Alert archive / Arkansas / Mesoscale Discussions in 2021
Mesoscale Discussion 693
The Storm Prediction Center issued this mesoscale discussion at May 20, 2021, 5:27 PM CDT for 14 counties in Arkansas; 7 counties in Oklahoma; 9 counties in Texas. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- May 20, 2021, 5:27 PM CDT (22:27 UTC)
- Expired
- May 20, 2021, 7:30 PM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
All 30 counties
Crawford County, AR, Franklin County, AR, Hempstead County, AR, Howard County, AR, Little River County, AR, Logan County, AR, Miller County, AR, Montgomery County, AR, Pike County, AR, Polk County, AR, Scott County, AR, Sebastian County, AR, Sevier County, AR, Washington County, AR, Adair County, OK, Haskell County, OK, Latimer County, OK, LeFlore County, OK, McCurtain County, OK, Pushmataha County, OK, Sequoyah County, OK, Bowie County, TX, Camp County, TX, Cass County, TX, Harrison County, TX, Marion County, TX, Morris County, TX, Red River County, TX, Titus County, TX, Upshur County, TX
The radar
The Western Arkansas radar (KSRX), 139 km from the middle of the area, began a volume at 22:28 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
Shreveport, LA (KSHV), launched 12:00Z, 10.5 hours before the alert went out and 185 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.
- Mixed-layer CAPE
- 4 J/kg
- Mixed-layer CIN
- -179 J/kg
- Mixed-layer LCL
- 739 m above ground
- 0-6 km bulk shear
- 20 kt
- 0-1 km storm-relative helicity
- 182 m²/s²
- 0-3 km storm-relative helicity
- 210 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
859
ACUS11 KWNS 202228
SWOMCD
SPC MCD 202227
ARZ000-LAZ000-TXZ000-OKZ000-210030-
Mesoscale Discussion 0693
NWS Storm Prediction Center Norman OK
0527 PM CDT Thu May 20 2021
Areas affected...Arklatex and Vicinity
Concerning...Severe potential...Watch unlikely
Valid 202227Z - 210030Z
Probability of Watch Issuance...5 percent
SUMMARY...A brief and weak tornado may occur with a storm or two,
should they intensify late this afternoon and early evening. Storm
organization will be limited as will storm coverage. No WW is
expected.
DISCUSSION...A storm within Marion County, TX, has shown weak, but
persistent, low-level rotation on KSHV radar imagery. This storm has
intensified along a diffuse heating boundary where a few cloud
breaks have allowed temperatures to rise into the mid/upper 70s.
Furthermore, visible satellite shows a weak mesovortex propagating
northward along the Sabine River that could contribute to storm
development. Low-level shear is sufficient for weak rotation and
perhaps a brief tornado. Deep-layer shear, however, is rather
marginal as flow aloft is nearly southerly. A narrow window for
storm development/intensification will exist before the boundary
layer begins to stabilize this evening. Cloud cover and subsidence
in the wake of an earlier MCV will limit development to the west
with precipitation/cooler temperatures similarly limiting areas to
the east. Marginal thermodynamics and limited storm coverage will
likely mean no WW will be necessary this evening.
..Wendt/Dial.. 05/20/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LZK...SHV...TSA...
LAT...LON 32779500 34369543 35759515 36219440 35859365 34369340
33269380 32609396 32459465 32779500Nearby
Mesoscale Discussions in Arkansas, 2021Mesoscale Discussions in Texas, 2021Mesoscale Discussions in Oklahoma, 2021Every 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.