"vv" weather icon?

[eddyg]

Unfortunately I didn't have verbose logging enabled to know which station this occurred on, but I ran into a situation a couple days ago where the icon property in an API response contained this URL:

[WARNING] Unable to map condition "vv" after parsing https://api.weather.gov/icons/land/night/vv?size=medium

vv is not listed by the API as a valid value, so I'm curious if anybody knows what might cause this to occur?