Ceaseless Wind

Storm Front 4/24/10 - Hwy 65 - Amber Nicholson

The atmosphere did produce storms and severe weather, including a tornado, on Saturday afternoon April 24, 2010.  As reviewed in my blog post early on Saturday, the conditions did end up being favorable for a tornado but further west than I think anyone would have thought.

Several storm lines where pivoting around an upper level low on this day.  Sunshine in-between these lines was allowing air to become unstable, feeding the next line.  There were three of these yesterday.

The first was swinging through the extreme eastern and northeastern portion of the KOLR/KSFX viewing area.  One cell along this line was exhibiting rotation aloft in southern Phelps County (the height of the radar beam at that distance makes the direct detection of low level rotation impossible) and was enough to issue a tornado warning.

The second line formed in northern Arkansas and moved NNE.  This was the one that blew through Greene County (photo left).  Strangely, a tornado was generated by this by a cell in this line at Table Rock State Park at about 1:40 pm (official NWS report here).  This tornado not obvious on radar and I would classify this as a bottom-up tornado where some sort of rotation near the surface was “spun-up” into a strong thunderstorm updraft. This stretches the rotation, decreases the radius of the rotation and causes an increase in wind speed.

The storm at about the time or shortly before the tornado had a strong updraft as noted in the 3D image.  North is left, south is right in this picture.  A strong updraft will often suspend larger rain droplets (or hail) aloft, leading to “weak echo region” (WER),  This mini “WER” is circled in the image. In large supercells, this feature is often very large and tall.  In this case, all of this is under 10,000 feet (legend on left of image). 

3D Reflectivity at 1:30 pm

Weak rotations were detected at the surface but had virtually no depth to them.  The nature of this type of tornado makes it difficult to tag these circulations as tornadoes.  The vast majority of these weak circulations (and there are often very many in thunderstorm lines/areas) do not produce a tornado so it cannot be assumed that a tornado is present.

Just to let you know, these types of tornadoes may not be warned upon for a long time.  It would take smaller radars scanning continuously, combined with more knowledge of how these types of storms form AND a dissemination system quick enough to warn people!