High sustained winds of 30-40 mph with gusts over 60 mph ripped across southern Minnesota and northern Iowa last weekend. Damage to tree limbs and roofing shingles were reported in southwest Minnesota and northwest Iowa late Saturday night and Sunday morning. A high wind warning was issued for the area at 10:47 Saturday night. Though there were severe thunderstorms south of the area, this event was unusual in that these winds were not associated with severe thunderstorms. Though weather conditions were favorable for a strong wind field in the area, some meteorologists noted that recorded wind speeds seemed unusually high for the synoptic weather situation. There is some evidence emerging that so called "gravity waves" may have enhanced the wind speeds in this event. Gravity waves are not well studied or understood by meteorologists, but they are believed to be generated near certain storm systems similar to the storm that caused the massive tornado outbreak last weekend.
There's a link on the right to a YouTube video of storm clouds in Iowa last weekend. As the video shows, gravity waves have ridges and troughs just like ocean waves. Surface pressure differences created between the passages for each successive trough and ridge couplet may have enhanced the wind speeds last weekend in parts of Minnesota and Iowa. Though we cannot be sure, this could be one explanation as to why unusually high and damaging winds occurred last weekend in the absence of severe thunderstorms in the area.