Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 207
The Storm Prediction Center issued this mesoscale discussion at Mar 17, 2021, 1:45 PM CDT for Mobile County, Alabama; 24 parishes in Louisiana; 15 counties in Mississippi. It was in force for 90 min.
The area
The outline as issued.
The facts
- Issued
- Mar 17, 2021, 1:45 PM CDT (18:45 UTC)
- Expired
- Mar 17, 2021, 3:15 PM CDT
- In force
- 90 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...tornado watch likely
- Chance of a watch
- 95%
All 40 counties
Mobile County, AL, Ascension Parish, LA, Assumption Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Pointe Coupee Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Amite County, MS, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson 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 12:00Z, 6.8 hours before the alert went out and 70 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
- 1786 J/kg
- Mixed-layer CIN
- -40 J/kg
- Mixed-layer LCL
- 644 m above ground
- 0-6 km bulk shear
- 44 kt
- 0-1 km storm-relative helicity
- 205 m²/s²
- 0-3 km storm-relative helicity
- 396 m²/s²
- Significant tornado parameter
- 2.0
- Supercell composite
- 9.9
The text
As transmitted.
420
ACUS11 KWNS 171846
SWOMCD
SPC MCD 171845
ALZ000-MSZ000-LAZ000-172015-
Mesoscale Discussion 0207
NWS Storm Prediction Center Norman OK
0145 PM CDT Wed Mar 17 2021
Areas affected...Southeast Louisiana and Southern Mississippi
Concerning...Severe potential...Tornado Watch likely
Valid 171845Z - 172015Z
Probability of Watch Issuance...95 percent
SUMMARY...A tornado watch will be needed in the next hour or two for
southeast Louisiana and southern Mississippi.
DISCUSSION...Warm air advection storms have progressively formed
farther south and low-level rotation has begun quite early in their
life cycle owing to a favorable low-level environment with an STP of
2 across southern Mississippi (per SPC mesoanalysis). If storms
continue to form farther south, the tornado threat may start to
increase south of watch 29.
In addition, established supercells are moving eastward across
southwest Louisiana and are expected to persist through the
afternoon. The tornado threat is not that high with these storms at
this time with mostly straight low-level hodographs per KLCH/KPOE
VWP, but the low-level jet is expected to strengthen later this
afternoon and surface winds are more backed across southeast
Louisiana which should increase tornado potential.
The combination of the warm air advection storms forming farther
south and storms moving toward the area from the west necessitate a
tornado watch across southeast Louisiana within the next hour or
two.
..Bentley/Grams.. 03/17/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MOB...JAN...LIX...LCH...
LAT...LON 31189171 31399056 31328833 30638813 29658909 29338987
29129101 29159159 29369229 31189171SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Mar 17, 10:56 AM CDT | Mesoscale Discussion | SPC | Autauga, Bibb, Chilton, Choctaw, Clarke, Coosa and 17 more | 2 hr |
| Mar 17, 11:36 AM CDT | Tornado Watch | SPC | Autauga, Bibb, Blount, Chilton, Choctaw, Clarke and 25 more | 7 hr |
| Mar 17, 12:02 PM CDT | Mesoscale Discussion | SPC | Choctaw, Clarke, Marengo | 58 min |
| Mar 17, 1:01 PM CDT | Mesoscale Discussion | SPC | Autauga, Chilton, Coosa, Elmore, Lowndes, Montgomery and 1 more | 89 min |
| Mar 17, 1:26 PM CDT | Tornado Watch | SPC | Calhoun, Chambers, Cherokee, Cleburne, Elmore, Etowah and 7 more | 5 hr |
| Mar 17, 2:24 PM CDT | Mesoscale Discussion | SPC | Bibb, Chilton, Dallas, Hale, Marengo, Perry | 96 min |
| Mar 17, 5:49 PM CDT | Mesoscale Discussion | SPC | Autauga, Bibb, Blount, Bullock, Butler, Calhoun and 32 more | 86 min |
| Mar 17, 6:09 PM CDT | Mesoscale Discussion | SPC | Colbert, Franklin, Lamar, Lauderdale, Lawrence, Marion | 66 min |
| Mar 17, 6:48 PM CDT | Tornado Watch | SPC | Autauga, Baldwin, Barbour, Bibb, Blount, Bullock and 44 more | 8 hr |
| Mar 17, 1:32 AM CDT | Mesoscale Discussion | SPC | Bienville, Bossier, Caddo, Claiborne, De Soto, Jackson and 6 more | 118 min |
| Mar 17, 4:04 AM CDT | Mesoscale Discussion | SPC | Bossier, Caddo | 86 min |
| Mar 17, 4:37 AM CDT | Severe Thunderstorm Watch | SPC | Bossier, Caddo | 5 hr |
| Mar 17, 6:40 AM CDT | Mesoscale Discussion | SPC | Bossier, Caddo, Claiborne, Webster | 95 min |
| Mar 17, 8:43 AM CDT | Tornado Watch | SPC | Bienville, Bossier, Caddo, Claiborne, De Soto, Jackson and 8 more | 4 hr |
| Mar 17, 11:35 AM CDT | Mesoscale Discussion | SPC | Allen, Beauregard, Bienville, Calcasieu, Cameron, De Soto and 8 more | 85 min |
| Mar 17, 11:53 AM CDT | Tornado Watch | SPC | Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 7 more | 6 hr |
| Mar 17, 12:15 PM CDT | Mesoscale Discussion | SPC | Caldwell, Catahoula, East Carroll, Franklin, Jackson, LaSalle and 9 more | 90 min |
| Mar 17, 12:57 PM CDT | Tornado Watch | SPC | Bienville, Caldwell, Catahoula, Concordia, East Carroll, Franklin and 15 more | 6 hr |
| Mar 17, 2:38 PM CDT | Tornado Watch | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Iberia, Iberville and 19 more | 8 hr |
| Mar 17, 2:56 PM CDT | Mesoscale Discussion | SPC | Caldwell, Catahoula, Concordia, East Carroll, Franklin, Grant and 7 more | 94 min |
| Mar 17, 5:34 AM CDT | Mesoscale Discussion | SPC | Alcorn, Benton, Bolivar, Calhoun, Coahoma, DeSoto and 15 more | 86 min |
| Mar 17, 5:53 AM CDT | Tornado Watch | SPC | Alcorn, Benton, Bolivar, Calhoun, Chickasaw, Coahoma and 20 more | 7 hr |
| Mar 17, 7:38 AM CDT | Mesoscale Discussion | SPC | Alcorn, Benton, Coahoma, DeSoto, Itawamba, Lafayette and 11 more | 67 min |
| Mar 17, 1:19 PM CDT | Mesoscale Discussion | SPC | Jefferson Davis, Lawrence, Lincoln, Simpson, Smith | 86 min |
Nearby
Mesoscale Discussions in Louisiana, 2021Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Alabama, 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.