Potentially Dangerous Tornado & High Wind Discussion for Monday, June 30

This discussion will focus on the anticipated tornado and high-wind threat on Monday, June 30.

SPC

The Storm Prediction Center has issued a Slight Risk of severe weather on Monday in the 15% shading, which extends from Oklahoma into Kansas, Missouri, Iowa, Illinois, Wisconsin, and into Michigan. An enhanced risk of severe weather exists from eastern Kansas into southeast Iowa, northern Missouri, much of Illinois and portions of Indiana and Wisconsin. This enhanced area is where we are watching for potentially significant severe weather on Monday, June 30, which may include tornadoes and a swath of damaging winds.

WPC

Short range analysis from the Weather Prediction Center, valid for Monday morning, shows multiple features relevant to tomorrow's expected severe weather outbreak. We see a decaying mesoscale convective system (MCS) progressing across Illinois, moving eastward as it does so. This complex of thunderstorms will have formed today (Sunday) out to the west, and will have produced additional severe weather in those areas (see Sunday's severe weather discussion here). We also see a stationary front draped across Nebraska, Iowa, and Wisconsin, which is the focus of some early-day convection in northwest Iowa per this forecast graphic. However, the main concern here is if the morning MCS over Illinois will limit convection later in the day due to the MCS-associated cloud cover.

COD

If we look at the forecasted relative humidity values at the 500mb level of the atmosphere from the NAM, valid in the early hours of Monday, we see only limited moisture across Illinois and Indiana, despite the expected presence of the decaying MCS. This tells me that while we can expect cloud cover in the aforementioned regions due to the thunderstorm complex moving east, the cloud deck shouldn't be thick or extensive enough to severely limit convection later in the day, and this is what makes me believe we are looking at a potentially more explosive environment on Monday afternoon.

COD

By Monday afternoon, we see extensive instability has developed over the Midwest, focused in on the areas projected to receive severe weather. We see a swath of 4000 j/kg CAPE (convective available potential energy) stretching from Oklahoma to Illinois, with a pocket of 5000 j/kg CAPE existing in south-central Iowa and northern Missouri, likely the initialization point of Monday's convection.

There is ample concern that Monday's event could produce tornadoes. This stems from a very dynamic wind field in the upper, middle, and lower levels of the atmosphere, thanks in part to the dominant upper level low in southern Canada. These dynamic wind fields then create ample wind shear, a necessary ingredient for tornadoes. With the aforementioned extreme instability, tornadoes are very possible with the initial cells that form Monday afternoon out in Iowa and northwest Illinois, prior to coagulation into a cluster of thunderstorms. From there, a potentially dangerous damaging wind threat may be expected to evolve. You can stay tuned to our Facebook Page and Twitter account for more frequent updates on the situation.

Andrew