Storm Cycle Update

Snow continues to stack up in the Wasatch and the red flag continues to fly for the backcountry avalanche danger.

Utah Avalanche Center Forecast Summary Issued 13 January 2024

From 5 AM MST Wednesday to 5 AM MST Saturday, the Alta-Collins automated snow-depth sensor has ticked off 30" of snow, putting us half way to the over-under that I set at that time for the remainder of the storm cycle through Monday (see Shall We Set the Over Under for This Storm Cycle?).  It also lifts us up to about 43" since Jan 9 and 68.5" since Jan 4.  These numbers are based on a mixture of data from the Alta Snowfall history and the automated snow stake so they may differ slightly from other estimates, especially given yesterday's wind.  I notice that the Alta web page is listing the storm total as 44", so they must be using Jan 9 as the start date. 

As I write this at 7:20 AM, we are in a bit of a lull, but I say that with a caveat. There are still some snow showers around, including three wind-parallel bands that extend downstream from the three primary ridges in the central Wasatch and into the Wasatch Back.  It is not unusual for the radar to exhibit echoes over those ridges due to ground clutter, but these bands clearly extend well downstream.  The one that extends downstream from the Mt. Raymond – Park City Ridgeline was best developed when I grabbed the image below and extended downstream to near Jordanelle Reservoir.  

Expect some periods of snow today, increasing in frequency and intensity later this afternoon as the next major system approaches.  The GFS forecast valid 0300 UTC 14 January (8 PM MST Saturday) shows  a compact upper-level trough over southern Oregon with strong integrated vapor transport, warm advection, and precipitation over or just upstream of northern Utah.  

This is a recipe for a transition to higher-density snow and potentially higher water-equivalent snowfall rates, especially as the trough approaches overnight, as illustrated below.

Tomorrow, with the trough through, we transition to northwesterly flow with, you guessed it, more snow.  

As noted above, the backcountry avalanche danger is high, with forecasts calling for it to rise to extreme.  In the video below, Trent Meisenheimer calls the avalanche danger "as wild as I've seen it in my tenure." 

My touring party yesterday elected to go for a "trail" tour for exercise, staying entirely in thick trees, and I think we have all decided to give up on mid- and upper-elevation ski touring and let Mother Nature have "fun" for a few days.  I often talk about outlier mode in meteorology, but these are outlier mode conditions for the snowpack and microterrain features in many "safe" zones are producing hair trigger avalanches that are catching experienced riders.  One skier was buried yesterday and fortunately recovered by their partners.  The provided a very honest and sobering write up that is available at https://t.co/s05EuP7ypl.  I am grateful all is well and thankful they had the courage to share this report.

Getting back to the forecast, I'll focus here on the the latest HRRR run for Alta/Little Cottonwood, which just arrived. Precipitation rates are forecast to be fairly low until about 2 PM, when they start to pick up.  Overnight, you know what hits the fan.  From 11 PM Saturday to 8 AM Sunday the HRRR puts out 1.4" of water and 15" of snow. For the period beginning 5 AM this morning and ending 5 PM Sunday, totals are 2.63" of water and 28" of snow.  This is higher density stuff than we've seen, with our algorithm going for snow-to-liquid ratios below 10:1 prior to the trough passage tonight and the wet-bulb zero level reaching almost 7000 feet.  This might push snow levels to just above the benches.   

The numbers from the GFS (not shown) are a bit lower for that overnight period (0.85" water/10" of snow) and the period from 5 AM this morning through 5 PM Sunday (1.7" water/21" snow).  The GFS is a bit cooler, with the wet-bulb zero level only reaching 6000 ft.  Nevertheless, it goes for the higher density snow tonight as well.  

I'll add that the GFS extends farther into the future than the HRRR and it continues to produce snow through 11 PM Monday with another storm on Wednesday.  The Euro is also on board with the Wednesday storm.  

I'm buckled up already, so I'm not sure what to recommend at this point except let the road maintenance, public safety, and snow safety teams have all your patience and respect.  We are deeply in outlier territory.