Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 212015
SPC MCD 212015

Mesoscale Discussion 0482
NWS Storm Prediction Center Norman OK
0315 PM CDT Mon May 21 2018

Areas affected...Parts of the mid Ohio Valley

Concerning...Severe potential...Watch possible

Valid 212015Z - 212115Z

Probability of Watch Issuance...40 percent

SUMMARY...Thunderstorms will continue to develop across
southern/central Indiana this afternoon, before moving into western
Ohio this evening. A few could become severe, with a primary threat
of damaging winds. Trends will be monitored for possible watch

DISCUSSION...Aided by broad/modest forcing for ascent along the
southeastern fringe of stronger southwesterly mid/upper flow, a
corridor of more vigorous convection has organized from western
Kentucky to southern Indiana late this afternoon. These cells appear
to be focused by differential heating on the edge of a mid/upper
cloud canopy associated with a warm-advection corridor ahead of the
primary cyclone. Regardless, cells over Kentucky are likely too far
south for sufficient organization (owing to weaker flow aloft) to
pose a sustained severe threat. Visible satellite data are
consistent with this conclusion, in that they show rather circular
anvil evolution, which would suggest weak mid/upper storm-relative

Farther north, although mixed-layer buoyancy is not as robust, weak
southerly warm/moist advection and adequate insolation are yielding
upwards of 500-1000 J/kg at present. Mid-level flow is slightly
stronger than points farther south as well, and recent KIND VWP data
sampled bulk 0-6km shear of 30-35 kt. Therefore, the strongest cells
may organize into occasional multicell or weak supercell structures
(especially as they reach greater boundary-layer moisture near the
IN/OH border) through early evening. Thereafter, an evolution into
localized bowing segments is possible, given relatively straight
hodographs. Such evolution would promote a few damaging gusts as the
primary threat, and convective trends will be monitored for possible
watch issuance.

..Picca/Weiss.. 05/21/2018

...Please see for graphic product...


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