Causes of Precipitation: Convection, Orographic Uplift & Frontal Uplift

Lesson Transcript
Instructor: Elizabeth (Nikki) Wyman

Nikki has a master's degree in teaching chemistry and has taught high school chemistry, biology and astronomy.

Discover what precipitation is and learn about what causes it. Understand and visualize how air masses are affected by changes in temperature and topographical features to produce precipitation.

What Causes Precipitation?

'And the forecast calls for two days of precipitation. Today, warm but rainy. Tomorrow, hot with a chance of thunderstorms in the afternoon.'

Depending on how much you love rain, you might be thinking about how the rain will affect your plans to go have fun outside! What you might not be thinking is, why is it going to rain?

Precipitation occurs when water droplets or crystals condense out of air saturated with water vapor and fall from the sky to the ground. It may occur when evaporation causes the amount of water vapor in the air to increase or when air cools and its capacity to hold water decreases.

Precipitation comes from clouds. Clouds are areas of the atmosphere where moisture has condensed into tiny water droplets or small grains of ice. All clouds are made out of water, but not all clouds produce precipitation.

There are two ways that air cools: at night when temperatures drop or as the air rises. In this video, we'll focus on the mechanisms that lead to air rising, often known as uplift mechanisms.

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Coming up next: Precipitation Forming Processes

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  • 00:00 What Causes Precipitation?
  • 1:03 Convective Uplift
  • 2:13 Frontal Uplift
  • 3:07 Orographic Uplift
  • 3:57 Lesson Summary
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Convective Uplift

Cumulonimbus clouds and cumulus clouds may look pretty different, but they're produced by the same oven-like effect: convective uplift. Convective uplift occurs when air near the ground is warmed by the sun and begins to rise.

The air rises and cools in a process known as adiabatic cooling. This leads to the formation of clouds and sometimes precipitations. For me, it is helpful to think of a conventional oven when remembering the process of convection. For one, the processes are similar. In a conventional oven, energy is added to heat up the air inside, which cooks the food within. Plus, the names are similar: conventional oven and convection.

When the ascending air mass is stable or the same temperature as the surrounding air masses, the result of convection is nice puffy cumulus clouds. However, if the ascending air mass is unstable, or warmer than the surrounding air masses, the result of convection is a cumulonimbus or thunder cloud. This happens because the warmer air keeps rising and expanding, disturbing the air masses at high altitudes.

Frontal Uplift

Next time you're watching the weather channel and hear a phrase like, 'There's a cold front coming in,' you can expect to see some clouds and maybe even some precipitation! Here's why:

Cold fronts are made of cooler, denser masses of air. When they encounter a warm mass of air, the warm air is forced up, over the top of the cooler air. As the warm air rises, water vapor in that air condenses and cools. As it does so, clouds form, eventually leading to precipitation.

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