SPC AC 230058
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0758 PM CDT Sun Aug 22 2021
Valid 230100Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL AND NORTHERN PLAINS...
...SUMMARY...
Scattered strong to severe thunderstorms will move eastward across
the central and northern Plains this evening. A threat for large
hail and wind damage will likely accompany the stronger storms. An
isolated tornado threat will also exist across parts of eastern
South Dakota.
...Northern and Central Plains/Mid Missouri Valley...
A negatively-tilted upper-level trough and an associated 45 to 60 kt
mid-level jet are located across the northern Plains according to
water vapor imagery. At the surface, a moist airmass is in place
from Kansas northward into the eastern Dakotas. The RAP is analyzing
a corridor of moderate to strong instability along the moist axis,
with MLCAPE across eastern South Dakota estimated to be from 1500 to
3000 J/kg. Strong to severe thunderstorms are ongoing along this
corridor of instability. In addition to the instability, deep-layer
shear is strong across the northern Plains. The WSR-88D VWP at
Aberdeen currently has 0-6 km shear near 60 kt, with veering winds
with height in the lowest kilometer. This wind profile will be
favorable for supercells this evening. Low-level shear will continue
to increase this evening helping to maintain a tornado threat across
eastern South Dakota for a few more hours. Supercells will also be
capable of large hail and wind damage.
Moderate instability is also present in eastern North Dakota where
the RAP is estimating MLCAPE in the 1200 to 1500 J/kg range. A
cluster of strong to severe thunderstorms is ongoing in eastern
North Dakota along the eastern edge of the stronger instability.
This combined with strong deep-layer shear, associated with a
mid-level speed max, will continue to be favorable for supercells
associated with large hail and wind damage. An isolated tornado
threat will also be possible for another hour or so. The severe
threat is expected to impact western Minnesota later this evening
but weaker instability further east will make the severe threat more
isolated.
Further to the south into east-central Nebraska, a pocket of strong
instability is analyzed by the RAP, with MLCAPE in the 3000 to 4000
J/kg range. A cluster of strong to severe thunderstorms is ongoing
along the southern side of the stronger instability, from the
vicinity of Grand Island southward to near the Kansas state-line.
The WSR-88D VWP just to the east of the storm cluster has 0-6 km
shear near 40 kt and veering winds with height in the lowest 2
kilometers. This will be favorable for supercells this evening, with
a threat for large hail and wind damage. An isolated severe threat
could impact part of the mid Missouri Valley later this evening.
..Broyles.. 08/23/2021
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