Alert archive / Louisiana / Mesoscale Discussions in 2012
Mesoscale Discussion 2183
The Storm Prediction Center issued this mesoscale discussion at Dec 19, 2012, 11:55 PM CST for 4 states. It was in force for 95 min.
The area
The outline as issued.
The facts
- Issued
- Dec 19, 2012, 11:55 PM CST (05:55 UTC)
- Expired
- Dec 20, 2012, 1:30 AM CST
- In force
- 95 min
- Issued by
- the Storm Prediction Center
All 61 counties
Ashley County, AR, Chicot County, AR, Allen Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Bienville Parish, LA, Bossier Parish, LA, Caddo Parish, LA, Calcasieu Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Claiborne Parish, LA, Concordia Parish, LA, De Soto Parish, LA, East Carroll Parish, LA, Evangeline Parish, LA, Franklin Parish, LA, Grant Parish, LA, Jackson Parish, LA, Jefferson Davis Parish, LA, LaSalle Parish, LA, Lincoln Parish, LA, Madison Parish, LA, Morehouse Parish, LA, Natchitoches Parish, LA, Ouachita Parish, LA, Rapides Parish, LA, Red River Parish, LA, Richland Parish, LA, Sabine Parish, LA, Tensas Parish, LA, Union Parish, LA, Vernon Parish, LA, Webster Parish, LA, West Carroll Parish, LA, Winn Parish, LA, Adams County, MS, Anderson County, TX, Angelina County, TX, Cherokee County, TX, Gregg County, TX, Harrison County, TX, Houston County, TX, Jasper County, TX, Leon County, TX, Madison County, TX, Marion County, TX, Nacogdoches County, TX, Newton County, TX, Panola County, TX, Polk County, TX, Rusk County, TX, Sabine County, TX, San Augustine County, TX, San Jacinto County, TX, Shelby County, TX, Smith County, TX, Trinity County, TX, Tyler County, TX, Upshur County, TX, Walker County, TX
The radar
The Shreveport radar (KSHV), 77 km from the middle of the area, began a volume at 05:58 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 00:00Z, 5.9 hours before the alert went out and 82 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.
- Mixed-layer CAPE
- 237 J/kg
- Mixed-layer CIN
- -56 J/kg
- Mixed-layer LCL
- 943 m above ground
- 0-6 km bulk shear
- 55 kt
- 0-1 km storm-relative helicity
- 385 m²/s²
- 0-3 km storm-relative helicity
- 445 m²/s²
- Significant tornado parameter
- 0.3
- Supercell composite
- 1.5
The text
As transmitted, in the capitals the NWS used until 2016.
568
ACUS11 KWNS 200555
SWOMCD
SPC MCD 200555
MSZ000-LAZ000-ARZ000-TXZ000-200730-
MESOSCALE DISCUSSION 2183
NWS STORM PREDICTION CENTER NORMAN OK
1155 PM CST WED DEC 19 2012
AREAS AFFECTED...EAST/NORTHEAST TX INTO MUCH OF LA/FAR WESTERN MS
CONCERNING...SEVERE THUNDERSTORM WATCH 687...
VALID 200555Z - 200730Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 687
CONTINUES.
SUMMARY...SEVERE TSTM WATCH 687 CONTINUES UNTIL 09Z WITH PRIMARY
RISK OF DAMAGING WINDS...ALTHOUGH A TORNADO MAY BE POSSIBLE AS WELL.
AT LEAST AN ISOLATED SEVERE THREAT WILL LIKELY CONTINUE TO SPREAD
EAST-SOUTHEASTWARD...SUCH THAT AN ADDITIONAL WATCH MAY BE NEEDED
OVERNIGHT FOR SOUTHEAST TX INTO LA AND PERHAPS WESTERN MS/SOUTHEAST
AR.
