Alert archive / Mississippi / Mesoscale Discussions in 2012

Mesoscale Discussion 1841

August 30, 2012Choctaw County, Sumter County, Washington County, Alabama; 42 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Aug 30, 2012, 7:15 PM CDT for Choctaw County, Sumter County, Washington County, Alabama; 42 counties in Mississippi. It was in force for 90 min.

The area

The outline as issued.

The facts

Issued: Aug 30, 2012, 7:15 PM CDT (00:15 UTC)
Expired: Aug 30, 2012, 8:45 PM CDT
In force: 90 min
Issued by: the Storm Prediction Center

All 45 counties

Choctaw County, AL, Sumter County, AL, Washington County, AL, Attala County, MS, Bolivar County, MS, Carroll County, MS, Choctaw County, MS, Claiborne County, MS, Clarke County, MS, Copiah County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, George County, MS, Greene County, MS, Hinds County, MS, Holmes County, MS, Humphreys County, MS, Jasper County, MS, Jefferson Davis County, MS, Jones County, MS, Kemper County, MS, Lamar County, MS, Lauderdale County, MS, Lawrence County, MS, Leake County, MS, Leflore County, MS, Lincoln County, MS, Madison County, MS, Marion County, MS, Neshoba County, MS, Newton County, MS, Noxubee County, MS, Perry County, MS, Rankin County, MS, Scott County, MS, Sharkey County, MS, Simpson County, MS, Smith County, MS, Sunflower County, MS, Walthall County, MS, Warren County, MS, Wayne County, MS, Winston County, MS, Yazoo County, MS

The radar

The Jackson/Brandon,MS radar (KDGX), 27 km from the middle of the area, began a volume at 00:17 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.

Tornado Watch 599Aug 30, 9:45 PM CDT

The nearest sounding before it

Jackson, MS (KJAN), launched 00:00Z, 0.3 hours before the alert went out and 35 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: 42 J/kg
Mixed-layer CIN: -83 J/kg
Mixed-layer LCL: 796 m above ground
0-6 km bulk shear: 37 kt
0-1 km storm-relative helicity: 303 m²/s²
0-3 km storm-relative helicity: 319 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.

040 
ACUS11 KWNS 310016
SWOMCD
SPC MCD 310015
ALZ000-MSZ000-LAZ000-310145-

MESOSCALE DISCUSSION 1841
NWS STORM PREDICTION CENTER NORMAN OK
0715 PM CDT THU AUG 30 2012

AREAS AFFECTED...MOST OF MS...EXTREME W-CNTRL AL...WASHINGTON PARISH
LA

CONCERNING...TORNADO WATCH 598...

VALID 310015Z - 310145Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 598 CONTINUES.

SUMMARY...THE TORNADO THREAT WILL LIKELY PERSIST ACROSS THE AREA AS
SHOWERS AND THUNDERSTORMS ASSOCIATED WITH TROPICAL DEPRESSION ISAAC
CONTINUE TO IMPACT THE REGION.

DISCUSSION...AT 2350Z...THE WATCH AREA WAS LARGELY FREE OF SHOWERS
AND TSTMS WITH THE EXCEPTION OF A FEW SHOWERS IN ERN MS. HOWEVER...A
BAND OF SHOWERS AND TSTMS IS CURRENTLY MOVING ACROSS SE LA AND IS
EXPECTED TO ENTER SRN MS SHORTLY. THE ENVIRONMENT ACROSS THE WATCH
AREA CONTINUES TO BE CHARACTERIZED HIGH LOW-LEVEL SHEAR /0-1 KM SRH
NEAR 300 M2/S2 AND 0-3 KM SRH ALSO AROUND 300 M2/S2/...WEAK
INSTABILITY /MLCAPE AOB 250 J/KG/...AND MODEST LARGE-SCALE SHEAR
/0-6 KM BULK SHEAR NEAR 40 KTS/. DRY AIR IS BEGINNING TO WORK INTO
THE SERN QUADRANT OF ISAAC...APPARENT ON BOTH WV SATELLITE IMAGERY
AND THE 00Z JAN SOUNDING...AND LIMITING THE EFFECTIVE INFLOW OF THE
SHOWERS AND TSTMS. 23Z MESOANAYLSIS DEPICTS THIS WELL AS BOTH
EFFECTIVE BULK SHEAR AND EFFECTIVE SRH SHOW MINIMUMS IN ANALYZED
VALUES ACROSS CNTRL MS. HOWEVER...GIVEN THE STRONG LOW-LEVEL
SHEAR...A FEW STORMS WILL LIKELY EXHIBIT TRANSIENT ROTATION WITH THE
POTENTIAL FOR A FEW SPIN UPS. ANY TORNADOES SHOULD BE SHORT-LIVED AS
THE INFLOW QUICKLY WANES.

AS DAYTIME HEATING CONTINUES TO DIMINISH AND DRY AIR CONTINUES TO
WRAP AROUND THE SYSTEM...THE FREQUENCY AND INTENSITY OF THE INFLOW
BANDS SHOULD WEAKEN. THIS IS EXPECTED TO LIMIT THE TORNADO THREAT
ACROSS THE REGION AND AN EXTENSION OF THE TORNADO WATCH DOES NOT
APPEAR LIKELY. HOWEVER...TRENDS WILL BE MONITORED CLOSELY AND THE
DECISION WHETHER OR NOT TO EXTEND THE CURRENT WATCH WILL BE MADE
CLOSER TO ITS EXPIRATION TIME AT 03Z.

..MOSIER.. 08/31/2012

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

ATTN...WFO...BMX...MOB...JAN...LIX...

LAT...LON   31389095 33869094 33098819 30648822 31389095

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 30, 9:05 PM CDT	Mesoscale Discussion	SPC	Adams, Attala, Bolivar, Carroll, Choctaw, Claiborne and 51 more	55 min
Aug 30, 9:44 PM CDT	Tornado Watch	SPC	Attala, Bolivar, Calhoun, Carroll, Chickasaw, Choctaw and 47 more	5 hr

Nearby

Mesoscale Discussions in Mississippi, 2012 Mesoscale Discussions in Alabama, 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.