Alert archive / Alabama / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 149

April 5, 201227 counties in Alabama

The Storm Prediction Center issued this severe thunderstorm watch at Apr 5, 2012, 6:14 PM CDT for 27 counties in Alabama. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Apr 5, 2012, 6:14 PM CDT (23:14 UTC)
Expired: Apr 5, 2012, 9:37 PM CDT
In force: 3 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 27 counties

Autauga County, AL, Bibb County, AL, Blount County, AL, Bullock County, AL, Calhoun County, AL, Chambers County, AL, Cherokee County, AL, Chilton County, AL, Clay County, AL, Cleburne County, AL, Coosa County, AL, Cullman County, AL, Dallas County, AL, Elmore County, AL, Etowah County, AL, Jefferson County, AL, Lee County, AL, Lowndes County, AL, Macon County, AL, Montgomery County, AL, Perry County, AL, Randolph County, AL, Russell County, AL, Shelby County, AL, St. Clair County, AL, Talladega County, AL, Tallapoosa County, AL

The radar

The Birmingham radar (KBMX), 37 km from the middle of the area, began a volume at 23:14 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.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 10%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 20%
One or more gusts of 65 knots or more: 10%
Ten or more severe hail reports: 30%
One or more hailstones of 2 inches or more: 20%
Six or more combined severe hail and wind reports: 50%

Warnings issued inside it

7 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Apr 5, 6:27 PM CDT	Severe Thunderstorm Warning	BMX	Autauga, Dallas, Lowndes	48 min
Apr 5, 6:33 PM CDT	Severe Thunderstorm Warning	BMX	Bibb, Chilton, Shelby	42 min
Apr 5, 6:37 PM CDT	Severe Thunderstorm Warning	BMX	Autauga, Chilton, Dallas, Elmore, Perry	53 min
Apr 5, 6:43 PM CDT	Severe Thunderstorm Warning	BMX	Jefferson, St. Clair, Shelby	47 min
Apr 5, 7:14 PM CDT	Severe Thunderstorm Warning	BMX	Chilton, Coosa, Shelby	32 min
Apr 5, 7:17 PM CDT	Severe Thunderstorm Warning	BMX	Autauga, Elmore, Lowndes, Montgomery	43 min
Apr 5, 7:20 PM CDT	Severe Thunderstorm Warning	BMX	Shelby, Talladega	40 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Birmingham, AL (KBMX), launched 12:00Z, 11.2 hours before the alert went out and 37 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: 315 J/kg
Mixed-layer CIN: -31 J/kg
Mixed-layer LCL: 754 m above ground
0-6 km bulk shear: 40 kt
0-1 km storm-relative helicity: -91 m²/s²
0-3 km storm-relative helicity: -43 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -1.5

Open this sounding in Storm Lab

The text

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

958 
WWUS20 KWNS 052317
SEL9
SPC WW 052317
ALZ000-060500-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 149
NWS STORM PREDICTION CENTER NORMAN OK
615 PM CDT THU APR 5 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

       CENTRAL AND EASTERN ALABAMA

EFFECTIVE THIS THURSDAY NIGHT FROM 615 PM UNTIL MIDNIGHT CDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 55
STATUTE MILES EAST AND WEST OF A LINE FROM 20 MILES WEST
NORTHWEST OF GADSDEN ALABAMA TO 30 MILES EAST SOUTHEAST OF
MONTGOMERY ALABAMA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE
THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...CONTINUE...WW 146...WW 147...WW 148...

DISCUSSION...STORMS HAVE INCREASED IN BOTH COVERAGE AND INTENSITY AS
COMPACT MID/UPPER LOW AND ASSOCIATED VORT CENTER DEVELOP SEWD ACROSS
TN VALLEY THIS EVENING. STEEPENING MID-LEVEL LAPSE RATES AND
STRENGTHENING FLOW FIELDS....IN CONCERT WITH ENHANCED DPVA SHOULD
COMPENSATE FOR LACK OF STRONGER CONVECTIVE INSTABILITY TO SUSTAIN A
FEW STOUT UPDRAFTS MOSTLY CAPABLE OF LARGE HAIL. SOME TENDENCY
TOWARD SMALL-SCALE LINEAR DEVELOPMENT ALSO SUGGESTS SOME INCREASE IN
LOCALLY STRONG WINDS AS CONVECTION BECOMES PREFERENTIALLY ALIGNED
WITH 65KT MID LEVEL JET STREAK MOVING INTO THE AREA.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 350. MEAN STORM
MOTION VECTOR 27030.


...CARBIN

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 5, 7:36 AM CDT	Mesoscale Discussion	SPC	Choctaw, Greene, Hale, Marengo, Perry, Pickens and 2 more	54 min
Apr 5, 9:14 AM CDT	Severe Thunderstorm Watch	SPC	Autauga, Barbour, Bibb, Bullock, Butler, Chambers and 34 more	8 hr
Apr 5, 10:41 AM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Butler, Chilton, Choctaw, Clarke and 15 more	94 min
Apr 5, 12:09 PM CDT	Mesoscale Discussion	SPC	Colbert, Cullman, Franklin, Lauderdale, Lawrence, Limestone and 4 more	96 min
Apr 5, 1:12 PM CDT	Mesoscale Discussion	SPC	Barbour, Bullock, Chambers, Clay, Coffee, Covington and 11 more	93 min
Apr 5, 1:21 PM CDT	Severe Thunderstorm Watch	SPC	Colbert, DeKalb, Franklin, Jackson, Lauderdale, Lawrence and 4 more	8 hr
Apr 5, 1:58 PM CDT	Severe Thunderstorm Watch	SPC	Coffee, Dale, Geneva, Henry, Houston	6 hr
Apr 5, 3:06 PM CDT	Mesoscale Discussion	SPC	Colbert, DeKalb, Franklin, Jackson, Lauderdale, Lawrence and 4 more	54 min
Apr 5, 3:46 PM CDT	Mesoscale Discussion	SPC	Blount, Calhoun, Cullman, Etowah, Fayette, Jefferson and 7 more	59 min
Apr 5, 3:49 PM CDT	Mesoscale Discussion	SPC	Geneva, Henry, Houston	86 min
Apr 5, 6:15 PM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Blount, Bullock, Calhoun, Chambers and 23 more	45 min

Nearby

Severe Thunderstorm Watches in Alabama, 2012 Every severe thunderstorm watch 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.