Alert archive / Arkansas / Mesoscale Discussions in 2011

Mesoscale Discussion 496

April 20, 201129 counties in Arkansas; 19 counties in Mississippi; McCurtain County, Oklahoma

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2011, 5:56 PM CDT for 29 counties in Arkansas; 19 counties in Mississippi; McCurtain County, Oklahoma. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Apr 20, 2011, 5:56 PM CDT (22:56 UTC)
Expired
Apr 20, 2011, 8:00 PM CDT
In force
2 hr
Issued by
the Storm Prediction Center
All 49 counties

Arkansas County, AR, Bradley County, AR, Calhoun County, AR, Clark County, AR, Cleveland County, AR, Dallas County, AR, Desha County, AR, Drew County, AR, Garland County, AR, Grant County, AR, Hempstead County, AR, Hot Spring County, AR, Howard County, AR, Jefferson County, AR, Lee County, AR, Lincoln County, AR, Little River County, AR, Lonoke County, AR, Monroe County, AR, Montgomery County, AR, Nevada County, AR, Ouachita County, AR, Phillips County, AR, Pike County, AR, Polk County, AR, Prairie County, AR, Pulaski County, AR, Saline County, AR, Sevier County, AR, Bolivar County, MS, Calhoun County, MS, Chickasaw County, MS, Clay County, MS, Coahoma County, MS, Grenada County, MS, Itawamba County, MS, Lafayette County, MS, Lee County, MS, Monroe County, MS, Panola County, MS, Pontotoc County, MS, Quitman County, MS, Sunflower County, MS, Tallahatchie County, MS, Tate County, MS, Tunica County, MS, Union County, MS, Yalobusha County, MS, McCurtain County, OK

The radar

The Little Rock radar (KLZK), 86 km from the middle of the area, began a volume at 22:56 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

Shreveport, LA (KSHV), launched 12:00Z, 10.9 hours before the alert went out and 218 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, Shreveport, LA at 12:00Z on 2011-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2758 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, Shreveport, LA at 12:00Z on 2011-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 238 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
2758 J/kg
Mixed-layer CIN
-95 J/kg
Mixed-layer LCL
664 m above ground
0-6 km bulk shear
29 kt
0-1 km storm-relative helicity
238 m²/s²
0-3 km storm-relative helicity
252 m²/s²
Significant tornado parameter
1.6
Supercell composite
11.7

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, 7:47 PM CDTMesoscale DiscussionSPCConway, Franklin, Howard, Johnson, Little River, Logan and 13 more88 min
Apr 19, 8:07 PM CDTMesoscale DiscussionSPCArkansas, Clay, Cleveland, Craighead, Crittenden, Cross and 18 more83 min
Apr 19, 10:14 PM CDTTornado WatchSPCAshley, Chicot7 hr
Apr 19, 11:17 PM CDTMesoscale DiscussionSPCColumbia, Hempstead, Lafayette, Little River, Miller, Nevada and 1 more58 min
Apr 19, 11:45 PM CDTSevere Thunderstorm WatchSPCColumbia, Hempstead, Lafayette, Little River, Miller, Nevada and 1 more3 hr
Apr 20, 3:37 AM CDTSevere Thunderstorm WatchSPCAshley, Chicot8 hr
Apr 20, 12:46 PM CDTMesoscale DiscussionSPCAshley, Bradley, Calhoun, Chicot, Columbia, Desha and 8 more89 min
Apr 20, 1:02 PM CDTSevere Thunderstorm WatchSPCAshley, Chicot, Lee, Phillips7 hr
Apr 20, 2:04 PM CDTSevere Thunderstorm WatchSPCArkansas, Bradley, Calhoun, Clark, Cleburne, Cleveland and 36 more7 hr
Apr 20, 5:24 PM CDTMesoscale DiscussionSPCChicot, Drew96 min
Apr 19, 9:39 PM CDTMesoscale DiscussionSPCAlcorn, Benton, Calhoun, Chickasaw, Grenada, Itawamba and 11 more66 min
Apr 19, 11:56 PM CDTMesoscale DiscussionSPCAlcorn, Benton, Calhoun, Chickasaw, Clay, Coahoma and 19 more94 min
Apr 20, 8:42 AM CDTMesoscale DiscussionSPCNoxubee63 min
Apr 20, 6:51 PM CDTMesoscale DiscussionSPCAttala, Calhoun, Carroll, Chickasaw, Choctaw, Clay and 18 more84 min

Nearby

Mesoscale Discussions in Arkansas, 2011Mesoscale Discussions in Mississippi, 2011Mesoscale Discussions in Oklahoma, 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.