Alert archive / Alabama / Mesoscale Discussions in 2011

Mesoscale Discussion 491

April 20, 201134 counties in Alabama; 4 counties in Georgia

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2011, 1:16 PM CDT for 34 counties in Alabama; 4 counties in Georgia. It was in force for 89 min.

The area

The outline as issued.

The facts

Issued
Apr 20, 2011, 1:16 PM CDT (18:16 UTC)
Expired
Apr 20, 2011, 2:45 PM CDT
In force
89 min
Issued by
the Storm Prediction Center
All 38 counties

Autauga County, AL, Barbour County, AL, Bibb County, AL, Blount County, AL, Bullock County, AL, Chambers County, AL, Chilton County, AL, Clay County, AL, Coosa County, AL, Crenshaw County, AL, Dallas County, AL, Elmore County, AL, Fayette County, AL, Greene County, AL, Hale County, AL, Jefferson County, AL, Lamar County, AL, Lee County, AL, Lowndes County, AL, Macon County, AL, Marengo County, AL, Montgomery County, AL, Perry County, AL, Pickens County, AL, Pike County, AL, Russell County, AL, Shelby County, AL, St. Clair County, AL, Sumter County, AL, Talladega County, AL, Tallapoosa County, AL, Tuscaloosa County, AL, Walker County, AL, Wilcox County, AL, Chattahoochee County, GA, Harris County, GA, Muscogee County, GA, Quitman County, GA

The radar

The Birmingham radar (KBMX), 45 km from the middle of the area, began a volume at 18:18 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

Birmingham, AL (KBMX), launched 12:00Z, 6.3 hours before the alert went out and 46 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, Birmingham, AL at 12:00Z on 2011-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2075 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, Birmingham, AL at 12:00Z on 2011-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 151 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
2075 J/kg
Mixed-layer CIN
-36 J/kg
Mixed-layer LCL
550 m above ground
0-6 km bulk shear
35 kt
0-1 km storm-relative helicity
151 m²/s²
0-3 km storm-relative helicity
166 m²/s²
Significant tornado parameter
1.3
Supercell composite
7.5

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, 1:33 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 20, 6:51 PM CDTMesoscale DiscussionSPCFayette, Greene, Lamar, Marion, Pickens, Tuscaloosa and 2 more84 min
Apr 20, 6:55 AM CDTSevere Thunderstorm WatchSPCBanks, Barrow, Bartow, Butts, Carroll, Catoosa and 50 more3 hr

Nearby

Mesoscale Discussions in Alabama, 2011Mesoscale Discussions in Georgia, 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; radar from the NEXRAD Level II archive.