Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 201806
SWOMCD
SPC MCD 201806
KYZ000-ILZ000-TNZ000-MOZ000-ARZ000-201930-

Mesoscale Discussion 1536
NWS Storm Prediction Center Norman OK
0106 PM CDT Sun Aug 20 2017

Areas affected...Southern Missouri...northern Arkansas...far
southwest Illinois...extreme west Kentucky...and far west Tennessee

Concerning...Severe potential...Watch unlikely

Valid 201806Z - 201930Z

Probability of Watch Issuance...5 percent

SUMMARY...Thunderstorms are developing within a very unstable
environment. These thunderstorms should persist through the
afternoon posing a threat for strong, gusty winds and isolated hail.

DISCUSSION...Surface temperatures in the low-to-mid 90s and dewpoint
temperatures around 80F have contributed to a very unstable airmass
across portions of northeast Arkansas and southern Missouri.
Thunderstorms initially developed across south-central Missouri,
then farther southeast along a weak convergence zone extending from
south-central Missouri into southwest Tennessee, but are now also
developing northeast toward southern Illinois, along the residual
outflow boundary from an overnight mesoscale convective system.
Despite weak deep-layer shear across the area, extreme instability
(most-unstable CAPE around/above 5000 J/kg), coupled with
precipitable water values approaching 2 inches, will yield a
potential for (primarily) strong downburst/outflow winds, although
some hail cannot be ruled out. Weak steering flow suggests that
overall storm motion and new development will be driven primarily by
propagation along outflow boundaries and outflow boundary
interactions. The isolated/brief/spotty nature of the threat should
preclude the need for a watch.

..Marsh/Grams.. 08/20/2017

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

ATTN...WFO...PAH...MEG...LSX...LZK...SGF...TSA...

LAT...LON   35078997 35159160 35639340 36499368 37349334 37889128
            38299001 38228988 37768894 36518869 35688909 35078997



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