Have you ever noticed that thunderstorms often appear to weaken or change direction just before hitting your area? This illusion is common everywhere, but in most cases, it is just an illusion.
One reason for this is parallax. This is the illusion that something is coming straight for you when it is actually moving almost, but not quite, straight toward you. It appears to change direction to one side or another as it passes by when, in reality, it was never headed right at you to begin with.
Another reason is the fact that storms pulse stronger and weaker and do not maintain their top strength very long. We usually report the worst and strongest conditions because this is the greatest threat, but these worst conditions usually affect only some of the area.
Of course, storms do change direction at times, but most casual Doppler observers only notice those changes when a storm is bearing down on them.
