Mesoscale Discussion 1005
NWS Storm Prediction Center Norman OK
0314 AM CDT Wed Jul 04 2018
Areas affected...northern South Dakota
Concerning...Severe Thunderstorm Watch 262...
Valid 040814Z - 040945Z
The severe weather threat for Severe Thunderstorm Watch 262
SUMMARY...Strong-to-severe thunderstorm wind gusts will remain
possible across portions of northern South Dakota for another 2-3
hours. This threat may require an extension in space and time of
Severe Thunderstorm 262 across far northeast South Dakota.
DISCUSSION...Initial isolated thunderstorm across Wyoming last
evening has grown upscale into a linear mesoscale convective system
(MCS) as it moved across South Dakota. As it did so, a measured 95
mph wind gust was recorded by the Mobridge, SD, ASOS station shortly
before 2AM CDT. Now, the South Dakota MCS has merged along the
southern end of a North Dakota MCS. The combined MCS continues to
move east, and will continue to do so through the morning.
The environment along and ahead of the MCS remains unstable with
most-unstable CAPE values in excess of 3000-4000 J/kg. Deep-layer
shear is sufficient for updraft maintenance, however, at 30-35
knots, is somewhat lower than farther north. Additionally, with
time, increasing surface-based convective inhibition associated with
a deepening nocturnal boundary layer should begin to limit the
potential for severe wind damage to reach the surface, and,
ultimately lead to a weakening in the convective intensity. In any
event, this environment should allow for another 2-3 hours of severe
potential, which would extend past the original expiration time of
Severe Thunderstorm Watch 262 and potentially to areas east of the
watch. As such, a small extension in space and time may be needed
before 10Z (5 AM CDT).
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 44000007 45120059 45859972 45899568 44179767 44000007