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ACUS11 KWNS 231217
SWOMCD
SPC MCD 231217
ALZ000-TNZ000-MSZ000-ARZ000-231415-

Mesoscale Discussion 0835
NWS Storm Prediction Center Norman OK
0717 AM CDT Sat Jun 23 2018

Areas affected...Far eastern Arkansas...northern Mississippi...and
northern Alabama

Concerning...Severe potential...Watch possible

Valid 231217Z - 231415Z

Probability of Watch Issuance...40 percent

SUMMARY...Long-lived thunderstorm cluster continues to move across
east-central Arkansas this morning. Additional thunderstorms to the
east, across northeast Mississippi and northern Alabama, continue to
increase in intensity and coverage. Hail and gusty winds will be
possible with both clusters of thunderstorms. Trends will be
monitored for a potential Severe Thunderstorm Watch.

DISCUSSION...Long-lived quasi-linear convective system (QLCS)
continues to maintain its intensity, or even slightly strengthen,
this morning as it moves along and south of I40 in eastern Arkansas. Additionally, to the east of this cluster of thunderstorms, another
cluster of thunderstorms continues to slowly intensify and increase
in coverage this morning across northeast Mississippi and northern
Alabama.

The QLCS across Arkansas continues to be fed by lower-tropospheric
theta-e advection as it traverses along the cool side of the theta-e
gradient, Farther east, the theta-e gradient becomes more diffuse,
with the ongoing thunderstorms across northeast Mississippi and
northern Alabama being in a relative theta-e minimum. Considerable
uncertainty remains with how these two distinct areas of convection
will interact and evolve this morning. Overnight thinking was that
the QLCS would eventually weaken this morning and thunderstorms
farther east would develop later. However, observations hint at the
development of a mesocale convective vortex within the parent
mesoscale convective system across Arkansas. This would suggest the
QLCS may persist through the morning and into the afternoon. This
idea is supported by the latest HRRR runs. Isolated large hail and
strong thunderstorm wind gusts would be the primary threat.

The thunderstorm cluster to the east of the QLCS is likely being
aided by warm-air advection, which may result in an isolated severe
hail or wind report, but the activity may decrease in intensity
later this morning as warm-air advection weakens. However if the
ongoing thunderstorms can develop a cold pool, they may become
better organized allowing them to persist into the afternoon and
pose a longer hail/wind threat.

Given the uncertainty in spatio-temporal evolution of the organized
severe threat, trends will continue to be monitored for possible
watch issuance.

..Marsh/Guyer.. 06/23/2018

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

ATTN...WFO...BMX...HUN...MEG...JAN...LZK...

LAT...LON 34039138 34719155 35279146 35219078 35058836 34128615
33438597 33328751 34039138



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