John Wheeler: When is rain a shower?
For those of us in the business of forecasting, a shower differs from rain by being convective in nature.
FARGO — Sometimes rain is called "rain" and sometimes it is referred to as a "shower." The classic meteorological definition is that a shower is brief and/or intermittent whereas rain is steady. However, there is no specific time limit for when a shower crosses the threshold and becomes just rain. For those of us in the business of forecasting, a shower differs from rain by being convective in nature.
This means that showers are caused by smaller scale updrafts of air and are briefer or more intermittent than a general area of rain which is caused by a general, gradual rising motion over a large area. Here again, however, there is no cutoff at which rising air is of too large of a scale to be considered a shower-making updraft. In general, if it is brief, short, or longer but highly variable in intensity, it is a shower. If it is of relatively long duration and generally steady intensity, it is rain.