DISCUSSION...A QUASI-LINEAR CONVECTIVE SYSTEM WITH EMBEDDED BOWING
STRUCTURES CONTINUES TO STEADILY MATURE/SPREAD GENERALLY EASTWARD
ACROSS THE ARKLATEX REGION AS OF 0545Z. THE REGION IS ON THE
SOUTHERN EDGE OF A DEEPENING PLAINS CYCLONE...WITH ATTENDANT STRONG
VERTICAL SHEAR/GRADUAL HEIGHT FALLS OVERSPREADING THE REGION LATE
THIS EVENING/OVERNIGHT. WHILE INSTABILITY IS NOT ROBUST...AN INFLUX
OF LOW-LEVEL MOISTURE...GENERALLY CHARACTERIZED BY MIDDLE/SOME UPPER
60S F SURFACE DEWPOINTS...IS CONTRIBUTING TO SBCAPE AS HIGH AS 500
J/KG AHEAD OF THE QLCS/COLD FRONT. DEEP LAYER FORCING/FRONTAL
INFLUENCE AND VERY STRONG DEEP LAYER SHEAR /70+ KT 0-6 KM PER SHV
WSR-88D VWP/ WILL HELP MAINTAIN A WELL-ORGANIZED QLCS OVERNIGHT WITH
A DAMAGING WIND THREAT...AND PERHAPS A TORNADO RISK WITH EMBEDDED
MESO-VORTICES.
AHEAD OF THE QLCS...SOME /ALBEIT SEEMINGLY LOW/ POTENTIAL EXISTS FOR
SEMI-DISCRETE STORMS TO DEEPEN/MATURE WITHIN A CORRIDOR OF LOW-LEVEL
CONFLUENCE ACROSS PORTIONS OF LA/MS. SHOULD THIS OCCUR...A SEVERE
THREAT WOULD BE POSSIBLE...ALTHOUGH A RESIDUAL WARM LAYER ALOFT MAY
PRECLUDE STRONG DEVELOPMENT UNTIL THE ARRIVAL OF THE QLCS.
..GUYER.. 12/20/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...JAN...LIX...LZK...LCH...SHV...HGX...FWD...
LAT...LON 30739639 31869578 33049468 32919384 33369127 31499105
30119278 30739639SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Dec 19, 7:07 PM CST | Mesoscale Discussion | SPC | Baxter, Benton, Boone, Carroll, Conway, Crawford and 24 more | 53 min |
| Dec 19, 7:36 PM CST | Tornado Watch | SPC | Baxter, Benton, Boone, Carroll, Clark, Cleburne and 36 more | 6 hr |
| Dec 19, 10:22 PM CST | Mesoscale Discussion | SPC | Baxter, Boone, Carroll, Clark, Cleburne, Conway and 29 more | 83 min |
| Dec 20, 12:50 AM CST | Mesoscale Discussion | SPC | Arkansas, Ashley, Bradley, Calhoun, Chicot, Cleveland and 23 more | 55 min |
| Dec 20, 1:07 AM CST | Severe Thunderstorm Watch | SPC | Arkansas, Ashley, Bradley, Calhoun, Chicot, Cleveland and 18 more | 5 hr |
| Dec 20, 4:08 AM CST | Mesoscale Discussion | SPC | Chicot, Crittenden | 67 min |
| Dec 19, 9:56 PM CST | Severe Thunderstorm Watch | SPC | Bossier, Caddo, De Soto | 5 hr |
| Dec 20, 4:23 AM CST | Tornado Watch | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Iberville, Livingston and 9 more | 9 hr |
| Dec 20, 7:09 AM CST | Mesoscale Discussion | SPC | Saint James, Saint John the Baptist, Saint Tammany, Tangipahoa, Washington | 96 min |
| Dec 20, 9:56 AM CST | Mesoscale Discussion | SPC | Ascension, East Baton Rouge, East Feliciana, Iberville, Livingston, Saint Helena and 6 more | 64 min |
| Dec 19, 9:00 PM CST | Mesoscale Discussion | SPC | Anderson, Camp, Cherokee, Dallas, Ellis, Falls and 19 more | 2 hr |
Nearby
Mesoscale Discussions in Louisiana, 2012Mesoscale Discussions in Texas, 2012Mesoscale Discussions in Arkansas, 2012Every mesoscale discussion in 2012
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.