Freezing Drizzle Possible Late Wednesday, Early Thursday
By Chris Spears
DENVER (CBS4) - It's fairly rare to talk about freezing rain or freezing drizzle in Colorado, but occasionally, we get the right set up for it to happen.
The most common way for a location to see this is when ice falling from a cloud melts in warmer air below. The rain or drizzle will arrive on the ground as a liquid but then freeze on contact if temperatures are 32°F or colder.
But in Colorado, it's often a more complicated scenario because winter temperatures both at and above the ground are often below freezing. So then why doesn't it snow?
The answer lies in the very complicated subject of cloud physics.
A cloud, which is made of thousands of tiny liquid water droplets, has a temperature threshold for those droplets to turn into tiny particles of ice. That temperature is right around -10°C, or 14°F. The formation of ice serves as building blocks for snowflakes to form.
If temperatures inside the cloud don't meet this criteria the droplets remain liquid, even though temperatures are below freezing, a concept called supercooled water.
When air between the cloud and the ground is moist enough, supercooled water droplets can fall out of the cloud and then freeze on contact when they reach the ground.
(If you are wondering how water can remain a liquid at temperatures below freezing, it has to do with the tiny size of the droplets)
Colorado's Weather Center is tracking a cold front that should push into northern Colorado sometime on Wednesday. In addition to much colder air it will also bring some moisture.
Because of the atmospheric set up described above, there's growing potential for freezing drizzle to develop in the urban corridor and on the northeast plains. While computer forecast models show the precipitation to be light, any freezing drizzle that develops could last for several hours.
If you have travel plans between Wednesday night and mid-morning Thursday you'll want to pay close attention to the forecast.
The last time widespread freezing drizzle hit the Front Range was Jan. 8-9, 2015.
Meteorologist Chris Spears writes about stories related to weather and climate in Colorado. Check out his bio, connect with him on Facebook or follow him on Twitter @ChrisCBS4.
