Mesoscale Discussion 1618
NWS Storm Prediction Center Norman OK
0355 PM CDT Fri Aug 27 2021
Areas affected...Northern High Plains
Concerning...Severe potential...Watch possible=20
Valid 272055Z - 272300Z
Probability of Watch Issuance...40 percent
SUMMARY...Isolated thunderstorm development is possible late this
afternoon into early evening. The strongest storms will be capable
of large hail and locally severe wind gusts.
DISCUSSION...An mid/upper-level trough is moving across Montana this
afternoon. Multiple vorticity maxima are evident on WV imagery
within the larger-scale trough, but a lobe of ascent appears to
moving across eastern MT, in conjunction with a weak surface
boundary, and gradually deepening cumulus is noted across southeast
MT. While surface temperatures are not particularly warm, relatively
cool midlevel temperatures are supporting SBCAPE of 750-1500 J/kg
(per recent mesoanalyses), with weakening SBCINH. Effective shear is
generally 30-40 kt across the region, with locally higher values
across northwest SD/southwest ND/southeast MT, where surface winds
are locally backed.=20
Isolated thunderstorm development is expected sometime late this afternoon/early evening, with the most likely area across northwest SD/southwest ND, where somewhat greater surface confluence is noted.
Long hodographs will favor a conditional potential for supercells,
with large hail and locally severe wind gusts the primary threats.
The need for a watch remains uncertain at this time, due to
potentially sparse storm coverage.
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