Alert archive / Alabama / Mesoscale Discussions in 2012

Mesoscale Discussion 1951

September 17, 201219 counties in Alabama; 12 counties in Georgia; 16 counties in Tennessee

The Storm Prediction Center issued this mesoscale discussion at Sep 17, 2012, 3:53 PM CDT for 19 counties in Alabama; 12 counties in Georgia; 16 counties in Tennessee. It was in force for 97 min.

The area

The outline as issued.

The facts

Issued: Sep 17, 2012, 3:53 PM CDT (20:53 UTC)
Expired: Sep 17, 2012, 5:30 PM CDT
In force: 97 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 47 counties

Blount County, AL, Calhoun County, AL, Cherokee County, AL, Clay County, AL, Cleburne County, AL, Cullman County, AL, DeKalb County, AL, Etowah County, AL, Jackson County, AL, Jefferson County, AL, Lawrence County, AL, Limestone County, AL, Madison County, AL, Marshall County, AL, Morgan County, AL, St. Clair County, AL, Talladega County, AL, Walker County, AL, Winston County, AL, Bartow County, GA, Catoosa County, GA, Chattooga County, GA, Dade County, GA, Floyd County, GA, Gilmer County, GA, Gordon County, GA, Haralson County, GA, Murray County, GA, Polk County, GA, Walker County, GA, Whitfield County, GA, Bledsoe County, TN, Bradley County, TN, Coffee County, TN, Franklin County, TN, Grundy County, TN, Hamilton County, TN, Lincoln County, TN, Marion County, TN, McMinn County, TN, Meigs County, TN, Moore County, TN, Polk County, TN, Rhea County, TN, Sequatchie County, TN, Van Buren County, TN, Warren County, TN

The radar

The Northeast Alabama radar (KHTX), 53 km from the middle of the area, began a volume at 20:52 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 640Sep 17, 5:40 PM CDT

The nearest sounding before it

Birmingham, AL (KBMX), launched 12:00Z, 8.9 hours before the alert went out and 174 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: 1021 J/kg
Mixed-layer CIN: -19 J/kg
Mixed-layer LCL: 617 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 44 m²/s²
0-3 km storm-relative helicity: 69 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 1.1

Open this sounding in Storm Lab

The text

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

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 17, 12:58 PM CDT	Mesoscale Discussion	SPC	Baldwin, Choctaw, Clarke, Mobile, Washington	92 min
Sep 17, 5:14 PM CDT	Mesoscale Discussion	SPC	Barbour, Dale, Henry, Houston	2 hr
Sep 17, 5:39 PM CDT	Tornado Watch	SPC	Baldwin, Banks, Barrow, Bartow, Bibb, Bleckley and 84 more	8 hr

Nearby

Mesoscale Discussions in Alabama, 2012 Mesoscale Discussions in Tennessee, 2012 Mesoscale Discussions in Georgia, 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.