South Dakota Mesoscale Discussion

Areas affected…Portions of South
Dakota…Minnesota…Iowa…Northeast Nebraska

Concerning…Heavy rainfall…Flash flooding possible

Valid 102255Z – 110345Z

Summary…There will be an increasing threat for flash flooding
over parts of eastern South Dakota, northeastern Nebraska into
adjacent portions of Minnesota and Iowa this evening. A
quasi-stationary front draped across northern Iowa will help focus
the activity as low level flow rides up and over the
boundary…with the potential for an MCS to develop later this

Discussion…Coverage of convection should be increasing during
the evening as storms move in from the west and from new
convection being formed in proximity of a quasi-stationary front
draped across northern Iowa into northeast Nebraska during the
evening. Low level flow should strengthen as an upper trough
approaches from the west. As a result, the low level will deepen
as shown by Precipitable Water values increasing to 1.5 inches or
greater…which is 1.5 to 2.5 standardized anomalies greater than
climatology for this time of the year The current expectation is
that convection along and north of the quasi-stationary boundary
will be elevated for a couple of hours this evening…with highest
rainfall rates gradually spreading from eastern South Dakota and
northeast Nebraska into Minnesota and Iowa late this evening.

The ARW core of the WRF…ARW 2.5 km and the HRRR seem to have a
reasonable handle on the evolution of the heavy rainfall threat
and are tending to keep the heaviest rainfall immediately along
and north of the boundary in the best gradient of MLCAPE and

Flash flood guidance ranges from 1.5 inches per 3 hours in central
South Dakota north of the Sand Hills…to near 2.5 inches in the
southwest portion of Minnesota and northeast Iowa. Given rainfall
rates perhaps reaching 2 inches per hour, these flash flood
guidance values may be reached or exceeded.


…Please see for graphic product…



LAT…LON 44589854 44269607 44059501 43599396 42999368
42639406 42429526 42059712 42189840 42589948
42970008 43959972

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