First, we have two troughs moving through the area, one that went through last night, the other scheduled for tomorrow (Tuesday). Temperatures will really bottom out in the wake of the 2nd trough and by Wednesday we are looking at 700-mb (10,000 ft) temperatures near -18ºC over the Wasatch Front. That means temperatures below zero fahrenheit above 10,000 ft.
|GFS 700-mb temperature forecast valid 1800 UTC (11 AM Wednesday MST) 7 December|
If we look at the precipitable water forecast for that time, we also see a tongue of vapor-rich air just upstream of the California coast.
|GFS precipitable water forecast valid 1800 UTC (11 AM Wednesday MST) 7 December|
|GFS 700-mb temperature forecast valid 0000 UTC (5 PM Thursday MST) 9 December|
How much moisture will get into northern Utah will depend, however, on the inland track of the atmospheric river and the impacts of the Sierra Nevada. A direct track across the southern high Sierra is usually bad for moisture transport into the Intermountain West due to the blocking of low-level moisture and the loss of water vapor on the western (windward) side of the range. As is often the case, and suggested in the precipitable water and precipitation forecast for Thursday afternoon (below), there is a major decrease in precipitable water across the Sierra due to these effects.
|GFS precipitable water forecast valid 0000 UTC (5 PM Thursday MST) 9 December|