, which, given the strong low-level shear, has then
resulted in rotation. Recent POE and LCH VAD profiles have sampled
0-1 km storm-relative helicity of 350+ and 150+ m2/s2, respectively,
over the past half hour. Moderate low-level flow responsible for
this increase in low-level vertical shear will likely persist for at
least the next few hours, resulting in at least a low-probability
tornado threat with any deep/persistent updrafts during this time
frame.
..Mosier/Guyer.. 05/17/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LCH...SHV...
LAT...LON 31239385 31449332 31429256 31179200 30219180 29549221
29539268 29609313 29619371 29639385 29899421 30529417
30839417 31239385SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 17, 2:55 PM CDT | Mesoscale Discussion | SPC | Acadia, Cameron, Iberia, Jefferson Davis, Lafayette, Saint Martin and 2 more | 2 hr |
| May 17, 6:25 PM CDT | Mesoscale Discussion | SPC | Acadia, Ascension, Assumption, Iberia, Iberville, Lafayette and 7 more | 65 min |
| 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, 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, 6:13 PM CDT | Mesoscale Discussion | SPC | Dimmit, La Salle, Webb | 92 min |
| May 17, 6:40 PM CDT | Severe Thunderstorm Watch | SPC | Dimmit, Frio, La Salle, Maverick, Webb, Zavala | 4 hr |
Nearby
Mesoscale Discussions in Louisiana, 2021Mesoscale 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.