Severe weather turned deadly suddenly on Saturday evening 5/21/11 when a tornado struck Reading KS (northeast of Emporia) around dark, killing 1 person, injuring others, and destroying a number of homes. Jim Saueressig's photo above shows the impressive storm structure of the Reading storm after dark.
The environment was one of the most rapidly changing that I've seen on Saturday. At late afternoon, the SPC Sig Tor Parameter (STP) was weak across eastern Kansas with marginal values due to both deep-layer shear and low-level shear being rather weak or marginal for tornadoes (0-6 km shear around 30 kts or less, 0-1 km storm-relative helicity/SRH < 100 m2/s2). This is why SPC issued only a severe thunderstorm watch for northeast Kansas. But by dark, low-level winds had strengthened and backed more than expected, causing much larger shear values, both in low-levels and through a deeper layer. This made STP values sky rocket as the eastern KS environment improved dramatically for supporting tornadoes. See the graphics above comparing STP over Kansas at late afternoon (2200 UTC) with just after dark (0300 UTC), and notice the change in wind profiles from late afternoon to after dark on local RUC analysis soundings at Topeka and Emporia.
The tornado struck Reading around 9:15 pm CDT (0215 UTC), and other tornadoes from the same complex continued to be reported during the following 90 minutes after dark. Notice the RUC 0-1 km EHI and low-level CAPE forecasts above for 0300 UTC, indicating strong CAPE/SRH combinations _and_ a surface-based setting after dark, important ingredients for nighttime tornadoes.
Shawna and I stayed in the local area north of Kansas City watching storms on Saturday evening, and were very saddened to hear about the strong tornado that hit Reading. After an enjoyable week of storm chasing with no deadly severe weather in the plains, last night brought things back to sober reality.
- Jon Davies 5/22/11
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