Snowpack Summary 24/12/2019
What to say about this season’s snowpack? It’s the focus of many conversations I’m having recently, mostly about when we are going to get one. From a ski and snowboard perspective, it’s a bit grim, high snow line, lots of exposed hazards, poor snowpack structure with multiple persistent weak layers.
The USGS snow water equivalent report for Dec. 23rd paints a better picture. We are below average snowpack depths, but not as much as perceived, at least at elevations above 7000′. The Upper Clark Fork watershed is at 91% of seasonal norms. Lower Clark fork is at 67%, Snowbowl and the Rattlesnake sit right at the border of these two regions. The Swan has the most snow in this zone. The Bitterroot sits at 74%, with the Southern Bitterroots having less than the north. Early in November, we had above seasonal norms for snowpack depth. Warm weather, dry spells, and at least one high elevation rain event have conspired to shrink the snowpack to its current below-average thickness.
Meteorologically it is a neutral year, meaning it is neither a La Nina or an El Nino year, and ocean currents are mostly normal. Past years with similar ocean currents to this year have had above heavier precipitation, and NOAA is predicting a 50% chance for above-average snowfall from Jan.2020 to march 2020. This is no promise but may offer some hope. Regardless more snow will come, and the snowpack will get deeper.
The snowpack we have is the result of weather that has come in waves. The lower snowpack consists mainly of crusts and facets that are the result of snowfall followed by high pressure and warm, and frigid temperatures. In Nov. we had rain into the alpine that created a very stout crust. In late Nov. and early Dec. we had a week of clear skies and frigid temps. The result of moisture in the snowpack, cold temps, and shallow depths has been extensive faceting of the snowpack. Facets are angular snow crystals that bond poorly and have low friction, meaning they slide fairly easily on slick surfaces like crusts. The current snowpack is rife with them, and despite a surprising lack of avalanches can not be trusted.
Just as we need more snow to slide on, we need more snow to consolidate this snowpack. Unfortunately, due to the extensiveness of faceting, we will likely be dealing with the issue for a good portion of the winter. As we get more snow, the weak layers may become more difficult to trigger, but the likelihood of larger slides will increase. With depth and time, they will heal, but it will take a long time.
This season is one that will require some patience. Don’t let powder fever draw you into steep terrain with the first deep snowfall. Give it some time, play in the lower angle terrain, and wait for conditions to stabilize.
WCMAC Forecaster Jeff Carty