Traveling north from SLC on I-15/I-84 into Idaho on a fairly regular basis, it is interesting to observe the behavior of these cold pools. When surface pressure drops to the north (such as near or to the west of a ridge axis), the cold pool usually deepens on the north side of the greater Salt Lake Basin and spills over into the Snake River Plain. At the same time, the inversion becomes very shallow in the Salt Lake Valley as the cold air migrates northward. The top of the inversion layer is only level in the absence of a low-level pressure gradient; the development of a gradient tends to skew it substantially. I think this is one (of several) reasons that the northern Wasatch Front tends to get more pre-frontal precipitation, especially snow, than SLC does.