[BNAWX] Severe Storm Outlook Narrative

[EMWIN Server]

ACUS11 KWNS 201759
SWOMCD
SPC MCD 201758
KYZ000-TNZ000-INZ000-ILZ000-MOZ000-ARZ000-201900-

Mesoscale Discussion 1101
NWS Storm Prediction Center Norman OK
1258 PM CDT Fri Jul 20 2018

Areas affected...Southeast MO...Southern IL...Southwest
KY...Northwest TN

Concerning...Severe potential...Watch likely

Valid 201758Z - 201900Z

Probability of Watch Issuance...80 percent

SUMMARY...Severe thunderstorm development expected soon. Primary
severe threats are very large hail and damaging wind gusts. Watch
will be needed to cover this anticipated threat.

DISCUSSION...Visible satellite imagery shows increasingly agitated
cumulus along the cold front in southeast MO and southern IL.
Mesoanalysis and modified forecast soundings indicate convective
inhibition currently remains in place across much of this area.
However, continued heating and moisture advection will likely erode
any remaining capping soon. Once this occurs, forcing provided by
the front as well as increasing large-scale forcing for ascent
provided by the approaching shortwave trough will result in rapid
thunderstorm development. Strong instability (i.e. MLCAPE over 3000
J/kg) is anticipated across the downstream airmass, supportive very
strong updrafts. Additionally, given the strong northwesterly flow
aloft and resulting strong vertical shear, updraft organization
appears probable.

All of these factors suggest a threat for very large hail and strong
wind gusts exists. Hail threat will likely be confined to the first
hour or so of development with upscale growth then contributing to a
enhancement of the damaging wind potential. Additionally, favorable
low-level moisture and strong vertical shear suggest a tornado
cannot be ruled out.

..Mosier/Hart.. 07/20/2018

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

ATTN...WFO...LMK...OHX...PAH...MEG...LSX...

LAT...LON   35989031 36649103 37189086 37559021 37688914 38068756
            37848677 36368698 35989031
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