Avalanche Forecast

A warm front should stay draped over the US/Canadian border Saturday, producing moderate precipitation at rapidly increasing snow levels to mainly the north Cascades on Saturday. Warming but only light precipitation is forecast for the central Cascades and the south Washington Cascades may even see filtered sun. 

Loose wet will be the primary concern on Saturday as a transition to rain loads new snowfall received on Friday or early Saturday in the north Cascades. Wet loose avalanches are becoming more likely if you see pinwheels or initial small natural wet loose releases. Moderate westerly winds on Friday may have built sensitive wind slab on lee easterly aspects in this region near and above treeline.  Shallow new storm slab that layers denser snow on top of less dense snow from Saturday morning may be concern at higher elevations by Saturday afternoon. Use caution on Saturday and expect increasing avalanche danger during the day. 

Triggering a wet slab avalanche to a deeper layer is unlikely, but this will continue to be an avalanche concern since recent heavy rain has allowed water to penetrate deep in the snowpack and a step down release to a weak layer/crust from mid-winter cannot be ruled out. To mitigate this concern, generally avoid large avalanche terrain over the weekend and wait for the moist upper snowpack to tighten up.  

Recent Weather Summary

Over the past month two major storm cycles moved across the Pacific Northwest. The most recent week long storm cycle occurred in early March and wound down last Sunday. This storm cycle produced similar water equivalents as the February cycle; water equivalents and snowfall totaled about 9-13 inches and 2-6 feet at most NWAC sites near and west of the crest. This cycle was warmer and featured mainly wet snow and rain leading to several natural avalanche cycles during the first week of March. Average freezing levels have been roughly 2000-3000 feet higher thus far in March versus February! 

The heaviest rain and warming came last weekend and was followed on Monday by a few inches of snow and cooling.  Drier and gradually warmer weather was seen late this week.  A front came through Friday morning with rain and gradual cooling, and deposited several inches of snow above 4000 feet in showers. Some of the heaviest accumulations were from a convergence zone focused on the Stevens Pass and Mtn Loop Hwy area through Friday afternoon. 

Recent avalanche observations

The ski patrol at Crystal Mountain on Sunday and Monday produced consistent large wet slab releases with large explosive charges releasing to deep layers from early this winter. These avalanches were generally on N to E slopes at about 6-7000 feet with crowns of 4 to 6 feet and up to 10 feet in spots with the High Campbell chair and some trees destroyed.  See photos at the Crystal Mt web site. They also reported similar natural releases were seen in the adjacent Mt Rainier National Park.

On Tuesday 11 March, NWAC observer Dallas Glass also found recent very large wet slab releases on Kendall Peak at Snoqualmie Pass. Several large to very large (very destructive) wet slab avalanches began at about the 5500 ft elevation on primarily W aspects on slopes of about 35-40 degrees and ran about 1000 feet. These slides likely released Sunday night or Monday when the area received over 3 inches of rain to elevations above 5500 feet. A video of the slide area and debris fields can be seen here  NWAC channel.  On Thursday, backcountry skier Andy Hill found wet slab debris from earlier in the week that stepped down to the firm January crust in Great Scott Bowl in the Alpental backcountry with an 8-10 ft crown.  Also, avalanche educator Gary Brill reported about a dozen large slab releases on N thru E aspects up to around 6000 ft following this storm cycle on a flight Wednesday along the west slopes.  

While it is unlikely these deep wet slab avalanches could be human triggered, it remains a possibility if initiated at a thin spot in the slab. WSDOT professionals and NWAC observers during the middle of the week reported moist snow and a lack of temperature gradient penetrating deep in the snowpack.  Wet slabs will remain a concern especially during times of rain or extended warm periods and are not necessarily tied to the period of heaviest rain or warmest temperatures. With more rain and mild temperatures forecast this weekend, wet slab avalanches will remain a concern near and west of the crest. Here is a link to more information about the wet slabs.

A natural wet loose cycle was reported near Stevens and Snoqualmie during the frontal passage and heavier precipitation Friday morning.  See NWAC obserever Jeff Hambelton's video on new wind slab concerns in the Mt. Baker backcountry from Friday.  

Photos by Andy Hill 3-11-14, Alpental backcountry off a D3/R3 wet slab from early last week.