Alert archive / Mississippi / Mesoscale Discussions in 2012

Mesoscale Discussion 454

April 5, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Apr 5, 2012, 7:36 AM CDT for 4 states. It was in force for 54 min.

The area

The outline as issued.

The facts

Issued
Apr 5, 2012, 7:36 AM CDT (12:36 UTC)
Expired
Apr 5, 2012, 8:30 AM CDT
In force
54 min
Issued by
the Storm Prediction Center
All 83 counties

Choctaw County, AL, Greene County, AL, Hale County, AL, Marengo County, AL, Perry County, AL, Pickens County, AL, Sumter County, AL, Tuscaloosa County, AL, Chicot County, AR, Caldwell Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, East Carroll Parish, LA, Franklin Parish, LA, Jackson Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, LaSalle Parish, LA, Lincoln Parish, LA, Madison Parish, LA, Morehouse Parish, LA, Orleans Parish, LA, Ouachita Parish, LA, Plaquemines Parish, LA, Richland Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint Tammany Parish, LA, Tensas Parish, LA, Terrebonne Parish, LA, Union Parish, LA, Washington Parish, LA, West Carroll Parish, LA, Adams County, MS, Attala 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, Hancock County, MS, Harrison County, MS, Hinds County, MS, Holmes County, MS, Humphreys County, MS, Issaquena County, MS, Jackson County, MS, Jasper County, MS, Jefferson 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, Lowndes County, MS, Madison County, MS, Marion County, MS, Montgomery County, MS, Neshoba County, MS, Newton County, MS, Noxubee County, MS, Oktibbeha County, MS, Pearl River County, MS, Rankin County, MS, Scott County, MS, Sharkey County, MS, Simpson County, MS, Smith County, MS, Stone County, MS, Walthall County, MS, Warren County, MS, Washington County, MS, Wayne County, MS, Webster County, MS, Winston County, MS, Yazoo County, MS

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 0.6 hours before the alert went out and 36 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, Slidell Radar S, LA at 12:00Z on 2012-04-05Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 443 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, Slidell Radar S, LA at 12:00Z on 2012-04-05The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 36 square meters per square second.19395878Sfc1 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
443 J/kg
Mixed-layer CIN
-99 J/kg
Mixed-layer LCL
765 m above ground
0-6 km bulk shear
53 kt
0-1 km storm-relative helicity
36 m²/s²
0-3 km storm-relative helicity
107 m²/s²
Significant tornado parameter
-0.0
Supercell composite
-0.4

Open this sounding in Storm Lab

The text

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

727 
ACUS11 KWNS 051236
SWOMCD
SPC MCD 051236 
ALZ000-MSZ000-LAZ000-ARZ000-051330-

MESOSCALE DISCUSSION 0454
NWS STORM PREDICTION CENTER NORMAN OK
0736 AM CDT THU APR 05 2012

AREAS AFFECTED...PORTIONS-CENTRAL AL...CENTRAL/SRN MS...SERN AND NRN
LA.

CONCERNING...TORNADO WATCH 141...142...

VALID 051236Z - 051330Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 141...142...CONTINUES.

BEFORE WW 141 IS SCHEDULED TO EXPIRE AT 14Z...REPLACEMENT WW MAY BE
REQUIRED FOR NRN PORTIONS OF WW 141 AREA AND EWD TO PARTS OF ERN MS
AND AL.

PRIMARY CONCERN ATTM IS WITH BAND OF STG-SVR TSTMS MOVING EWD 30-35
KT ACROSS PORTIONS WRN/CENTRAL MS...LOCATED BETWEEN TVR-GWO AS OF
1230Z.  THIS ACTIVITY IS MOVING THROUGH AIR MASS LEFT BEHIND OUTFLOW
BOUNDARY FROM EARLIER CONVECTION.  THIS BOUNDARY WAS ANALYZED IN ARC
FROM NOXUBEE COUNTY SWWD ACROSS JAN AREA...DECELERATING AND
WEAKENING WITH TIME DUE TO LACK OF REINFORCING CONVECTION. 
ACCORDINGLY MODIFIED JAN RAOB SUGGESTS SHALLOW/NEAR-SFC STABLE LAYER
WILL BE MODULATED FAIRLY EASILY BY COMBINATION OF WAA AND EVENTUAL
DIABATIC SFC HEATING.  IN FACT...EFFECTIVE LIFTED PARCELS ARE NEARLY
SFC-BASED BEHIND OUTFLOW BOUNDARY DESPITE SHALLOW LAYER OF CINH AND
STATIC STABILITY.  MLCAPE 1500-2000 J/KG WAS EVIDENT OVER CENTRAL MS
AHEAD OF ONGOING ACTIVITY...ALONG WITH 50-60 KT EFFECTIVE SHEAR
MAGNITUDES.  THIS WILL SUPPORT CONTINUED SVR POTENTIAL EWD AT LEAST
TO AL BORDER...PERHAPS FARTHER E.

