A number of intense low-level vortices were encountered at a height of 30 m over the boreal forest by a Twin Otter atmospheric research aircraft. They imposed strong vertical and lateral accelerations on this aircraft: the most energetic had an updraft speed in excess of 11 m s-1, only 20 m above the forest. All were associated with large sensible heat fluxes, low wind speeds, and deep boundary layers. ¿ 1997 American Geophysical Union