Alert archive / Alabama / Mesoscale Discussions in 2011

Mesoscale Discussion 489

April 20, 201117 counties in Alabama; Noxubee County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2011, 8:42 AM CDT for 17 counties in Alabama; Noxubee County, Mississippi. It was in force for 63 min.

The area

The outline as issued.

The facts

Issued
Apr 20, 2011, 8:42 AM CDT (13:42 UTC)
Expired
Apr 20, 2011, 9:45 AM CDT
In force
63 min
Issued by
the Storm Prediction Center

Counties Autauga County, AL, Bibb County, AL, Chilton County, AL, Clay County, AL, Coosa County, AL, Elmore County, AL, Fayette County, AL, Greene County, AL, Hale County, AL, Jefferson County, AL, Perry County, AL, Pickens County, AL, Shelby County, AL, St. Clair County, AL, Talladega County, AL, Tallapoosa County, AL, Tuscaloosa County, AL, Noxubee County, MS

The radar

The Birmingham radar (KBMX), 27 km from the middle of the area, began a volume at 13:42 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 nearest sounding before it

Birmingham, AL (KBMX), launched 12:00Z, 1.7 hours before the alert went out and 26 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, Birmingham, AL at 12:00Z on 2011-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 2075 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, Birmingham, AL at 12:00Z on 2011-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 151 square meters per square second.193958Sfc1 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
2075 J/kg
Mixed-layer CIN
-36 J/kg
Mixed-layer LCL
550 m above ground
0-6 km bulk shear
35 kt
0-1 km storm-relative helicity
151 m²/s²
0-3 km storm-relative helicity
166 m²/s²
Significant tornado parameter
1.3
Supercell composite
7.5

Open this sounding in Storm Lab

The text

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

055 
ACUS11 KWNS 201342
SWOMCD
SPC MCD 201342 
ALZ000-MSZ000-201445-

MESOSCALE DISCUSSION 0489
NWS STORM PREDICTION CENTER NORMAN OK
0842 AM CDT WED APR 20 2011

AREAS AFFECTED...NRN AND CNTRL AL AND ERN MS

CONCERNING...SEVERE THUNDERSTORM WATCH 166...

VALID 201342Z - 201445Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 166
CONTINUES.

AN ISOLATED SEVERE THREAT WILL LIKELY CONTINUE THIS MORNING ACROSS
CNTRL AL WITH WIND DAMAGE THREAT BEING THE MAIN THREAT. THE THREAT
SHOULD MOVE EWD WITH TIME AND WW ISSUANCE TO REPLACE THE CURRENT WW
166 IS STILL POSSIBLE.

A CLUSTER OF STRONG TO SEVERE THUNDERSTORMS WITH A SHORT BOWING-LINE
SEGMENTS IS ONGOING IN ERN MS AND WRN AL ON THE NRN EDGE OF MODERATE
INSTABILITY. MESOANALYSIS ESTIMATES MLCAPE VALUES ARE THE 1000 TO
1500 J/KG RANGE AND THE LINE SHOULD MOVE ESEWD ALONG THE INSTABILITY
GRADIENT INTO CNTRL MS AND WRN AL OVER THE NEXT FEW HOURS. THE LINE
IS ALSO LOCATED ON THE SRN EDGE OF A THE STRONGER MID-LEVEL FLOW
WHICH IS HELPING TO CREATE MODERATE DEEP LAYER SHEAR PROFILES WHICH
IS SUPPORTING A WIND DAMAGE THREAT. HOWEVER...THE MID-LEVEL FLOW
WILL BEGIN TO WEAKEN AS AN UPPER-LEVEL TROUGH OVER THE SRN AND CNTRL
APPALACHIAN MTNS MOVES AWAY FROM THE REGION. THIS MAY ALLOW THE
SEVERE THREAT TO BECOME INCREASINGLY MARGINAL BY LATE THIS MORNING.

..BROYLES.. 04/20/2011

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

ATTN...WFO...BMX...JAN...

LAT...LON   32348572 32708804 33098878 33668818 33798727 33718556
            32348572

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 19, 9:39 PM CDTMesoscale DiscussionSPCColbert, Franklin, Lauderdale66 min
Apr 19, 11:56 PM CDTMesoscale DiscussionSPCColbert, Franklin, Lamar, Lauderdale, Lawrence, Limestone and 4 more94 min
Apr 20, 3:19 AM CDTMesoscale DiscussionSPCBlount, Calhoun, Cherokee, Cullman, DeKalb, Etowah and 16 more86 min
Apr 20, 3:37 AM CDTSevere Thunderstorm WatchSPCBibb, Blount, Calhoun, Chambers, Cherokee, Chilton and 33 more8 hr
Apr 20, 5:39 AM CDTMesoscale DiscussionSPCCalhoun, Cherokee, Cleburne, St. Clair66 min
Apr 20, 1:16 PM CDTMesoscale DiscussionSPCAutauga, Barbour, Bibb, Blount, Bullock, Chambers and 28 more89 min
Apr 20, 1:33 PM CDTSevere Thunderstorm WatchSPCAutauga, Barbour, Bibb, Bullock, Butler, Chambers and 33 more6 hr
Apr 20, 5:24 PM CDTMesoscale DiscussionSPCAutauga, Bibb, Chilton, Coosa, Elmore, Fayette and 10 more96 min
Apr 20, 6:51 PM CDTMesoscale DiscussionSPCFayette, Greene, Lamar, Marion, Pickens, Tuscaloosa and 2 more84 min
Apr 19, 10:14 PM CDTTornado WatchSPCAlcorn, Benton, Bolivar, Calhoun, Carroll, Chickasaw and 24 more7 hr
Apr 20, 12:46 PM CDTMesoscale DiscussionSPCBolivar, Carroll, Grenada, Holmes, Humphreys, Issaquena and 6 more89 min
Apr 20, 1:02 PM CDTSevere Thunderstorm WatchSPCAlcorn, Attala, Benton, Bolivar, Calhoun, Carroll and 52 more7 hr
Apr 20, 5:56 PM CDTMesoscale DiscussionSPCBolivar, Calhoun, Chickasaw, Clay, Coahoma, Grenada and 13 more2 hr

Nearby

Mesoscale Discussions in Alabama, 2011Mesoscale Discussions in Mississippi, 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.