Mesoscale Discussion 568

Issued

May 9, 2021, 12:14 PM CDT (17:14 UTC)

Expired

May 9, 2021, 1:45 PM CDT

In force

91 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

80%

The Little Rock radar (KLZK), 129 km from the middle of the area, began a volume at 17:15 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.

• Severe Thunderstorm Watch 157May 9, 1:15 PM CDT
• Severe Thunderstorm Watch 158May 9, 2:25 PM CDT
• Severe Thunderstorm Watch 159May 9, 3:00 PM CDT

885 
ACUS11 KWNS 091715
SWOMCD
SPC MCD 091714 
TNZ000-MSZ000-MOZ000-ARZ000-LAZ000-TXZ000-OKZ000-091845-

Mesoscale Discussion 0568
NWS Storm Prediction Center Norman OK
1214 PM CDT Sun May 09 2021

Areas affected...Northeast TX...Far southeast OK...Much of
AR...Northern LA/MS...Western TN

Concerning...Severe potential...Watch likely 

Valid 091714Z - 091845Z

Probability of Watch Issuance...80 percent

SUMMARY...Severe thunderstorm development is expected this afternoon
along a cold front. Watch issuance is likely by 18-19Z. Very large
hail, damaging winds, and a couple of tornadoes will be possible.

DISCUSSION...At 17Z, a cold front draped from the Ozarks region into
north TX is moving eastward, with an outflow boundary located across
northern AR. Elevated thunderstorm activity has been ongoing north
of the outflow boundary across far northern AR, and also across
portions of east TX/northwest LA, and separately across northern MS.
Some threat for marginally severe hail will persist in the short
term with this elevated activity. 

The greater severe threat is expected to evolve later this
afternoon, near/south of the outflow boundary and along and east of
the advancing cold front, where moderate-to-strong instability and
sufficient deep-layer shear will favor the potential for organized
convection, including a few supercells. 

Very steep midlevel lapse rates (noted in 12Z observed soundings)
will support a threat of hail (potentially significant) with any
semi-discrete supercells that can develop. Cell mergers and linear
forcing along the cold front will likely result in some
upscale-growing clusters later this afternoon, with a corresponding
risk of damaging winds. Low-level flow/shear will tend to weaken
with time, especially across the western portion of the threat area,
but some tornado threat will be present with any stronger supercell
this afternoon, especially over the Ark-La-Miss vicinity. 

Some uncertainty remains regarding the timing of surface-based
initiation, but issuance of one or more watches is likely by 18-19Z
as development becomes increasingly likely with time this afternoon.

..Dean/Thompson.. 05/09/2021

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

ATTN...WFO...MEG...JAN...LZK...SHV...HGX...FWD...

LAT...LON   34009472 34259437 34489401 34799358 35199304 35489268
            36029208 36159071 36118915 36088809 34598835 33418962
            32799073 32299171 31669285 31229505 31269637 31999677
            32529662 33179591 33529534 34009472

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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.