Ag Weather Forum

As clean-up and recovery continue in Oklahoma following the tremendous tornado outbreak last month, there is also a lot of post-tornado analysis going on. It's in that vein that I posed a question to our DTN ag weather group during our weekly long-range forecast conference call Wednesday, June 5.

My question had a prominent agricultural history. It was this--"Did the drought in the southwest Plains help to give the dynamics for the spate of tornadoes a boost?"

The reason why I posed the question is that, in an air mass collision, dry air can act like a cold front in terms of its interaction with warm, moisture air. Just as with colder air, drier air is denser--heavier--and, when it runs up against a warmer and wetter air mass, both the colder air and the drier air sink, and force the warmer and wetter air up. This forcing causes the updrafts that can lead to thunderstorms, and if the supporting jet stream energy is available, tornadoes.

These updrafts are not mild little wafting breezes. They are high-velocity shots skyward. Speeds can reach 50 mph, and in extreme cases (such as with a cold front AND a dry air influence) over 100 mph.

In other words, the influence of the dry air out of the southwestern Plains may have turbo-charged the storms, helping them to achieve the monstrous dimensions that they reached over central Oklahoma.

My colleagues thought the idea was interesting, and Jeff Johnson, forecaster with our ownership company Schneider Electric in Burnsville, Minnesota, posed the question to his co-workers as well. One of them, meteorologist Brad Nelson, actually was in Oklahoma chasing the tornadoes. Following is his commentary on the build-up to that event, using the killer El Reno, Oklahoma tornado as his focus:

"There was definitely a dryline involved as well as a stalled front and the storms, much like the Moore tornado, blew up on the intersection of a stalled boundary and the dryline. I’m not sure the dry spring had that much to do with it, but it may have led to a stronger dryline.

However, the dryline was also the main player in supercell development the 2 days leading up to Friday’s El Reno tornado, but both of these previous days did not produce much of any tornadoes--2 on the 29th and none with the dryline storms on the 30th.

The big difference to Friday’s set-up compared to the previous few days was the dew points--which were in the middle 70s F and I even saw a couple 77F dew points which appeared to be valid, while the days before that could only muster upper 60s to near 70F dew points.

In addition, the area was at the base of an upper-air trough and a more pronounced wind speed maximum at 500mb (about 18,000 feet altitude) and at jet stream level (about 30,000 feet) was moving across Oklahoma on Friday May 31.

The 00Z upper level charts depicted this really well and the 00Z Oklahoma City sounding was astounding. Here’s the event archive:

http://www.spc.noaa.gov/…

Those are my thoughts anyway. I haven’t done a thorough analysis, but the dry spring leading to a more pronounced dryline is an interesting theory and I would not argue against that. But it seemed to me to be a case of a lot of the environmental parameters coming together for a significant event."

I also have a question on this angle in to the Storm Prediction Center, and will post the response from that group when I receive it. Considering the extremity of the southwest Plains drought, I think it's a question worth asking.

Bryce

Twitter @BAndersonDTN

(CZ/SK)

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