Alert archive / Mississippi / Mesoscale Discussions in 2011

Mesoscale Discussion 497

April 20, 20118 counties in Alabama; 24 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2011, 6:51 PM CDT for 8 counties in Alabama; 24 counties in Mississippi. It was in force for 84 min.

The area

The outline as issued.

The facts

Issued
Apr 20, 2011, 6:51 PM CDT (23:51 UTC)
Expired
Apr 20, 2011, 8:15 PM CDT
In force
84 min
Issued by
the Storm Prediction Center
All 32 counties

Fayette County, AL, Greene County, AL, Lamar County, AL, Marion County, AL, Pickens County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL, Attala County, MS, Calhoun County, MS, Carroll County, MS, Chickasaw County, MS, Choctaw County, MS, Clay County, MS, Grenada County, MS, Holmes County, MS, Itawamba County, MS, Lafayette County, MS, Lee County, MS, Leflore County, MS, Lowndes County, MS, Monroe County, MS, Montgomery County, MS, Noxubee County, MS, Oktibbeha County, MS, Pontotoc County, MS, Sunflower County, MS, Tallahatchie County, MS, Union County, MS, Webster County, MS, Winston County, MS, Yalobusha County, MS

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

The nearest sounding before it

Jackson, MS (KJAN), launched 12:00Z, 11.9 hours before the alert went out and 172 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 2011-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1998 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 2011-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 227 square meters per square second.193958Sfc1 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
1998 J/kg
Mixed-layer CIN
-92 J/kg
Mixed-layer LCL
569 m above ground
0-6 km bulk shear
29 kt
0-1 km storm-relative helicity
227 m²/s²
0-3 km storm-relative helicity
366 m²/s²
Significant tornado parameter
1.1
Supercell composite
9.9

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

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SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 19, 9:39 PM CDTMesoscale DiscussionSPCColbert, Franklin, Lauderdale66 min
Apr 19, 11:56 PM CDTMesoscale DiscussionSPCColbert, Franklin, Lamar, Lauderdale, Lawrence, Limestone and 4 more94 min
Apr 20, 3:19 AM CDTMesoscale DiscussionSPCBlount, Calhoun, Cherokee, Cullman, DeKalb, Etowah and 16 more86 min
Apr 20, 3:37 AM CDTSevere Thunderstorm WatchSPCBibb, Blount, Calhoun, Chambers, Cherokee, Chilton and 33 more8 hr
Apr 20, 5:39 AM CDTMesoscale DiscussionSPCCalhoun, Cherokee, Cleburne, St. Clair66 min
Apr 20, 8:42 AM CDTMesoscale DiscussionSPCAutauga, Bibb, Chilton, Clay, Coosa, Elmore and 11 more63 min
Apr 20, 1:16 PM CDTMesoscale DiscussionSPCAutauga, Barbour, Bibb, Blount, Bullock, Chambers and 28 more89 min
Apr 20, 1:33 PM CDTSevere Thunderstorm WatchSPCAutauga, Barbour, Bibb, Bullock, Butler, Chambers and 33 more6 hr
Apr 20, 5:24 PM CDTMesoscale DiscussionSPCAutauga, Bibb, Chilton, Coosa, Elmore, Fayette and 10 more96 min
Apr 19, 10:14 PM CDTTornado WatchSPCAlcorn, Benton, Bolivar, Calhoun, Carroll, Chickasaw and 24 more7 hr
Apr 20, 12:46 PM CDTMesoscale DiscussionSPCBolivar, Carroll, Grenada, Holmes, Humphreys, Issaquena and 6 more89 min
Apr 20, 1:02 PM CDTSevere Thunderstorm WatchSPCAlcorn, Attala, Benton, Bolivar, Calhoun, Carroll and 52 more7 hr
Apr 20, 5:56 PM CDTMesoscale DiscussionSPCBolivar, Calhoun, Chickasaw, Clay, Coahoma, Grenada and 13 more2 hr

Nearby

Mesoscale Discussions in Mississippi, 2011Mesoscale Discussions in Alabama, 2011Every mesoscale discussion in 2011

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.