Sunday, June 29, 2014

Severe Weather Outbreak Discussion for Sunday, June 29

A severe weather outbreak is expected today, June 29.

The Storm Prediction Center has posted a Moderate Risk of severe weather for southeast Nebraska, northeast Kansas, northern Missouri, and the southern half of Iowa in advance of severe weather expected today. Current discussions indicate ongoing convection over Iowa will be clearing later on in the day, paving the way for diurnal heating to develop and destabilize the environment to provide a breeding ground for severe thunderstorms.

The NAM model indicates deep instability will develop over Iowa and Nebraska later on this evening, where convective available potential energy (CAPE) values look to exceed 3000 j/kg in spots. The development of this instability depends severely on the morning convection over the same areas right now. If cloud cover tends to linger over the area, we could see a reduced severe weather risk, as destabilization will be limited. However, if cloud cover can clear quickly enough, such CAPE values will be easy to come by.

When the storms do form, it looks like they will have decent potential to be originally tornadic. The NAM model places over 50 knots of shear near Iowa, increasing the likelihood that these initial cells that form may have a tornadic component to them. With such deep instability and shear, it is no wonder the Storm Prediction Center elected to go for a higher-level tornado threat for this Moderate Risk area. As the night progresses, the initial cells are expected to come together to form a mesoscale convective system (MCS), also known as a body of severe thunderstorms, that will be moving to the east.

To summarize, those in the Moderate Risk area today should prepare for:
• Damaging winds in eastern Iowa
• Tornadoes and very large hail in central Iowa into Missouri with the initial cells
• General poor weather conditions across the Plains and Midwest


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