South Dakota Mesoscale Discussion

Areas affected…Northeast NE…Eastern SD…West-Central MN

Concerning…Heavy rainfall…Flash flooding possible

Valid 120706Z – 121306Z

Summary…Repeating rounds of thunderstorms over increasingly
saturated soils may lead to further flash flooding across portions
of eastern SD and southwest to western MN early this morning.
Additional rainfall totals of 2-3″ through 12Z are likely.

Discussion…Over the last several hours, there has been a gradual
northward jog with the better instability due to the strength of
the low-level jet and approach of an area of low pressure from
Nebraska. This has pushed the MUCAPE boundary northward into
east-central SD and southwest MN where values 1500-2000 J/kg exist
per the latest mesoanalysis. This aligns with the highest PWs,
with around 1.7 to 1.8″ exists based off the blended TPW product.
Radar imagery and GOES IR imagery continues to show that
deepening/intense convection around and north of FSD.

As the low tracks northeast, the strong frontogentical forcing
should keep rain rates in the 1-2″/hr range through the early
morning hours. MUCAPE is expected to remain up around 1000-1500
J/kg while the 850 mb moisture transport axis focuses on western
MN, eastern SD. All of the ingredients for heavy rainfall remain
in place through at least 12Z. The latest model guidance shows the
potential for an additional 2-3″ with locally 3-5″ totals

MRMS 6-hour precipitation analysis shows amounts of 2-4″ across
portions of northeast NE, southeast SD, and southwest MN. Local
higher amounts up to 4-5″ have been analyzed. As a result, flash
flood guidance continues to lower and with increasing saturated
soils, the additional rainfall will exacerbate the flooding


…Please see for graphic product…



LAT…LON 45609708 45279506 44559324 43639314 43819529
43269610 42279680 42139768 43619784 43879783

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