Weatherz School: Precipitation types
It’s that messy time of year where we can get rain, snow and everything in between. Mixed precipitation forecasting can get tricky because a temperature shift of just a few degrees can sometimes determine whether the commute is wet, icy, or snowy.
Precipitation type is dependent on the temperature. Rain is what we get when the temperature is warmer than freezing from cloud to ground. Snow is when the temperature is consistently below 32°F.
Precipitation type gets more complicated when the temperature from the cloud to the ground rises and falls below freezing. That’s when we get sleet and freezing rain. These can bring dangerous road conditions.
When driving through black ice, the safest response is to keep the steering wheel straight, avoid breaking, and instead slow down by taking the foot off the accelerator.
Those are the main precipitation types. A wintry mix can include something called graupel. Graupel begins its journey as snow. It then falls through a layer of supercooled water droplets.
What does that mean? Water doesn’t immediately turn to ice when the temperature drops to 32°F. Water drops at temperatures below freezing become supercooled droplets. They remain liquid until they come in contact with a frozen surface, then they freeze. That’s how we get freezing rain.
The droplets freeze when they come into contact with the snowflake. The thin coating of ice that results is called rime.
What we end up with at the surface are tiny, white pellets that resemble small hail. The key difference between graupel and hail is that graupel is soft and crushable.
Whatever greets you on the pavement, we’ve got you covered on our website and mobile app.