Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 331
The Storm Prediction Center issued this mesoscale discussion at Apr 7, 2021, 11:44 PM CDT for 18 parishes in Louisiana; 7 counties in Mississippi. It was in force for 3 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 7, 2021, 11:44 PM CDT (04:44 UTC)
- Expired
- Apr 8, 2021, 2:15 AM CDT
- In force
- 3 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 25 counties
Acadia Parish, LA, Ascension Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Saint Helena Parish, LA, Saint John the Baptist 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, Amite County, MS, Forrest County, MS, Lamar County, MS, Marion County, MS, Pearl River County, MS, Pike County, MS, Walthall County, MS
The nearest sounding before it
Slidell Radar S, LA (KSIL), launched 00:00Z, 4.7 hours before the alert went out and 131 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
- 1186 J/kg
- Mixed-layer CIN
- 0 J/kg
- Mixed-layer LCL
- 722 m above ground
- 0-6 km bulk shear
- 43 kt
- 0-1 km storm-relative helicity
- 147 m²/s²
- 0-3 km storm-relative helicity
- 175 m²/s²
- Significant tornado parameter
- 0.9
- Supercell composite
- 5.8
The text
As transmitted.
874
ACUS11 KWNS 080444
SWOMCD
SPC MCD 080444
MSZ000-LAZ000-080715-
Mesoscale Discussion 0331
NWS Storm Prediction Center Norman OK
1144 PM CDT Wed Apr 07 2021
Areas affected...Portions of southern MS/LA
Concerning...Severe potential...Watch unlikely
Valid 080444Z - 080715Z
Probability of Watch Issuance...20 percent
SUMMARY...An isolated severe risk may persist overnight, but watch
issuance will probably not be needed.
DISCUSSION...A long-lived supercell has persisted as it moved
eastward across central/eastern LA into far southwestern MS.
Low/mid-level rotation has been noted with this storm, with
additional convection in a loosely organized line extending
southwestward across southern LA. This activity may continue to pose
an isolated strong/gusty wind threat for at least the next few hours
as it moves slowly eastward across southern LA/MS. A rich low-level
airmass exists along/south of the ongoing storms, with around
1000-1500 J/kg of MLCAPE available. The VWP from KLCH shows
low/mid-level winds have veered to westerly, likely reducing the
tornado threat across southwestern LA. Farther east into
southeastern LA and southern MS, recent surface observations and the
VWP from KLIX indicate the presence of southeasterly surface winds
veering to southwesterly in the boundary layer. Sufficient low-level
shear remains present to support updraft rotation, and a brief
tornado still appears possible in the short term, mainly with the
ongoing supercell along the LA/MS border. Regardless, the primary
large-scale forcing for ascent should continue to shift northward
and away from this region overnight. Overall severe threat will
likely remain rather isolated, and watch issuance appears unlikely
at this time.
..Gleason/Grams.. 04/08/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MOB...JAN...LIX...LCH...
LAT...LON 30379317 30749226 31249114 31429005 31418909 31048904
30668919 30378970 30079059 29979182 30039270 30379317SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 7, 7:00 PM CDT | Mesoscale Discussion | SPC | Caldwell, Catahoula, Concordia, Franklin, Grant, Jackson and 12 more | 60 min |
| Apr 7, 8:52 PM CDT | Mesoscale Discussion | SPC | Acadia, Allen, Avoyelles, Beauregard, East Baton Rouge, East Feliciana and 10 more | 2 hr |
| Apr 8, 2:08 AM CDT | Mesoscale Discussion | SPC | Livingston, Orleans, Saint Bernard, Saint Charles, Saint John the Baptist, Saint Tammany and 2 more | 2 hr |
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.