Alert archive / Mississippi / Mesoscale Discussions in 2011

Mesoscale Discussion 620

April 27, 20115 counties in Alabama; 7 parishes in Louisiana; 59 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Apr 27, 2011, 10:45 AM CDT for 5 counties in Alabama; 7 parishes in Louisiana; 59 counties in Mississippi. It was in force for 90 min.

The area

The outline as issued.

The facts

Issued
Apr 27, 2011, 10:45 AM CDT (15:45 UTC)
Expired
Apr 27, 2011, 12:15 PM CDT
In force
90 min
Issued by
the Storm Prediction Center
All 71 counties

Greene County, AL, Lamar County, AL, Marion County, AL, Pickens County, AL, Sumter County, AL, Concordia Parish, LA, East Carroll Parish, LA, Franklin Parish, LA, Madison Parish, LA, Richland Parish, LA, Tensas Parish, LA, West Carroll Parish, LA, Adams County, MS, Attala County, MS, Benton County, MS, Calhoun County, MS, Carroll County, MS, Chickasaw County, MS, Choctaw County, MS, Claiborne County, MS, Clarke County, MS, Clay County, MS, Copiah County, MS, Covington County, MS, Franklin County, MS, Grenada County, MS, Hinds County, MS, Holmes County, MS, Humphreys County, MS, Issaquena County, MS, Itawamba County, MS, Jasper County, MS, Jefferson County, MS, Jefferson Davis County, MS, Jones County, MS, Kemper County, MS, Lafayette County, MS, Lauderdale County, MS, Lawrence County, MS, Leake County, MS, Lee County, MS, Leflore County, MS, Lincoln County, MS, Lowndes County, MS, Madison County, MS, Marshall County, MS, Monroe County, MS, Montgomery County, MS, Neshoba County, MS, Newton County, MS, Noxubee County, MS, Oktibbeha County, MS, Panola County, MS, Pontotoc County, MS, Prentiss County, MS, Rankin County, MS, Scott County, MS, Sharkey County, MS, Simpson County, MS, Smith County, MS, Sunflower County, MS, Tallahatchie County, MS, Tippah County, MS, Tishomingo County, MS, Union County, MS, Warren 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), 59 km from the middle of the area, began a volume at 15:48 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.

The nearest sounding before it

Jackson, MS (KJAN), launched 12:00Z, 3.8 hours before the alert went out and 57 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, Jackson, MS at 12:00Z on 2011-04-27Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 890 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, Jackson, MS at 12:00Z on 2011-04-27The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 449 square meters per square second.1939587897Sfc1 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
890 J/kg
Mixed-layer CIN
-102 J/kg
Mixed-layer LCL
609 m above ground
0-6 km bulk shear
61 kt
0-1 km storm-relative helicity
449 m²/s²
0-3 km storm-relative helicity
786 m²/s²
Significant tornado parameter
0.0
Supercell composite
21.2

Open this sounding in Storm Lab

The text

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

950 
ACUS11 KWNS 271545
SWOMCD
SPC MCD 271545 
ALZ000-MSZ000-LAZ000-ARZ000-271715-

MESOSCALE DISCUSSION 0620
NWS STORM PREDICTION CENTER NORMAN OK
1045 AM CDT WED APR 27 2011

AREAS AFFECTED...FAR EASTERN LA AND NORTHERN/CENTRAL PORTIONS OF MS
INTO AL

CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

VALID 271545Z - 271715Z

A LONG LEAD-TIME/LONG DURATION PARTICULARLY DANGEROUS /PDS/ TORNADO
WATCH WILL LIKELY BE ISSUED SOON...MOST CERTAIN ACROSS
NORTHERN/CENTRAL PORTIONS OF MS.

VISIBLE SATELLITE/SURFACE OBSERVATIONAL TRENDS IMPLY RELATIVELY
QUICK AIRMASS RECOVERY/DESTABILIZATION IS OCCURRING FROM LA INTO
MS/AL THROUGH MID/LATE MORNING. THIS IS THE CASE NOT ONLY FOR IN THE
VICINITY OF EARLY MORNING WEST-EAST OUTFLOW ACROSS MS/AL...WHERE
SURFACE TEMPERATURES/DEWPOINTS HAVE EACH INCREASED 8-12F OVER THE
PAST 2 HR...BUT ALSO IN THE WAKE OF AN APPARENT WAVE-LIKE FEATURE
SPREADING EASTWARD CROSS CENTRAL PORTIONS OF MS/LA AS A CU FIELD
OTHERWISE CONTINUES TO INCREASE/MATURE ACROSS NORTHEAST LA.

