Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 356
The Storm Prediction Center issued this mesoscale discussion at Apr 9, 2021, 11:00 PM CDT for 22 parishes in Louisiana; 16 counties in Mississippi. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 9, 2021, 11:00 PM CDT (04:00 UTC)
- Expired
- Apr 10, 2021, 1:00 AM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 86
All 38 counties
Acadia Parish, LA, Allen Parish, LA, Ascension Parish, LA, Avoyelles Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Rapides Parish, LA, Saint Helena Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Copiah County, MS, Covington County, MS, Franklin County, MS, Jefferson County, MS, Jefferson Davis County, MS, Lamar County, MS, Lawrence County, MS, Lincoln County, MS, Marion County, MS, Pearl River County, MS, Pike County, MS, Simpson County, MS, Walthall County, MS, Wilkinson County, MS
The watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Slidell Radar S, LA (KSIL), launched 00:00Z, 4.0 hours before the alert went out and 155 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
- 2977 J/kg
- Mixed-layer CIN
- -20 J/kg
- Mixed-layer LCL
- 599 m above ground
- 0-6 km bulk shear
- 39 kt
- 0-1 km storm-relative helicity
- 243 m²/s²
- 0-3 km storm-relative helicity
- 269 m²/s²
- Significant tornado parameter
- 3.4
- Supercell composite
- 18.1
The text
As transmitted.
000
ACUS11 KWNS 100401
SWOMCD
SPC MCD 100400
MSZ000-LAZ000-100600-
Mesoscale Discussion 0356
NWS Storm Prediction Center Norman OK
1100 PM CDT Fri Apr 09 2021
Areas affected...southern Louisiana and Mississippi
Concerning...Severe Thunderstorm Watch 86...
Valid 100400Z - 100600Z
The severe weather threat for Severe Thunderstorm Watch 86
continues.
SUMMARY...Severe wind gusts remain possible with storms oriented
along an outflow boundary from central Louisiana into central
Mississippi. A tornado risk may eventually develop later tonight
south of this outflow boundary, and convective trends will continue
to be monitored.
DISCUSSION...A long-lived thunderstorm corridor persists, and is
gradually translating east/southeast as outflow pushes south with
time. Many of these storms are elevated north of the boundary, but
may still produce strong wind gusts, and perhaps severe immediately
along it.
Of note in the surface analysis is a limiting streamline extending
from the northern Gulf of Mexico into south-central MS, with lower
70s F dewpoints west of this line. Bands of shallow
convection/showers are currently observed, and trends will need to
be monitored closely for more vigorous thunderstorms forming south
of the outflow boundary.
With 0-1 SRH over 200 m2/s2 observed on VWPs, and ample instability,
a conditional risk of tornadoes exists with any cells that can form
away from the undercutting outflow.
..Jewell.. 04/10/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...JAN...LIX...LCH...SHV...
LAT...LON 31399244 31709138 32159026 32219014 32178979 31828947
31088926 30568951 30308968 30209000 30179086 30079184
30279285 30719314 31029306 31399244SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 9, 10:25 PM CDT | Severe Thunderstorm Watch | SPC | Avoyelles, Catahoula, Concordia, East Baton Rouge, East Feliciana, Evangeline and 10 more | 6 hr |
| Apr 9, 10:47 PM CDT | Mesoscale Discussion | SPC | De Soto, Natchitoches, Red River, Sabine, Vernon | 118 min |
| Apr 10, 12:16 AM CDT | Tornado Watch | SPC | Acadia, Allen, Ascension, Assumption, Avoyelles, East Baton Rouge and 19 more | 7 hr |
| Apr 10, 12:52 AM CDT | Severe Thunderstorm Watch | SPC | Bienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 11 more | 3 hr |
| Apr 9, 7:20 PM CDT | Mesoscale Discussion | SPC | Alcorn, Lee, Prentiss, Tishomingo | 115 min |
| Apr 10, 1:52 AM CDT | Mesoscale Discussion | SPC | George, Greene, Jackson | 113 min |
| Apr 10, 4:06 AM CDT | Mesoscale Discussion | SPC | George, Greene, Jackson | 114 min |
Nearby
Mesoscale Discussions in Louisiana, 2021Mesoscale Discussions in Mississippi, 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.