As anticipated in Monday's post, a messy storm has arrived in northern Utah.
Let's start with the big picture. The 6-hour GFS forecast valid at 1200 UTC (5 AM MST) this morning shows high integrated water-vapor transport (IVT) values associated with an atmospheric river curving anticyclonically (clockwise) from near Hawaii over a high-pressure system off the coast of California and across Oregon and Idaho towards Utah.
A closeup for the western U.S. shows atmospheric river conditions extending into northern Utah.
This pathway across Oregon and southern Idaho is one of two key ones for atmospheric river penetration into northern Utah as it minimizes water vapor loses to precipitation over high barriers such as the Sierra Nevada. The other key pathway comes up the lower Colorado River Valley and through western Utah.
This morning's 1200 UTC (5 AM MST) sounding from the Salt Lake City airport shows saturated conditions near and above 700 mb (about 10,000 feet), but drier air below that level, Thus, moisture transport has come in aloft over the drier air that was resident over the Salt Lake Valley and Great Salt Lake Basin.
This is consistent with the view looking south from the University of Utah this morning which shows layered clouds based at about 9000 or 10000 feet above sea level. Note also the transition from west (right) to east (left) with the mountains becoming obscured, a tell-tale sign of orographic precipitation enhancement as the flow moves over the mountain barrier.