Sunday, February 9, 2020

East Winds and Snowfall Break

I'm at the Salt Lake airport to do my duties as a principal investigator and suffer through a week on the east coast away from snow.  The view this morning of the northern Wasatch was beautiful, with a spectacular lenticular cloud sitting right on the Wasatch crest.  

Such a cloud pattern is consistent with easterly downslope flow, as are the low level cumulus clouds closer to the airport.  Those clouds are likely forming in the updraft where the downslope flow experiences a hydraulic jump, similar to what occurs in some situations during water flow over a rock. 

The easterlies are quite evident in the weather observations near the mountains and to the east.

Source: MesoWest
Curiously, if you look carefully, you can find observations with westerly flow just to the west of bountiful and at the Salt Lake City Airport.  That is evidence of a rotor, a circulation that typically forms just downstream of the hydraulic jump.  Below is a conceptual model of the flow in cases like this.  Imagine that you are looking southward along the northern Wasatch, with easterly flow from left to right and the rotor just downstream.  Note the shallow cumulus cloud that forms downstream of the hydraulic jump over the rotor circulation. 

Source: Whiteman (2000)
Givent that I'm leaving town, you might be excited about more snow, but the Steenburgh effect doesn't seem to be working this week.  The NAEFS keeps things pretty dry until the 14th.

That's probably for the best.  Our snow safety teams need a break. 

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