Alert archive / Texas / Mesoscale Discussions in 2021

Mesoscale Discussion 137

February 28, 20216 counties in Arkansas; 13 counties in Texas

The Storm Prediction Center issued this mesoscale discussion at Feb 28, 2021, 2:25 PM CST for 6 counties in Arkansas; 13 counties in Texas. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Feb 28, 2021, 2:25 PM CST (20:25 UTC)
Expired: Feb 28, 2021, 4:30 PM CST
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 12

Counties Hempstead County, AR, Howard County, AR, Little River County, AR, Miller County, AR, Pike County, AR, Sevier County, AR, Bowie County, TX, Camp County, TX, Cass County, TX, Franklin County, TX, Hopkins County, TX, Kaufman County, TX, Morris County, TX, Rains County, TX, Red River County, TX, Titus County, TX, Upshur County, TX, Van Zandt County, TX, Wood County, TX

The radar

The Shreveport radar (KSHV), 136 km from the middle of the area, began a volume at 20:25 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.

Severe Thunderstorm Watch 14Feb 28, 5:50 PM CST

The nearest sounding before it

Shreveport, LA (KSHV), launched 12:00Z, 8.4 hours before the alert went out and 140 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: 458 J/kg
Mixed-layer CIN: -126 J/kg
Mixed-layer LCL: 573 m above ground
0-6 km bulk shear: 53 kt
0-1 km storm-relative helicity: 321 m²/s²
0-3 km storm-relative helicity: 414 m²/s²
Significant tornado parameter: 0.4
Supercell composite: 1.2

Open this sounding in Storm Lab

The text

As transmitted.

383 
ACUS11 KWNS 282025
SWOMCD
SPC MCD 282025 
ARZ000-LAZ000-TXZ000-OKZ000-282230-

Mesoscale Discussion 0137
NWS Storm Prediction Center Norman OK
0225 PM CST Sun Feb 28 2021

Areas affected...northeast Texas through southwest Arkansas

Concerning...Severe Thunderstorm Watch 12...

Valid 282025Z - 282230Z

The severe weather threat for Severe Thunderstorm Watch 12
continues.

SUMMARY...A few instances of large hail and locally strong to
damaging wind gusts remain possible through early evening across the
remaining portion of severe thunderstorm watch 12 from northeast
Texas into southwest Arkansas.

DISCUSSION...General trend has been for storms to decrease in
coverage in wake of initial activity, possibly due to weak forcing
for ascent upstream of early impulse. Low-level winds have veered to
southwesterly in the warm sector, and widespread clouds persist
which is limiting boundary layer destabilization. However, a minor
upstream vorticity maximum will move northeast and interact with the
cold front later this afternoon, and might contribute to development
of additional storms along the front. Instability remains modest
with with MLCAPE from 1000-1500 J/kg. Though low-level winds are
relatively weak and veered immediately in advance of the cold front,
strong effective bulk shear in excess of 60 kt should support a
conditional risk for a few organized structures with large hail and
damaging wind the main threats.

..Dial.. 02/28/2021

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

ATTN...WFO...LZK...SHV...FWD...

LAT...LON   32689654 34009477 34569385 34529339 33599343 33019396
            32489527 32359607 32689654

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Feb 28, 9:59 AM CST	Mesoscale Discussion	SPC	Howard, Polk, Sevier	91 min
Feb 28, 10:43 AM CST	Severe Thunderstorm Watch	SPC	Hempstead, Howard, Lafayette, Little River, Miller, Montgomery and 5 more	7 hr
Feb 28, 1:01 PM CST	Mesoscale Discussion	SPC	Arkansas, Clark, Clay, Cleburne, Cleveland, Conway and 32 more	119 min
Feb 28, 2:22 PM CST	Tornado Watch	SPC	Arkansas, Bradley, Calhoun, Clark, Clay, Cleburne and 32 more	8 hr
Feb 28, 4:40 PM CST	Mesoscale Discussion	SPC	Arkansas, Bradley, Calhoun, Clark, Cleveland, Craighead and 23 more	95 min
Feb 28, 5:28 PM CST	Mesoscale Discussion	SPC	Hempstead, Howard, Lafayette, Little River, Miller, Nevada and 2 more	2 hr
Feb 28, 5:54 PM CST	Severe Thunderstorm Watch	SPC	Columbia, Hempstead, Lafayette, Miller, Nevada, Union	4 hr

Nearby

Mesoscale Discussions in Texas, 2021 Mesoscale Discussions in Arkansas, 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.