Alert archive / Alabama / Mesoscale Discussions in 2021

Mesoscale Discussion 536

May 4, 20214 states

The Storm Prediction Center issued this mesoscale discussion at May 4, 2021, 4:46 PM CDT for 4 states. It was in force for 89 min.

The area

The outline as issued.

The facts

Issued
May 4, 2021, 4:46 PM CDT (21:46 UTC)
Expired
May 4, 2021, 6:15 PM CDT
In force
89 min
Issued by
the Storm Prediction Center
Concerning
Tornado watch 149
All 46 counties

Autauga County, AL, Baldwin County, AL, Bibb County, AL, Butler County, AL, Chilton County, AL, Choctaw County, AL, Clarke County, AL, Conecuh County, AL, Coosa County, AL, Covington County, AL, Crenshaw County, AL, Dallas County, AL, Elmore County, AL, Escambia County, AL, Greene County, AL, Hale County, AL, Lowndes County, AL, Marengo County, AL, Mobile County, AL, Monroe County, AL, Montgomery County, AL, Perry County, AL, Sumter County, AL, Tallapoosa County, AL, Washington County, AL, Wilcox County, AL, Escambia County, FL, Santa Rosa County, FL, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, Clarke County, MS, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Jones County, MS, Lamar County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS, Stone County, MS, Walthall County, MS, Wayne County, MS

The radar

The Mobile radar (KMOB), 92 km from the middle of the area, began a volume at 21:48 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 nearest sounding before it

Jackson, MS (KJAN), launched 12:00Z, 9.8 hours before the alert went out and 187 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, Jackson, MS at 12:00Z on 2021-05-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2428 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Jackson, MS at 12:00Z on 2021-05-04The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 170 square meters per square second.19395878Sfc1 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
2428 J/kg
Mixed-layer CIN
-6 J/kg
Mixed-layer LCL
646 m above ground
0-6 km bulk shear
35 kt
0-1 km storm-relative helicity
170 m²/s²
0-3 km storm-relative helicity
235 m²/s²
Significant tornado parameter
2.8
Supercell composite
13.2

Open this sounding in Storm Lab

The text

As transmitted.

830 
ACUS11 KWNS 042147
SWOMCD
SPC MCD 042146 
ALZ000-FLZ000-MSZ000-LAZ000-042315-

Mesoscale Discussion 0536
NWS Storm Prediction Center Norman OK
0446 PM CDT Tue May 04 2021

Areas affected...Portions of far southeastern LA...southern
MS...southern/central AL...and the far western FL Panhandle

Concerning...Tornado Watch 149...

Valid 042146Z - 042315Z

The severe weather threat for Tornado Watch 149 continues.

SUMMARY...A widespread damaging wind threat will continue with a
bowing line of storms moving eastward. Isolated embedded tornadoes
also remain possible.

DISCUSSION...A well-organized bow will move quickly eastward late
this afternoon from from southeastern LA/southern MS into
southern/central AL over the next couple of hours. The most
progressive portion of this line is advancing around 40-45 kt into
west-central AL as of 2145Z. Other storms have formed along an
outflow boundary extending from near Tuscaloosa to just south of
Birmingham to near Auburn AL. This outflow boundary will likely
serve as the northern limit to any substantial severe threat. Given
the current intensity of the bowing complex, the presence of
moderate to locally strong instability downstream (MLCAPE generally
2000-2500 J/kg), sufficient deep-layer shear, and steepened
low-level lapse rates from diurnal heating, widespread
severe/damaging winds of 60-70+ mph will remain the primary severe
threat in the short term. Although low-level winds are not very
strong ahead of the ongoing severe convection, up to 100 m2/s2 of
0-1 km SRH may still support some potential for embedded low-level
circulations and a brief/isolated tornado threat.

..Gleason.. 05/04/2021

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

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

LAT...LON   30749079 31598960 32258842 33268783 33008574 32698585
            31328633 30468677 30188959 30339014 30749079

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 3, 7:13 PM CDTMesoscale DiscussionSPCAutauga, Bullock, Chambers, Coosa, Elmore, Lee and 4 more62 min
May 4, 5:13 AM CDTSevere Thunderstorm WatchSPCJackson, Lauderdale, Limestone, Madison5 hr
May 4, 7:31 AM CDTMesoscale DiscussionSPCJackson, Lauderdale, Limestone, Madison89 min
May 4, 8:33 AM CDTMesoscale DiscussionSPCChoctaw, Clarke, Dallas, Greene, Hale, Marengo and 4 more117 min
May 4, 9:03 AM CDTMesoscale DiscussionSPCBlount, Calhoun, Cherokee, Clay, Cleburne, Cullman and 20 more117 min
May 4, 9:18 AM CDTTornado WatchSPCAutauga, Bibb, Blount, Calhoun, Cherokee, Chilton and 28 more7 hr
May 4, 2:17 PM CDTMesoscale DiscussionSPCChoctaw, Greene, Marengo, Sumter88 min
May 4, 3:03 PM CDTMesoscale DiscussionSPCBibb, Blount, Calhoun, Cherokee, Chilton, Clay and 19 more117 min
May 4, 3:31 PM CDTTornado WatchSPCAutauga, Baldwin, Bibb, Butler, Chilton, Choctaw and 20 more6 hr
May 4, 5:20 PM CDTMesoscale DiscussionSPCBarbour, Bullock, Chambers, Coffee, Covington, Dale and 7 more85 min
May 4, 6:10 PM CDTMesoscale DiscussionSPCAutauga, Coosa, Elmore, Lowndes, Macon, Montgomery and 1 more65 min
May 4, 6:26 PM CDTSevere Thunderstorm WatchSPCBarbour, Bullock, Chambers, Coffee, Covington, Crenshaw and 8 more6 hr
May 3, 9:10 PM CDTSevere Thunderstorm WatchSPCBossier, Caddo, Webster7 hr
May 4, 6:44 AM CDTMesoscale DiscussionSPCBienville, Bossier, Caddo, Claiborne, De Soto, Lincoln and 3 more2 hr
May 4, 10:52 AM CDTTornado WatchSPCAllen, Avoyelles, Beauregard, Bienville, Bossier, Caddo and 31 more7 hr
May 4, 12:16 PM CDTMesoscale DiscussionSPCCaldwell, Catahoula, Concordia, East Carroll, Franklin, Grant and 9 more89 min
May 4, 11:58 AM CDTMesoscale DiscussionSPCAlcorn, Benton, Calhoun, Chickasaw, Coahoma, DeSoto and 13 more2 hr
May 4, 12:18 PM CDTSevere Thunderstorm WatchSPCAlcorn, Benton, Calhoun, Chickasaw, Coahoma, DeSoto and 16 more5 hr

Nearby

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