Alert archive / Louisiana / Mesoscale Discussions in 2021

Mesoscale Discussion 329

April 7, 202118 parishes in Louisiana; Newton County, Texas

The Storm Prediction Center issued this mesoscale discussion at Apr 7, 2021, 7:00 PM CDT for 18 parishes in Louisiana; Newton County, Texas. It was in force for 60 min.

The area

The outline as issued.

The facts

Issued: Apr 7, 2021, 7:00 PM CDT (00:00 UTC)
Expired: Apr 7, 2021, 8:00 PM CDT
In force: 60 min
Issued by: the Storm Prediction Center
Concerning: Tornado watch 75

Counties Caldwell Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, Franklin Parish, LA, Grant Parish, LA, Jackson Parish, LA, LaSalle Parish, LA, Lincoln Parish, LA, Madison Parish, LA, Morehouse Parish, LA, Natchitoches Parish, LA, Ouachita Parish, LA, Rapides Parish, LA, Richland Parish, LA, Sabine Parish, LA, Vernon Parish, LA, West Carroll Parish, LA, Winn Parish, LA, Newton County, TX

The radar

The Ft Polk radar (KPOE), 66 km from the middle of the area, began a volume at 00:00 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 nearest sounding before it

Shreveport, LA (KSHV), launched 00:00Z, 0.0 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.

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: 203 J/kg
Mixed-layer CIN: -107 J/kg
Mixed-layer LCL: 1097 m above ground
0-6 km bulk shear: 58 kt
0-1 km storm-relative helicity: -49 m²/s²
0-3 km storm-relative helicity: 72 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

As transmitted.

473 
ACUS11 KWNS 080000
SWOMCD
SPC MCD 080000 
LAZ000-TXZ000-080100-

Mesoscale Discussion 0329
NWS Storm Prediction Center Norman OK
0700 PM CDT Wed Apr 07 2021

Areas affected...Portions of LA

Concerning...Tornado Watch 75...

Valid 080000Z - 080100Z

The severe weather threat for Tornado Watch 75 continues.

SUMMARY...An isolated severe threat continues across southern
portions of Tornado Watch 75 and vicinity.

DISCUSSION...Convection has continued struggling to intensify across
much of Tornado Watch 75 early this evening. A feed of greater
low-level moisture is present across LA, where generally mid 60s
surface dewpoints are present along/south of ongoing convection. One
cell in northern LA has recently developed low/mid-level rotation,
and VWPs from area radars show sufficiently veering/strengthening
wind profile with height to support continued updraft rotation. A
tornado remains possible in the short term with any storms that
remain at least semi discrete. Isolated strong/gusty winds also
appear possible. At this point, the need for a downstream watch
remains uncertain, but trends are being closely monitored.

..Gleason.. 04/08/2021

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

ATTN...WFO...JAN...LCH...SHV...

LAT...LON   30939441 31399377 31919326 32739273 32929200 32859125
            32309121 31389165 30929222 30779381 30939441

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 7, 8:52 PM CDT	Mesoscale Discussion	SPC	Acadia, Allen, Avoyelles, Beauregard, East Baton Rouge, East Feliciana and 10 more	2 hr
Apr 7, 11:44 PM CDT	Mesoscale Discussion	SPC	Acadia, Ascension, East Baton Rouge, East Feliciana, Iberville, Jefferson Davis and 12 more	3 hr
Apr 8, 2:08 AM CDT	Mesoscale Discussion	SPC	Livingston, Orleans, Saint Bernard, Saint Charles, Saint John the Baptist, Saint Tammany and 2 more	2 hr
Apr 8, 4:58 PM CDT	Mesoscale Discussion	SPC	Bosque, Comanche, Coryell, Hamilton, Lampasas, Mills	2 hr

Nearby

Mesoscale Discussions in Louisiana, 2021 Mesoscale Discussions in Texas, 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; radar from the NEXRAD Level II archive.