Monday, November 16, 2015

Impacts of Shallow Upslope?

We're currently post-frontal, but the depth of the northwesterly flow is quite shallow.  I'm not sure if this explains the radar distribution seen below, but there does appear to be enhancement on the west side of the Stansburys, Oquirrhs, and central Wasatch with more limited penetration into the high terrain.  The enhancement on the Oquirrhs also wraps around the NE side for reasons I can't explain.

On the other hand, the flow is weak and it's a complicated pattern, so other ideas welcomed.


  1. Given the shallow flow and its reduced ability to rise above the Wasatch, perhaps the flow would be essentially channeled in the valley and forced to rise slightly up the north slope of the valley from Magna and WVC to West Jordan. This might help explain that odd band on the north side of the valley and enhanced low elevation flanking the Oquirrh. Its almost a strictly hydrodynamic answer, and probably too simple, but I'd be interested in your thoughts as to these topographical effects, if any, when the winds and flow are this strong at surface level but not so much further aloft.

    1. Hydrodynamic views actually work pretty good in situations like this where the flow is strongly constrained to flow around topographic obstacles. In such situations, we sometimes see such channeling, although I'm not sure I see it in the current MesoWest data (it doesn't take much though and sometimes the wind shift is difficult to see in observed data).

      Another possible player is snow transport. The flow is fairly strong now at low levels.

  2. This was a strange storm. It seemed like there were basically two separate wind layers (roughly divided near the 700-mb level), and the lower one was actually fairly dry. However, since there was little stability or thermal separation between the two, the lowest atmospheric layer was locally much deeper around certain terrain obstacles (such as the Oquirrhs) and was lifting a moist layer above it, which had a more northeasterly flow direction. So you see development in unexpected areas around some of the terrain features due to this secondary lifting of an overlying layer. That is my theory for this event.