MD 1350 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR THE WESTERN DAKOTAS INTO NORTHWEST NEBRASKA
Mesoscale Discussion 1350
NWS Storm Prediction Center Norman OK
0219 PM CDT Sat Jun 27 2026
Areas affected...the western Dakotas into northwest Nebraska
Concerning...Severe potential...Watch likely
Valid 271919Z - 272145Z
Probability of Watch Issuance...95 percent
SUMMARY...Severe thunderstorm development is expected to become
increasingly likely by 21-22Z. All severe weather hazards are
possible, including large to very large hail in excess of two
inches, a strong tornado or two, and damaging winds with gusts of
80+ mph. A Tornado Watch is likely.
DISCUSSION...A surface low currently analyzed northeast of Gillette,
WY, is forecast to develop into northwest SD by late afternoon or
early evening with an associated trough or pseudo-dryline moving
into western parts of SD and the Nebraska Panhandle. The observed
18Z UNR sounding is a good representation of the warm sector ahead
of those surface features with a pronounced EML and associated cap
atop a relatively shallow moist layer. The cap is expected to
inhibit surface-based thunderstorm development for the next couple
of hours.
Current water vapor imagery shows a cirrus streak and related
mid-level convection moving into southern and central parts of WY,
indicative of strong forcing for ascent within the exit region of
mid/upper-level wind maxima moving through the Great Basin. That
forcing for ascent is expected to overspread the discussion area
late this evening, effectively eroding the cap and allowing for
widely scattered thunderstorm development amidst a moderate to
strongly unstable environment.
Steadily strengthening deep-layer shear will support supercells as
the initial storm mode with the primary hazard being large to very
large hail. Low-level shear is forecast to strengthen this evening
in the vicinity of the surface low in northwest SD and southwest ND
with a conditional threat for a strong tornado or two. However,
there is some uncertainty in convective mode at that time as
deep-layer shear vectors tend to back to a more northerly direction
in the vicinity of a stalled surface front along the MT border,
which will be conducive for mixed storm modes.
By late evening into tonight, latest short-term guidance indicates
the evolution of a bow echo across western into central ND with more
discrete storms persisting over western into central SD. Swaths of
destructive winds with gusts of 80+ mph appear likely with the bow
echo, while large hail and some tornado potential will exist with
the SD storms.
Storm initiation farther south into western NE remains uncertain.
However, if a storm or two can develop, the environment will support
a large to very large hail threat and perhaps a tornado.
..Mead/Guyer.. 06/27/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...ABR...BIS...LBF...UNR...
LAT...LON 43470266 44330345 46580382 48360401 49070348 49050194
47120107 44260079 42530127 42680260 43470266
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
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