When the NWS issues tornado and severe thunderstorm warnings, they include a storm motion speed and direction (warning example). The featured chart summaries these storm motion vectors for tornado warnings issued by NWS Des Moines since mid 2007 (inception of implementation of this encoding). The warnings for the recent tornado outbreak on Friday are denoted with red crosses. The tricky part with understanding this plot is the storm motion direction. A value of south indicates a south to north movement or one might say "from the south". Anyway, the storm motions on Friday were mostly within the most common direction and speed combinations, that being about 40 MPH from the southwest.

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