LAS VEGAS (KTNV) — We all know rain and snow, but there is a long list of different forms of precipitation possible in the forecast. From drizzle and mist, to sleet and hail, even freezing rain! They all form after water vapor condenses in a cloud, but the temperature of the air in the atmosphere as it falls to the earth below dictates which type of precipitation it becomes!
There are four primary types of precipitation that occur most frequently.
First of course, rain! Rain develops when the water vapor in a cloud condenses and gets so heavy that it falls from the sky. When the water droplet travels through air that is warmer than freezing, the droplet remains liquid before hitting the ground, and a raindrop reaches the surface.
But what happens when the air below is colder than 32º F? That's how we get snow! In fact in the case of snow, the water vapor condensing in a cloud is so cold that it never goes through the liquid state; rather from water vapor directly to an ice crystal that never melts before reaching the ground and accumulating.
Sometimes, the layers of air between the cloud and ground vary in temperature and aren't consistently above or below freezing the entire stretch. When water vapor condenses into an ice crystal in the cloud, but melts and refreezes a few times before reaching the ground, it's considered sleet or graupel.
Hail also forms through cycles of freezing and refreezing, but hail needs the updraft of a thunderstorm cloud to help it develop. The tops of strong thunderstorms are usually very cold because they’re very high in the atmosphere, turning the water droplets in the cloud to ice. A hailstone eventually gets heavy enough to fall, but the strong updraft in a thunderstorm picks it back up, and sends it around again. Sometimes a few times! In extremely strong, or severe, thunderstorms, hail stones can grow as large as a softball or grapefruit before falling to the ground!
Looking at local precipitation, Las Vegas is one of the driest climates in the country and accumulates just over 4 inches of rainfall per year. Some winters don’t even bring snow to the valley floor! The yearly average is less than a half inch of snowfall in Las Vegas. Hail falls on occasion, most commonly during our monsoon season which helps supply the moisture necessary to develop thunderstorms.