Freezing drizzle: How it forms

 

A mix of snow flurries, drizzle, and freezing drizzle have all been reported Wednesday evening as low pressure moves into southwest Wisconsin. Snow and drizzle accumulations have been light, but enough to cause some slick conditions on some of the area roads, as well as in parking lots and on sidewalks. Scattered snow flurries will continue during the overnight, becoming a little steadier into the afternoon Thursday. Highs on Thursday warm into the middle 30s.

Freezing drizzle can be harder to detect, and notice, not only on radar but also as it occurs because of how it forms in the atmosphere. Freezing rain develops when the air temperature above is greater than 32 degrees (to get rain), but surface temperatures are below 32 degrees. As the rain hits the surface it freezes on contact. The formation of freezing drizzle is a little more complicated.

Drizzle forms from clouds that are a little lower in height in the atmosphere. Freezing drizzle forms within a cloud layer with a specific temperature, which is between 0°C to -10°C - roughly 32°F to 14°F. If the temperature within the cloud is colder, snowflakes will form. The water droplets that form within that temperature range - 0°C to -10°C - remain in their liquid state but are 'supercooled' and known as supercooled water droplets. These water droplets don't freeze while in the atmosphere and fall from the cloud as drizzle. As the droplet makes contact with the ground, or surface, at or below freezing it will freeze on contact. Freezing drizzle can be very dangerous and cause ice accumulations to occur quickly.

As we get further into the night the process that forms drizzle will become a little less, leading to the production of more snowflakes. This means that scattered snow flurries and snow showers will become more common through the morning and afternoon Thursday.