Alert archive / Louisiana / Mesoscale Discussions in 2021

Mesoscale Discussion 237

March 23, 202110 parishes in Louisiana; Adams County, Wilkinson County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Mar 23, 2021, 7:05 AM CDT for 10 parishes in Louisiana; Adams County, Wilkinson County, Mississippi. It was in force for 85 min.

The area

The outline as issued.

The facts

Issued: Mar 23, 2021, 7:05 AM CDT (12:05 UTC)
Expired: Mar 23, 2021, 8:30 AM CDT
In force: 85 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Acadia Parish, LA, Avoyelles Parish, LA, Cameron Parish, LA, Concordia Parish, LA, Evangeline Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Pointe Coupee Parish, LA, Saint Landry Parish, LA, West Feliciana Parish, LA, Adams County, MS, Wilkinson County, MS

The radar

The Ft Polk radar (KPOE), 84 km from the middle of the area, began a volume at 12:06 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 12:00Z, 0.1 hours before the alert went out and 246 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: -58 J/kg
Mixed-layer LCL: 858 m above ground
0-6 km bulk shear: 67 kt
0-1 km storm-relative helicity: 311 m²/s²
0-3 km storm-relative helicity: 359 m²/s²
Significant tornado parameter: 0.3
Supercell composite: 1.9

Open this sounding in Storm Lab

The text

As transmitted.

492 
ACUS11 KWNS 231205
SWOMCD
SPC MCD 231205 
LAZ000-MSZ000-231330-

Mesoscale Discussion 0237
NWS Storm Prediction Center Norman OK
0705 AM CDT Tue Mar 23 2021

Areas affected...southwest LA into far southwest MS

Concerning...Severe potential...Watch unlikely 

Valid 231205Z - 231330Z

Probability of Watch Issuance...20 percent

SUMMARY...Transient embedded supercells could produce locally strong
gusts or a brief tornado this morning.

DISCUSSION...A band of training thunderstorms with some transient
embedded supercells is persisting across southwest LA toward far
southwest MS this morning. Just to the west of this convection,
additional thunderstorms ahead of a cold front are producing an
eastward-advancing outflow boundary, which could further aid in
cold-pool generation and undercut any surface-based convection to
the east. This should also aid in a slow east/southeastward shift in
training convection through the morning. 

Weak instability in the presence of strong shear is resulting in
transient supercells occasionally exhibiting weak to moderate
rotation. VWP data from KLCH shows an enlarged low-level hodograph
with 0-1 km SRH greater than 200 m2/s2. Furthermore, these embedded
supercells are occurring on the margins of stronger moisture return
in the vicinity of a northwest to southeast oriented warm front.
While some weak surface-based inhibition is present, a narrow
corridor may exist where a storm could briefly produce a tornado or
locally damaging wind gust. The overall threat is expected to remain
limited and transient, and a watch is not expected at this time,
though trends will be monitored closely.

..Leitman/Edwards.. 03/23/2021

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

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

LAT...LON   30439307 31139226 31339195 31569148 31459121 31069117
            30619144 30189193 29709308 29639373 29869386 30439307

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Mar 23, 9:41 AM CDT	Mesoscale Discussion	SPC	Ascension, Assumption, East Baton Rouge, Iberia, Iberville, Lafourche and 10 more	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; radar from the NEXRAD Level II archive.