Mesoscale Discussion 1582

Issued

Aug 23, 2021, 2:56 PM CDT (19:56 UTC)

Expired

Aug 23, 2021, 5:00 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

Counties Aurora County, SD, Brule County, SD, Buffalo County, SD, Charles Mix County, SD, Gregory County, SD, Jones County, SD, Lyman County, SD, Mellette County, SD, Todd County, SD, Tripp County, SD

The North Platte radar (KLNX), 193 km from the middle of the area, began a volume at 19:57 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Severe Thunderstorm Watch 458Aug 23, 5:20 PM CDT

048 
ACUS11 KWNS 231957
SWOMCD
SPC MCD 231956 
SDZ000-NEZ000-232200-

Mesoscale Discussion 1582
NWS Storm Prediction Center Norman OK
0256 PM CDT Mon Aug 23 2021

Areas affected...Parts of south central South Dakota and adjacent
north central Nebraska

Concerning...Severe potential...Watch possible 

Valid 231956Z - 232200Z

Probability of Watch Issuance...40 percent

SUMMARY...Isolated supercell development, posing a risk for large
hail and strong downbursts, is possible across parts of south
central South Dakota, including areas near or south of Pierre,
through 4-6 PM CDT. It is not yet certain that a severe weather
watch will be needed, but trends are being monitored for this
possibility.

DISCUSSION...Deepening convective development is evident southeast
of Philip, SD, near a zone of enhanced low-level confluence and
convergence, within general surface troughing encompassing much of
the Great Plains.  This is also near the southwestern flank of a
low/mid-level wind shift, which demarcates the northern fringe of
deeper low-level moisture/higher precipitable water, which is
forecast to begin returning northeastward late this afternoon.  

The higher moisture content is contributing to sizable CAPE on the
order of 2000-3000 J/kg, beneath warm and capping elevated
mixed-layer air.  With mid-levels temperatures tending to warm above
the retreating low-level wind shift, it is not certain that ongoing
attempts at deep convective development will be able to overcome
mid-level inhibition.  However, forcing aloft associated with an
upstream perturbation emanating from the Rockies could provide
additional support for this during the next few hours.  

If thunderstorm development is able to initiate and be maintained,
deep-layer shear, beneath a 30-40+ kt west-southwesterly 500 mb jet
streak propagating across the region, is strong and supportive of
supercells capable of producing large hail and strong downbursts.

..Kerr/Dial.. 08/23/2021

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

ATTN...WFO...FSD...ABR...LBF...UNR...

LAT...LON   43970157 44339968 43769813 42939879 43020103 43970157

Mesoscale Discussions in South Dakota, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.