Scattered to numerous severe thunderstorm gusts (some 75+ mph), large hail and a few tornadoes are expected over parts of the eastern Dakotas, eastern Nebraska, western Iowa, and central/southern Minnesota this afternoon into tonight.
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Other severe storms are expected across the southern Plains and Lower Mississippi Valley.
Severe gusts ranging from 60-100 mph are possible in the short-term over NE into southeast SD over the next several hours.
In general, scattered to numerous thunderstorms are expected to develop in an arc near the surface low and cold front by mid/late afternoon, from central/eastern South Dakota southward across central/eastern Nebraska and into at least northern Kansas.
A brief interval, early in the convective cycle, may support discrete to semi-discrete supercells before the convection becomes quasi-linear.
The most common severe type should evolve quickly to thunderstorm gusts through early evening some of which may be significant (65+ kt) strength, especially from parts of eastern South Dakota and southeast North Dakota into western Minnesota.
The warm sector is forecast to destabilize throughout the day, with a combination of at least weak large-scale ascent (increasing northward), diurnal heating and related lift from below, and ultimately frontal convergence, eliminating a basal EML inversion and supporting convection initiation.
Activity is expected to intensify quickly as it impinges on a narrow but very favorable prefrontal corridor where 60s to near 70 F surface dewpoints contribute to MLCAPE in the 3500-4500 J/kg range in and near the "moderate" area, decreasing gradually with southward extent as more low-level moisture is mixed out.
Low-level and deep shear will be greatest near the triple point and warm front across South Dakota, with 300-500 m2/s2 effective SRH and 45-55-kt effective-shear magnitudes.
A substantial component of mid/upper winds parallel to the axis of convective forcing indicates potential for fairly fast merging of early discrete and sporadically supercellular convection.
Surges of wind from resulting LEWP/bowing segments will pose the greatest overall severe hazard, with line-embedded mesovortices and perhaps a few associated tornadoes also possible.
With the warm sector's not being very broad, the convective event should diminish late this evening into early overnight hours as it outruns the most favorable instability. ■