Wonder Wednesday: Precipitation

Size comparison on how big sleet is. Usually small pieces of transparent ice. Image courtesy of wikimedia.commons.

For most storm systems, precipitation is a main component, with the four main types being rain, hail, snow, and sleet. While the basic genetics of each type is the same (all are made of some state of water), the formation of each depends on the temperatures in the air and at surface level, as well as the strength of the wind.

As moisture rises into the atmosphere, known as evaporation, this invisible bubble of air gets smaller because of the cooler temperatures in the upper atmosphere, until it reaches a size which is completely filled with the moist air (saturation). This bubble will go through condensation, transforming the air to a liquid. The droplet continues to travel up in the atmosphere, until it turns to a crystal, making it a snowflake. As the snowflake/dendrite gets heavier, the winds keeping it suspended in air starts to lose the ability to keep it suspended, letting gravity take over.

A look at how temperatures impact what type of precipitation we get. Picture courtesy of wikimedia.commons.

As the crystalized water falls, depending on the temperatures will depend on what type of precipitation we will experience once it reaches the surface of the earth. If the temperatures continues to remain around the freezing point (32 degrees Fahrenheit or 0 degrees Celsius), we will see the snow. If there is warmer air towards the surface, the snow can melt, and turn to freezing rain. If the warmer air is higher in the atmosphere, but drops back to the freezing point, this becomes sleet, which is small ice pellets. This can also result in mixed precipitation, depending on how big the area of warmer air is in the upper atmosphere. However, if the temperature is warmer than the freezing point all the way to the surface, the snowflakes turn to rain drops and will fall as so.

But what about hail? Hail is a bit on the tricky side. A single snowflake can melt, and become a small water droplet, but is still light enough to be lifted back into the air. This will freeze the droplet, which would typically be sleet. However, other water droplets may collect on this piece of ice, and will cool on contact, adding another layer of ice. With the heavier weight, the ice can fall towards Earth once again, but with stronger winds, gets lifted in the air again. Think of this cycle similar to dryer, tumbling clothes, but instead of warming, it’s cooling things down. Depending on the strength of the upward winds will depend on the size of the hail. Hail is measured compared to common everyday objects. However, comparing to a marble isn’t helpful since marbles are in several different sizes. The larger the hail, the stronger the updraft and more water accumulation gathered.

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