Charles Kuster
EF4
Along the same lines as Mike Johnston's post, I thought I would share a couple observations about this setup. This outbreak was characterized by widespread instability combined with very strong low level shear. Low level instability was also present which I believe is a very important factor in tornado production due to the fact that a strong low level updraft is needed to stretch, and therefore intensify, existing low level vorticity. This is evident on the 18z Birmingham sounding which shows 116 J/kg of 0-3km CAPE. While this value is not exceedingly impressive, RUC forecasts suggested that 0-3km CAPE would approach 160-200 J/kg in northern AL. Either way, a modest amount of 0-3km CAPE was present on 4/27/11.
I have included a hodograph produced from the 0Z Birmingham sounding below.
It provides values of 535 m^2/s^2 for 0-1km SRH and 635 m^2/s^2 for 0-3km SRH. For comparison 5/10/10 had 0-1km SRH of 297 and 0-3km SRH of 645 in Oklahoma. Essentially the 0-1km SRH was extremely high for this event. It is also interesting to note, that out of 25 other tornado cases that I have studied, the 0-3km SRH was almost always at least 2-3 times greater than the 0-1km SRH, but that was certainly not the case on 4/27/11. The Birmingham sounding also showed approximately 66 knot winds at 1km! This is evident by the 0-1km bulk shear of 26.2 m/s given by the above hodograph (5/10/10 had 0-1km bulk shear of 15.8 m/s).
I have also included a hodograph from the 20z Okolona, MS wind profiler. Data was missing from 3-7km and from 9-10km so a great deal of interpolation was used to construct the hodograph, so it is probably relatively inaccurate. Values of 0-1km SRH were 208 and 0-3km SRH was 315.
This was undoubtedly a historic and tragic tornado outbreak. My thoughts and prayers are with all of the people who have been affected by this event.
(Note: I used storm dir/speed of 240/51, which I calculated using radar data, to produce the above values, and the SRH values are quite sensitive to changes in the direction of storm motion).
I have included a hodograph produced from the 0Z Birmingham sounding below.
It provides values of 535 m^2/s^2 for 0-1km SRH and 635 m^2/s^2 for 0-3km SRH. For comparison 5/10/10 had 0-1km SRH of 297 and 0-3km SRH of 645 in Oklahoma. Essentially the 0-1km SRH was extremely high for this event. It is also interesting to note, that out of 25 other tornado cases that I have studied, the 0-3km SRH was almost always at least 2-3 times greater than the 0-1km SRH, but that was certainly not the case on 4/27/11. The Birmingham sounding also showed approximately 66 knot winds at 1km! This is evident by the 0-1km bulk shear of 26.2 m/s given by the above hodograph (5/10/10 had 0-1km bulk shear of 15.8 m/s).
I have also included a hodograph from the 20z Okolona, MS wind profiler. Data was missing from 3-7km and from 9-10km so a great deal of interpolation was used to construct the hodograph, so it is probably relatively inaccurate. Values of 0-1km SRH were 208 and 0-3km SRH was 315.
This was undoubtedly a historic and tragic tornado outbreak. My thoughts and prayers are with all of the people who have been affected by this event.
(Note: I used storm dir/speed of 240/51, which I calculated using radar data, to produce the above values, and the SRH values are quite sensitive to changes in the direction of storm motion).
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