NCAR Science on Twitter: "#FBF In 1999, Carlye Calvin took this spectacular photo of a unique cloud formation fanning out over Boulder… but what is it? Tell us your guess in the
![A winter tree with its branches fanning outward stands with heavy clouds behind it. There is grass in the foreground and hedges beyond Stock Photo - Alamy A winter tree with its branches fanning outward stands with heavy clouds behind it. There is grass in the foreground and hedges beyond Stock Photo - Alamy](https://c8.alamy.com/comp/2ATY8PM/a-winter-tree-with-its-branches-fanning-outward-stands-with-heavy-clouds-behind-it-there-is-grass-in-the-foreground-and-hedges-beyond-2ATY8PM.jpg)
A winter tree with its branches fanning outward stands with heavy clouds behind it. There is grass in the foreground and hedges beyond Stock Photo - Alamy
FSWN Fanning Springs - FSWN Fanning Springs at sunset and it's 66.9 F - https://dixie.weatherstem.com/fswnfanningsprings. Tag image: https://www.weatherstem.com/clouds?ts=1609281010&camera=1648 | Facebook
![A winter tree with its branches fanning outward stands with heavy clouds behind it. There is grass in the foreground and hedges beyond Stock Photo - Alamy A winter tree with its branches fanning outward stands with heavy clouds behind it. There is grass in the foreground and hedges beyond Stock Photo - Alamy](https://c8.alamy.com/comp/2ATY8TG/a-winter-tree-with-its-branches-fanning-outward-stands-with-heavy-clouds-behind-it-there-is-grass-in-the-foreground-and-hedges-beyond-2ATY8TG.jpg)