In previous posts, I have discussed some of the predictability issues associated with this weekend's storm. I still think this is a remarkably difficult forecast for northern Utah. There's much to talk about, but I'm going to concentrate primarily on Saturday, which may prove to be a very notable weather day.
The GFS forecast for 1800 UTC (1200 MDT) Saturday 17 March puts a digging upper-level trough off the California coast. Strong southwesterly flow ahead of this feature contributes to the development of a strong Intermountain cyclone centered near Wendover.
Yesterday's model forecasts for Saturday placed the frontal precipitation band associated with the cyclone in various locations (see previous post), which reflects one of the predictability challenges for this event, determining where the cyclone and frontal band will be located. The GFS forecast from last night keeps the frontal band to north and west of Salt Lake City and the central Wasatch through Saturday evening. Similarly, so does this morning's NAM, which puts the cyclone center over the West Desert at 0000 UTC 18 March (1800 MDT Saturday 17 March).
While we can't rule out the front sagging a bit further south, especially on Friday night when the models suggest it comes close before being shunted back north (not shown), the model consistency I'm seeing suggests the Salt Lake Valley and central Wasatch will remain in the warm, windy airmass ahead of the Intermountain cyclone and front through Saturday evening. We could see some valley rain/mountain snow showers pop up in the southerly flow, possibly accompanied by a little thunder and lightning.
In addition, there is significant potential for high winds across much of western Utah on Saturday, including the Salt Lake Valley and Wasatch Mountains. The GFS forecast above calls for 55 knot (27.5 m/s) at 700 mb near Delta, with a very strong sea level pressure gradient (nearly 12 mb from Page, AZ to Wendover). The NAM is also "breezy." This is a recipe for strong southerly winds and dust, which I like to call the Utah Sirocco as it reminds me of the Mediterranean Sirocco, a warm, southerly wind that often transports dust from the Sahara into Europe.
Beyond Saturday, it remains a very difficult forecast with a wide range of possibilities. This is a situation where the moisture accompanying the system is torn up into pieces and predicting position, timing, and intensity is very difficult at these long lead times.