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RegisterMar 14th, 2017–Mar 15th, 2017
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We have already experienced a region-wide avalanche cycle such that the overall likelihood of wet snow avalanches has diminished. However, destructive wet slab avalanches are still being reported in isolated areas. Realize that wet snow avalanches, specifically wet slab avalanches, are very hard to predict and demand an extra amount of caution when engaging with avalanche terrain.
The relatively high snow levels will continue with rain forecast below 6000-7000 feet through early Wednesday morning. Steady precipitation will continue during the day on Wednesday but snow levels will gradually lower with rain turning to snow above treeline first in the northwest Cascades by late morning and later in the day for the southwest Cascades. Check the mountain weather forecast for details on the gradual cool down. Periods of moderate W-SW winds above treeline will continue to transport new and recent snowfall in the upper portion of the above treeline band Tuesday night through Wednesday.
We have already experienced a region-wide avalanche cycle such that the overall likelihood of wet snow avalanches has diminished. However, destructive wet slab avalanches are still being reported in isolated areas. Realize that wet snow avalanches, specifically wet slab avalanches, are very hard to predict and demand an extra amount of caution when engaging with avalanche terrain. The cooling trend on Wednesday is not occurring fast enough to lower the regional avalanche danger.
Wet slab avalanches are highly unpredictable and not necessarily tied to peak warming or rainfall. Besides their huge destructive potential, wet slab avalanches often surprise backcountry travelers when they run further than expected.
Loose wet avalanches are possible on steeper slopes with the additional rainfall. While most loose wet avalanches will be shallow, a few may gouge down to deeper layers and become more powerful than you expect.
Cornices have been weakened and prone to failure due to rain and mild temperatures. Very large cornices have been reported in many areas and have been involved in recent accidents and close calls. A cornice failure could trigger a large and destructive wet slab avalanche.
If you manage to venture into the above treeline zone Wednesday, expect new or previous wind slab mainly on NW-SE aspects due to recent SW-W winds. Continue to watch for firmer wind transported snow on all aspects especially in areas of complex terrain.
Weather and Snowpack
The first week or so of March was very cool and snowy. NWAC stations along the west slopes of the Cascades piled up about 3 to 8 ft of snow with the most at Mt Baker.
A strong frontal system brought increasing precipitation and winds along with a warming trend to the Cascades on Thursday 3/9. On Thursday night rain pushed up to about 5000 feet in the northwest Cascades and about 6500 feet in the southwest Cascades. This caused a region-wide avalanche cycle with several large to very large wet avalanches impacting mountain roadways.
Moist W-SW flow and a stalled frontal boundary have produced periods of moderate to occasionally heavy rainfall at most locations throughout the west slopes of the Cascades on Monday and Tuesday. Rainfall totals through 4 PM PST (or 5 PM PDT)
Recent Observations
North
The Mt Baker patrol reported natural avalanches last Thursday night. A very large avalanche released during avalanche control work on Shuksan Arm Friday 3/10 producing a 8 ft x 75-100 yd crown.
Shuksan Arm avalanche crown from Friday 3/10. Photo Mt Baker Ski Area.
NWAC observer Lee Lazzara was out near the Mt Baker ski area on Sunday 3/12 and reported 20-25 cm of homogeneous moist snow well bonded to the 3/10 crust over deep dense snow. Cornices were huge with ski triggered loose wet avalanches possible.
On Tuesday Mt. Baker pro-patrol reported hearing a very large natural avalanche high on Mt. Shuskan as well as observing fresh debris in Rumble Gully from wet slab avalanches releasing off Shuskan Arm. Due to poor visibility, start zones could not be identified other than placing them in the above treeline zone.
Central
The Stevens Patrol and Stevens and Snoqualmie WSDOT crews reported many wet slab and loose wet avalanches from control work and natural cycles Wednesday 3/8 to Friday 3/10. Several large slab avalanches ran on the south side of Granite Mountain near Snoqualmie Pass during this period.
NWAC observer Dallas Glass was in the Alpental Valley Sunday 3/12 through Tuesday 3/14 and reported tough travel conditions and no natural avalanche activity in the terrain he observed near and below treeline despite the persistent rain.
Stevens Pass Pro Patrol reported 4 natural D3 (very large) wet snow avalanches on the Tye Mill side of Cowboy Ridge that occurred between Monday night and mid-day Tuesday. Two of the avalanches occurred mid-day Tuesday and were classified as wet slabs with 3' crowns and 15' debris piles. A shallow loose wet cycle was also noted in the Susan Jane area outside the ski area early Tuesday morning.
South
Dallas was in the Crystal backcountry on Friday 3/10 and reported that a wet slab cycle had occurred on Thursday night with several releases on the ridge running from 3 Way to Crown Point on W-NW-N slopes in the 5800-6000 range. Natural loose wet avalanches also ran from steep and rocky terrain.
The NPS rangers at Paradise reported that a large natural wet slab or loose wet avalanche had covered the road to Paradise on Friday 3/10. This occurred on a NW aspect at about 4500 ft.
Just above the Nisqually Bridge to Paradise on Friday morning 3/10. Photo Doug Jones.
