Alert archive / Louisiana / Mesoscale Discussions in 2021
Mesoscale Discussion 1637
The Storm Prediction Center issued this mesoscale discussion at Aug 29, 2021, 5:07 AM CDT for 4 states. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 29, 2021, 5:07 AM CDT (10:07 UTC)
- Expired
- Aug 29, 2021, 7:30 AM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch likely
- Chance of a watch
- 95%
All 22 counties
Baldwin County, AL, Mobile County, AL, Escambia County, FL, Santa Rosa County, FL, Ascension Parish, LA, Assumption Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Terrebonne Parish, LA, George County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Pearl River County, MS, Stone County, MS
The radar
The Mobile radar (KMOB), 122 km from the middle of the area, began a volume at 10:09 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Slidell Radar S, LA (KSIL), launched 00:00Z, 10.1 hours before the alert went out and 72 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
- 790 J/kg
- Mixed-layer CIN
- -14 J/kg
- Mixed-layer LCL
- 1003 m above ground
- 0-6 km bulk shear
- 12 kt
- 0-1 km storm-relative helicity
- 31 m²/s²
- 0-3 km storm-relative helicity
- 67 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
989
ACUS11 KWNS 291007
SWOMCD
SPC MCD 291007
ALZ000-FLZ000-MSZ000-LAZ000-291230-
Mesoscale Discussion 1637
NWS Storm Prediction Center Norman OK
0507 AM CDT Sun Aug 29 2021
Areas affected...Southeast Louisiana...Far Southern Mississippi
Concerning...Severe potential...Watch likely
Valid 291007Z - 291230Z
Probability of Watch Issuance...95 percent
SUMMARY...A tornado threat will develop across southeast Louisiana
and far southern Mississippi this morning. A tornado watch will need
to be issued across the central Gulf Coast.
DISCUSSION...Hurricane Ida is currently located 60 statute miles
south from southeast tip of Louisiana. The National Hurricane Center
is forecasting Hurricane Ida to move into southeast Louisiana early
this afternoon. Ahead of the center of Ida, two well-defined
circular rainbands are present. The outer band will move inland
across southeast Louisiana and southern Mississippi over the next 2
to 4 hours. Short lines of convection are ongoing near New Orleans
and to the south of Biloxi, Mississippi within this outer band. The
RAP is currently analyzing moderate instability from southeast
Louisiana into southern Mississippi where MLCAPE is estimated in the
1000 to 1500 J/kg range. Precipitable water values are above 2.25
inches, which is helping to create LCL heights between 500 and 700
meters above ground level. The New Orleans WSR-88D VWP currently has
0-1 km shear near 30 kt but RAP forecast soundings gradually
increase 0-1 km shear to about 40 kt by 12Z. This will make
low-level shear increasingly favorable for tornadoes over the next
few hours. The more discrete cells within these outer bands of Ida
will have potential to become supercells and could be associated
with tornadoes. For this reason, a tornado watch will be issued in
the 11Z to 12Z timeframe for parts of southeast Louisiana and far
southern Mississippi.
..Broyles/Thompson.. 08/29/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MOB...JAN...LIX...LCH...
LAT...LON 29599117 28939103 28919035 28858967 28808920 29018882
29308862 29508849 29778832 29958775 30018717 30268695
30648686 30958706 31118799 31018917 30699022 30359082
30109102 29599117SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 29, 6:07 AM CDT | Tornado Watch | SPC | Baldwin, Escambia, Mobile, Washington | 13 hr |
| Aug 29, 10:04 AM CDT | Mesoscale Discussion | SPC | Baldwin, Mobile, Washington | 4 hr |
| Aug 29, 5:37 PM CDT | Mesoscale Discussion | SPC | Baldwin, Escambia, Mobile | 83 min |
| Aug 29, 6:49 PM CDT | Tornado Watch | SPC | Baldwin, Clarke, Conecuh, Escambia, Mobile, Monroe and 1 more | 11 hr |
Nearby
Mesoscale Discussions in Louisiana, 2021Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Alabama, 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.