Small plane and a gust front
A small plane crashed into the side of a road on the northeast side of Sheldon, Iowa Tuesday morning. According to an Associated Press article carried in the Chicago Tribune, the FAA says the plane crash occurred about 11 a.m. when “thunderstorms with heavy rain were moving through the area.”
An examination of radar imagery suggests heavy rain was not occurring over the crash site. Assuming the plane went down at 11 a.m., the rainfall from a line of thunderstorms was still approximately ten miles west of Sheldon. But cold air surging out ahead of the thunderstorms was just reaching Sheldon in the form of a gust front at 11 a.m.
The “outflow boundary” is clearly visible on radar as a faint line of weak reflectivity. When this same north-south boundary passed over Sioux Falls airport an hour earlier, it produced a 43 mph wind gust at the surface. At 11:15 a.m., the automated sensor at Sheldon airport (KSHL) registered a short-lived, westerly wind gust of 39 knots, or 45 miles per hour.
A pilot clearly would have seen the line of thunderstorms approaching from the west, with dark clouds that lined the horizon. But the gust front, while visible on radar, might have been sudden and invisible to the eye. While it will be months before the FAA investigation is complete, my guess is that this unseen “wall of wind” played a role in the aviation accident.
