Alert archive / Arkansas / Mesoscale Discussions in 2011

Mesoscale Discussion 490

April 20, 20114 states

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2011, 12:46 PM CDT for 4 states. It was in force for 89 min.

The area

The outline as issued.

The facts

Issued
Apr 20, 2011, 12:46 PM CDT (17:46 UTC)
Expired
Apr 20, 2011, 2:15 PM CDT
In force
89 min
Issued by
the Storm Prediction Center
All 39 counties

Ashley County, AR, Bradley County, AR, Calhoun County, AR, Chicot County, AR, Columbia County, AR, Desha County, AR, Drew County, AR, Hempstead County, AR, Lafayette County, AR, Little River County, AR, Miller County, AR, Nevada County, AR, Ouachita County, AR, Union County, AR, Claiborne Parish, LA, East Carroll Parish, LA, Morehouse Parish, LA, Union Parish, LA, West Carroll Parish, LA, Bolivar County, MS, Carroll County, MS, Grenada County, MS, Holmes County, MS, Humphreys County, MS, Issaquena County, MS, Leflore County, MS, Montgomery County, MS, Sharkey County, MS, Sunflower County, MS, Tallahatchie County, MS, Washington County, MS, Bowie County, TX, Camp County, TX, Cass County, TX, Franklin County, TX, Marion County, TX, Morris County, TX, Titus County, TX, Upshur County, TX

The radar

The Little Rock radar (KLZK), 164 km from the middle of the area, began a volume at 17:48 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

Shreveport, LA (KSHV), launched 12:00Z, 5.8 hours before the alert went out and 199 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.

065 
ACUS11 KWNS 201747
SWOMCD
SPC MCD 201746
MSZ000-ARZ000-LAZ000-TXZ000-OKZ000-201915-

MESOSCALE DISCUSSION 0490
NWS STORM PREDICTION CENTER NORMAN OK
1246 PM CDT WED APR 20 2011

AREAS AFFECTED...NE TX...SRN AR...NRN LA...WRN MS

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 201746Z - 201915Z

A SEVERE THREAT IS EXPECTED TO DEVELOP ACROSS NE TX...FAR NRN
LA...SRN AR AND WRN MS THIS AFTERNOON. LARGE HAIL AND WIND DAMAGE
WILL BE THE PRIMARY THREATS WITH THE ACTIVITY. A WW MAY BECOME
NECESSARY ACROSS THE REGION AS STORMS INITIATE.

A SLOW MOVING COLD FRONT IS CURRENTLY LOCATED FROM NE TX EWD ACROSS
SRN AR INTO NW MS. ALONG AND SOUTH OF THE BOUNDARY...SFC DEWPOINTS
ARE IN THE UPPER 60S AND LOWER 70S F. MESOANALYSIS ACROSS THE WARM
SECTOR SHOWS STRONG INSTABILITY IN PLACE WITH MLCAPE VALUES OF 2000
TO 3500 J/KG. IN ADDITION...THE SRN EDGE OF THE STRONGER MID-LEVEL
FLOW IS LOCATED FROM THE BOUNDARY NWD SUGGESTING THE GREATEST
POTENTIAL FOR SEVERE STORMS WILL EXIST ALONG THE BOUNDARY WHERE THE
COMBINATION OF INSTABILITY AND SHEAR IS MAXIMIZED. AS LOW-LEVEL
CONVERGENCE INCREASES THIS AFTERNOON...CONVECTIVE INITIATION SHOULD
OCCUR ALONG THE BOUNDARY. THE MORE INTENSE CELLS MAY OBTAIN
SUPERCELL STRUCTURE WITH LARGE HAIL LIKELY. STEEPENING LOW-LEVEL
LAPSE RATES SHOULD ALSO PROMOTE A WIND DAMAGE THREAT WITH THE
GREATEST POTENTIAL OVER CNTRL MS WHERE LOW-LEVEL FLOW SHOULD BE A
BIT STRONGER.

..BROYLES.. 04/20/2011

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MEG...JAN...LZK...SHV...

LAT...LON   34029060 34038996 33768960 33358951 32958971 32819035
            32649116 32669224 32839365 32659491 33189528 33659497
            33979397 33899242 33829162 34029060

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, 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 20, 5:56 PM CDTMesoscale DiscussionSPCArkansas, Bradley, Calhoun, Clark, Cleveland, Dallas and 23 more2 hr
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
Apr 19, 9:03 PM CDTMesoscale DiscussionSPCBell, Coryell, Falls, Freestone, Henderson, Hill and 3 more57 min
Apr 20, 1:52 PM CDTMesoscale DiscussionSPCBell, Bosque, Brown, Burnet, Coleman, Comanche and 21 more53 min
Apr 20, 2:21 PM CDTSevere Thunderstorm WatchSPCBandera, Bell, Blanco, Burnet, Concho, Coryell and 20 more8 hr
Apr 20, 5:47 PM CDTMesoscale DiscussionSPCBlanco, Burnet, Concho, Crockett, Edwards, Gillespie and 15 more58 min

Nearby

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