Avalanche Forecast

Warm front moisture should begin moving into the Northwest on Tuesday especially to the Olympics and north to central Cascades. But rain or snow and warming should also begin to increase over the south Cascades on Tuesday. The avalanche danger levels will be a moving target as they rise on Tuesday especially in the north to central Cascades.

SW alpine winds are likely to begin to build new wind slab on mainly N-SE slopes on Tuesday. Alpine winds have been predominately from the SW-WSW the pasts few days with some SE winds. Hence NW to SE slopes will be indicated. But watch for firmer wind transported snow that indicates wind slab on all aspects in areas of more complex terrain.

New storm slab is likely in areas that rapidly accumulate more than a few inches of new snow. The warming trend will also help build upside down denser snow over initial lower density snow.

Recent cornices are very large. Make sure to avoid areas on ridges where there may be an overhanging cornice as well as travel on steep slopes below cornices! Natural cornice releases and resulting slab avalanches are unpredictable. See a blog post regarding cornices here.

Loose wet avalanches will not be listed as an avalanche problem but will be possible in the below treeline where there is significant rain, solar effects or warming. Watch for wet surface snow deeper than a few inches, pinwheels or initial but growing natural releases.

You will need to keep a sharper than usual eye on weather conditions if you take a trip into the backcountry on Tuesday. Be prepared to ratchet back your plans if winds become stronger and snow or rain becomes heavier than you expect and you see signs of instability such as cracking of new snow layers or loose wet avalanches before Tuesday night.

The avalanche danger should continue to significantly increase on Tuesday night.

Special Note: For more information on the massive natural cornice triggered avalanche on the north side of Ruby Mountain on Sunday 3/19 and general thoughts about low-likelihood/high consequence avalanches, please see NWAC's blog post issued Sunday, March 26. 

Weather and Snowpack

The first week or so of March was very cool and snowy. NWAC and NRCS stations indicate about 2 feet of snow in the northeast Cascades with less elsewhere along the Cascade east slopes. 

The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately, these systems delivered more rain than snow to lower/mid elevations along the east slopes of the Cascades. At least two regional avalanche cycles occurred during the stretch. The most recent cycle from mid-March had many massive slides that covered Hwy 20 near Washington Pass up to 40' deep in places! Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. Far less precipitation was seen further east of the crest during this period for areas like Blewett/Mission Ridge. 

A strong low pressure system brought 6-12 inches of snow in the northeast and central-east slopes of the Cascades Friday, 3/17 and mostly rain for the southeast Cascades. This was followed by snow levels rising to 6000-6500 ft in the northeast and central-east Cascades and likely 7000 ft in the southeast Cascades by Saturday morning 3/18. 

This past week has also been active weather-wise, but water amounts/snowfall totals have been slightly lower relative to the extreme wetness of the past few weeks.It looks like NWAC and NRCS stations east of the Cascade crest had about 6-12 in on snow in the 5 days ending Monday morning.  The guides at the Barron Yurt near Hart's Pass reported about 8 in of recent storm snow as of Saturday afternoon.

Recent Observations

North

The NCMG near Washington Pass Tuesday, 3/21 reported hearing many natural avalanches near midday following a prolonged sunbreak and subsequent brief warm up. Numerous avalanches were likely small, however, some avalanches sounded much larger, likely involving deeper layers below the relatively shallow recent storm snow.  

NCHG reported no significant new avalanche activity observed outside of one small natural storm slab on a north aspect above treeline Thursday.

Reports from the NCMG at the Barron Yurt on Friday and again Saturday indicate the recent wind transport was mainly shallow but evident near ridges. Recent SW winds were building shallow wind slabs as of Saturday and were avoided. There were a few small natural avalanches that occurred on very steep shaded terrain, mainly above 40 degree's. These were D1-D1.5 in size and unknown whether they loose-dry or shallow wind slabs. No triggered slides were observed Saturday.

The NCMG was in the Cutthroat area on Monday and found 15-20 cm of recent snow on a firm base. Loose wet avalanches and cornices were the main concerns. 

Central

On Friday, the Mission Ridge patrol reported very sensitive storm and/or wind slab up to 6-8 inches deep on lee aspects near and above treeline. NW aspects were especially sensitive.

NWAC observer Tom Curtis was on the lower slopes of Mt. Cashmere Friday below treeline. About 5 cm (2 in.) of new snow had accumulated in this area. On steep test slopes, Tom easily triggered loose wet avalanches entraining moist underlying snow with the potential to become large. Although not directly observed, Tom heard several large natural avalanches release up the Trout Cr drainage along ridge-crest in the morning. It is possible these avalanches were cornice triggered.  

South

No recent observations.