South Dakota Mesoscale Discussion

Areas affected…Southwest South Dakota…Northwest Nebraska…Far
Eastern Wyoming

Concerning…Heavy rainfall…Flash flooding possible

Valid 102051Z – 110230Z

Summary…Flash Flooding is possible this afternoon and early
evening as convection becomes better organized over portions of
southwest South Dakota, the northern Nebraska panhandle and
northwest Nebraska, and far eastern Wyoming.

Discussion…Satellite imagery showed convection developing along
and near the Pine Ridge in the Nebraska panhandle early this
afternoon. Convection capable of producing locally heavy rainfall
later today becomes more likely as low level winds back and
accelerate in response to an approaching trough from the west. By
00Z, the RAP and the ARW2 both show the nose of a Precipitable
Water maximum getting drawn westward in response to the low level
wind field. The maximum PW values are forecast to increase to
between 1.00 inches and 1.25 inches, which is roughly 2
standardized anomalies above climatology for this time of year.
As a result, the expectation is that as moisture deepens during
the afternoon and the Convective Inhibition weakens that
convection will be capable of producing locally heavy rainfall
over an area where the 1- and 3-hour flash flood guidance was only
on the order of 1 to 1.5 inches. The threat for excessive
rainfall is expected to continue beyond 0230Z.


…Please see for graphic product…



LAT…LON 44320351 44190205 44010082 43789995 43299974
42479986 42020252 42240475 42940492 43330475
43730458 44090424

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