Alert archive / Mississippi / Mesoscale Discussions in 2012

Mesoscale Discussion 1839

August 30, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Aug 30, 2012, 6:33 AM CDT for 4 states. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued: Aug 30, 2012, 6:33 AM CDT (11:33 UTC)
Expired: Aug 30, 2012, 8:30 AM CDT
In force: 117 min
Issued by: the Storm Prediction Center

All 71 counties

Baldwin County, AL, Butler County, AL, Choctaw County, AL, Clarke County, AL, Coffee County, AL, Conecuh County, AL, Covington County, AL, Crenshaw County, AL, Dallas County, AL, Escambia County, AL, Geneva County, AL, Lowndes County, AL, Marengo County, AL, Mobile County, AL, Monroe County, AL, Pike County, AL, Sumter County, AL, Washington County, AL, Wilcox County, AL, Escambia County, FL, Holmes County, FL, Okaloosa County, FL, Santa Rosa County, FL, Walton County, FL, Ascension Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, Amite County, MS, Clarke County, MS, Copiah County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Jasper County, MS, Jefferson Davis County, MS, Jones County, MS, Kemper County, MS, Lamar County, MS, Lauderdale County, MS, Lawrence County, MS, Lincoln County, MS, Marion County, MS, Newton County, MS, Pearl River County, MS, Perry County, MS, Pike County, MS, Rankin County, MS, Scott County, MS, Simpson County, MS, Smith County, MS, Stone County, MS, Walthall County, MS, Wayne County, MS

The radar

The Mobile radar (KMOB), 106 km from the middle of the area, began a volume at 11:33 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 597Aug 30, 7:15 AM CDT

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 11.6 hours before the alert went out and 84 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: 408 J/kg
Mixed-layer CIN: 0 J/kg
Mixed-layer LCL: 464 m above ground
0-6 km bulk shear: 55 kt
0-1 km storm-relative helicity: 299 m²/s²
0-3 km storm-relative helicity: 301 m²/s²
Significant tornado parameter: 0.8
Supercell composite: 6.3

Open this sounding in Storm Lab

The text

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

021 
ACUS11 KWNS 301134
SWOMCD
SPC MCD 301133
FLZ000-ALZ000-MSZ000-LAZ000-301330-

MESOSCALE DISCUSSION 1839
NWS STORM PREDICTION CENTER NORMAN OK
0633 AM CDT THU AUG 30 2012

AREAS AFFECTED...PORTIONS SERN LA...CENTRAL/SRN MS...WRN/SRN
AL...WRN PANHANDLE OF FL.

CONCERNING...TORNADO WATCH 596...

VALID 301133Z - 301330Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 596 CONTINUES.

SUMMARY...TORNADO POTENTIAL WITH TS ISAAC IS EXPECTED TO CONTINUE
THROUGH REMAINDER MORNING BEYOND SCHEDULED 13Z EXPIRATION OF WW
596...WHILE SHIFTING/EXPANDING INLAND IN STEP WITH BOTH DIURNAL
DESTABILIZATION AND TRANSLATION OF TS ISAAC.  AS SUCH...REPLACEMENT
WW WILL BE NECESSARY...WITH SLGT NWD SHIFT AND SOME EWD EXPANSION
COMPARED TO WW 596.

DISCUSSION...NNWWD MOVEMENT OF CIRCULATION ENVELOPE IS FCST BY NHC
THROUGH TODAY.  THIS WILL LEAD TO ENLARGING OF ALREADY FAVORABLE
LOW-LEVEL HODOGRAPHS PORTIONS MS/AL WITH TIME...N OF PRESENT WW.
MEANWHILE...EXPECT WEAKENING LOW-LEVEL SHEAR OVER EXTREME SERN LA
WITHIN RELATIVELY PRECIP-FREE SLOT ALREADY APPARENT IN LONG-DURATION
REFLECTIVITY ANIMATIONS.  MEANWHILE...TWO PRIMARY AREAS OF CONCERN
WILL SHIFT NNWWD AS WELL...

1. HIGH-SHEAR/WEAK-CAPE REGION WILL INCLUDE EMBEDDED WITHIN PRECIP
SHIELD N THROUGH ESE OF CENTER.  AIR MASS INSIDE OUTERMOST BAND
SHOULD DESTABILIZE ONLY NOMINALLY AT BEST...GIVEN EXTENSIVE CLOUD
COVER AND PRECIP.  STILL...BOUNDARY-LAYER THETAE WILL REMAIN AT
LEAST MRGLLY SUFFICIENT FOR SFC-BASED EFFECTIVE INFLOW
PARCELS...WITH MLCAPE IN 100-500 J/KG RANGE OVER CENTRAL/SRN
MS..JUXTAPOSED WITH CORRIDORS OF EFFECTIVE SRH 300-800 J/KG BASED ON
TRENDS IN JAN VWP.  EMBEDDED SUPERCELLS AND QLCS MESOVORTICES ARE
POSSIBLE.

2. GREATER CAPE...WEAKER BUT SUFFICIENT SHEAR...IN OUTER RIM OF
CIRCULATION ENVELOPE BEYOND OUTER SPIRAL BAND.  THIS AREA SHOULD
EXPERIENCE SLOW DIURNAL HEATING.  RELATIVE MAX IN BUOYANCY SHOULD BE
MAINTAINED AND PERHAPS REINFORCED DUE TO DIFFUSE DIABATIC HEATING
THROUGH CLOUD COVER...COMBINED WITH LESS OVERALL PRECIP.  EFFECTIVE
SRH WILL DECREASE WITH EWD EXTENT FROM 300 J/KG JUST E OF OUTER BAND
TO LESS THAN 150 J/KG OVER SERN AL.  CONVECTIVE MODE SHOULD REMAIN
MORE DISCRETE IN THIS REGIME...WITH GREATER SUPPORT FOR DISCRETE
MINI-SUPERCELLS.

..EDWARDS.. 08/30/2012

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

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

LAT...LON   29079019 30659129 32169065 32898867 32088586 30208567
            30408661 30258750 30178814 30238868 30178920 30048883
            29778886 29498906 29418923 29238903 29178893 28958912
            29038924 28868941 29068934 29218945 29308977 29208998
            29079019

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 29, 8:21 PM CDT	Mesoscale Discussion	SPC	Baldwin, Mobile, Washington	84 min
Aug 29, 11:06 PM CDT	Mesoscale Discussion	SPC	Baldwin, Mobile, Washington	84 min
Aug 29, 11:42 PM CDT	Tornado Watch	SPC	Mobile, Washington	8 hr
Aug 30, 3:18 AM CDT	Mesoscale Discussion	SPC	Baldwin, Butler, Choctaw, Clarke, Coffee, Conecuh and 7 more	117 min
Aug 30, 7:13 AM CDT	Tornado Watch	SPC	Autauga, Baldwin, Butler, Choctaw, Clarke, Conecuh and 15 more	9 hr
Aug 30, 12:57 PM CDT	Mesoscale Discussion	SPC	Baldwin, Butler, Choctaw, Clarke, Conecuh, Dallas and 8 more	93 min
Aug 30, 3:56 PM CDT	Tornado Watch	SPC	Choctaw, Greene, Sumter, Washington	6 hr

Nearby

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