Clashing air masses spawn Great Plains storm tragedies

Weather Journal columnist Kevin Myatt will be heading out on a storm chasing trip next week.

Associated Press

People walk through a neighborhood after a tornado struck south Oklahoma City and Moore, Okla., on Monday.

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Local efforts launched to send relief supplies to Oklahoma

Kevin Myatt | 981-3341

Tuesday, May 21, 2013

The sleeping giant has awakened.

Tornado season in America went on an almost unprecedented slumber from April 15, 2012, to May 14, 2013.

Fewer tornado deaths (seven) were reported in that 13-month period than any similar period in U.S. history since 1899-1900. Though sparse historical tornado records make it uncertain, it is widely believed by severe weather experts that 2012 had the fewest tornadoes nationally in the past 60 years.

We can quit talking about that now.

Monday’s shocking images out of Moore, Okla., where at least 24 were killed in a violent tornado, came on the heels of similar destruction and additional deaths at Shawnee, Okla., on Sunday and Granbury, Texas, last Wednesday.

There have been about 100 tornado reports nationally in the past week, about a third of the year’s total to date, which is still less than half of the typical total by this point in the year.

It shouldn’t be extremely surprising that severe weather has suddenly cropped up violently this May. The unusual intrusions of cold and snow far to the south so late in the seasons were delays, not denials, for tornado season.

Those cold shots might even have been enablers.

The jet stream didn’t run off to Canada as it did during last year’s abnormally warm spring, and its presence over the United States helped spin the storms incredibly once the right conditions for severe weather finally showed up.

Those conditions are more right, more often in the central U.S. than anywhere in the world.

The relatively flat shelf of the Great Plains allows both balmy, moist air from the Gulf of Mexico and cold, dry air from the polar regions to run almost unchecked north and south. Dry air blowing in from the deserts and mountains to the west cut into those air masses at a right angle.

Boundaries between clashing air masses are where strong thunderstorms arise. When strong winds aloft give those storms a spin, long-lasting rotating storms known as “supercells” can produce enormous hail, powerful downburst winds and, occasionally, violent and long-lived tornadoes.

Sprawling metro areas have made the urban targets a little bigger in the open plains. Moore, the Oklahoma City suburb that was the scene of a similar subdivision-flattening tornado in 1999 that killed 36, has gained more than 10,000 people in those intervening years.

It was against this backdrop of terror and tragedy that meteorology students from Virginia Tech have been tracking and observing severe storms in the central U.S. for the past week.

They have not been up close to the most deadly tornadoes, as populated areas are usually avoided for storm chasing, but they have seen lots of violent storms and at least one possible tornado while communities not far away have been paralyzed by suffering.

And it is into this atmosphere that I will help lead another group of meteorology students into the field starting next week.

The weather pattern we chase storms in probably will not be as ballistic as what has just occurred, but there will likely be some severe storms to be tracked.

It only takes one storm with the right conditions in the wrong place to make a heart-crushing tragedy.

Weather Journal appears on Wednesdays.

Monday, August 12, 2013