Register for an account and never miss a forecast again!
RegisterRegister for an account and never miss a forecast again!
RegisterMar 17th, 2016–Mar 18th, 2016
.
A mixed bag of spring avalanche problems Friday will keep heightened avalanche conditions in specific terrain. You can mitigate the loose wet and cornice risk by being aware of the terrain you are connected with and by recognizing the rapidly increasing hazard in locations that warm quickly. Firm wind transported snow and snowpack cracking that might be found on any aspect can be good signs of wind slab layers.
Sun on Friday morning should give way to some high clouds by Friday afternoon with warmer temperatures. Strong east winds are likely in places along the Cascade crest especially over lower parts of the crest and in the Cascade passes. But this should affect mainly the west slopes.
Stronger mid-March sun should make loose wet avalanches possible on steeper solar aspects on Friday after quickly breaking down sun or melt-freeze crusts. Loose wet avalanches may start small but could have the ability to entrain recent moist snow in specific terrain. Watch for rapidly increasing hazard in locations that warm quickly.
Northwest winds on Wednesday likely continued to build wind slab on lee aspects in the upper elevations of the above treeline band. This wind slab will mostly likely be found on N-SE facing slopes. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.
Recently formed cornices have grown large and can become sensitive when it is warm and sunny. Avoid areas on ridges or summits where there may be a cornice and avoid slopes below cornices in the spring.
The persistent slab avalanche problem involving the 2/27 buried surface hoar will not be listed in the northeast zone due to an abundance of other avalanche problems, high unlikelihood of triggering due to depth, and general strengthening of this interface over the last few weeks.
Weather and Snowpack
During a period of fair weather in late February, widespread surface hoar formed in the northeast zone mainly surviving outside of steeper solar aspects and wind affected terrain. A weak front buried the surface hoar layer in the Washington Pass area about 2/27 and to a lesser extent the central-east zone.
Storms moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels. Two deep surface low-pressure systems moved across the Olympic Peninsula last week with the first passing last Thursday, March 10th and the next on Sunday, March 13th. These systems caused very stormy weather.
Cool and showery weather Monday and Tuesday with prolonged westerly winds deposited additional snow at lower snow levels. Storm snow amounts along the east slopes were in the 1.5 - 3.5 foot range for Wednesday, March 9th to Tuesday, March 15th.
Recent storm instabilities have been slow to consistently settle out throughout the east slopes. Specifically in the Washington Pass zone the last week has seen many natural and human triggered storm and wind slab avalanches. The recent storms have also built large cornices along ridges in many areas with several large cornice releases noted over the last few days by the North Cascade Mountain Guides.
We are no longer tracking any layers of concern formed earlier this winter in the mid or lower snowpack due to lack of recent activity at these interfaces and confirming field observations.
Recent Observations
NWAC pro-observer Tom Curtis tested conditions in the Blewett Pass area Monday, 3/14 following the strong storm Sunday. Sensitive storm and wind slabs of up to 20 inches were found in open terrain, especially wind affected slopes. Easy failure in test pits was noted on a crust-facet layer buried beneath the current storm snow, about 16-20 inches. Failures were found with PST and ECT tests on this interface.
A report via the NWAC Observations page for the east central zone on Monday, 3/14 indicated that most of the area visited had wind affected snow.
Recent guide reports from the Washington Pass area Tuesday, 3/15 indicated an active avalanche day. There was a partial skier burial due to a ski triggered 45 cm storm slab on a north slope at about 6800 feet in the Hairpin Valley. More details are being gathered but gladly there were no injuries. Ski cuts were giving better propagation than expected also in the Hairpin Valley and a large size 3 avalanche from Spire Gully was possibly caused by a cornice triggering a storm slab on the slope below.
Recent storm slab in the Washington Pass area was reported to be more sensitive due to surface hoar that may have been buried there about during a couple day period March 10-12th.
Tom Curtis was out again on Mt Cashmere on Thursday, 3/17 and found 35 cm of storm snow well bonded to an underlying crust from last week. An extended column test did not indicate propagation and only small loose wet avalanches were seen on steep solar slopes. Temperatures were not greatly affecting the snowpack.