Sunday, May 11, 2008

Deadly tornado setting on 5/10/08 in northeast OK & southwest MO

Tornadoes in northeast Oklahoma and southwest Missouri late afternoon on Saturday May 10 killed at least 18 people. This deadly event was the result of a classic tornadic supercell setting with a strong weather system and storms moving rapidly (around 40 m.p.h). People in the town of Picher OK (see radar above) had around 15 minutes warning from NWS before a large wedge tornado (see Chris Wilburn's image, also above) plowed into town; sadly, 6 people were killed in Picher. The rapid storm movement and hazy conditions may have caught some people unaware. This was a very different and much more dangerous situation than the 5/8/08 western KS landspout (see my previous post) with a storm chaser running up to it, a point not properly highlighted or emphasized in chaser TV interviews following that event. I elected not to chase on Saturday due to the fast storm motion in poor visibility terrain that was more than 3 hours from my place north of Kansas City, and instead monitored the situation from home.

Shown above at 22z (5 p.m. CDT) are SPC mesoanalysis graphics of storm-relative helicity (SRH, low-level wind shear that can be tilted into storms for low-level rotation) and CAPE below 3 km (suggesting instability that is strongly surface-based). These suggested that the newly-formed Picher supercell (located at circled "s") with a storm-free area to its south was moving toward an area of strongly enhanced low-level wind shear within a strongly surface-based environment.

Also shown above at 22z is a graphic of 0-1 km EHI (energy-helicity index, combinations of SRH and instability), which, like the prior graphic, also confirmed potential for strong low-level rotation in the supercell moving across extreme southeast KS into northeast OK and southwest MO. The RUC analysis profile for Grove OK (located between Tulsa and Joplin) at late afternoon also showed a large clockwise wind profile (hodograph shown at upper left of EHI graphic), indicating large low-level wind shear in a surface-based environment with large CAPE as well as deep layer shear. So it came as no surprise that this supercell (see earlier radar) proceded to produce tornadoes over the next 2 hours on its trek into southwest MO.

Morning forecasts from both the NAM/WRF model (shown in last graphic above) and the RUC (not shown) did a reasonable job of indicating the supercell tornado potential for late afternoon. These showed a deepening upper trough moving through the central plains with midlevel wind flow of 50-75 kts spreading out (diverging to induce upward motion) over southeast KS/southwest MO/eastern OK/northwest AR, as well as strong CAPE/low-level shear combinations over the same area in bright colors south of a surface warm front (not shown). Large low-level CAPE (a surface-based unstable environment) was also indicated on the forecasts, which did a good job highlighting the strong tornado potential. Unfortunately, that potential was realized, resulting in more deaths than with the Greensburg tornado last year.

Jon Davies - 5/11/08

1 comment:

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