Posted: November 15th, 2021
In this lab we will explore precipitation formation and how to forecast different precipitation types.
Part I Precipitation Formation
In previous activities we found that to form a cloud you have to bring the air to saturation, or to a relative humidity of 100%. The two ways this can happen is by reducing the temperature of the air or adding water vapor to the air. In the atmosphere this usually occurs by reducing the temperature of the air by lift. In previous chapters they discussed some of the lifting mechanisms in the atmosphere including fronts, convection, mountains, and convergence. All of these will make it more likely that a cloud will form. Further, having an unstable atmosphere will make it more likely that air will continue to rise and increase the changes of cloud formation.
However, to create precipitation that will actually fall to ground we have to grow cloud droplets or crystals to a large enough size so they will fall to the ground due to gravity. Condensation alone is much to slow to form precipitation sized droplets on their own, so the two ways we can get large droplets or crystals are collision/coalescence and the bergeron-findeisen processes. Watch the video below, which reviews these two processes, and when they occur:
Part II Precipitation Types
Once droplets or crystals become large enough that they begin to fall to the ground we have precipitation. However, depending on the temperature structure of the atmosphere, different types of precipitation are likely to occur. The main types of precipitation include rain, snow, freezing rain, and sleet. Hail is a particular precipitation type that forms mostly in severe thunderstorms, so we won’t be discussing it in detail here.
Watch this video that gives a brief review of when we will get these different precipitation types:
From previous activities you should now be familiar with stuve diagrams. These diagrams show the temperature and moisture (dew point) of the atmosphere above a certain location at a certain time, as measured from a radiosonde (also known as a weather balloon).
In the activity below you will be analyzing four stuve diagrams and using them to then forecast the most likely kind of precipitation that fell at those locations on the days the sounding was taken. You will likely need to use your textbook to help you answer some of the questions and complete the forecasts. As you complete the activity feel free to ask questions in a discussion or send me a message.
After you complete the activity, upload it to canvas to submit it.
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