South Dakota Mesoscale Discussion

Corrected for SUMMARY

Areas affected…Eastern WY…Southwest SD…Western NE

Concerning…Heavy rainfall…Flash flooding possible

Valid 112215Z – 120345Z

SUMMARY…A broken line of heavy showers and thunderstorms with
intense rainfall rates will eject east across far eastern WY,
southwest SD and western NE through the evening hours. Given the
wet antecedent conditions across these areas, some enhanced runoff
and/or flash flooding will be possible.

DISCUSSION…The latest radar imagery shows an intensifying and
expanding line of heavy showers and thunderstorms across eastern
WY which is expected to eject east out across especially areas of
southwest SD (generally south of the Black Hills) and down across
western NE. The environment ahead of the convection is quite moist
and very unstable with PWATs of 1.2 to 1.4 inches, and MLCAPE
values of 2000 to 3000 j/kg. Shear profiles are increasing across
the region out ahead of the upper low/trough crossing the northern
Rockies, and effective bulk shear profiles are on the order of 30
to 40 kts, with the higher end of this situated over southwest SD.

Much of the area across southwest SD and down through western NE
has been quite wet over the last week, with rainfall totals as
much as 400 to 600 percent of normal. This has led to lower FFG
values as a result, and thus a greater sensitivity to heavier
rainfall rates.

The upstream convection will be capable of producing as much as 2
inches of in an hour or even less considering the PWAT environment
over the region which is locally over 2 standard deviations above
normal, and the degree of aforementioned instability/shear which
will facilitate organized and deep cold cloud-topped convection.

A look at the latest HRRR suggests the model may not have enough
convection across western NE when looking at the latest satellite
and radar trends, but in general the heaviest rainfall should be
over southwest SD and south of the Black Hills. Expect as much as
2 to 3 inches with isolated heavier amounts over the region going
through the evening. Given the wet antecedent conditions, some
enhanced runoff and/or flash flooding will be possible.


…Please see for graphic product…



LAT…LON 44000394 43980294 43740201 43410170 42960182
42330259 41840277 41480261 41400269 41430283
41560344 41640401 41560458 41520478 41520487
42060514 42680509 43150477 43740464

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