Alert archive / Arkansas / Mesoscale Discussions in 2011

Mesoscale Discussion 829

May 20, 20114 states

The Storm Prediction Center issued this mesoscale discussion at May 20, 2011, 4:00 PM CDT for 4 states. It was in force for 60 min.

The area

The outline as issued.

The facts

Issued
May 20, 2011, 4:00 PM CDT (21:00 UTC)
Expired
May 20, 2011, 5:00 PM CDT
In force
60 min
Issued by
the Storm Prediction Center
All 62 counties

Calhoun County, AR, Clark County, AR, Columbia County, AR, Conway County, AR, Dallas County, AR, Faulkner County, AR, Garland County, AR, Grant County, AR, Hempstead County, AR, Hot Spring County, AR, Howard County, AR, Lafayette County, AR, Little River County, AR, Logan County, AR, Miller County, AR, Montgomery County, AR, Nevada County, AR, Ouachita County, AR, Perry County, AR, Pike County, AR, Polk County, AR, Pope County, AR, Pulaski County, AR, Saline County, AR, Scott County, AR, Searcy County, AR, Sevier County, AR, Union County, AR, Van Buren County, AR, Yell County, AR, Bossier Parish, LA, Caddo Parish, LA, Claiborne Parish, LA, Webster Parish, LA, Choctaw County, OK, LeFlore County, OK, McCurtain County, OK, Pushmataha County, OK, Anderson County, TX, Bowie County, TX, Camp County, TX, Cass County, TX, Delta County, TX, Franklin County, TX, Freestone County, TX, Gregg County, TX, Harrison County, TX, Henderson County, TX, Hopkins County, TX, Lamar County, TX, Leon County, TX, Marion County, TX, Morris County, TX, Panola County, TX, Rains County, TX, Red River County, TX, Rusk County, TX, Smith County, TX, Titus County, TX, Upshur County, TX, Van Zandt County, TX, Wood County, TX

The radar

The Shreveport radar (KSHV), 141 km from the middle of the area, began a volume at 21:02 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, 9.0 hours before the alert went out and 140 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 2011-05-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2656 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 2011-05-20The 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
2656 J/kg
Mixed-layer CIN
-44 J/kg
Mixed-layer LCL
648 m above ground
0-6 km bulk shear
15 kt
0-1 km storm-relative helicity
151 m²/s²
0-3 km storm-relative helicity
231 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

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

661 
ACUS11 KWNS 202100
SWOMCD
SPC MCD 202100 
ARZ000-LAZ000-TXZ000-OKZ000-202200-

MESOSCALE DISCUSSION 0829
NWS STORM PREDICTION CENTER NORMAN OK
0400 PM CDT FRI MAY 20 2011

AREAS AFFECTED...SERN OK...WRN AR...NERN TX AND NWRN LA

CONCERNING...TORNADO WATCH 312...

VALID 202100Z - 202200Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 312 CONTINUES.

A FEW COUNTIES ALONG THE SWRN EXTENT OF WW 312 WILL BE ADDED TO THIS
WATCH PER SPC COORDINATION WITH WFO SHV.  GIVEN THE UPCOMING 23Z
EXPIRATION OF WW 312...A NEW WW MAY BE NEEDED IF ACTIVITY OVER NORTH
CENTRAL TX AND NEW ACTIVITY RECENTLY FORMED IN LEON AND ANDERSON
COUNTIES TX REMAIN ROBUST. 

GREATEST TORNADO THREAT THROUGH THE LATE AFTERNOON AND POTENTIALLY
INTO THE EARLY EVENING EXISTS ACROSS THE SRN HALF OF WW 312. 
MEANWHILE...HAIL AND HEAVY RAINFALL APPEAR TO BE THE PRIMARY THREATS
OVER THE NRN EXTENT OF THIS WATCH...GENERALLY NORTH OF A LINE FROM
PUSHMATAHA COUNTY OK TO CONWAY COUNTY AR.  

