The reason behind the different storm formations you might notice on radar

When looking at radar, you might often notice there are two distinct types of storm formations: isolated storms and storms that have formed into one large line. Each of these carry their own types of most likely severe weather hazards, and they each come with different types of severe weather criteria.

In the case of April 17th, small differences in pressure and surface conditions lead to isolated areas of rising motion ahead of the main lifing mechansim, that being the large cold front. This resulted in isolated storms popping up and being able to have their own environment to work with. The cold front acts much differently. Because of the strong temperature gradient behind the front, the cold, dense air forces all of the warm, energetic air into the atmosphere. This leads to storms forming across the entire front, eventually creating a line.

The more isolated type of storm, that being a supercell, feeds itself through the storm's inflow. These are strong, warm surface winds working together with cold upper-level winds to tighten the storm's circulation. As long as these storms stay isolated and continue to stay in a favorable environment, these kidney bean-like radar signatures often are associated with a greater chance of producing a tornado due to the circulation. These types of storms are also the most likely to produce the strongest tornadoes, as they will have free range in the environment rather than being impeded by another storm. If, however, rain begins to take over that region of warm surface winds, the air begins to cool, and the storm inevitably falls apart.

The linear storm feature, which is a QLCS, is the most likely storm threat for tonight. As storms form, warm air rises ahead of the previous storm. New storms develop because of this, and this process can continue for miles. There is still a threat of tornadoes, but damaging winds are the main concern. As all of the storms run into each other, they congeal into a line, but some areas can get in front of the activity and strengthen into a more damaging system.

On radar, lower reflectivity behind the line means strong downdraft winds, while low reflectivity ahead of the line shows where the storm's updraft is. This gives you a good idea of how efficiently the storm is "feeding" itself. Notches on the leading edge mean that there is circulation and potential tornadoes, and bow echoes or arcs in the storm line are most likely where your strongest winds will be. The notches are most likely on the bow echo formations, as they are the strongest portions of the storm. These tornadoes are harder to reach the same strength as supercellular tornadoes can, and this is because the constant formation of new storms takes away from the more ideal conditions needed to strengthen properly.