Radar echoes this morning extend from border to border. It's a busy weather day in the western United States! Looks like southern California is once again bearing the brunt of the storm, at least so far.
In Utah, we are presently in large-scale southwesterly flow with warm advection ahead of an approaching cold front. The morning sounding summarizes the situation fairly well. The atmosphere is absolutely stable above about 775 mb. Veering winds with height above this level reflect to some degree the ageostrophic flow in the Salt Lake Valley, but also the large-scale warm advection.
Steady precipitation is falling over the entire Wasatch Range this morning. The persistent development of radar echoes upstream of the Wasatch strongly suggests that orographic processes are essential for precipitation at this time.
One might wonder why the radar echoes start so far upstream of the initial slope of the Wasatch Mountains. In stable situations, the flow can be strongly blocked, and a blocking front and related ascent can form upstream of the Wasatch Mountains, typically near Antelope Island. This appears to be the case today. MesoWest data show along-barrier south-southeasterly flow extending along the Wasatch Front from Salt Lake to Roy. In contrast, the flow at Hat Island is SSW.
Cox et al. (2005) examined a similar case of precipitation enhancement near Ogden using dual-Doppler analysis and developed a simple conceptual model for events like this. The blocked along-barrier flow is found beneath the dashed line in the cross section.
Situations like this are usually big precip producers on Ben Lomond Peak north of Ogden. From 2 to 7 am this morning, the snow depth at the Ben Lomond SNOTEL site increased 11 inches, with nearly 2 inches of water. It appears they are getting hammered with high density snow.
That's what is happening this morning. The storm dynamics will change today, however, with the approach and passage of the cold front.