BULK OF SVR THREAT FOR CONVECTION AFFECTING WW 142 HAS WEAKENED
AND/OR SHIFTED OVER GULF.  ADDITIONAL DEVELOPMENT CANNOT BE RULED
OUT...ESPECIALLY ACROSS AREAS OF SERN LA FROM TERREBONNE PARISH EWD
AND SEWD...BUT PROBABILITY IS DIMINISHING WITH TIME.  MODIFIED RAOBS
AND FCST SOUNDINGS SUGGEST 1500-2000 J/KG MLCAPE IN AIR MASS OVER
S-CENTRAL LA COAST...WHERE SFC DEW POINTS LOW 70S F REMAIN. 
EFFECTIVE SHEAR MAGNITUDES 35-45 KT STILL ARE EVIDENT OVER THIS
AREA...DESPITE VEERED LOW-LEVEL FLOW.  HOWEVER...THAT SAME VEERING
IS REDUCING LOW-LEVEL LIFT...AND THEREFORE POTENTIAL FOR
SUSTAINED/SVR CONVECTIVE DEVELOPMENT BEHIND EARLIER WAVE OF COASTAL
TSTMS.

FARTHER N ACROSS CENTRAL LA TO SWRN MS...MID-UPPER LEVEL DRY SLOT
WAS WELL-DEFINED IN MOISTURE CHANNEL IMAGERY...S OF COLD-CORE REGIME
THAT ACCOMPANIES EWD-MOVING MID-UPPER VORTEX OVER AR.  RELATIVE MIN
IN CONVECTIVE POTENTIAL MAY REMAIN BETWEEN THOSE TWO REGIMES. 
ACCORDINGLY LOCATED PORTIONS OF BOTH WWS HAVE BEEN CLEARED BY
AFFECTED WFOS.

..EDWARDS.. 04/05/2012

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

ATTN...WFO...BMX...MOB...JAN...LIX...LCH...SHV...

LAT...LON   32529298 33299155 33729000 33648853 33438764 32938714
            32148733 31568884 30958910 30468843 29988879 29528906
            29408929 29218906 29048910 28938937 28918946 29148944
            29268962 29338982 29218999 29079020 29029043 29059070
            29159100 29319119 29639109 29899068 30099039 30489033
            31419040 31409202 32529298

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 5, 9:14 AM CDTSevere Thunderstorm WatchSPCAutauga, Barbour, Bibb, Bullock, Butler, Chambers and 34 more8 hr
Apr 5, 10:41 AM CDTMesoscale DiscussionSPCAutauga, Bibb, Butler, Chilton, Choctaw, Clarke and 15 more94 min
Apr 5, 12:09 PM CDTMesoscale DiscussionSPCColbert, Cullman, Franklin, Lauderdale, Lawrence, Limestone and 4 more96 min
Apr 5, 1:12 PM CDTMesoscale DiscussionSPCBarbour, Bullock, Chambers, Clay, Coffee, Covington and 11 more93 min
Apr 5, 1:21 PM CDTSevere Thunderstorm WatchSPCColbert, DeKalb, Franklin, Jackson, Lauderdale, Lawrence and 4 more8 hr
Apr 5, 1:58 PM CDTSevere Thunderstorm WatchSPCCoffee, Dale, Geneva, Henry, Houston6 hr
Apr 5, 3:06 PM CDTMesoscale DiscussionSPCColbert, DeKalb, Franklin, Jackson, Lauderdale, Lawrence and 4 more54 min
Apr 5, 3:46 PM CDTMesoscale DiscussionSPCBlount, Calhoun, Cullman, Etowah, Fayette, Jefferson and 7 more59 min
Apr 5, 3:49 PM CDTMesoscale DiscussionSPCGeneva, Henry, Houston86 min
Apr 5, 6:14 PM CDTSevere Thunderstorm WatchSPCAutauga, Bibb, Blount, Bullock, Calhoun, Chambers and 21 more3 hr
Apr 5, 6:15 PM CDTMesoscale DiscussionSPCAutauga, Bibb, Blount, Bullock, Calhoun, Chambers and 23 more45 min
Apr 4, 8:31 PM CDTMesoscale DiscussionSPCCalhoun, Clark, Columbia, Conway, Crawford, Dallas and 24 more119 min
Apr 5, 1:35 AM CDTMesoscale DiscussionSPCAshley, Chicot85 min
Apr 5, 1:53 AM CDTTornado WatchSPCAshley, Chicot9 hr
Apr 5, 3:30 AM CDTMesoscale DiscussionSPCAshley, Chicot, Union2 hr
Apr 5, 12:18 PM CDTSevere Thunderstorm WatchSPCCrittenden, Mississippi5 hr
Apr 4, 8:25 PM CDTMesoscale DiscussionSPCAcadia, Allen, Ascension, Assumption, Beauregard, Calcasieu and 21 more95 min
Apr 5, 3:56 AM CDTTornado WatchSPCAscension, Assumption, East Baton Rouge, East Feliciana, Iberville, Jefferson and 16 more6 hr
Apr 5, 10:43 AM CDTSevere Thunderstorm WatchSPCClarke, Covington, Forrest, Franklin, Jasper, Jefferson Davis and 7 more4 hr
Apr 5, 2:22 PM CDTMesoscale DiscussionSPCAlcorn, Benton, Calhoun, Chickasaw, DeSoto, Itawamba and 14 more53 min

Nearby

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