Lack of Severe Weather of Late

There has been severe weather recently. Just not across Northern Illinois and Southern Wisconsin. The strong thunderstorms through the last week or April were confined to areas south and southwest of Rockford. The temperatures on Saturday evening provide a very good explanation as to why that has been true. It is much warmer just to our south in the southern half of the state into Missouri, Arkansas, Kentucky, and Tennessee. Those states, along with the Plains states, have seen plenty of severe weather recently. That is because of the track of recent low pressure systems and the placement of their associated frontal boundaries.

The lows of late have developed in the Rocky Mountains and shifted east towards Illinois, but have generally remained just south of our area. That keeps us in the "cold sector" of the systems, which means no thunderstorms. If those lows were to move further north -- a pattern that is more common this time of year than what we are seeing now -- then we would be in the "warm sector" like the states to our south have been. As a result, severe weather would be happening more often. Also, on a few occasions a boundary has moved through the area, but stalled just to our south. Add that boundary, which is keeping us cooler here in the Stateline, with low pressures that track south of here, and you get a lack of thunderstorms and severe weather.

The cool temperatures are the reason behind a lack of severe weather here in the northern half of Illinois. One of the variables meteorologists look at to predict severe weather is instability, or CAPE (Convective Available Potential Energy). CAPE is simply the fuel, or food, for thunderstorm development and maintenance. If CAPE is not present, it is typically much more difficult to get thunderstorms, especially strong to severe thunderstorms. The cool temperatures disallow CAPE to be present because CAPE requires warmth, moisture, and sunshine to materialize. Those are three things the clouds and rain have prevented from being present here in the Stateline. You can see where the CAPE is tonight by looking at the above map. There is simply no CAPE here because of the clouds, cool temperatures, and showers.

So, yes, we are seeing a lack of severe weather here locally, but severe weather is happening -- just a few hundred miles south. We can thank the unseasonably cold temperatures for that!