Alert archive / Alabama / Mesoscale Discussions in 2021

Mesoscale Discussion 209

March 17, 20216 counties in Alabama

The Storm Prediction Center issued this mesoscale discussion at Mar 17, 2021, 2:24 PM CDT for 6 counties in Alabama. It was in force for 96 min.

The area

The outline as issued.

The facts

Issued: Mar 17, 2021, 2:24 PM CDT (19:24 UTC)
Expired: Mar 17, 2021, 4:00 PM CDT
In force: 96 min
Issued by: the Storm Prediction Center
Concerning: Tornado watch 29...33

Counties Bibb County, AL, Chilton County, AL, Dallas County, AL, Hale County, AL, Marengo County, AL, Perry County, AL

The radar

The Birmingham radar (KBMX), 86 km from the middle of the area, began a volume at 19:29 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, 7.4 hours before the alert went out and 86 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: 658 J/kg
Mixed-layer CIN: -112 J/kg
Mixed-layer LCL: 759 m above ground
0-6 km bulk shear: 59 kt
0-1 km storm-relative helicity: 169 m²/s²
0-3 km storm-relative helicity: 301 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 2.1

Open this sounding in Storm Lab

The text

As transmitted.

534 
ACUS11 KWNS 171925
SWOMCD
SPC MCD 171924 
ALZ000-172100-

Mesoscale Discussion 0209
NWS Storm Prediction Center Norman OK
0224 PM CDT Wed Mar 17 2021

Areas affected...Central AL

Concerning...Tornado Watch 29...33...

Valid 171924Z - 172100Z

The severe weather threat for Tornado Watch 29, 33 continues.

SUMMARY...A corridor more favorable for the development of strong
tornadoes may be evolving across central AL.

DISCUSSION...Radar imagery from BMX, GWX, and MOB continues to show
a cluster of supercells over west-central AL. The downstream air
mass is characterized by temperatures in the low/mid 70s and
dewpoints in the upper 60s. As noted in the recent BMX sounding,
this air mass is less buoyant than farther west (along the central
MS/AL border) where this cluster initially developed. However, in
contrast to the slightly less favorable thermodynamics, surface
winds here are more southeasterly, veering to southerly in the
low-levels, and then southwesterly farther aloft. This is resulting
in considerable low-level vertical shear. Recent VAD profile from
BMX sampled 350+ m2/s2 of 0-1 km storm-relative helicity. Given the
already organized character of these storms, potential exists for
the development of strong tornadoes if a more discrete nature can be
maintained.

..Mosier.. 03/17/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BMX...MOB...

LAT...LON   32938782 33178747 33038674 32158666 31978763 32298791
            32938782

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Mar 17, 10:56 AM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Chilton, Choctaw, Clarke, Coosa and 17 more	2 hr
Mar 17, 11:36 AM CDT	Tornado Watch PDS	SPC	Autauga, Bibb, Blount, Chilton, Choctaw, Clarke and 25 more	7 hr
Mar 17, 12:02 PM CDT	Mesoscale Discussion	SPC	Choctaw, Clarke, Marengo	58 min
Mar 17, 1:01 PM CDT	Mesoscale Discussion	SPC	Autauga, Chilton, Coosa, Elmore, Lowndes, Montgomery and 1 more	89 min
Mar 17, 1:26 PM CDT	Tornado Watch	SPC	Calhoun, Chambers, Cherokee, Cleburne, Elmore, Etowah and 7 more	5 hr
Mar 17, 1:45 PM CDT	Mesoscale Discussion	SPC	Mobile	90 min
Mar 17, 5:49 PM CDT	Mesoscale Discussion	SPC	Autauga, Bibb, Blount, Bullock, Butler, Calhoun and 32 more	86 min
Mar 17, 6:09 PM CDT	Mesoscale Discussion	SPC	Colbert, Franklin, Lamar, Lauderdale, Lawrence, Marion	66 min
Mar 17, 6:48 PM CDT	Tornado Watch PDS	SPC	Autauga, Baldwin, Barbour, Bibb, Blount, Bullock and 44 more	8 hr

Nearby

Mesoscale Discussions in Alabama, 2021 Every mesoscale discussion 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.