Alert archive / Mississippi / Mesoscale Discussions in 2012

Mesoscale Discussion 1750

August 13, 20126 counties in Arkansas; 26 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Aug 13, 2012, 7:48 AM CDT for 6 counties in Arkansas; 26 counties in Mississippi. It was in force for 87 min.

The area

The outline as issued.

The facts

Issued: Aug 13, 2012, 7:48 AM CDT (12:48 UTC)
Expired: Aug 13, 2012, 9:15 AM CDT
In force: 87 min
Issued by: the Storm Prediction Center
Chance of a watch: 20%

All 32 counties

Ashley County, AR, Bradley County, AR, Chicot County, AR, Cleveland County, AR, Desha County, AR, Drew County, AR, Attala County, MS, Bolivar County, MS, Calhoun County, MS, Carroll County, MS, Choctaw County, MS, Clay County, MS, Coahoma County, MS, Grenada County, MS, Holmes County, MS, Humphreys County, MS, Leake County, MS, Leflore County, MS, Madison County, MS, Montgomery County, MS, Neshoba County, MS, Oktibbeha County, MS, Panola County, MS, Quitman County, MS, Sharkey County, MS, Sunflower County, MS, Tallahatchie County, MS, Washington County, MS, Webster County, MS, Winston County, MS, Yalobusha County, MS, Yazoo County, MS

The radar

The Jackson/Brandon,MS radar (KDGX), 165 km from the middle of the area, began a volume at 12:52 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 nearest sounding before it

Little Rock, AR (KBYH), launched 12:00Z, 0.8 hours before the alert went out and 143 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: 1586 J/kg
Mixed-layer CIN: -113 J/kg
Mixed-layer LCL: 909 m above ground
0-6 km bulk shear: 35 kt
0-1 km storm-relative helicity: 163 m²/s²
0-3 km storm-relative helicity: 211 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 8.0

Open this sounding in Storm Lab

The text

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

451 
ACUS11 KWNS 131248
SWOMCD
SPC MCD 131248 
MSZ000-ARZ000-LAZ000-131415-

MESOSCALE DISCUSSION 1750
NWS STORM PREDICTION CENTER NORMAN OK
0748 AM CDT MON AUG 13 2012

AREAS AFFECTED...PORTIONS SERN AR...EXTREME NERN LA...CENTRAL/WRN
MS.

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 131248Z - 131415Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...INCREASINGLY DENSE AND ORGANIZED CLUSTER OF STG/POSSIBLY
SEVERE TSTMS OVER SERN AR MAY POSE THREAT FOR SPORADIC WIND DAMAGE
WITH MAINLY SUB-SEVERE GUSTS...AS IT MOVES SEWD OVER PORTIONS
WRN/CENTRAL MS.  CONVECTIVE TRENDS WILL BE MONITORED FOR ANY
SUBSTANTIAL UPSCALE GROWTH/INTENSIFICATION THAT MAY RAISE MORE WW
CONCERN.

DISCUSSION...EARLIER TSTMS THAT HAD PRODUCED MEASURED SUB-SVR
GUSTS...BUT SOME MINOR WIND DAMAGE...IN LIT AREA HAVE DISSIPATED. 
HOWEVER...CONVECTION THAT DEVELOPED IN THEIR WAKE HAS BECOME BETTER
ORGANIZED...AND APPEARS TO BE EXPANDING WHILE CATCHING UP TO OUTFLOW
FROM INITIAL ACTIVITY OVER SERN AR.  MEANWHILE...SFC MESOANALYSIS
INDICATES TWO KEY DEVELOPMENTS DOWNSHEAR...
1. WARM FRONT AND RELATED THETAE/INSTABILITY GRADIENT IS MOVING
NNEWD 10-15 KT OVER NWRN...CENTRAL AND SERN MS...FROM 12Z POSITION
NEAR UTA-MEI LINE.  BULK OF CONVECTION SHOULD MOVE ESEWD TO SEWD
ALONG AND S OF WARM FRONT. 
2. MOISTURE TRANSPORT/ADVECTION HAS RESULTED IN INCREASING DEW
POINTS AROUND GLH AND GWO.  THIS IN TURN REDUCES MLCINH TO LESS THAN
50 J/KG AND BOOSTS MLCAPE INTO 1500-2500 J/KG PRIOR TO ONSET OF
SUBSTANTIAL DIABATIC HEATING...PER MODIFIED 12Z RAOB.  

LATTER ALSO REDUCES SUBCLOUD DCAPE AVAILABLE...RENDERING
DAMAGING-WIND POTENTIAL MORE OF A FUNCTION OF PRECIP LOADING OR
ORGANIZED COLD-POOL GROWTH.  HOWEVER...SFC OBS INDICATE LACK OF
ROBUST COLD POOL BEHIND THIS SYSTEM...AND PROSPECTS FOR STG
COLD-POOL DEVELOPMENT APPEAR SMALL DUE TO WARM/MOIST CONDITIONS
THROUGH DEEP LAYER.  AS SUCH...POTENTIAL FOR WELL-ORGANIZED
WIND-DAMAGE EVENT CURRENTLY APPEARS SMALL AND CONDITIONAL AT BEST. 
INSTEAD...SPORADIC DAMAGE WITH SUB-50 KT GUSTS APPEARS MOST
PROBABLE.

..EDWARDS/HART.. 08/13/2012

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

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

LAT...LON   33879249 34009121 34389062 34729028 34288939 33358847
            32498888 32379010 33369226 33879249

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 12, 10:26 PM CDT	Mesoscale Discussion	SPC	Crawford, Franklin, Howard, Little River, Logan, Montgomery and 5 more	94 min
Aug 12, 10:49 PM CDT	Severe Thunderstorm Watch	SPC	Benton, Boone, Carroll, Conway, Crawford, Franklin and 16 more	5 hr
Aug 13, 1:45 AM CDT	Mesoscale Discussion	SPC	Arkansas, Baxter, Benton, Boone, Carroll, Cleburne and 36 more	2 hr
Aug 13, 3:15 PM CDT	Mesoscale Discussion	SPC	Arkansas, Ashley, Bradley, Chicot, Crittenden, Cross and 9 more	30 min
Aug 13, 3:32 PM CDT	Severe Thunderstorm Watch	SPC	Arkansas, Chicot, Crittenden, Cross, Desha, Drew and 7 more	7 hr
Aug 13, 12:38 PM CDT	Severe Thunderstorm Watch	SPC	Wayne	4 hr
Aug 13, 5:14 PM CDT	Mesoscale Discussion	SPC	Alcorn, Attala, Benton, Calhoun, Carroll, Chickasaw and 20 more	91 min

Nearby

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