Published: 2008-04-30 13:35:27
Updated: 2008-04-30 13:35:27
Posted April 30, 2008
By Tracy Proctor
Related question - "I was driving southwest of Wendell this morning on Old Battle Bridge Rd. just south of Hwy. 64 Business. There were several wheat fields that had areas where the wheat looked flattened. Most were about 10-20 feet long and about 5-10 feet wide. There didn't seem to be any pattern to them. I was thinking that this could have been caused from downdrafts since there was a very strong storm that went over this area last night. I've never seen anything like this before and was just wondering what it was that caused it." Andy
MIKE MOSS SAYS: Tracy and Andy, It seems quite likely you both saw the effects of localized microbursts, which are small scale intense downdraft wwinds associated with strong or severe thunderstorms. Turbulent flow within the downdraft columns can cause large irregularities from place to place in what the peak wind speeds are, so over a wide space in a uniform material like a wheat field you can especially make out locations where the winds were strong enough to overcome the threshold of resistance by the wheat plants and push them over. In cases where the downdraft winds are moving almost straight down (directly beneath a slow-moving styorms, for example) the pattern could appear circular, perhaps with plants laying out radially from a center location, while a combination of downburst and ambient winds, or a pattern formed away from the center a downdraft, might have more of a horizontal component causing more linear streak of damage with most of the plants pushed over in one direction. Of course, not having seen the damage pattern and correlated them with specific storm locations and times, this is somewhat speculative, but seems like a plausible explanation of what you both reported.
You can sometimes visualize how capricious stronger wind gusts are on blustery (but not severe wind) days by watching the tops of a wheat or smooth grass field, or sometimes the surface of a large puddle or small pond, where you can see whorls and streaks of higher winds speed dancing across the surfaces. It can be kind of a mesmerizing thing to watch (at least to a meteorologist!)