Avalanche Forecast

Earlier this week, shallow, low density, storm snow buried a variety of thin surface crusts which were observed all the way to ridgecrest.

Windy conditions began early on 1/8 with new snowfall and strong shifting winds building wind slabs on a variety of lee and cross loaded aspects in all elevation bands. Two skier triggered slab avalanches were reported in the Crystal backcountry mid-day Tuesday as conditions quickly deteoriated. This strong over weak snowpack structure will be further stressed by continued loading and warming, and has become and our main focus moving forward.

This latest round of storms in early January continues to highlight some of this season’s region-wide themes in our snowpack. I’d describe them as Bottom to Top, North to South, and East to West. Let’s take a look at each of these.

In general, this winter has been on the warm side in the Cascades. Nowhere is that more evident than in the lack of low elevation snow. Heavy rain events continue to wash-away and thoroughly wet the lower elevation snowpack. In most regions, you will see a substantial increase in the height of snow from low elevations (3000 ft), to mid elevations (4500 ft), and again at upper elevations  (5500/6000 ft). Above the typical rain lines (5000-6000 ft) a deep and cold mid-winter snowpack exists.

With few exceptions, this season’s storm tracks have favored the North Cascades. Sunday, Mt Baker’s Heather Meadows weather station passed 100 inches of snow on the ground. A quick look around the state’s weather stations demonstrates just how deep this snowpack is. Most other locations are reporting between 50 and 75 inches. The massive amounts of snow for the northern forecast zones are reflected in several impressive avalanche cycles spread out over the last month.

Several stacked persistent weak layers have been buried in the eastern forecast zones. This isn’t unusual, but it is noteworthy. The thickness of the slabs over these weak layers can vary greatly. Closer to the Cascade Crest, the deep snowpack may more closely resemble Stevens or Snoqualmie Passes. Further east, shallower snowpacks and significant variability are keeping snowpack assessment tricky.

So what now? Well, on January 3 and 4 a high elevation rain event impacted areas from Mt Baker to Mt Hood. In many locations, this has created a firm and thickening crust. In these locations, this new crust is limiting the impacts of any deeper weak layers. In locations that didn’t receive as much rain like WA Pass, Mission Ridge, Crystal Mt, and White Pass, how the small amount of rain impacted the mid and lower snowpacks remain to be seen.

The easterly flow will decrease Wednesday night following the passage of the shortwave trough and without much cooling aloft, snow levels will remain elevated in most areas with further erosion of the cold air east of the Cascade Crest. Stevens Pass should change to rain by about daybreak on Thursday. SW winds should generally decrease Wednesday night through Thursday. 

A warm front will brush the region on Thursday, bringing generally light rain and snow on a southerly flow. 

Thursday night and Friday should see some clearing as most of the weather action stays to our west and a ridge centered over eastern Washington and Idaho builds over the region.