Season Update

November 8th 2023
Flathead Avalanche

Chapter 1 of our season ended as an Atmospheric River entered the forecast region on January 12th. Earlier weather events advertised as rivers underperformed and resembled streams, creeks, or even babbling brooks. However, this one was a game-changer. It arrived as an old school Pineapple Express with over 2 inches of water, freezing levels to 7000 feet, and wind gusts that reached 100 mph. The danger rose to HIGH, and we issued an Avalanche Warning for all zones. A widespread avalanche cycle ensued, with large dry slab avalanches occurring during the early part of the storm before temperatures rose and precipitation transitioned to rain. Impressive piles of dry and wet debris reached valley floors in many locations, with at least two large slides impacting a popular groomed snowmobile trail in Canyon Creek. Debris piles were up to D3 in size, large enough to destroy a wood frame house. 

This storm’s lasting impact was a widespread surface crust found on all aspects and elevations throughout the area. Interestingly, due to orographic lifting, the crust generally increased in thickness with elevation. 

Post-Pineapple Express, most of our area experienced a drought that lasted nearly two weeks. The exception was a quick-hitting disturbance that impacted the Swan Range with 1.1 inch of water and 8 inches of snow in a 7-hour window ( Noisy Basin SNOTEL). An observer noted a natural storm slab cycle with 4-6 inch crowns on top of the 1/13 crust. Otherwise, we experienced cold, clear nights, mild weather, and seven consecutive days where we rated the avalanche danger LOW. Riding was sporty, as we learned to navigate an unforgiving crust. The calm weather resulted in a variable snow surface of either a widespread layer of surface hoar or facet development above the crust. Dribs and drabs of snowfall characterized this period, burying weak layers under a few inches of snow.

Substantial snowfall returned in late January and lasted into early February. It dramatically improved the riding but elevated the avalanche danger. The danger rose to HIGH February 4th – 8th in the Swan and the Flathead zones, and February 7th – 8th for the Whitefish zone.  Reports of intentionally-, remotely-, and accidentally-triggered avalanches continued for nine consecutive days through February 6th. Most of these failed in the weak layers above the 1/13 crust. Slides ran far and fast on top of the slick crust. Riders reported several close calls, including separate incidents where a skier and snowmobiler were caught and carried. Unfortunately, a snowmobile fatality occurred on February 6th in Wounded Buck Creek in the Swan Range. Preliminary reports indicate an avalanche hit the whole party of 5, one of whom did not survive.

On Super Bowl Sunday, a cold arctic air mass spilled over the Continental Divide resulting in frigid air temperatures, breezy north and east winds, and dry conditions. The deep freeze was long-lasting, five days and **counting as of the publishing of this post. The cold temperatures and partly cloudy conditions lead to surface hoar development and faceting in the near-surface snowpack. Yet another weak layer to track when the storms return. The bitterly cold weather inhibits the strengthening of buried weak layers and keeps the Persistent Slab as a lingering problem going forward. 

Despite what appears to be a relatively dry season, the Flathead River Basin reports 99% average SWE on February 11th, with Flattop in central GNP leading the charge with 113%. Noisy Basin in the Swan Range weighs in at 106%, and even a low-elevation site, Emery Creek, reports near average SWE. Perhaps not the La Nina year we hoped for, but still better than most across the western U.S.