Juicy

TL;DR: Skiing and riding conditions remain excellent in Utah, with a light refresh today and a large snowstorm to wrap up the weekend.

Nowcast: Resorts last reported new snow yesterday (Thursday, Dec 8). Overcast skies and some snow showers prevail this morning. While the Wasatch front resorts are not seeing any snow right now (7:00 a.m. local time), Deer Valley's Silver Lake Lodge webcam is looking quite snowy.

Source: Deer Valley Resort

KMTX radar imagery confirms precipitation is occurring in the Wasatch Back, while the Wasatch Front remains dry right now. 

Source: University of Utah Department of Atmospheric Science

Short-Term Forecast: A low amplitude, shortwave trough is responsible for today's storminess. Over the course of the day, the flow will shift from southerly to northwesterly near the surface, as the trough passes through the region. The plot shown below is a time height from the 0600 UTC HRRR model, and it is read from right to left (today is on the right side, and Sunday is on the left side).  Notice how in the period on Friday afternoon (circled in magenta), there is a distinct shift in the wind direction from southwesterly to west-northwesterly, and a drop in temperature, signifying the passage of the trough axis.

Source: University of Utah Department of Atmospheric Science

With modest relative humidity values, we should be able to squeeze some precipitation out of this system.

Look for precipitation to first impact the region at around 9:00 a.m. local time and continue through the early afternoon. This is not a big event. The HRRR initialized at 0600 UTC shows a modest 0.08 in. of precipitation for Alta through 2:00 p.m. local time, which would correspond with about an inch or so of snow.

Source: University of Utah Department of Atmospheric Science

Mid - Long Range Forecast: The main event is a long-duration event, which will begin on Sunday and won't wrap up until Tuesday. This one looks like one of those classic Utah storms that we love. A plume of high integrated vapor transport (IVT) (think high moisture), will make its way into the interior United States from the southwest, bypassing the highest terrain of the Sierra Nevada, which will be north of this plume. This is evident in the bottom right panel of the 0600 UTC GFS data, where we see IVT values ranging from 100 kg/m*s to 250 kg/m*s throughout Utah. Not remarkable by California or Pacific Northwest standards, but that is a lot of vapor transport for our region.

Source: University of Utah Department of Atmospheric Science

In this phase of the storm, we'll see moist southwesterly flow with gusty winds and an upper-level low just to our left (see top right panel above). We'll see high precipitation rates in this prefrontal southwesterly phase, with widespread areas of precipitation rates in the 0.05 to 0.10 in/hr range, which would correspond with just below an inch of snow per hour (see 1 hr precipitation for 0000 UTC on Monday in the plot below). Prior model runs were more excited about more organized intense precipitation rates in the Wasatch, but the latest GFS has backed off on this a bit.

 

Source: University of Utah Department of Atmospheric Science

The frontal passage occurs overnight on Sunday into Monday, with an abrupt shift in the flow direction from southwesterly to northwesterly. During this phase, the northwesterly flow that we all love will take control, bringing post-frontal orographic convection to the Wasatch, and delivering additional low-density snow to the mountains through Tuesday morning. 

This event is shaping up to be a right-side-up event, starting warm and moist in the prefrontal southwesterly flow period, and transitioning to cold with low-density snow in the postfrontal period.

Snowfall Forecasts: It's tough to narrow down on exact numbers at this point, but here is my best guess for the central Wasatch.

Today:

Little Cottonwood Canyon: 1-2"

Big Cottonwood Canyon: 1-2"

Park City: 1-2"

Sunday-Monday Storm:

Little Cottonwood Canyon: 18"-2 FEET (with potentially more depending on post-frontal orographic convection)

Big Cottonwood Canyon: 18" - 2 FEET

Park City: 16" - 22"

Bottom Line: This forecast is looking juicy, and skiing and riding will remain excellent. Enjoy!

Backcountry Comments: If you will be traveling in the backcountry make sure you have the proper equipment and know before you go. For the most recent avalanche forecast and all things avalanche head over to our friends at the Utah Avalanche Center.