Alert archive / Alabama / Mesoscale Discussions in 2011

Mesoscale Discussion 487

April 20, 201122 counties in Alabama

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2011, 3:19 AM CDT for 22 counties in Alabama. It was in force for 86 min.

The area

The outline as issued.

The facts

Issued: Apr 20, 2011, 3:19 AM CDT (08:19 UTC)
Expired: Apr 20, 2011, 4:45 AM CDT
In force: 86 min
Issued by: the Storm Prediction Center

All 22 counties

Blount County, AL, Calhoun County, AL, Cherokee County, AL, Cullman County, AL, DeKalb County, AL, Etowah County, AL, Fayette County, AL, Jackson County, AL, Jefferson County, AL, Lamar County, AL, Lawrence County, AL, Limestone County, AL, Madison County, AL, Marion County, AL, Marshall County, AL, Morgan County, AL, Shelby County, AL, St. Clair County, AL, Talladega County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL

The radar

The Birmingham radar (KBMX), 84 km from the middle of the area, began a volume at 08:22 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

Birmingham, AL (KBMX), launched 00:00Z, 8.3 hours before the alert went out and 83 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: 1717 J/kg
Mixed-layer CIN: -103 J/kg
Mixed-layer LCL: 1046 m above ground
0-6 km bulk shear: 42 kt
0-1 km storm-relative helicity: 184 m²/s²
0-3 km storm-relative helicity: 282 m²/s²
Significant tornado parameter: 1.4
Supercell composite: 4.6

Open this sounding in Storm Lab

The text

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

960 
ACUS11 KWNS 200820
SWOMCD
SPC MCD 200819
GAZ000-ALZ000-MSZ000-200945-

MESOSCALE DISCUSSION 0487
NWS STORM PREDICTION CENTER NORMAN OK
0319 AM CDT WED APR 20 2011

AREAS AFFECTED...NRN AL

CONCERNING...TORNADO WATCH 160...165...

VALID 200819Z - 200945Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 160...165...CONTINUES.

AN ADDITIONAL WATCH MAY BE NEEDED ACROSS PARTS OF NORTHERN
ALABAMA...LIKELY REPLACING WW 160...WITHIN THE NEXT HOUR OR SO.

BROAD UPPER TROUGHING IS BEGINNING TO LIFT NORTHEAST OF THE MIDDLE
MISSISSIPPI VALLEY REGION...BUT FORCING FOR UPWARD VERTICAL MOTION
REMAINS STRONG ENOUGH TO SUPPORT CONTINUING CONVECTIVE DEVELOPMENT
AHEAD OF AN ASSOCIATED SURFACE COLD FRONT AS FAR SOUTH AS THE NORTH
CENTRAL GULF STATES.  THIS FORCING APPEARS LIKELY TO SPREAD ACROSS
NORTHERN ALABAMA AND MIDDLE/EASTERN TENNESSEE...INTO THE SOUTHERN
APPALACHIANS...BETWEEN NOW AND 11-13Z...ACCOMPANIED BY STRONG/SEVERE
STORMS.  MOIST LOW-LEVELS AND STEEP MID-LEVEL LAPSE RATES ARE
CONTRIBUTING TO MODERATELY LARGE CAPE UP TO AROUND 2000 J/KG ACROSS
THE REGION...IN THE PRESENCE OF STRONG SHEAR BENEATH 50 KT WESTERLY
500 MB FLOW.  LARGE HAIL MAY BE THE PRIMARY THREAT ACROSS NORTHERN
ALABAMA...BUT CONDITIONS COULD STILL REMAIN SUFFICIENT FOR THE
DEVELOPMENT OF ANOTHER VIGOROUS COLD POOL CAPABLE OF SUPPORTING
POTENTIALLY DAMAGING WIND GUSTS.

..KERR.. 04/20/2011

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

ATTN...WFO...FFC...BMX...HUN...MEG...JAN...

LAT...LON   33668832 34858756 34858549 33938548 33358610 33088738
            33668832

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 19, 9:39 PM CDT	Mesoscale Discussion	SPC	Colbert, Franklin, Lauderdale	66 min
Apr 19, 11:56 PM CDT	Mesoscale Discussion	SPC	Colbert, Franklin, Lamar, Lauderdale, Lawrence, Limestone and 4 more	94 min
Apr 20, 3:37 AM CDT	Severe Thunderstorm Watch	SPC	Bibb, Blount, Calhoun, Chambers, Cherokee, Chilton and 33 more	8 hr
Apr 20, 5:39 AM CDT	Mesoscale Discussion	SPC	Calhoun, Cherokee, Cleburne, St. Clair	66 min
Apr 20, 8:42 AM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Chilton, Clay, Coosa, Elmore and 11 more	63 min
Apr 20, 1:16 PM CDT	Mesoscale Discussion	SPC	Autauga, Barbour, Bibb, Blount, Bullock, Chambers and 28 more	89 min
Apr 20, 1:33 PM CDT	Severe Thunderstorm Watch	SPC	Autauga, Barbour, Bibb, Bullock, Butler, Chambers and 33 more	6 hr
Apr 20, 5:24 PM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Chilton, Coosa, Elmore, Fayette and 10 more	96 min
Apr 20, 6:51 PM CDT	Mesoscale Discussion	SPC	Fayette, Greene, Lamar, Marion, Pickens, Tuscaloosa and 2 more	84 min

Nearby

Mesoscale Discussions in Alabama, 2011 Every 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.