Tuesday, March 29, 2011

Return of the Dirty Ridge

The Wasatch are facing a couple of days with warm advection in northwesterly flow downstream of a low amplitude upper-level ridge.  The pattern, sometimes referred to as a dirty ridge sets up tomorrow

and is progged by the NAM model to persist through early Thursday.

In this type of pattern, which we've had on a few occasions this year, we often have a shallow altostratus deck that can produce a little snow, but also rime.  Rime is produced when supercooled liquid water (i.e., cloud droplets or drizzle that is below freezing but remains liquid) freezes on contact with the snow surface, trees, the ski lift, your googles, etc.

Riming in the Wasatch is tame compared to that in coastal ranges, but can still be a pain.  We'll have to see how things pan out over the next 48 hours, but it will be interesting to see what happens on the higher peaks and ridges of the Wasatch if things come together as forecast by the NAM model.

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