Observation: Brighton Perimeter

Potential riming was in the forecast, and my first clue was sitting at home when I noticed some of the upper elevation wind stations stopped working - speed and/or direction - combined with 100% relative humidity. This often can mean they've rimed up.

Went to check it out - definitely riming. The rime feathers grow into the wind, so the wind was coming from left to right here.

Rime crusts (compared to rain crusts) are:

• rougher • more opaque • aspect dependent • thicker on the windward side of terrain These trees today are a great example of how with westerly winds, the westerly facing objects and slopes will have rime crusts, while more easterly facing slopes may not. You can't just go by the predominate wind direction only, though, because in the mountains winds are terrain forced, and wind direction can vary by slopes or drainage. Reports from Little Cottonwood are of rime on all aspects today.

The rime crust is actually quite thin in this area, especially compared to the build up on the trees and poles. (In these pictures there is still additional snow sticking to the crust, so the crust is way thinner than it looks) A concern for the future is that the crust is covering the weak facets beneath on the shady slopes, and will help protect and preserve the facets from heat and wind. While quite thin, these crusts can still be significantly durable. Today's riming event was also very elevation dependent - above about 9,500' in some places, as low as 8,500' in other places. Checking out a few lower elevation sites on my way back down the canyon, the surface snow certainly has warmed. However, the weak facets layer is so deep on the shady slopes, that there are still plenty of facets beneath the now stronger surface layers.