South Dakota Mesoscale Discussion

Areas affected…southeast WY…western NE Panhandle…far northern
CO

Concerning…Severe potential…Watch possible

Valid 202030Z – 202130Z

Probability of Watch Issuance…60 percent

SUMMARY…Isolated storms are forecast to develop over the next 1-3
hours. Storm coverage will likely increase during the evening.
Large to very large hail is possible with any supercell developing
in the moist axis over southeast WY and the NE Panhandle.
Elsewhere, microbursts (isolated severe gusts) associated with
high-based thunderstorms are possible.

DISCUSSION…Visible satellite imagery shows convective initiation
occurring near the WY/NE/SD border with a separate area of agitated
cumulus located east of the Front Range in far northern CO. Despite
neutral to weak mid-level height rises, low-level upslope flow and
strong heating are contributing to storm development over the
central High Plains.

Forecast soundings indicate effective shear supportive of supercells
but becoming more marginal with southward extent. Very steep
700-500mb lapse (9-9.5 deg C/km) rates sampled by the Denver and
North Platte raobs this morning will favor hail growth and downdraft
potential with stronger storms. A severe thunderstorm watch will
likely need to be considered before storms are expected to increase
in coverage with several of these likely becoming severe.

..Smith/Thompson.. 08/20/2019

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

ATTN…WFO…UNR…BOU…CYS…

LAT…LON 42860478 43080441 42930319 41230330 40650391 40740504
42860478

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