South Dakota Mesoscale Discussion

Areas affected…Parts of far southern South Dakota into eastern

Concerning…Severe potential…Watch unlikely

Valid 202248Z – 210045Z

Probability of Watch Issuance…5 percent

SUMMARY…A few instances of damaging wind gusts and marginally
severe hail are possible over the next few hours. Given the isolated
and marginal nature of the severe threat, a WW issuance is not
expected at this time.

DISCUSSION…As a vertically stacked low continues to slowly
propagate eastward, marginally adequate low-level moisture to
support convection will continue to advect northwestward within a
confluence zone, immediately ahead of a cold front. Frontogenetic
forcing, along with appreciable upper-level divergence (with the
region being under the left exit region of a 300 mb jet streak) will
provide ample deep-layer ascent to support widespread convective
development along the cold front, with initiation now underway along
the NE/SD border.

The latest RAP forecast soundings depict low-level directional shear
within the sfc-700 mb layer, with a more unidirectional wind profile
exhibiting modest speed shear aloft. 8 C/km mid-level lapse rates,
generated by an eastward advecting cold pocket aloft associated with
the stacked low, will also accompany the aforementioned shear
profile. As such, a broken band of linear segments and semi-discrete
cells is expected to evolve over the next few hours. Some
hail/damaging wind gusts may accompany the stronger storms given the
steep lapse rate environment. Given the overall mediocre low-level
moisture/buoyancy, the severe threat is expected to remain isolated
and brief in nature, precluding a WW issuance.

..Squitieri/Grams.. 10/20/2019

…Please see for graphic product…


LAT…LON 42439850 42509858 43249874 43439852 43529804 43249701
43049685 42129602 41269559 40809557 40749624 40789714
40989772 41529830 42439850

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