MID AFTERNOON SURFACE ANALYSIS SHOWED AN OUTFLOW BOUNDARY EXTENDING
FROM CENTRAL AR /JUST S OF LIT/ WSWWD THROUGH SWRN AR /JUST N OF
DEQ/ TO NORTH CENTRAL TX INVOF A SUB-SYNOPTIC SURFACE LOW IN GRAYSON
COUNTY.  AIR MASS ALONG AND S OF THIS BOUNDARY REMAINS STRONGLY
UNSTABLE /MLCAPE 2000-3000 J PER KG/.  ALTHOUGH DEEP LAYER SHEAR IS
SOMEWHAT WEAK ACROSS WW 312 FOR ORGANIZED STORMS...A 40-45 KT SSWLY
LLJ ACROSS THIS AREA IS MAINTAINING EFFECTIVE SRH 200-400 M2/S2
SUPPORTIVE OF A TORNADO THREAT.  CONCERN EXISTS WITH THE ENEWD
MOVING CLUSTER OF TSTMS EXTENDING FROM SERN OK TO NORTH CENTRAL
TX...WITH THIS ACTIVITY EVOLVING INTO AN MCS WITH AN ADDITIONAL
THREAT FOR DAMAGING WINDS AND HAIL SPREADING EWD INTO SRN HALF OF WW
312.  THIS WOULD LIKELY BE A SEVERE WEATHER THREAT UP TO AND BEYOND
23Z RESULTING IN THE NEED FOR A NEW WW.

..PETERS.. 05/20/2011

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

ATTN...WFO...LZK...SHV...TSA...HGX...FWD...OUN...

LAT...LON   36089232 35289216 34319226 33739235 32779261 32239334
            32139452 31869523 31169572 31039622 31839640 33019578
            34089603 34569585 34979459 35409350 36119286 36089232

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 20, 9:11 AM CDTMesoscale DiscussionSPCBenton, Washington2 hr
May 20, 10:30 AM CDTMesoscale DiscussionSPCArkansas, Baxter, Boone, Bradley, Calhoun, Carroll and 53 more60 min
May 20, 11:03 AM CDTTornado WatchSPCClark, Columbia, Conway, Crawford, Dallas, Franklin and 26 more7 hr
May 20, 1:28 PM CDTMesoscale DiscussionSPCBaxter, Boone, Calhoun, Carroll, Clark, Cleburne and 47 more62 min
May 20, 5:56 PM CDTTornado WatchSPCClark, Columbia, Dallas, Garland, Grant, Hempstead and 16 more3 hr
May 19, 7:47 PM CDTMesoscale DiscussionSPCCaddo, Canadian, Comanche, Cotton, Grady, Kiowa and 1 more118 min
May 19, 11:39 PM CDTSevere Thunderstorm WatchSPCHarmon, Jackson, Tillman6 hr
May 20, 2:58 AM CDTMesoscale DiscussionSPCComanche, Jackson, Kiowa, Tillman, Washita92 min
May 20, 1:52 PM CDTMesoscale DiscussionSPCEllis, Harper, Woods, Woodward113 min
May 20, 2:32 PM CDTSevere Thunderstorm WatchSPCAlfalfa, Ellis, Garfield, Grant, Harper, Major and 2 more7 hr
May 20, 6:01 PM CDTMesoscale DiscussionSPCAlfalfa, Ellis, Garfield, Grant, Harper, Major and 2 more59 min
May 19, 9:36 PM CDTMesoscale DiscussionSPCBorden, Briscoe, Childress, Coke, Collingsworth, Cottle and 28 more84 min
May 20, 12:08 PM CDTMesoscale DiscussionSPCAnderson, Bandera, Bastrop, Bell, Blanco, Bosque and 56 more67 min
May 20, 12:28 PM CDTSevere Thunderstorm WatchSPCAnderson, Bandera, Bastrop, Bell, Bexar, Blanco and 60 more10 hr
May 20, 5:34 PM CDTMesoscale DiscussionSPCAnderson, Bandera, Bastrop, Bell, Bexar, Blanco and 41 more116 min

Nearby

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