- Day Three
acus03 kwns 210938
Storm Prediction Center ac 210937
Day 3 convective outlook resent 1
National Weather Service Storm Prediction Center Norman OK
0437 am CDT Tue Aug 21 2018
Valid 231200z - 241200z
..there is a slight risk of severe thunderstorms across eastern South Dakota
and far southwest Minnesota...
Severe thunderstorms are possible across eastern South Dakota and
far southwest Minnesota on Thursday afternoon and evening.
A shortwave trough is expected to progress across the
northern/Central Plains on Thursday while downstream shortwave
ridging moves across the upper Great Lakes. Another shortwave trough
will likely move into the Pacific northwest late Thursday
night/early Friday morning while largely stationary ridging across
the southern third of the Continental U.S. Gradually begins to dampen.
At the surface, a low attendant to the northern/Central Plains
shortwave trough will move just ahead of its parent upper system. As
it does, surface troughing will also pushing eastward, with
resulting dryline separating the warm and drier air emanating from
the High Plains with the more moist air from the Southern Plains and
..northern/Central Plains...Upper/Middle MO valley...
moderate moisture return is anticipated across the region ahead of
the approaching shortwave trough and its attendant surface low.
There is some chance this moist advection is impeded by ongoing
showers and thunderstorms across Kansas but the consensus amongst the
most recent guidance is that mid 60s dewpoints will extend across
far north as the NE/South Dakota border by Thursday afternoon. Combination of
this increased low-level moisture, surface convergence, and ascent
from the approaching shortwave will likely lead to thunderstorm
development over central South Dakota Thursday afternoon. Expectation would be
for these thunderstorms to then track southeastward towards
southeast South Dakota and vicinity along the instability gradient. Steep
mid-level lapse rates and moderate vertical shear result in the
potential for these storms to be organized and capable of severe
hail and/or strong wind gusts. Severe coverage is expected to be
high enough across eastern South Dakota to merit a slight risk.
For areas farther south (i.E. Central/eastern ne), despite favorable
low-level moisture, warm mid-level temperatures and displacement
south of the stronger forcing for ascent will likely keep the warm
sector free of convection. An isolated storm or two is possible in
area of strong surface convergence and the airmass is supportive of
a severe threat if an updraft can persist.
..north-Central/Northeast Kansas...Lower MO valley...
on Thursday evening, a strengthening low-level jet is expected to
lead to increased warm-air advection atop the outflow left by
antecedent thunderstorms. Current guidance suggests this warm-air
advection will be enough to lift parcels to their lfcs, leading to
the development of showers and thunderstorms. Isolated severe hail
is possible within the strongest cells.