South Dakota Mesoscale Discussion

Areas affected…Parts of eastern Wyoming…southwestern South
Dakota and northwestern Nebraska

Concerning…Severe potential…Watch unlikely

Valid 150729Z – 150930Z

Probability of Watch Issuance…20 percent

SUMMARY…A relatively isolated, but intense storm probably will
continue to pose at least a localized severe hail and wind threat
across northern portions of the Nebraska panhandle through daybreak.
Barring further upscale growth, it is not certain that a watch is
needed, but trends will continue to be monitored.

DISCUSSION…A number of generally low amplitude mid/upper waves
appear to be progressing through broader-scale anticyclonic
mid/upper flow across the northern Rockies and Plains. In
association with one of these perturbations, forcing for ascent
appears to be aiding ongoing thunderstorm development now south of
the Black Hills, near the western Nebraska/South Dakota border area.

The strongest convection, mainly limited to an isolated but
sustained supercell, has been confined to areas west/southwest of
the Black Hills during the past few hours, aided by inflow of
moderate CAPE of 1500-3000 J/kg, in the presence of steep
lower/mid-tropospheric lapse rates. Large-scale forcing for ascent
associated with warm advection along a tightening mid-level thermal
gradient (roughly around 700 mb) also appears to be providing
support for this storm. This front extends east-southeastward
across northern portions of the Nebraska panhandle, and may provide
a continuing focus and support for the maintenance of intense
convective development into areas northeast of Alliance NE through

Reflectivity associated with the isolated supercell has recently
transitioned to more of a bowing structure, in the presence of
strong deep-layer shear, likely accompanied by at least localized
strong to severe surface gusts. This threat may continue, along
with a risk for severe hail through daybreak.

..Kerr/Thompson.. 08/15/2019

…Please see for graphic product…


LAT…LON 43660482 43610386 43290276 42800174 42210127 41830188
42040296 42330354 42730405 43250463 43660482

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