Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 414
The Storm Prediction Center issued this mesoscale discussion at Apr 23, 2021, 10:29 PM CDT for 16 parishes in Louisiana; 12 counties in Mississippi. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 23, 2021, 10:29 PM CDT (03:29 UTC)
- Expired
- Apr 24, 2021, 12:30 AM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 104
All 28 counties
Allen Parish, LA, Avoyelles Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Saint Helena Parish, LA, Saint John the Baptist Parish, LA, Saint Landry 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, George County, MS, Hancock County, MS, Lamar County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS, Pike County, MS, Stone 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, 3.5 hours before the alert went out and 137 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 873 m above ground
- 0-6 km bulk shear
- 62 kt
- 0-1 km storm-relative helicity
- 156 m²/s²
- 0-3 km storm-relative helicity
- 263 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
636 ACUS11 KWNS 240329 SWOMCD SPC MCD 240329 MSZ000-LAZ000-240530- Mesoscale Discussion 0414 NWS Storm Prediction Center Norman OK 1029 PM CDT Fri Apr 23 2021 Areas affected...Parts of central and southern Louisiana into southern Mississippi and adjacent southwestern Alabama Concerning...Tornado Watch 104... Valid 240329Z - 240530Z The severe weather threat for Tornado Watch 104 continues. SUMMARY...The evolving cluster of storms could still become better organized with increasing risk for damaging wind gusts and perhaps a couple of tornadoes through Midnight-1 AM CDT. DISCUSSION...A large cluster of thunderstorms continues to develop east-northeastward, with a low-amplitude wave on the northern periphery of mid-level subtropical ridging, beneath a strongly divergent upper-level flow field. While this activity, in general, has struggled to become well organized, new convective development aided by lower/mid tropospheric warm advection is ongoing inland of coastal Louisiana and Mississippi, and will continue to gradually merge into the larger-scale cluster. Particularly on the southwestern flank of the evolving cluster, there appears potential for stronger convection to consolidate and become better organized during the next few hours. The latest Rapid Refresh, supported by VWP data from Lake Charles and Slidell, suggests that south-southwesterly lower/mid tropospheric flow is in the process of strengthening across this region. As this continues, enlarging low-level level hodographs, and perhaps a somewhat better low-level moisture inflow off the northwestern Gulf of Mexico, may finally contribute to convective intensification supportive of a more substantive risk for damaging wind gusts. The risk for tornadoes may could also increase through 05-06Z, particularly with the more discrete storms, perhaps including areas as far south as the Lake Pontchartrain vicinity. ..Kerr.. 04/24/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...MOB...JAN...LIX...LCH...SHV... LAT...LON 30699313 31489186 31478907 30728844 30049004 30699313
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 23, 8:30 PM CDT | Tornado Watch | SPC | Allen, Avoyelles, Beauregard, Catahoula, Concordia, East Baton Rouge and 16 more | 8 hr |
| Apr 24, 3:04 AM CDT | Mesoscale Discussion | SPC | Ascension, Assumption, Livingston, Orleans, Saint Charles, Saint James and 4 more | 116 min |
| Apr 24, 12:29 PM CDT | Mesoscale Discussion | SPC | Livingston, Orleans, Saint Bernard, Saint Charles, Saint Helena, Saint John the Baptist and 3 more | 2 hr |
| Apr 24, 1:00 AM CDT | Mesoscale Discussion | SPC | Forrest, George, Greene, Hancock, Harrison, Jackson and 2 more | 3 hr |
| Apr 24, 1:00 AM CDT | Mesoscale Discussion | SPC | Forrest, George, Greene, Hancock, Harrison, Jackson and 2 more | 3 hr |
| Apr 24, 1:23 AM CDT | Tornado Watch | SPC | George, Greene, Hancock, Harrison, Jackson, Perry and 2 more | 8 hr |
| Apr 24, 4:26 AM CDT | Mesoscale Discussion | SPC | George, Greene | 2 hr |
| Apr 24, 1:17 PM CDT | Severe Thunderstorm Watch | SPC | George, Greene, Perry, Stone, Wayne | 8 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.