Alert archive / Louisiana / Mesoscale Discussions in 2012

Mesoscale Discussion 1827

August 28, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Aug 28, 2012, 12:37 PM CDT for 4 states. It was in force for 83 min.

The area

The outline as issued.

The facts

Issued: Aug 28, 2012, 12:37 PM CDT (17:37 UTC)
Expired: Aug 28, 2012, 2:00 PM CDT
In force: 83 min
Issued by: the Storm Prediction Center

All 42 counties

Baldwin County, AL, Escambia County, AL, Mobile County, AL, Washington County, AL, Bay County, FL, Escambia County, FL, Holmes County, FL, Okaloosa County, FL, Santa Rosa County, FL, Walton County, FL, Washington County, FL, Ascension Parish, LA, Assumption 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, Terrebonne Parish, LA, Washington Parish, LA, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS, Jones County, MS, Lamar County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS, Pike County, MS, Stone County, MS, Walthall County, MS, Wayne County, MS

The radar

The Mobile radar (KMOB), 62 km from the middle of the area, began a volume at 17:39 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 592Aug 28, 12:55 PM CDT

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 5.6 hours before the alert went out and 164 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: 41 J/kg
Mixed-layer CIN: -110 J/kg
Mixed-layer LCL: 650 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 272 m²/s²
0-3 km storm-relative helicity: 266 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.

843 
ACUS11 KWNS 281737
SWOMCD
SPC MCD 281737 
FLZ000-ALZ000-MSZ000-LAZ000-281900-

MESOSCALE DISCUSSION 1827
NWS STORM PREDICTION CENTER NORMAN OK
1237 PM CDT TUE AUG 28 2012

AREAS AFFECTED...SERN LA/SERN MS/SWRN AL/WRN FL PANHANDLE

CONCERNING...TORNADO WATCH 591...

VALID 281737Z - 281900Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 591 CONTINUES.

SUMMARY...TORNADO THREAT ACROSS THE NRN GULF COAST REGION IS
BEGINNING TO SHIFT FARTHER INLAND AS WELL...AND THUS THREE COUNTIES
/WASHINGTON COUNTY AL...AND GREENE/PERRY COUNTIES MS/ ALONG THE NRN
EXTENT OF WW 591 HAVE BEEN ADDED TO THIS TORNADO WATCH PER
COORDINATION BETWEEN THE SPC AND WFO MOBILE.  TRENDS WILL BE
MONITORED FOR ANY FURTHER INLAND TORNADO THREAT...N OF WW 591...AND
THE POTENTIAL ADDITION OF COUNTIES AND/OR THE ISSUANCE OF A NEW WW.

DISCUSSION...TRENDS IN REGIONAL MOSAIC RADAR IMAGERY SHOWED A
PERSISTENT CONVECTIVE BAND /ON THE NRN PERIPHERY OF HURRICANE ISAAC/
HAS CONTINUED TO MOVE NNWWD THROUGH WW 591...AND WAS BEGINNING TO
SHIFT FARTHER INLAND.  THIS HAS RESULTED IN THE INCLUSION OF THREE
MORE COUNTIES TO WW 591.  

SURFACE HEATING AND AN INCREASE IN MOISTURE WILL SUPPORT FURTHER
DESTABILIZATION...WITH THE POTENTIAL FOR ADDITIONAL DEEP/SUSTAINED
UPDRAFTS...AS HAS BEEN OBSERVED RECENTLY IN EXTREME SERN MS WITH THE
DETECTION OF A FEW CG LIGHTNING STRIKES.  GIVEN THE GREATER
INSTABILITY /ALBEIT SOMEWHAT MARGINAL AT THIS TIME/...AND THE VERY
FAVORABLE KINEMATIC ENVIRONMENT /0-1 KM SRH AROUND 200-250 M2/S2 -
PER MOBILE AL AND SLIDELL LA WSR-88D VADS AND A STORM MOTION TOWARD
THE W/WNW AT 30-35 KT/...THE LIKELIHOOD FOR ADDITIONAL PERSISTENT
LOW LEVEL ROTATIONAL COUPLETS AND TORNADO THREAT WILL PERSIST
THROUGH THE AFTERNOON.

..PETERS.. 08/28/2012

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

ATTN...WFO...TAE...MOB...JAN...LIX...LCH...

LAT...LON   28669140 29499121 31079069 31588940 31798826 31508760
            31218676 31028644 30908547 29858528 29268499 29428584
            29938629 29728827 28528869 28669140

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 28, 7:01 AM CDT	Mesoscale Discussion	SPC	Baldwin, Clarke, Coffee, Conecuh, Covington, Escambia and 4 more	2 hr
Aug 28, 9:46 AM CDT	Tornado Watch	SPC	Baldwin, Choctaw, Clarke, Conecuh, Escambia, Mobile and 2 more	9 hr
Aug 28, 3:46 PM CDT	Mesoscale Discussion	SPC	Baldwin, Clarke, Escambia, Mobile, Monroe, Washington	89 min
Aug 28, 5:48 PM CDT	Mesoscale Discussion	SPC	Baldwin, Conecuh, Covington, Escambia, Mobile, Monroe and 1 more	87 min
Aug 28, 6:47 PM CDT	Tornado Watch	SPC	Baldwin, Choctaw, Clarke, Conecuh, Escambia, Mobile and 2 more	21 hr
Aug 28, 12:56 PM CDT	Tornado Watch	SPC	Covington, Forrest, Jefferson Davis, Jones, Lamar, Lawrence and 2 more	6 hr

Nearby

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