How does sleet form

Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. Most people think of a blizzard as a bad snowstorm, but a winter storm must meet certain criteria to be classified as a blizzard. According to the National Weather Service, a blizzard is a weather event that includes low temperatures, wind speeds greater than 56 kilometers 35 miles per hour, and a large amount of falling or blowing snow that lowers visibility to 0.

These whiteout conditions can cause car accidents and people on foot to become lost. Additionally, the colder temperatures that often follow a blizzard can put people at risk of frostbite or hypothermia. Explore more about blizzards with this collection of resources. Precipitation is any type of water that forms in the Earth's atmosphere and then drops onto the surface of the Earth. Water vapor, droplets of water suspended in the air, builds up in the Earth's atmosphere before precipitating.

Snowpack is snow on the ground in mountainous areas that persists until the arrival of warmer weather. Melting snowpack is an important source of water for many areas. During an avalanche, a mass of snow, rock, ice, soil, and other material slides swiftly down a mountainside. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content.

Sometimes, however, a temperature inversion occurs. Normally, the temperature decreases with increasing altitude. A temperature inversion is when a layer of warm air intrudes between the ground and the clouds. Under these conditions, when the falling snow reaches the layer of warm air, it melts.

This all happens very fast, and the result is tiny ice pellets called sleet. Add the two values together and then divide by two. The resulting value is your ice accumulation. Sleet is measured much the same way snow depth is measured. You will need a ruler, and possibly a piece of paper and a pen. Locate a surface that is solid, level and in the open.

Avoid measuring sleet depth under trees or directly next to buildings. Slide the ruler directly downward into the sleet until it reaches the ground. Read the value on the ruler to the nearest tenth of an inch, if possible. Record this value on your piece of paper. Complete our storm report form. When making your report, please remember to include the following information, if known:.

Please Contact Us. Please try another search. Multiple locations were found. Please select one of the following:. Location Help. A warm front is a mass of relatively warm air that moves across the surface, displacing cold air in its path.

In the cross section shown here, the warm air is on the left side on top of the frontal boundary and cold air is on the right side of below the boundary. The warm air is less dense than the cold air, so it is wedged up and over the colder air mass. If warm air resides above colder air, it creates a temperature inversion. As the warm air is forced to rise, it cools, forming clouds and rain above and along the boundary.

Close to the surface position of the front, rain produced along the front only falls through a short vertical interval of cold air. If raindrops pass through this zone without refreezing, they will reach the ground as normal rain. This is the first type of precipitation that announces the arrival of the warm front. Farther back from the surface location of the front, the ground may still be at freezing temperatures. In this case, the rain freezes upon encountering the ground and other cold objects on the surface, producing freezing rain.

As the warm front passes over an area hovering near freezing temperatures, therefore, normal rain follows freezing rain. Even farther back from the surface warm front, rain produced aloft must pass through a thicker column of cold air.

Thus, raindrops have enough time to freeze on the way down, forming sleet. Snow can be associated with a warm front if the warm air rises so high off the ground that it is below freezing.