South Dakota Mesoscale Discussion

Areas affected…Portions of central/southern SD and
northern/central NE

Concerning…Severe Thunderstorm Watch 620…621…

Valid 260605Z – 260700Z

The severe weather threat for Severe Thunderstorm Watch 620, 621

SUMMARY…Severe, damaging wind gusts will likely remain the primary
threat across Severe Thunderstorm Watches 620 and 621 in the short
term. The greatest severe risk will be with a small bowing cluster
in northern/central Nebraska.

DISCUSSION…Storms have congealed into a broken line along/ahead of
a surface front from central SD southward into parts of northern NE.
These storms are being supported by a convectively augmented
shortwave trough moving eastward across the northern Plains. A
veering wind profile with height through low/mid levels and the
presence of a 55-60 kt mid-level jet is providing ample shear to
support storm organization. Latest objective analysis suggests this
ongoing activity is moving across a relative maximum in instability,
which is located in a narrow north-south corridor from south-central
SD into parts of northern/central NE. Mid-level lapse rates quickly
weaken with eastward extent in SD/NE, as shown by the 00Z sounding
from OAX. Low-level moisture also gradually decreases from central
into eastern NE per recent surface observations. Strong to severe
winds will likely remain the primary threat in the short term given
a linear storm mode dominating. The small cluster moving quickly
southeastward around 40 kt across northern/central NE should have
the greatest potential to produce severe winds. Current expectations
are for these storms to slowly weaken as they move eastward into a
progressively less unstable airmass. Downstream watch issuance may
not be needed if this weakening trend occurs as expected.

..Gleason.. 08/26/2019

…Please see for graphic product…


LAT…LON 41660150 42090160 43180129 43560107 43920098 44320079
44360039 44019972 42839843 41999860 41259924 41200025

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