516
ACUS11 KWNS 171812
SWOMCD
SPC MCD 171811
MNZ000-IAZ000-NEZ000-SDZ000-172015-

Mesoscale Discussion 0749
NWS Storm Prediction Center Norman OK
0111 PM CDT Sun May 17 2026

Areas affected...southeast SD...northeast NE...northwest IA...and
southwest MN

Concerning...Severe potential...Tornado Watch likely

Valid 171811Z - 172015Z

Probability of Watch Issuance...95 percent

SUMMARY...Severe potential will increase over the next couple of
hours across southeast South Dakota and northeast Nebraska into
adjacent portions of Minnesota and Iowa. A substantial all-hazards
severe risk is expected by mid-afternoon into this evening. Very
large hail to 3.5 inch diameter, strong tornadoes, and intense wind
gusts to 90 mph appear likely. A tornado watch will likely be issued
by 19z to 20z.

DISCUSSION...A cluster of elevated convection is ongoing across
north-central NE ahead of the surface cold front. The downstream
airmass is quickly destabilizing as rich boundary-layer moisture
(mid to upper 60s F dewpoints) spreads north and west amid strong
heating. Immediately downstream from the ongoing thunderstorm
cluster, latest mesoanalysis indicates weakening midlevel capping.
This is supported by increasing cumulus from Brown to Knox and
Antelope Counties in NE in the vicinity of a quasi-stationary
boundary/warm front. Increasing midlevel southwesterly flow is
evident in the past couple of hours on region VWP. This trend should
continue, with additional strengthening of low-level flow in
response to surface pressure falls. Vertically veering wind profiles
with 40+ kt effective shear magnitudes within moderate to strong
instability (by mid/late afternoon) will support robust supercell
development within the warm sector on the nose of the midlevel dry
slot across the northeast NE vicinity. Discrete supercells will pose
a risk for very large hail, strong tornadoes, and damaging wind
gusts.

Additional linear convection is expected along the cold front,
particularly across SD into southern MN. Given favorable low-level
shear, line-embedded cells/mesovortices will pose a tornado risk
even in linear convection. As linear convection organizes and a
low-level jet increases toward late afternoon into the evening, a
substantial damaging wind risk may evolve.

..Leitman/Mosier.. 05/17/2026

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

ATTN...WFO...DMX...FSD...OAX...GID...LBF...UNR...

LAT...LON   41509588 41419680 41489786 41779924 42209988 42570005
            42989990 43169978 43529913 44229752 44329681 44329625
            44229587 43959537 43419522 42589536 41979555 41509588

MOST PROBABLE PEAK TORNADO INTENSITY...120-145 MPH
MOST PROBABLE PEAK WIND GUST...75-90 MPH
MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN