Alert archive / Arkansas / Mesoscale Discussions in 2012

Mesoscale Discussion 2184

December 20, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Dec 20, 2012, 12:50 AM CST for 4 states. It was in force for 55 min.

The area

The outline as issued.

The facts

Issued: Dec 20, 2012, 12:50 AM CST (06:50 UTC)
Expired: Dec 20, 2012, 1:45 AM CST
In force: 55 min
Issued by: the Storm Prediction Center
Chance of a watch: 95%

All 75 counties

Arkansas County, AR, Ashley County, AR, Bradley County, AR, Calhoun County, AR, Chicot County, AR, Cleveland County, AR, Craighead County, AR, Crittenden County, AR, Cross County, AR, Dallas County, AR, Desha County, AR, Drew County, AR, Grant County, AR, Independence County, AR, Jackson County, AR, Jefferson County, AR, Lawrence County, AR, Lee County, AR, Lincoln County, AR, Lonoke County, AR, Mississippi County, AR, Monroe County, AR, Phillips County, AR, Poinsett County, AR, Prairie County, AR, St. Francis County, AR, Union County, AR, White County, AR, Woodruff County, AR, Bienville Parish, LA, Caldwell Parish, LA, Claiborne Parish, LA, East Carroll Parish, LA, Franklin Parish, LA, Jackson Parish, LA, Lincoln Parish, LA, Madison Parish, LA, Morehouse Parish, LA, Ouachita Parish, LA, Red River Parish, LA, Richland Parish, LA, Tensas Parish, LA, Union Parish, LA, West Carroll Parish, LA, Winn Parish, LA, Bolivar County, MS, Carroll County, MS, Claiborne County, MS, Coahoma County, MS, DeSoto County, MS, Grenada County, MS, Hinds County, MS, Holmes County, MS, Humphreys County, MS, Issaquena County, MS, Lafayette County, MS, Leflore County, MS, Marshall County, MS, Panola County, MS, Quitman County, MS, Sharkey County, MS, Sunflower County, MS, Tallahatchie County, MS, Tate County, MS, Tunica County, MS, Warren County, MS, Washington County, MS, Yalobusha County, MS, Yazoo County, MS, Crockett County, TN, Fayette County, TN, Haywood County, TN, Lauderdale County, TN, Shelby County, TN, Tipton County, TN

The radar

The Little Rock radar (KLZK), 166 km from the middle of the area, began a volume at 06:51 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

Jackson, MS (KJAN), launched 00:00Z, 6.8 hours before the alert went out and 182 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1606 m above ground
0-6 km bulk shear: 60 kt
0-1 km storm-relative helicity: 206 m²/s²
0-3 km storm-relative helicity: 246 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.

273 
ACUS11 KWNS 200650
SWOMCD
SPC MCD 200650 
TNZ000-MSZ000-ARZ000-LAZ000-200745-

MESOSCALE DISCUSSION 2184
NWS STORM PREDICTION CENTER NORMAN OK
1250 AM CST THU DEC 20 2012

AREAS AFFECTED...ERN AR...NRN LA...WRN MS AND WRN TN

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

VALID 200650Z - 200745Z

PROBABILITY OF WATCH ISSUANCE...95 PERCENT

SUMMARY...A NEW WW WILL BE COORDINATED AND ISSUED SOON TO THE EAST
OF WW/S 686 AND 687...WITH THE NEW WW LIKELY INCLUDING ERN AR...NRN
LA...WRN MS AND PERHAPS PARTS OF WRN TN.  DAMAGING WINDS WILL BE THE
PRIMARY THREAT...THOUGH A TORNADO OR TWO CANNOT BE RULED OUT.

DISCUSSION...LATEST TRENDS IN SURFACE OBSERVATIONS AND OBJECTIVE
ANALYSES INDICATED THE PRE-SQUALL LINE/COLD FRONT AIR MASS ACROSS
ERN AR INTO FAR WRN TN AND SWD IS SLOWLY MODIFYING WITH SURFACE
DEWPOINTS INTO THE LOWER 50 AROUND KMEM.  MODIFIED 06Z LIT SPECIAL
SOUNDING SUGGESTED SURFACE DEWPOINTS OF 59-60 F ARE NEEDED FOR
PARCELS TO BE SURFACE-BASED.  PREDOMINANT DEEP LAYER SHEAR VECTORS
ORIENTED PARALLEL TO THE EWD MOVING SQUALL LINE AND STRONG FORCING
FOR ASCENT WITH THE CENTRAL PLAINS STORM SYSTEM WILL TEND TO
MAINTAIN A LINEAR STORM MODE WITH DAMAGING WINDS THE PRIMARY THREAT.
 HOWEVER...LARGE HODOGRAPH CURVATURE NOTED ON THE 06Z LIT SOUNDING
ALSO SUGGESTS A TORNADO THREAT CANNOT BE RULED OUT...ESPECIALLY WITH
ANY EMBEDDED MESOVORTICES IN THE LINE.

STORM MOTIONS OVER NERN TX/FAR NWRN LA ARE AT 40-45 KT WHILE FARTHER
N INTO NRN AR MOTIONS ARE AT 35-40 KT.  DESPITE THE DIFFERENT
SPEEDS...THE SSW-NNE ORIENTATION OF THE LINE WILL RESULT IN MUCH OF
THE MS RIVER REGION BEING AFFECTED BY THESE STORMS AROUND 10Z.

..PETERS/EDWARDS.. 12/20/2012

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

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

LAT...LON   31919369 34209257 36459123 35949037 35908891 33418973
            32039056 31729113 31729223 31919369

SPC 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 19, 11:55 PM CST	Mesoscale Discussion	SPC	Ashley, Chicot	95 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

Nearby

Mesoscale Discussions in Arkansas, 2012 Mesoscale Discussions in Mississippi, 2012 Mesoscale Discussions in Louisiana, 2012 Every 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.