Avalanche Forecast

Thursday morning update: 

Up to 12 inches of new snow accumulated from Wednesday afternoon through early Thursday morning. This new snow accumulated along with a slight warming trend and switch from east to west winds. Due to shifting winds over the last week, expect wind slab to be found on a variety of aspects above treeline. In addition, there is some uncertainty about the potential for previously formed wind slabs formed earlier this week that may be unlikely to trigger but could still produce larger and more dangerous avalanches above treeline. 

Previous discussion: 

A low pressure and frontal system will pass by to the south across Oregon and north California on Wednesday. This system will cause southeast winds at Mt Hood and snow late Wednesday.

Light snow showers should end Thursday morning with lighter winds and continued cool temperatures.

New local wind slab is possible on Thursday depending on the local strength of the east to southeast winds. This should be mainly on northeast to southwest aspects at Mt Hood. Older wind slab from the latest storm cycle should have mostly stabilized so the northeast to southwest aspects will be indicated. But watch for firmer wind transported snow on all aspects mainly near and above treeline.

The may be enough new snow at Mt Hood late Wednesday to cause some shallow new storm slab. Evaluate snow carefully if you find yourself in an area with where there has been more than a few inches of rapidly accumulated snow.

A report from Stevens Pass indicates the December 8th layer is still possibly reactive in the Washington Cascades but we don't have any evidence of a persistent weak layer at Mt Hood. This type of layer is less common at Mt Hood and it won't be listed here as an avalanche problem. But head for lower angle slopes and ratchet back your plans if you experience collapsing or whoomping or have evidence of this layer such as from snowpits.

Loose dry avalanches from snow from the latest storm aren't expected to still be an avalanche problem. But in steep terrain lacking a slab structure continue to watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences. 

With deep unconsolidated snow in sheltered areas there remains a risk for tree well and snow immersion suffocation. When near trees ride or ski with a partner and keep them in sight at all times!

Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks.

Weather and Snowpack

Cold and fair weather early last week.

The latest storm cycle began about December 8th starting with a couple day warming trend as southwest flow eroded an Arctic air mass over the Northwest. The warming trend leveled off with temperatures staying well below freezing December 10th and 11th and snowfall tapered off by December 12th. NWAC stations at Mt Hood had about 4 feet of snowfall for the 4 days ending Monday morning.

Recent Observations

A regional avalanche cycle was seen December 8th-11th with some avalanches releasing on a December 8th persistent weak layer. There was also a snow immersion fatality at Snoqualmie on December 11th and apparently a snow immersion close call at Stevens on December 10th.

The Mt Hood Meadows pro-patrol on Monday reported mostly cold stable powder including in non-previously skied terrain. Limited 12-18 inch storm slabs were found on N-NE  slopes in teh 5500-6500 foot range.

A report is available via the NWAC Observations tab for the Tilly Jane drainage on Monday. Deep but generally homogenous storm snow was indicated with very small wind slab on a N-NE slopes near a ridge line.

A report is also available for Monday via Turns All Year for the Barlow Snowpark area with good stability in deep storm snow indicated.

By Tuesday the Mt Hood Meadows pro-patrol found only pockets of 1-2 foot wind slab on southeast slopes in the 6-7000 foot range with hand charges.