When a storm develops, a common question to ask is “where is it moving?”. It can also be asked “what causes a storm to move in a particular direction?”. A storm is a process that is constantly evolving and changing. These changes can result from size changes, change in the stage of the storm, precipitation intensity changes, speed of movement change and direction of movement change. Air and moisture move into a storm and then out of a storm. During that time the moisture can condense to rain and hail. Some of the moisture will make it to the surface, some will remain as cloud droplets and some will evaporate back into the gaseous form.

As far as storm movement in the middle latitudes of the Northern Hemisphere, there are some important factors that determine storm movement. One factor is the wind direction in the middle and upper troposphere. Since much of the storm is exposed to these winds, these winds have a strong influence on storm movement. Often in the middle latitudes the wind flows from the west to the east or some variation of this tendency. This is the same tendency that the jet stream has. Thus, storms will often approach from the northwest, west or southwest. Another factor in storm movement are the random factors involved with the developing storm structure. As a storm is growing it has the ability to grow in any direction. This is why storms can temporary seem like they are not being steered by the upper level winds. Storms can grow in various directions. A third factor is the presence and movement of a strong convergence boundary such as a cold front, warm front or dry line. Since storms will often form on and near these boundaries, the storms will be steered with the movement of these boundaries. Like with upper level wind steering, these convergence boundaries will tend to have a west to east direction of movement or some variation of this. Storms can also be influenced by more local convergence boundaries such as sea breezes and mountain terrain. The position relative to a low pressure system will also impact storm motion. Winds move cyclonically around a low pressure system. Often low pressure systems move more or less west to east also but storms can move in a different direction under the influence of the overall circulation around a low pressure system or mesolow system. While middle and upper level winds are the dominate factor in steering storms, other factors also play a role.