Alert archive / Alabama / Severe Thunderstorm Watches in 2021

Severe Thunderstorm Watch 77

April 9, 202125 counties in Alabama

The Storm Prediction Center issued this severe thunderstorm watch at Apr 9, 2021, 12:54 PM CDT for 25 counties in Alabama. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: Apr 9, 2021, 12:54 PM CDT (17:54 UTC)
Expired: Apr 9, 2021, 7:50 PM CDT
In force: 7 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 25 counties

Autauga County, AL, Bibb County, AL, Blount County, AL, Chilton County, AL, Coosa County, AL, Dallas County, AL, Elmore County, AL, Fayette County, AL, Greene County, AL, Hale County, AL, Jefferson County, AL, Lamar County, AL, Lowndes County, AL, Marengo County, AL, Marion County, AL, Montgomery County, AL, Perry County, AL, Pickens County, AL, Shelby County, AL, St. Clair County, AL, Sumter County, AL, Talladega County, AL, Tuscaloosa County, AL, Walker County, AL, Winston County, AL

The radar

The Birmingham radar (KBMX), 58 km from the middle of the area, began a volume at 17:55 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: 30%
One or more gusts of 65 knots or more: 10%
Ten or more severe hail reports: 40%
One or more hailstones of 2 inches or more: 30%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Apr 9, 1:22 PM CDT	Severe Thunderstorm Warning	BMX	Blount, Jefferson, Walker	36 min
Apr 9, 1:36 PM CDT	Severe Thunderstorm Warning	BMX	Walker, Winston	39 min
Apr 9, 1:52 PM CDT	Severe Thunderstorm Warning	BMX	Blount, Jefferson, St. Clair	38 min
Apr 9, 1:55 PM CDT	Severe Thunderstorm Warning	BMX	Dallas, Lowndes	65 min
Apr 9, 2:05 PM CDT	Severe Thunderstorm Warning	BMX	Walker	55 min
Apr 9, 2:21 PM CDT	Severe Thunderstorm Warning	BMX	Lowndes	54 min
Apr 9, 2:39 PM CDT	Severe Thunderstorm Warning	BMX	Blount, Jefferson, Walker	51 min
Apr 9, 4:13 PM CDT	Severe Thunderstorm Warning	BMX	Greene, Hale, Marengo, Sumter	47 min
Apr 9, 4:54 PM CDT	Severe Thunderstorm Warning	BMX	Greene	25 min
Apr 9, 5:47 PM CDT	Severe Thunderstorm Warning	BMX	Pickens, Tuscaloosa	28 min
Apr 9, 6:11 PM CDT	Severe Thunderstorm Warning	BMX	Fayette, Pickens, Tuscaloosa	37 min
Apr 9, 6:15 PM CDT	Severe Thunderstorm Warning	BMX	Pickens	23 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, 5.9 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-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: 89 J/kg
Mixed-layer CIN: -208 J/kg
Mixed-layer LCL: 1321 m above ground
0-6 km bulk shear: 44 kt
0-1 km storm-relative helicity: 70 m²/s²
0-3 km storm-relative helicity: 141 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.0

Open this sounding in Storm Lab

The text

As transmitted.

409 
WWUS20 KWNS 091749
SEL7  
SPC WW 091749
ALZ000-100000-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 77
NWS Storm Prediction Center Norman OK
1250 PM CDT Fri Apr 9 2021

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Central and west central Alabama

* Effective this Friday afternoon and evening from 1250 PM until
  700 PM CDT.

* Primary threats include...
  Scattered large hail and isolated very large hail events to 2
    inches in diameter possible
  Isolated damaging wind gusts to 70 mph possible

SUMMARY...Scattered thunderstorm development is expected through the
afternoon across west central into central Alabama. The strongest
storms could develop some supercell structures and pose a threat for
large hail and isolated damaging winds, prior to weakening this
evening.

The severe thunderstorm watch area is approximately along and 50
statute miles north and south of a line from 35 miles west southwest
of Tuscaloosa AL to 45 miles southeast of Birmingham AL. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU7).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 76...

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 500. Mean storm motion vector
27020.

...Thompson

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 9, 2:49 AM CDT	Mesoscale Discussion	SPC	Baldwin, Mobile	2 hr
Apr 9, 7:38 AM CDT	Mesoscale Discussion	SPC	Autauga, Barbour, Bullock, Butler, Chambers, Clarke and 17 more	3 hr
Apr 9, 11:44 AM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Blount, Calhoun, Chambers, Chilton and 28 more	2 hr
Apr 9, 5:54 PM CDT	Mesoscale Discussion	SPC	Fayette, Greene, Lamar, Marion, Pickens, Sumter and 2 more	96 min

Nearby

Severe Thunderstorm Watches in Alabama, 2021 Every severe thunderstorm watch in 2021

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.