Updraft® - Minnesota Weather News

Winter magic: Stunning rime ice decorates trees Monday morning

What's the difference between rime ice and hoar frost?

Rime ice Monday morning.
Rime ice Monday morning.
Duluth National Weather Service

Minnesota awoke to a beautiful display of wintry magic Monday morning.

Freezing fog overnight deposited a beautiful layer of rime ice on trees.

The intricate icy coating covered much of Minnesota as a blanket of freezing fog rolled across the state early this morning. The Duluth NWS office shared this spectacular image. There’s also an equally spectacular view of an icy fence from St. Paul.

Rime ice Monday morning.
Rime ice Monday morning.
Duluth National Weather Service

Anatomy of rime ice

Rime ice forms when light winds blow supercooled water droplets in freezing fog onto frozen objects. Notice how the ice accumulates on one side of the trees in the photos above? That’s because light wind deposits the ice on the windward side of tree branches and fences. Or on this cool windmill piece in Luverne.

Hoar frost or rime ice?

This morning’s display was largely rime ice. Here’s a good description of the difference between rime and hoar frost from the Twin Cities NWS office.

De-icing anyone?

Ever had your plane de-iced even when it’s not raining or snowing at the airport? That’s because clouds aloft can deposit dangerous rime ice on planes as they ascend through the wet layer.

Ice threat aloft
Ice threat aloft
NOAA COMET Program

Accumulating rime ice can add dangerous weight to aircraft, and mess with the aerodynamics of wings.

Icing effects on flight
Icing effects on flight
NOAA COMET Program

Rime ice is a big danger for aircraft. But it’s beautiful on the trees.