AIDED BY STRONG AMPLIFICATION/INTENSIFICATION OF AN INCREASINGLY
NEGATIVE TILT SHORTWAVE TROUGH/ASSOCIATED JET STREAK LATER TODAY...A
VOLATILE SCENARIO IS EXPECTED TO UNFOLD THROUGH THE AFTERNOON.
CONVECTIVE INITIATION OF VIGOROUS CONVECTION BY EARLY/MID AFTERNOON
IS WELL SUPPORTED BY EXPERIMENTAL GUIDANCE SUCH AS SEVERAL RECENT
HRRR RUNS AND THE 12Z WRF-NMM. SHORT TERM FORECAST SOUNDINGS FROM
GUIDANCE SUCH AS THE RUC/12Z NAM...ACCENTUATED BY VERY LONG/STRONGLY
CURVED LOW LEVEL HODOGRAPHS...SUPPORT THE NOTION OF SUPERCELLS
CAPABLE OF STRONG/POTENTIALLY VIOLENT TORNADOES THIS AFTERNOON/EARLY
EVENING ESPECIALLY ACROSS THE HIGH RISK AREA.

..GUYER.. 04/27/2011

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

ATTN...WFO...BMX...HUN...MOB...MEG...JAN...LIX...

LAT...LON   31159161 32529178 34858972 34838959 34778787 32968780
            31678864 31309016 31159161

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 26, 7:59 PM CDTMesoscale DiscussionSPCColbert, Franklin, Lamar, Lauderdale, Lawrence, Limestone and 1 more2 hr
Apr 26, 9:33 PM CDTTornado Watch PDSSPCColbert, Franklin, Lauderdale7 hr
Apr 26, 11:33 PM CDTMesoscale DiscussionSPCColbert, Franklin, Lamar, Lauderdale, Marion117 min
Apr 27, 1:56 AM CDTMesoscale DiscussionSPCBibb, Blount, Cullman, Fayette, Greene, Hale and 12 more64 min
Apr 27, 2:26 AM CDTTornado WatchSPCBibb, Blount, Calhoun, Cherokee, Chilton, Clay and 29 more6 hr
Apr 27, 8:08 AM CDTTornado WatchSPCColbert, Cullman, DeKalb, Fayette, Franklin, Jackson and 10 more6 hr
Apr 27, 11:39 AM CDTMesoscale DiscussionSPCCullman, DeKalb, Jackson, Madison, Marshall, Morgan66 min
Apr 27, 1:05 PM CDTMesoscale DiscussionSPCBibb, Blount, Calhoun, Cherokee, Chilton, Choctaw and 27 more85 min
Apr 27, 1:42 PM CDTTornado Watch PDSSPCAutauga, Bibb, Blount, Butler, Calhoun, Cherokee and 41 more8 hr
Apr 27, 2:56 PM CDTMesoscale DiscussionSPCBibb, Blount, Calhoun, Cherokee, Chilton, Choctaw and 33 more2 hr
Apr 27, 5:01 PM CDTMesoscale DiscussionSPCAutauga, Bibb, Blount, Butler, Calhoun, Cherokee and 38 more89 min
Apr 27, 5:41 PM CDTMesoscale DiscussionSPCBarbour, Bullock, Chambers, Crenshaw, Elmore, Lee and 6 more34 min
Apr 27, 5:52 PM CDTTornado Watch PDSSPCBarbour, Bullock, Chambers, Elmore, Lee, Macon and 5 more9 hr
Apr 27, 6:39 PM CDTMesoscale DiscussionSPCAutauga, Bibb, Blount, Calhoun, Cherokee, Chilton and 26 more66 min
Apr 26, 8:53 PM CDTMesoscale DiscussionSPCBeauregard, Bienville, Bossier, Caddo, Claiborne, De Soto and 12 more97 min
Apr 26, 9:42 PM CDTTornado WatchSPCAvoyelles, Beauregard, Rapides, Vernon7 hr
Apr 27, 3:29 AM CDTMesoscale DiscussionSPCBossier, Caddo2 hr
Apr 27, 4:53 AM CDTSevere Thunderstorm WatchSPCBienville, Bossier, Caddo, Caldwell, Catahoula, Claiborne and 16 more5 hr
Apr 27, 9:48 AM CDTMesoscale DiscussionSPCBienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 14 more27 min
Apr 27, 11:02 AM CDTTornado Watch PDSSPCCatahoula, Concordia, East Carroll, Franklin, Madison, Morehouse and 3 more8 hr
Apr 26, 9:13 PM CDTMesoscale DiscussionSPCBenton, Bolivar, Coahoma, DeSoto, Marshall, Panola and 3 more62 min
Apr 26, 9:58 PM CDTTornado WatchSPCDeSoto, Tunica7 hr
Apr 27, 6:25 AM CDTMesoscale DiscussionSPCAlcorn, Attala, Benton, Bolivar, Calhoun, Carroll and 33 more65 min
Apr 27, 6:27 PM CDTMesoscale DiscussionSPCClarke, Clay, Copiah, Covington, Forrest, Jasper and 22 more33 min
Apr 27, 6:42 PM CDTTornado WatchSPCClarke, Covington, Forrest, Jasper, Jefferson Davis, Jones and 13 more3 hr

Nearby

Mesoscale Discussions in Mississippi, 2011Mesoscale Discussions in Louisiana, 2011Mesoscale Discussions in Alabama, 2011Every mesoscale discussion in 2011

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.