Alert archive / Mississippi / Mesoscale Discussions in 2021
Mesoscale Discussion 2068
The Storm Prediction Center issued this mesoscale discussion at Dec 28, 2021, 1:18 PM CST for 13 parishes in Louisiana; 22 counties in Mississippi. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Dec 28, 2021, 1:18 PM CST (19:18 UTC)
- Expired
- Dec 28, 2021, 3:45 PM CST
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 35 counties
Ascension Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Pointe Coupee Parish, LA, Saint Helena Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Amite County, MS, Copiah County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, Hinds County, MS, Jasper County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lawrence County, MS, Lincoln County, MS, Marion County, MS, Newton County, MS, Pearl River County, MS, Pike County, MS, Rankin County, MS, Scott County, MS, Simpson County, MS, Smith County, MS, Walthall County, MS, Wilkinson County, MS
The nearest sounding before it
Slidell Radar S, LA (KSIL), launched 12:00Z, 7.3 hours before the alert went out and 97 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
- 650 J/kg
- Mixed-layer CIN
- -186 J/kg
- Mixed-layer LCL
- 577 m above ground
- 0-6 km bulk shear
- 50 kt
- 0-1 km storm-relative helicity
- 176 m²/s²
- 0-3 km storm-relative helicity
- 193 m²/s²
- Significant tornado parameter
- 0.1
- Supercell composite
- 3.4
The text
As transmitted.
324
ACUS11 KWNS 281919
SWOMCD
SPC MCD 281918
MSZ000-LAZ000-282145-
Mesoscale Discussion 2068
NWS Storm Prediction Center Norman OK
0118 PM CST Tue Dec 28 2021
Areas affected...portions of eastern Louisiana into southern
Mississippi
Concerning...Severe potential...Watch unlikely
Valid 281918Z - 282145Z
Probability of Watch Issuance...20 percent
SUMMARY...An isolated severe threat may develop in the next couple
of hours across portions of eastern Louisiana into southern
Mississippi. The strongest, longest lasting storms may produce a
couple of damaging wind gusts/marginally severe hail stones or a
brief tornado. A WW issuance is not currently expected given the
sparse nature of the severe threat.
DISCUSSION...Warm-air advection continues to transport moisture
north from the Gulf of Mexico into the TN Valley in advance of a 999
mb surface low along the KS/MO border. This moist low-level airmass
remains modestly capped, though continued warming and moistening
beneath the inversion layer has been gradually eroding the cap
across eastern LA into southern MS per 18Z mesoanalysis. In
addition, visible satellite depicts a gravity wave propagating
across central MS/LA, which may act as an additional source of lift.
Finally, both 12Z NAM and 19Z RAP forecast soundings show cooling of
the inversion layer in the 20-22Z time frame. As such, convective
initiation appears likely within the next couple of hours despite
overall weak synoptic forcing for ascent.
925-850 mb flow is expected to either remain modest or even weaken
further as the surface low weakens while tracking northeast.
Nonetheless, modest veering and strengthening within the lowest 3 km
supports 150-300 m2/s2 0-3km SRH per DGX/LIX VWPs sampled within the
last half hour. Given semi-discrete/discrete storms modes, 30-40 kts
of effective bulk shear, and 1000-2000 J/kg MLCAPE (driven by 7 C/km
mid-level lapse rates atop near 70 F dewpoints), transient
supercells will likely be the dominant storm mode. Any stronger,
more sustained supercell structure that can materialize may produce
damaging gusts, marginally severe hail, or perhaps a brief tornado
(as 150-200 m2/s2 SRH sampled in the VWPs resides in the 0-1 km
layer). However, given the isolated nature of the severe threat, a
WW issuance is not currently anticipated.
..Squitieri/Hart.. 12/28/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MOB...JAN...LIX...LCH...
LAT...LON 30508956 29978990 30039043 30179116 30559186 32369058
32678976 32408875 31518910 30508956Nearby
Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Louisiana, 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.