South Dakota Mesoscale Discussion

Areas affected…Parts of southeast Montana into extreme southwest
North Dakota…far northeast Wyoming…western South
Dakota…extreme northwest Nebraska

Concerning…Severe potential…Watch unlikely

Valid 012209Z – 020015Z

Probability of Watch Issuance…5 percent

SUMMARY…A couple storms may sustain themselves during the
afternoon hours. Organized storms may pose a large hail and damaging
wind threat. The very isolated coverage suggests that a WW issuance
is not currently warranted.

DISCUSSION…Isolated strong to severe storms have developed in
Custer County, MT over the past hour or so, despite convection
failing to become sustained earlier along the buoyancy axis (mainly
along the WY/SD border). Peak afternoon heating and weak vertical
ascent associated with a weak vorticity max cresting the ridge in
western ND are supporting this more recent, successful attempt at
convection. Should this storm or any other cell become established
across the discussion area, ample instability (1500 J/kg MLCAPE)
and deep-layer shear (around 50 knots of bulk effective shear) is in
place to foster the development of highly organized multicellular
clusters or perhaps supercells. Given relatively steep mid-level
lapse rates (7 C/km), and potential for mid-level rotation, some of
the more organized cells may produce large hail in addition to
damaging wind gusts.

Nonetheless, deep-layer ascent is quite weak across the area (as
supported by the 12Z HREF and the last several runs of the HRRR),
with low confidence in a substantial increase in convective coverage
through the early evening hours. As such, a WW issuance is not

..Squitieri/Edwards.. 09/01/2019

…Please see for graphic product…


LAT…LON 44340538 45750661 46400630 46410509 46080308 45700258
44700190 44130182 43330185 42870214 42770286 42950393
43320464 44340538

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