000
ACUS11 KWNS 220046
SWOMCD
SPC MCD 220046
NDZ000-SDZ000-220215-

Mesoscale Discussion 1386
NWS Storm Prediction Center Norman OK
0746 PM CDT Fri Jul 21 2017

Areas affected...Western into southeast ND...North-central SD

Concerning...Severe Thunderstorm Watch 428...

Valid 220046Z - 220215Z

The severe weather threat for Severe Thunderstorm Watch 428
continues.

SUMMARY...The severe threat continues in and near WW 428. A
conditional threat also exists further north near the international
border.

DISCUSSION...Convection across the western portion of WW 428 has
thus far been more isolated compared to areas further east, but a
few stronger cells have recently evolved across far south-central ND
into north-central SD. Buoyancy and shear across the region are
sufficient for supercell development, and a threat of large hail and
locally damaging winds will persist for the next 1-2 hours with the
strongest discrete cells. Later this evening, increasing SBCINH will
result in a weakening trend for any remaining discrete cells, though
any clusters that grow somewhat upscale may persist a little longer
with an attendant threat for locally damaging wind.

Additional convection just outside of WW 428 across McLean and
Mercer counties has thus far failed to intensify, but a conditional
wind/hail risk will exist if any supercell can evolve from that
activity.

Meanwhile, further north toward the international border, the
airmass north of a surface boundary has largely been unaffected by
convection further to the south, and moderate buoyancy has
developed, with MLCAPE in the 1500-2500 J/kg range per recent
mesoanalyses. Easterly flow at the surface veering to westerly aloft
is resulting in effective shear of 45-55 kt, more than sufficient
for supercells. A cluster of strong storms is ongoing near the
international border now and may persist for awhile this evening,
with a corresponding threat of severe hail/wind and perhaps a
tornado.

..Dean.. 07/22/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FGF...FSD...ABR...BIS...UNR...

LAT...LON   44219983 45530198 47620245 48510267 49040253 48989847
            48389842 48039993 47139987 47169857 47209730 46079758
            44919872 44189866 44219983