Alert archive / Louisiana / Mesoscale Discussions in 2021

Mesoscale Discussion 1917

October 27, 202119 parishes in Louisiana; 10 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Oct 27, 2021, 3:25 PM CDT for 19 parishes in Louisiana; 10 counties in Mississippi. It was in force for 95 min.

The area

The outline as issued.

The facts

Issued: Oct 27, 2021, 3:25 PM CDT (20:25 UTC)
Expired: Oct 27, 2021, 5:00 PM CDT
In force: 95 min
Issued by: the Storm Prediction Center
Concerning: Tornado watch 542

All 29 counties

Ascension Parish, LA, Assumption Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Iberville Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, Amite County, MS, Franklin County, MS, Hancock County, MS, Jefferson County, MS, Lawrence County, MS, Lincoln County, MS, Marion County, MS, Pearl River County, MS, Pike County, MS, Walthall County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 8.4 hours before the alert went out and 103 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

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

Open this sounding in Storm Lab

The text

As transmitted.

456 
ACUS11 KWNS 272025
SWOMCD
SPC MCD 272025 
MSZ000-LAZ000-272200-

Mesoscale Discussion 1917
NWS Storm Prediction Center Norman OK
0325 PM CDT Wed Oct 27 2021

Areas affected...southeast Louisiana into southern Mississippi

Concerning...Tornado Watch 542...

Valid 272025Z - 272200Z

The severe weather threat for Tornado Watch 542 continues.

SUMMARY...Threat for damaging wind and tornadoes including potential
for a couple of strong tornadoes will persist across southeast LA
and far southern MS into the early evening.

DISCUSSION...Warm front is moving northward and currently extends
from southeast LA near New Orleans northwest into southwest MS.
Numerous discrete showers and a few supercells continue developing
across southeast LA within the weakly capped warm sector along and
south of the warm front where the atmosphere remains moderately
unstable. The Slidell VWP indicates a large hodograph with veering
winds in the lowest 1 km supporting up to 350 m2/s2 storm relative
helicity along the low level jet corridor. Some of the pre-frontal
convection will likely evolve into mature supercells and become
capable of producing tornadoes, especially as they interact with the
warm front. Otherwise, embedded bowing segments, mesovortices and
occasional supercells continue to be observed within the squall
line, supporting a threat for damaging wind and QLCS tornadoes.

..Dial.. 10/27/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MOB...JAN...LIX...LCH...

LAT...LON   29349193 30289140 30869114 31789108 31548980 30688917
            29738949 29009099 29349193

SPC 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, 12:50 PM CDT	Mesoscale Discussion	SPC	Acadia, Ascension, Assumption, Avoyelles, Concordia, East Baton Rouge and 24 more	85 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, 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, 2021 Mesoscale Discussions in Mississippi, 2021 Every 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.