Alert archive / Mississippi / Mesoscale Discussions in 2021

Mesoscale Discussion 1645

August 30, 20214 states

The Storm Prediction Center issued this mesoscale discussion at Aug 30, 2021, 2:44 AM CDT for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Aug 30, 2021, 2:44 AM CDT (07:44 UTC)
Expired
Aug 30, 2021, 4:45 AM CDT
In force
2 hr
Issued by
the Storm Prediction Center
Concerning
Tornado watch 474
All 34 counties

Baldwin County, AL, Clarke County, AL, Conecuh County, AL, Escambia County, AL, Mobile County, AL, Monroe County, AL, Washington County, AL, Escambia County, FL, Okaloosa County, FL, Santa Rosa County, FL, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, Covington County, MS, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lawrence County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS, Pike County, MS, Stone County, MS, Walthall County, MS, Wayne County, MS

The radar

The Mobile radar (KMOB), 74 km from the middle of the area, began a volume at 07:48 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, 7.7 hours before the alert went out and 90 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-pSkew-T log-p diagram, Slidell Radar S, LA at 00:00Z on 2021-08-30Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 25 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Slidell Radar S, LA at 00:00Z on 2021-08-30The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 36 square meters per square second.1939587897Sfc1 km3 km6 km9 kmRMLM
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
25 J/kg
Mixed-layer CIN
-2 J/kg
Mixed-layer LCL
679 m above ground
0-6 km bulk shear
41 kt
0-1 km storm-relative helicity
36 m²/s²
0-3 km storm-relative helicity
73 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

924 
ACUS11 KWNS 300744
SWOMCD
SPC MCD 300744 
FLZ000-ALZ000-MSZ000-LAZ000-300945-

Mesoscale Discussion 1645
NWS Storm Prediction Center Norman OK
0244 AM CDT Mon Aug 30 2021

Areas affected...Central Gulf Coast

Concerning...Tornado Watch 474...

Valid 300744Z - 300945Z

The severe weather threat for Tornado Watch 474 continues.

SUMMARY...A tornado threat will continue across the central Gulf
Coast region today. A new tornado watch will be needed when WW 474
expires at 11Z.

DISCUSSION...Hurricane Ida is currently located in southeast
Louisiana about 25 statute miles to the north of Baton Rouge. Radar
imagery shows a large area of moderate to heavy rainfall located to
the north and east of the center of Ida, across far southeast
Louisiana, southern Mississippi and southern Alabama. Although weak
instability is in place across most of the area, the latest WSR-88D
VWP from Mobile has 0-1 km shear of 35 kt. This will be favorable
for storm rotation. Cells that remain semi-discrete within this
large area of rain may become supercellular with a tornado threat.
Although Ida will continue to weaken, the tornado threat should
persist across much of the central Gulf Coast for much of the day.

..Broyles/Thompson.. 08/30/2021

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

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

LAT...LON   28678895 28648912 28678922 28878938 28978938 29068931
            29208942 29348977 29368994 29579002 29729004 29999010
            30069028 30149040 30229051 30319053 30389048 30509056
            31309050 31339020 31689023 31848848 31718848 31718803
            31778811 31938801 31938771 31848754 31828690 31558687
            31498665 31288669 31058666 30978635 30018646 30038684
            29938746 29828812 29848833 29618848 29458863 29368867
            29048864 28948869 28748886 28668898 28678895

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Aug 30, 5:48 AM CDTTornado WatchSPCBaldwin, Butler, Choctaw, Clarke, Conecuh, Covington and 6 more10 hr
Aug 30, 12:02 PM CDTMesoscale DiscussionSPCBibb, Chilton, Colbert, Fayette, Franklin, Jefferson and 8 more2 hr
Aug 30, 12:03 PM CDTMesoscale DiscussionSPCBibb, Chilton, Colbert, Fayette, Franklin, Jefferson and 8 more4 hr
Aug 30, 3:13 PM CDTMesoscale DiscussionSPCAutauga, Baldwin, Bibb, Butler, Chilton, Choctaw and 17 more2 hr

Nearby

Mesoscale Discussions in Mississippi, 2021Mesoscale Discussions in Alabama, 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; radar from the NEXRAD Level II archive.