Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 1967
The Storm Prediction Center issued this mesoscale discussion at Dec 6, 2021, 7:17 AM CST for 20 parishes in Louisiana; 11 counties in Mississippi. It was in force for 118 min.
The area
The outline as issued.
The facts
- Issued
- Dec 6, 2021, 7:17 AM CST (13:17 UTC)
- Expired
- Dec 6, 2021, 9:15 AM CST
- In force
- 118 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 31 counties
Avoyelles Parish, LA, Beauregard Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, East Carroll Parish, LA, Franklin Parish, LA, Grant Parish, LA, Jackson Parish, LA, LaSalle Parish, LA, Madison Parish, LA, Natchitoches Parish, LA, Ouachita Parish, LA, Rapides Parish, LA, Richland Parish, LA, Sabine Parish, LA, Tensas Parish, LA, Vernon Parish, LA, West Carroll Parish, LA, Winn Parish, LA, Adams County, MS, Claiborne County, MS, Copiah County, MS, Franklin County, MS, Hinds County, MS, Issaquena County, MS, Jefferson County, MS, Rankin County, MS, Sharkey County, MS, Warren County, MS, Yazoo County, MS
The radar
The Ft Polk radar (KPOE), 78 km from the middle of the area, began a volume at 13:19 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, 1.3 hours before the alert went out and 164 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
- 2110 J/kg
- Mixed-layer CIN
- -1 J/kg
- Mixed-layer LCL
- 479 m above ground
- 0-6 km bulk shear
- 49 kt
- 0-1 km storm-relative helicity
- 317 m²/s²
- 0-3 km storm-relative helicity
- 286 m²/s²
- Significant tornado parameter
- 3.3
- Supercell composite
- 15.3
The text
As transmitted.
110
ACUS11 KWNS 061318
SWOMCD
SPC MCD 061317
MSZ000-LAZ000-TXZ000-061515-
Mesoscale Discussion 1967
NWS Storm Prediction Center Norman OK
0717 AM CST Mon Dec 06 2021
Areas affected...central Louisiana vicinity into southwestern
Mississippi
Concerning...Severe potential...Watch possible
Valid 061317Z - 061515Z
Probability of Watch Issuance...40 percent
SUMMARY...Ongoing/limited severe risk may modestly/gradually
increase over the next 1 to 2 hours. A WW may be considered,
depending upon convective evolution.
DISCUSSION...Latest radar loop shows a lone supercell -- which
likely produced a small/brief tornado earlier -- moving eastward
across Vernon Parish in western Louisiana. The storm remains
well-organized, with a cyclic increase in low-level rotation noted
once again, in the latest volume scan. With low-level flow
veering/increasing with height through the lowest 1km per recent
KPOE VWP, shear is sufficient to support continued low-level
rotation with this storm, given background mixed-layer CAPE in
excess of 1000 J/kg.
Meanwhile, an increase in convective coverage is ongoing across
northern Louisiana, ahead of the narrow/forced frontal band just to
the northwest. With an environment at least marginally supportive
of organized updrafts as noted, an additional supercell or two
cannot be ruled out. While severe risk is expected to remain
limited in coverage, we will monitor convective evolution for any
signs that areal risk could become sufficient to warrant WW
consideration.
..Goss/Edwards.. 12/06/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...JAN...LIX...LCH...SHV...
LAT...LON 30909367 31449378 31959347 32649215 33059041 32238982
31479088 30859216 30589346 30909367SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Dec 6, 10:06 AM CST | Mesoscale Discussion | SPC | Catahoula, Concordia, LaSalle | 114 min |
| Dec 6, 1:08 PM CST | Mesoscale Discussion | SPC | Washington | 2 hr |
| Dec 6, 5:06 AM CST | Mesoscale Discussion | SPC | Alcorn, Benton, Coahoma, DeSoto, Itawamba, Lafayette and 13 more | 114 min |
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; radar from the NEXRAD Level II archive.