Updated: May 1, 2019
Too many pilots see the word "showers" and think it's just some harmless light rain event. When, in fact, a forecast for showery precipitation should get your attention since rain showers are a result of a convective process. In many cases, forecasters often use showery precipitation (SHRA or VCSH) when they have a fair amount of uncertainly about a future convective event. Forecasters won't include TSRA or VCTS in a TAF unless they feel certain thunderstorms will impact the airport's terminal area.
Here's an example. Consider you are making a short flight from Cedar Rapids (KCID) in Iowa to Chicago Executive (KPWK) around 12Z on the morning of May 11th. The previous evening you fire up the Imagery view and take a look at the HREF Model graphics. You notice an area of convection with echo top heights greater than 30,000 feet is forecast to be poised just to the west and northwest of your route by 08Z as shown below. With such a high probability of tops above 30,000 feet MSL, this area of weather is likely to contain dangerous convective turbulence at 08Z.
However, as you forward the loop to 12Z (below) you notice that the high probability of 30,000 ft echo top heights has diminished, indicating this area of convective weather is expected to weaken with time. Therefore, forecasters also will likely treat this weather system as a weakening area of weather.