Soft rime on a branch (photo from Wikimedia Commons)

21 November 2025

Freezing fog made weather history yesterday when the National Weather Service in Pittsburgh issued its first ever freezing fog advisory. The advisory was issued for Westmoreland, Indiana, Armstrong, Butler, Lawrence, Clarion, Venango and Forest counties until 9 a.m, 20 November. The southwest corner of the state, including Pittsburgh, was unaffected.

This historical record may seem odd if you’ve ever been to Somerset County in winter, especially on the Turnpike. I myself have been in freezing fog at the Allegheny Front Hawk Watch (yup, no birds), but Somerset County is in the State College forecast area so they get to predict freezing fog.

The cool thing about freezing fog is that in a wind it forms rime ice, shaped like needles, on the windward side of twigs and branches. Check out the vintage article, below, about rime ice, but before you go you’ll want to watch this video from Mount Washington Observatory in New Hampshire, the Bad Weather Capital of the World. Amazing!