Alert archive / Mississippi / Mesoscale Discussions in 2021

Mesoscale Discussion 2076

December 29, 2021Washington Parish, Louisiana; 5 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Dec 29, 2021, 2:49 PM CST for Washington Parish, Louisiana; 5 counties in Mississippi. It was in force for 86 min.

The area

The outline as issued.

The facts

Issued: Dec 29, 2021, 2:49 PM CST (20:49 UTC)
Expired: Dec 29, 2021, 4:15 PM CST
In force: 86 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 5%

Counties Washington Parish, LA, Forrest County, MS, Lamar County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 8.8 hours before the alert went out and 88 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: 1219 J/kg
Mixed-layer CIN: -5 J/kg
Mixed-layer LCL: 538 m above ground
0-6 km bulk shear: 30 kt
0-1 km storm-relative helicity: 110 m²/s²
0-3 km storm-relative helicity: 132 m²/s²
Significant tornado parameter: 0.6
Supercell composite: 4.5

Open this sounding in Storm Lab

The text

As transmitted.

695 
ACUS11 KWNS 292049
SWOMCD
SPC MCD 292049 
MSZ000-LAZ000-292215-

Mesoscale Discussion 2076
NWS Storm Prediction Center Norman OK
0249 PM CST Wed Dec 29 2021

Areas affected...extreme eastern Louisiana into far southern
Mississippi

Concerning...Severe potential...Watch unlikely 

Valid 292049Z - 292215Z

Probability of Watch Issuance...5 percent

SUMMARY...A damaging gust or brief tornado is possible with one of
the more organized, longer-lasting storms. A WW issuance is not
expected given the brief, localized nature of the severe threat.

DISCUSSION...KLIX radar shows that a couple of storms in
Washington/St. Tammany Parish have exhibited transient supercell
structures and very brief bouts of modest low-level rotation over
the last hour. These storms are supported largely by strong surface
heating, with temperatures and dewpoints around 80/70F,
respectively. MLCAPE has increased to around 2000 J/kg in the
presence of 40+ kt effective bulk shear. Nonetheless, mechanically
driven deep-layer ascent remains negligible across the region, and
the 2028Z KLIX VWP shows only modest veering/curvature in the 0-3 km
layer, with SRH under 200 m2/s2 across the region. The
kinematic/thermodynamic environment does support a very localized
threat for a damaging gust or brief tornado. However, more
widespread and robust storm organization is not expected, and a WW
issuance appears unlikely.

..Squitieri/Hart.. 12/29/2021

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

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

LAT...LON   30639020 31189006 31568978 31548892 31218879 30938899
            30588965 30639020

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 29, 9:25 AM CST	Mesoscale Discussion	SPC	Bossier, Caddo, Claiborne, Lincoln, Union, Webster	2 hr
Dec 29, 10:44 AM CST	Mesoscale Discussion	SPC	East Carroll, Morehouse, West Carroll	2 hr
Dec 29, 12:05 PM CST	Tornado Watch	SPC	Claiborne, East Carroll, Lincoln, Morehouse, Ouachita, Union and 1 more	7 hr
Dec 29, 3:41 PM CST	Mesoscale Discussion	SPC	Morehouse, West Carroll	64 min
Dec 29, 4:44 PM CST	Mesoscale Discussion	SPC	Bossier, Caddo, Claiborne, Webster	2 hr
Dec 29, 1:18 PM CST	Mesoscale Discussion	SPC	Bolivar, Calhoun, Carroll, Chickasaw, Coahoma, Grenada and 15 more	87 min
Dec 29, 2:03 PM CST	Mesoscale Discussion	SPC	Adams, Claiborne, Copiah, Covington, Franklin, Hinds and 18 more	87 min
Dec 29, 4:38 PM CST	Mesoscale Discussion	SPC	Calhoun, Chickasaw, Clay, Itawamba, Lee, Lowndes and 6 more	2 hr

Nearby

Mesoscale Discussions in Mississippi, 2021 Mesoscale Discussions in Louisiana, 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.