Eight years ago today, a large tornado outbreak affected portions of Iowa, Illinois, Indiana, Michigan, Ohio, and Pennsylvania.
My memories of that day are foggy. I do remember the day, though, as it happened during VORTEX-2, the massive tornado field project. That day, as with many days in 2010, we chose poorly. If I remember correctly, we decided to play Nebraska the day before, which put us out of position for eastern Iowa / Illinois. Thus, some time around midday on June 5th, we decided to call the day “down.” I distinctly remember eating an Omaha steakhouse that evening with Justin Walker and Herb Stein. When images of the Yates City, Illinois tornado appeared, I sank my head in misery.
It had been a tough season. We had already screwed up May 22nd, the day of the infamous Bowdle, South Dakota EF4. We called that day “down,” too. (I must sheepishly admit that I was the stand-in Day 1 forecaster for that day. So I probably share some of the blame for that mistake.) I don’t know why, but we picked some very bad times to sit out. I think we also sat out Campo Day, too. (Though, to be fair, that day was *much* less obvious.) So when the June 5th outbreak happened, it was insult to injury, to say the least.
Interestingly, prior to the outbreak, June 5 did not seem like it would be a big day. Many of the models, including the NAM, forecasted that a cold front would drive the moisture / potential instability far away from the stronger flow to the north.
About 24 hours before the outbreak, the modeled position of the front began to trend northward. This raised confidence in the potential for tornadoes. Thus, the Storm Prediction Center upgradedd from slight to moderate, with a 10% risk of tornadoes along the boundary.
Storms formed the morning of the 5th, along and north of the boundary. However, the storms were not strong. Thus, the cooling effects of the rain were outweighed by the strength of the return flow. So the front stayed closer to the strong upper flow.
As with most big days involving boundaries, the air north of the boundary cooked under the late spring sun.
This resulted in warm surface temperatures north of the boundary. With high-octane Gulf moisture in place, the surface component for explosive storm development was in place.
A sounding from central Illinois (ILX) at 00Z showed an strong-tornado-supporting environment. Surface-based CAPE was near 3000 j/kg. Deep-layer shear was above 50 kts. And the all-important 0-1 km storm relative helicity was greater than 200 m**2/s**2.
Around 2300Z, powerful thunderstorms developed in eastern Iowa and northern Illinois.
By 0130Z, a full-fledged tornado outbreak was underway.
In all, 43 tornadoes struck that day. I suppose that one could reasonably describe it as a “regional tornado outbreak.”
Granted, most of the tornadoes were on the weak end of significant. But it was still a fairly impressive outbreak.
The most significant tornado struck the small town of Millbury, Ohio — just outside of Toledo. The late-night tornado was not large: only 100 yards at its widest. However, it was fierce, producing EF4 winds. In all, five people were killed.