NEW: Video of Storm Chase Day 6 linked here.

3 photo links — Large version of inset tornado photo below — cone tornado as it begins its path — wild cloud structure above chase van.

PIERRE, S.D. — We’ve struggled through long drives, extreme chaser traffic, road construction and cap busts in our first 5 days in the Plains, but on Saturday, everything came together perfectly for an extreme tornado intercept in north-central South Dakota. The Virginia Tech storm chase team started the day at North Platte, Neb., and headed north across the Sand Hills toward South Dakota, where atmospheric conditions developed throughout the day that were increasingly favorable for tornadoes — particularly, an extreme amount of instability (hot air at the surface rising into cold air aloft), very humid conditions for South Dakota (dew points in the 70s — a sticky day even in Virginia), and violent wind shear, with strong jet stream winds from the southwest roaring over gusty winds of different directions lower in the atmosphere. After following a cluster of cumulus clouds north of South Dakota’s capital of Pierre, the updrafts finally broke through a layer of warm air aloft called the cap around 5 p.m. local time. Within minutes, the first tornado warning was issued as radar indicated tight circulation within the storm. We were in prime position to move up on the east side of the storm and watch as a wall cloud lowered and tightened to our west. After a short drive south to make sure we would not be in the path of the developing circulation, we pulled alongside the highway near a horse pasture. When the spinning mass of clouds passed just north of our location, it became obvious quickly that within it was a funnel, spinning sheets of rain around it as it raced east to east-northeast. We watched the funnel cross the road a mile or two north near where we had been minutes earlier. The horses in the pasture grouped together and scampered away at the sight of the tornado, and we were buffeted by strong wind gusts being pulled into the tornado, called a “rear flank downdraft.” Later we were able to catch back up with the storm and saw amazing cloud formations called “striations,” layers of cloud chiseled by the high winds aloft.

We maneuvered around the storms so well that we never had even one ping of hail. Unlike some of our other tornado intercepts in years past, we were able to be outside as the tornado formed and moved by just north of us. It’s also good that, apparently, no towns were hit by the tornadoes that sprang from this amazing supercell thunderstorm … the only tornado reports in the entire country Saturday.

Eventually I’ll get more photos up and will link to video. For now, it’s time to rest and prepare for whatever Sunday brings.

For more on the 2010 Virginia Tech Storm Chase, go to Hokie Storm Chasers blog linked here.