"Null Event: Central Plains Severe Weather"
18 April 2000

This case is the second in our collection of non-events. It concerns 18 April 2000, and the severe weather setup for that afternoon and evening. It is a good example of what happens when the environment is so capped that despite many other favorable conditions, no convection can occur. Early in the day, the models and model soundings showed indications of the potential for severe weather in the Central Plains states, mainly Kansas, Oklahoma and northern Texas. There was a strong cap present over much of the area of concern; though if the cap were overcome, the convection would most likely be severe. By late in the day, mostly clear skies dominated the region, with some cloudiness due to a shortwave in west-central Texas, as the cap prevailed over Kansas, Oklahoma and north central Texas.

Using the 12Z run of the Eta, one can see that the model presented a potential for severe weather early in the day. All of the severe convection parameters were well into the range for supporting severe weather, and in hindsight, were quite accurate when compared to the RUC analyses at the valid time, 0000Z 19 April 2000. Below are the Eta's forecasts for certain severe weather parameters and the RUC analyses at 0000Z 19 April.

The Storm Prediction Center discussion that day also mentioned the potential for severe weather in the Central/Southern Plains. The threat was there, but given the strong cap, doubts were aired about convective initiation. The discussion mentioned that deep heating/mixing along the dryline as well as greater moisture at a higher elevation might reduce convective inhibition enough for isolated storms. Using the 0000Z soundings from Oklahoma City and Fort Worth as guides, it seems the cap was too strong and deep to allow convection, even with convection indices showing large instability (CAPE 3000 J/kg, Totals 55, Lifted Index -6.5, etc); and so the area of concern was spared from severe weather that day.

Case Study 31