Alert archive / Mississippi / Mesoscale Discussions in 2021
Mesoscale Discussion 423
The Storm Prediction Center issued this mesoscale discussion at Apr 24, 2021, 12:29 PM CDT for 10 counties in Alabama; 9 parishes in Louisiana; 23 counties in Mississippi. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 24, 2021, 12:29 PM CDT (17:29 UTC)
- Expired
- Apr 24, 2021, 2:30 PM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 60%
All 42 counties
Baldwin County, AL, Choctaw County, AL, Clarke County, AL, Conecuh County, AL, Escambia County, AL, Marengo County, AL, Mobile County, AL, Monroe County, AL, Washington County, AL, Wilcox County, AL, Livingston Parish, LA, Orleans Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, Clarke County, MS, Covington County, MS, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Jasper County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lauderdale County, MS, Lawrence County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS, Pike County, MS, Simpson County, MS, Smith County, MS, Stone County, MS, Walthall County, MS, Wayne County, MS
The radar
The Mobile radar (KMOB), 83 km from the middle of the area, began a volume at 17:29 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 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 12:00Z, 5.5 hours before the alert went out and 123 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
- 1240 J/kg
- Mixed-layer CIN
- -6 J/kg
- Mixed-layer LCL
- 645 m above ground
- 0-6 km bulk shear
- 65 kt
- 0-1 km storm-relative helicity
- 242 m²/s²
- 0-3 km storm-relative helicity
- 371 m²/s²
- Significant tornado parameter
- 2.2
- Supercell composite
- 8.6
The text
As transmitted.
522
ACUS11 KWNS 241730
SWOMCD
SPC MCD 241729
ALZ000-FLZ000-MSZ000-LAZ000-241930-
Mesoscale Discussion 0423
NWS Storm Prediction Center Norman OK
1229 PM CDT Sat Apr 24 2021
Areas affected...portions of far northeast Louisiana...southeast
Mississippi...southwest Alabama
Concerning...Severe potential...Watch possible
Valid 241729Z - 241930Z
Probability of Watch Issuance...60 percent
SUMMARY...An increasing severe threat is anticipated over the next
couple of hours. Large hail and damaging wind gusts will be the
primary threat with the stronger storms. A Severe Thunderstorm Watch
may be needed soon for parts of this area.
DISCUSSION...Clearing skies and resultant ample insolation have
supported low-level airmass modification over the past few hours
across portions of the central Gulf Coast in the wake of a passing
MCS. Current visible satellite imagery depicts an expanding CU field
within a region of broad low-level confluence across eastern LA into
southern MS and AL. Latest high-resolution guidance consensus
depicts convective initiation occurring around 18-19Z. Modest
mid-level lapse rates (6.5-7 C/km) advecting eastward atop mid 60s
to near 70F dewpoints, along with the aforementioned heating,
supports 1000-2000 J/kg MLCAPE in the modified central Gulf Coast
airmass. While ample wind speed increases with height will support
50-70 kts of effective bulk shear, tropospheric winds appear nearly
unidirectional, and are oriented roughly parallel to the confluence
zone. As such, semi-discrete cellular clusters and linear segments
are expected to be the predominant mode of convection, though brief,
transient supercells are possible.
The strong deep-layer shear and modest lapse rates will promote
severe hail with any of the more intense, sustained storms. Adequate
boundary-layer mixing in advance of developing storms may also
steepen low-level lapse rates sufficiently enough to support a few
damaging gusts as well. With an increase in storm coverage expected
to take place in a couple of hours, a Severe Thunderstorm Watch
issuance may be necessary to address the increasing severe threat.
..Squitieri/Hart.. 04/24/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BMX...MOB...JAN...LIX...
LAT...LON 30698723 30138797 29868888 29788951 29909039 30089074
30229086 30379092 30489095 30589094 31099061 31909009
32318922 32528878 32548859 32578829 32418776 32158718
31908678 31578662 31228679 30698723SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 24, 1:00 AM CDT | Mesoscale Discussion | SPC | Baldwin, Coffee, Conecuh, Covington, Escambia, Geneva and 2 more | 3 hr |
| Apr 24, 1:00 AM CDT | Mesoscale Discussion | SPC | Baldwin, Coffee, Conecuh, Covington, Escambia, Geneva and 2 more | 3 hr |
| Apr 24, 1:23 AM CDT | Tornado Watch | SPC | Baldwin, Clarke, Conecuh, Covington, Escambia, Mobile and 2 more | 8 hr |
| Apr 24, 3:04 AM CDT | Mesoscale Discussion | SPC | Baldwin, Mobile, Washington | 116 min |
| Apr 24, 4:26 AM CDT | Mesoscale Discussion | SPC | Conecuh, Covington, Escambia, Monroe, Washington | 2 hr |
| Apr 24, 5:22 AM CDT | Tornado Watch | SPC | Coffee, Dale, Geneva, Henry, Houston | 9 hr |
| Apr 24, 7:29 AM CDT | Mesoscale Discussion | SPC | Coffee, Dale, Geneva, Henry, Houston | 91 min |
| Apr 24, 1:17 PM CDT | Severe Thunderstorm Watch | SPC | Autauga, Baldwin, Barbour, Bullock, Butler, Choctaw and 23 more | 8 hr |
| Apr 24, 1:22 PM CDT | Mesoscale Discussion | SPC | Blount, Calhoun, Cherokee, Clay, Cleburne, Colbert and 22 more | 113 min |
| Apr 24, 3:40 PM CDT | Mesoscale Discussion | SPC | Autauga, Barbour, Bullock, Butler, Clarke, Coffee and 19 more | 95 min |
| Apr 24, 4:52 PM CDT | Severe Thunderstorm Watch | SPC | Bibb, Blount, Calhoun, Chambers, Cherokee, Chilton and 15 more | 4 hr |
| Apr 24, 5:56 PM CDT | Mesoscale Discussion | SPC | Barbour, Bullock, Coffee, Dale, Henry, Houston and 1 more | 94 min |
| Apr 24, 6:13 PM CDT | Mesoscale Discussion | SPC | Calhoun, Chambers, Cherokee, Clay, Cleburne, Coosa and 6 more | 2 hr |
| Apr 23, 8:30 PM CDT | Tornado Watch | SPC | Allen, Avoyelles, Beauregard, Catahoula, Concordia, East Baton Rouge and 16 more | 8 hr |
| Apr 23, 10:29 PM CDT | Mesoscale Discussion | SPC | Allen, Avoyelles, Concordia, East Baton Rouge, East Feliciana, Evangeline and 10 more | 2 hr |
Nearby
Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Alabama, 2021Mesoscale Discussions in Louisiana, 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.