Weather Alerts for North Carolina

This map shows recent moisture content over North America. Bright and colored areas show high moisture (ie, clouds); brown indicates very little moisture present; black indicates no moisture.

Weather Topic: What is Precipitation?

Home - Education - Precipitation - Precipitation

Next Topic: Rain

Precipitation can refer to many different forms of water that may fall from clouds. Precipitation occurs after a cloud has become saturated to the point where its water particles are more dense than the air below the cloud.

In most cases, precipitation will reach the ground, but it is not uncommon for precipitation to evaporate before it reaches the earth's surface. When precipitation evaporates before it contacts the ground it is called Virga. Graupel, hail, sleet, rain, drizzle, and snow are forms of precipitation, but fog and mist are not considered precipitation because the water vapor which constitutes them isn't dense enough to fall to the ground.

Next Topic: Rain

Weather Topic: What are Shelf Clouds?

Home - Education - Cloud Types - Shelf Clouds

Shelf Clouds Next Topic: Sleet

A shelf cloud is similar to a wall cloud, but forms at the front of a storm cloud, instead of at the rear, where wall clouds form.

A shelf cloud is caused by a series of events set into motion by the advancing storm; first, cool air settles along the ground where precipitation has just fallen. As the cool air is brought in, the warmer air is displaced, and rises above it, because it is less dense. When the warmer air reaches the bottom of the storm cloud, it begins to cool again, and the resulting condensation is a visible shelf cloud.

Next Topic: Sleet