Ask a Climatologist: Is that ice fog or freezing fog?

Ice fog is made up of tiny ice crystals that form when it’s at least -30 degrees Fahrenheit. In urban areas, the crystals often form around pollution particles from vehicle emissions or wood smoke. (Photo by Joseph Hall)
Ice fog is made up of tiny ice crystals that form when it’s at least -30 degrees Fahrenheit. In urban areas, the crystals often form around pollution particles from vehicle emissions or wood smoke. (Photo by Joseph Hall)

Anchorage residents have been waking up to fog most days recently. But do the cold temperatures that go along with it make it technically “ice fog”?

To answer that question, we spoke with Brian Brettschneider, a climatologist in Anchorage who closely tracks Alaska climate data and trends. Alaska’s Energy Desk is checking in with him regularly as part of the segment, Ask-A -limatologist.

He told Energy Desk editor Annie Feidt you can’t have ice fog unless it’s at least 30 below zero.

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Interview Transcript:

Brian: Even though it’s been in the single digits and even close to zero the last few days in Anchorage, it’s actually regular fog. It’s no different than a fog that would happen in July or August, it’s just colder outside. The fog particles themselves are actually little microscopic liquid water droplets.

Annie: How is that different than an ice fog?

Brian: With ice fog, instead of liquid water droplets, the fog particles are actually ice crystals. That doesn’t happen until you’re at a minimum of -30 degrees Fahrenheit. In rural areas you wouldn’t see it until it’s at least -40 or -45 Fahrenheit.

Annie: Is it something you can just see is different?

Brian: No. You can’t actually see what the fog is made out of. Even though you see fog and have reduced visibility, you’re not actually seeing the water droplets. It can condense out into mist or even ice crystals or snowflakes. But you can’t see the particles, so you wouldn’t know by looking whether it’s freezing fog or ice fog, you would need to look at the thermometer.

Annie: Does ice fog act differently in how it forms or how it dissipates?

Brian: It’s a very, very cold phenomenon. The nucleus of the fog particles is typically pollution- automobile exhaust or even smoke particles from fire places. When it gets cold enough, there becomes a point where it’s so cold that it’s almost impossible not to have ice fog. I think if it’s -60 or -70, no matter where you are, possibly with the exception of Antarctica, you’re going to get ice fog, whether the atmospheric conditions are conducive for fog or not, it’s just so cold that any little particle in the atmosphere is going to start collecting ice crystals on it.

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Annie Feidt is the Managing Editor for Alaska's Energy Desk, a collaboration between Alaska Public Media in Anchorage, KTOO Public Media in Juneau and KUCB in Unalaska. Her reporting has taken her searching for polar bears on the Chukchi Sea ice, out to remote checkpoints on the Iditarod Trail, and up on the Eklutna Glacier with scientists studying its retreat. Her stories have been heard nationally on NPR and Marketplace. Annie’s career in radio journalism began in 1998 at Minnesota Public Radio, where she produced the regional edition of All Things Considered. She moved to Anchorage in 2004 with her husband, intending to stay in the 49th state just a few years. She has no plans to leave anytime soon. afeidt (at) alaskapublic (dot) org  |  907.550.8443 | About Annie