As we discussed in the previous post, the models are forecasting a serious blast of cold air to move into Utah this week, with the arctic air arriving Monday night and Tuesday.
The 12Z initialized NAM from this morning (Sunday) drops Salt Lake's 700-mb temperatures down to a brutal -23C by Tuesday afternoon. There are not many days around here where the 700-mb temperature is that low.
This morning's 0900 UTC initialized SREF is event colder with a forecast ensemble mean 700-mb temperature for KSLC of -25C.
The GFS remains the "warmer" model, with a forecast 700-mb temperature of -22C. Warm here is clearly a relative term!
The setup for the arctic blast involves interactions between large-scale features in the high latitudes and the mid-latitude Pacific Ocean. In the high latitudes, a deep low is presently centered near Hudson Bay, with an upper-level ridge centered over interior Alaska. Note how this yields equatorward flow at upper levels that extends nearly to the pole, opening the "door" for cold air to move southward.
By tomorrow morning, strong warm advection and latent heating ahead of a cyclone over the mid-latitude Pacific Ocean build a high amplitude ridge over the northeast Pacific Ocean.
This Pacific ridge continues to build through Tuesday afternoon, ultimately merging with the aforementioned high-latitude upper-level ridge. This yields northeasterly upper-level flow that opens the door for cold air to spill southward and westward into the Intermountain West.
Thanks to the Continental Divide, we will be spared the coldest air, but this is still going to be an impressively cold airmass.