Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 527
The Storm Prediction Center issued this mesoscale discussion at May 4, 2021, 12:16 PM CDT for 15 parishes in Louisiana; 10 counties in Mississippi. It was in force for 89 min.
The area
The outline as issued.
The facts
- Issued
- May 4, 2021, 12:16 PM CDT (17:16 UTC)
- Expired
- May 4, 2021, 1:45 PM CDT
- In force
- 89 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 144...146
All 25 counties
Caldwell Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, East Carroll Parish, LA, Franklin Parish, LA, Grant Parish, LA, Jackson Parish, LA, LaSalle Parish, LA, Madison Parish, LA, Natchitoches Parish, LA, Ouachita Parish, LA, Rapides Parish, LA, Richland Parish, LA, Tensas Parish, LA, Winn Parish, LA, Adams County, MS, Claiborne County, MS, Copiah County, MS, Franklin County, MS, Hinds County, MS, Issaquena County, MS, Jefferson County, MS, Madison County, MS, Warren County, MS, Yazoo County, MS
The radar
The Ft Polk radar (KPOE), 146 km from the middle of the area, began a volume at 17:19 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
Jackson, MS (KJAN), launched 12:00Z, 5.3 hours before the alert went out and 171 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
- 2428 J/kg
- Mixed-layer CIN
- -6 J/kg
- Mixed-layer LCL
- 646 m above ground
- 0-6 km bulk shear
- 35 kt
- 0-1 km storm-relative helicity
- 170 m²/s²
- 0-3 km storm-relative helicity
- 235 m²/s²
- Significant tornado parameter
- 2.8
- Supercell composite
- 13.2
The text
As transmitted.
236 ACUS11 KWNS 041717 SWOMCD SPC MCD 041716 MSZ000-LAZ000-041845- Mesoscale Discussion 0527 NWS Storm Prediction Center Norman OK 1216 PM CDT Tue May 04 2021 Areas affected...Central LA into Southwest MS Concerning...Tornado Watch 144...146... Valid 041716Z - 041845Z The severe weather threat for Tornado Watch 144, 146 continues. SUMMARY...A corridor of relatively greater severe risk may be developing across central LA and west-central MS. DISCUSSION...Ongoing line of thunderstorms extending from far southern AR back westward into far southeast TX is beginning to show signs of more forward progression, particularly within the portion of the line over northern LA. Air mass downstream of this cluster is very unstable, with mesoanalysis currently estimating MLCAPE over 3000 J/kg, and strongly sheared. Additionally, recent surface observations and radar imagery appear to reveal a modest boundary acting as an effective warm front, roughly from JAN (in Rankin County MS) southwestward to just east of AEX (in Rapides Parish LA). Temperatures south of this boundary are in the 80s with dewpoints in the mid 70s. This boundary could act as an impetus for additional storm intensification/organization, with the corridor along this effective frontal zone experiencing a heightened threat for strong damaging wind gusts as well as hail and brief QLCS tornadoes. ..Mosier.. 05/04/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...JAN...LCH...SHV... LAT...LON 32209323 32759178 32798995 31679011 30889296 32209323
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 3, 9:10 PM CDT | Severe Thunderstorm Watch | SPC | Bossier, Caddo, Webster | 7 hr |
| May 4, 6:44 AM CDT | Mesoscale Discussion | SPC | Bienville, Bossier, Caddo, Claiborne, De Soto, Lincoln and 3 more | 2 hr |
| May 4, 8:33 AM CDT | Mesoscale Discussion | SPC | Avoyelles, Caldwell, Catahoula, Concordia, East Carroll, East Feliciana and 14 more | 117 min |
| May 4, 10:52 AM CDT | Tornado Watch | SPC | Allen, Avoyelles, Beauregard, Bienville, Bossier, Caddo and 31 more | 7 hr |
| May 4, 3:31 PM CDT | Tornado Watch | SPC | East Baton Rouge, Livingston, Saint Tammany, Tangipahoa, Washington, West Baton Rouge | 6 hr |
| May 4, 4:46 PM CDT | Mesoscale Discussion | SPC | Saint Tammany, Tangipahoa, Washington | 89 min |
| May 4, 9:03 AM CDT | Mesoscale Discussion | SPC | Clay, Lowndes, Monroe, Oktibbeha | 117 min |
| May 4, 9:18 AM CDT | Tornado Watch | SPC | Attala, Carroll, Choctaw, Clarke, Clay, Copiah and 26 more | 7 hr |
| May 4, 11:58 AM CDT | Mesoscale Discussion | SPC | Alcorn, Benton, Calhoun, Chickasaw, Coahoma, DeSoto and 13 more | 2 hr |
| May 4, 12:18 PM CDT | Severe Thunderstorm Watch | SPC | Alcorn, Benton, Calhoun, Chickasaw, Coahoma, DeSoto and 16 more | 5 hr |
| May 4, 2:17 PM CDT | Mesoscale Discussion | SPC | Attala, Choctaw, Claiborne, Clarke, Copiah, Covington and 26 more | 88 min |
| May 4, 3:03 PM CDT | Mesoscale Discussion | SPC | Chickasaw, Choctaw, Clay, Itawamba, Kemper, Lowndes and 5 more | 117 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; radar from the NEXRAD Level II archive.