SPC MD 1839
MD 1839 CONCERNING SEVERE THUNDERSTORM WATCH 557... FOR PORTIONS OF SOUTHEASTERN SOUTH DAKOTA INTO NORTHEAST NEBRASKA AND NORTHWESTERN IOWA

Mesoscale Discussion 1839
NWS Storm Prediction Center Norman OK
0730 PM CDT Tue Jul 29 2025

Areas affected...portions of southeastern South Dakota into
northeast Nebraska and northwestern Iowa

Concerning...Severe Thunderstorm Watch 557...

Valid 300030Z - 300200Z

The severe weather threat for Severe Thunderstorm Watch 557
continues.

SUMMARY...The severe gust threat should persist with the ongoing MCS
for at least a couple more hours. It is unclear how far southeast
the MCS will progress, so conditions will continue to be monitored
for the need of any downstream Severe Thunderstorm Watches.

DISCUSSION...A cold-pool-driven MCS, with a history of several
reported severe wind gusts, continues to gradually propagate to the
east-southeast over southeastern SD. Extreme buoyancy (i.e.
3000-5000 J/kg MLCAPE) precedes the MCS, but with marginal
deep-layer shear and weak low-level shear. As such, the MCS
continues to propagate forward at only 30 kts, with MRMS mosaic
radar data showing slight weakening trends (i.e. overall weaker
echoes exceeding 50 kft). It is unclear how far southeast the MCS
will propagate, especially since a residual northwest-to-southeast
oriented frontal boundary continues to push southwestward across the
MCS path with cooler and potentially more stable air. Nonetheless,
given existent strong to extreme buoyancy, MCS behavior will
continue to be monitored for the possible need of a downstream
Severe Thunderstorm Watch issuance.

..Squitieri/Mosier.. 07/30/2025

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

ATTN...WFO...DMX...FSD...OAX...LBF...

LAT...LON   43859779 43699654 43269549 42629510 42199521 41999570
            42029652 42189764 42389843 42499868 43859779 

MOST PROBABLE PEAK WIND GUST...65-80 MPH

Read more
https://www.spc.noaa.gov/products/md/md1839.html