A Recipe for Disaster (Tornadoes) – Redux

Yogi Berra is noted for his, “déjà vu, all over again,” remark. Well, April 16, 2011 (Fig. 1) may well be close to a duplicate of March 28, 1984…at least when it comes to Carolina tornadoes. When comparing it to a larger-scale perspective (for the entire April 14 – 16 period), April 3-4, 1974 jumps to the forefront (note: this link is to a somewhat technical paper).

And while both may appear to be the worst “ever,” keep in mind that well-documented tornado data spans only about a 60-year period and that other factors (including improved detection and reporting procedures) also contribute to our awareness of what happened and how fast we know about things.

Early Saturday morning, April 16, 2011, I told my wife that North Carolina was on target for a massive tornado outbreak. I noted that the pattern was reminiscent of events associated with the March 28, 1984 North-South Carolina Tornado Outbreak in which the “dry line” had once again moved well east of its geographically-intended position (Fig. 2). The “dry line” is a frontal-like boundary that is often present along the sloping High Plains terrain from west Texas northward into Nebraska. The boundary separates desert-generated dry air to its west (where terrain is at a higher altitude) from moisture-laden Gulf of Mexico air to the east. The air wasn’t as dry as it was the day before across north Texas, but it was quite dry compared to the air mass in place over the Carolinas.

Of course, other factors, such as atmospheric instability, a weather system with a tornadic history, diverging upper winds associated with the jet stream (Fig. 3), significant turning of winds with height and other factors were also present. But the “dry line,” was the key. It yelled that the weather pattern would be more like that seen in “tornado alley.”

With an outbreak that is bound to be the worst in recent North Carolina history, the death toll (albeit tragic) was still dramatically low. Early watches and warnings issued by the National Weather Service and distributed by numerous media outlets, apparent effective use of social media and a population that somehow knew (either by instinct and/or education) how to get to safe places all acted in consort. There were many instances in which store employees, family members and others got people to safety. In the Sanford, NC Lowe’s hardware store, manager Mike Hollowell, following the company’s safety procedures, was credited with saving 100 lives. In some cases, plain, old-fashioned, good luck saved lives.

As much as last year had an almost non-existent tornado season to date (95 twisters through 4/17/10), this year’s numbers are running about six times greater (Fig. 4). Still, more twisters were logged through April 17th in 2008 (622) and almost as many in 2006 (553).

Another severe storm outbreak (although mainly hail and high wind) started yesterday and will be ongoing today. And, yet several others loom for the upcoming week.

Meanwhile, a significant snowstorm added to already high seasonal snowfall totals (e.g., Green Bay reported nearly 10 inches of snowfall on April 19, the greatest daily snowfall so late in the season). And widespread flooding continues to affect waterways from the northern Plains into New England, while a major drought and very high fire danger afflicts New Mexico and west Texas (Fig. 5).

So, welcome to spring. It’s really more typical than you think.

© H. Michael Mogil, 2011