Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 1915
The Storm Prediction Center issued this mesoscale discussion at Oct 27, 2021, 12:50 PM CDT for 30 parishes in Louisiana; 19 counties in Mississippi. It was in force for 85 min.
The area
The outline as issued.
The facts
- Issued
- Oct 27, 2021, 12:50 PM CDT (17:50 UTC)
- Expired
- Oct 27, 2021, 2:15 PM CDT
- In force
- 85 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 540
All 49 counties
Acadia Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Avoyelles Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Jefferson Parish, LA, Lafayette Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Pointe Coupee Parish, LA, Rapides Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Vermilion Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, Hancock County, MS, Harrison County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lawrence County, MS, Lincoln 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, 5.8 hours before the alert went out and 150 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
- 1792 m above ground
- 0-6 km bulk shear
- 47 kt
- 0-1 km storm-relative helicity
- 186 m²/s²
- 0-3 km storm-relative helicity
- 274 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
248
ACUS11 KWNS 271751
SWOMCD
SPC MCD 271750
MSZ000-LAZ000-271915-
Mesoscale Discussion 1915
NWS Storm Prediction Center Norman OK
1250 PM CDT Wed Oct 27 2021
Areas affected...southern Louisiana through southern Mississippi
Concerning...Tornado Watch 540...
Valid 271750Z - 271915Z
The severe weather threat for Tornado Watch 540 continues.
SUMMARY...Threat for damaging wind and tornadoes including potential
for a couple of strong tornadoes should persist over southern LA,
spreading east through southeast LA and southern MS during the
afternoon. A new tornado watch will likely be needed for this area
by 19Z.
DISCUSSION...A line of storms with embedded bowing segments and some
supercell structures continues moving through western LA at around
35 kt. East of this line the warm sector continues to expand
northward south of a warm front that extends from southeast through
north central LA. A very moist boundary layer is in place south of
this front with mid 70s F dewpoints, and diabatic warming has
boosted surface temperatures into the low to mid 80s F supporting up
to 2000 J/kg MLCAPE. Several northwest-southeast oriented
convergence bands are evident on visible imagery extending into
southern LA from the Gulf. The 18Z RAOB from Slidell modified for
surface conditions in warm sector indicates minimal inhibition. This
suggests that, in addition to the arrival of the line of storms, the
potential will exist for discrete storms develop as the boundary
layer continues to destabilize. The low-level jet is forecast to
undergo further strengthening, supporting large hodographs with 0-1
km storm relative helicity from 250-350 m2/s2. Threat for damaging
wind and tornadoes will persist through the remainder of the
afternoon into early evening in this region.
..Dial/Thompson.. 10/27/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MOB...JAN...LIX...LCH...SHV...
LAT...LON 29709288 30359283 31129279 31429201 31599145 31848993
31568868 30548864 29309009 29399090 29709174 29709288SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Oct 27, 7:36 AM CDT | Mesoscale Discussion | SPC | Acadia, Beauregard, Calcasieu, Cameron, Iberia, Jefferson Davis and 4 more | 84 min |
| Oct 27, 7:55 AM CDT | Tornado Watch | SPC | Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 13 more | 9 hr |
| Oct 27, 9:44 AM CDT | Mesoscale Discussion | SPC | Bienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 7 more | 2 hr |
| Oct 27, 10:08 AM CDT | Tornado Watch | SPC | Bienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 6 more | 5 hr |
| Oct 27, 10:59 AM CDT | Mesoscale Discussion | SPC | Beauregard, Vernon | 91 min |
| Oct 27, 12:52 PM CDT | Mesoscale Discussion | SPC | Bienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 7 more | 83 min |
| Oct 27, 1:53 PM CDT | Tornado Watch | SPC | Ascension, Assumption, Catahoula, Concordia, East Baton Rouge, East Feliciana and 18 more | 8 hr |
| Oct 27, 3:25 PM CDT | Mesoscale Discussion | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Iberville, Jefferson and 13 more | 95 min |
| Oct 27, 5:13 PM CDT | Mesoscale Discussion | SPC | Orleans, Saint Bernard, Saint John the Baptist, Saint Tammany, Tangipahoa, Washington | 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.