A lot of attention has been focused on Friday as far as the severe potential goes - so I wanted to talk a little more about it. There are several parameters that meteorologists look at as far as determining if severe weather will occur. They are; lift, moisture and instability. Looking at the forecast for tomorrow we will have a few of the ingredients needed to produce severe weather but lacking in a few others. The first image on the left shows the moisture advection into the region, or Theta-E. Dew points will continue to rise as winds gust in from the south today and tomorrow. So moisture will be there. Next, we will have a pretty significant jetstream moving just to the west of us with winds coming in around 120 - 140 knots! That means if storms do develop, they would be fast moving storms with damaging winds. The last is the measure of instability in the atmosphere, or CAPE (Convective Available Potential Energy). Any time you begin to get a value of CAPE more than about 1000, the potential for severe weather increases. As of right now we are beginning to approach that value across northern Illinois, but the higher values remain south in central-Illinois. This is what we'll have to watch over today and tomorrow. If we can get sunshine for a good part of the day Friday, the CAPE values will likely increase. However, if the day starts off cloudy because of ongoing storms in Iowa we might not see it rise throughout the day. Thunderstorms will be likely Friday afternoon and into the evening, we'll just have to monitor the conditions throughout the day to see if we can get strong ones to develop. We are in a slight risk for severe weather Friday afternoon so be sure to continue to monitor the weather conditions throughout the afternoon!
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