Tomorrow's severe weather chances hinge on a lot of factors. Hopefully this clears things up just a little bit. Tomorrow morning, a round of thunderstorms is likely going to come through the area. This may bring thunder, lightning and even some small hail. We're not concerned about that part being severe.
Defining the "cap"
However, as those storms pass through, they will likely leave behind clouds. These clouds will be an important ingredient for whether or not storms can re-fire in the afternoon. In the meteorology world, we refer to these leftover clouds as a "cap".
This "cap" can prevent heat from the sun from warming the surface of the earth. In severe thunderstorm development, rising air from surface heating is a KEY component in growing a thunderstorm.
Think about it like a planting analogy. You wouldn't want a plant that requires sunlight to grow in a dark room. In the same manner, for a thunderstorm to grow and become severe, it needs light, warmth and heat from below to force it upward.
The bottom line:
This is a very, very important thing that we'll have to keep a close eye on tomorrow, for whether or not storms grow into the evening hours. If the clouds stick around for too long, they will likely leave us with little to no severe storm activity.
The reason for the uncertainty is that it can sometimes be tough to forecast exactly when clouds may clear out-- and that can tip the scale in either direction, very quickly.
It's a tough balancing act, for sure.