Dec 17

Issued: Sat, Dec 17, 2016 at 12PM

Expires: Sat, Dec 17, 2016

We are experiencing technical difficulties. If you are seeing this outdated post please try another browser or link to our advisory. There is a new forecast for Dec 24 with a considerable avalanche hazard at upper elevations.

Above 3,500ft Moderate

2,500 to 3,500ft Moderate

Below 2,500ft Low

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

AVALANCHE PROBLEM 1: PERSISTENT SLAB

Avalanches are unlikely but possible to human trigger in specific locations, mostly on leeward, upper elevation ridgelines where older wind deposited snow sits over very weak faceted snow (depth hoar). Expect the snow to react in these specific areas with whumphing, shooting cracks and the possibility of triggering an avalanche on steep slopes (35º +) where the snow is deeper than about 1 foot.

Whumph and Shooting Crack, Marmot Lower Test Roll, West, 3920′, 34 degree slope

AVALANCHE PROBLEM 2:  LOOSE SNOW

While this is not a major hazard this weekend, you will be able to trigger loose snow on steep slopes (40°+) where low density, new snow sits over older, smooth wind slab or basal facets. By this evening expect approximately a foot of low density snow able to produce moderate volume but high speed sluffing.

HAZARD SPECIFICS

Moderate avalanche hazard in specific areas at upper elevations near ridgelines, on leeward slopes, where previous wind slabs and wind deposited snow up to a foot deep sit on well developed, weak, basal facets (depth hoar). This hazard may also be present in isolated areas at mid-elevation. The avalanche hazard will rise to considerable in very specific areas  at upper elevations in the alpine if wind speeds continue to rise through today and into tomorrow.

At lower to mid-elevations the snowpack is so thin, bushy and rocky that it barely exists as a snowpack at all. Avalanches in these areas are unlikely. However, triggering even a small slide that carries you into these shallowly buried hazards could injure you. Stay out of the runnout of steeper slopes at upper elevations above you.

Observations at this time are minimal and HPAC is only now beginning to collect significant data. So if you are getting adventurous and hiking out to the huts or scraping your way through the bushes and rocks into the alpine, consider the avalanche hazard to be considerable until proven otherwise. For most people getting into the backcountry, the alpine will be off limits until travel conditions improve with significantly more snow coverage.

Recent Avalanche Activity

Recent Weather

Additional Info & Media

RECENT ACTIVITY, CONDITIONS, WEATHER HISTORY

While it is mid-December, Hatcher Pass is still stuck in an early season snowpack that resembles October. Since Thursday night, snow flurries have been cloaking the landscape in a thin, winter white.  The new snow is a blessing, but Hatchers still lacks a good snow base and shallowly buried hazards are everywhere.

Low density snow has been falling intermittently since Thursday evening, with 4-6 inches of new snow on 12/16. We picked up a few inches overnight. Gold Chord Weather Station (4050′), just above Independence Mine,  is reporting a total of 7″ of new snow since Thursday. Snow totals at Independence Mine have reached a whopping 15 inches for the season. NWS is calling for another 2-5″ today in the Valley, 4-6″ at 4000′ at HP.

Winds this week at 4500′ averaged 5 mph, gusting 10 mph SSE.

Temps this week averaged 19° F at 4500′.  You may have noticed a slight warming and then cooling trend in the storm overnight which will transfer to a storm density change within the new snow. Temps at Independence Mine Snotel (3550′) ranged from 25ºF yesterday morning rising to 31ºF by the afternoon and then cooling back down to 25ºF at 6am this morning.

Observations have been minimal at this time since recreating in this shallow snowpack is not popular at the moment. We are also just getting out into the snow and accumulating data because this snow year has been so slow to start.

One important point on the weather history should be noted. Early season snow, followed by a prolonged period of clear and cold weather has weakened the early season, basal snow severely. Expect this buried weak layer to become naturally active once the snow begins to add up and tip the strength/stress balance.

Coverage observation, Marmot Mt, SW face 12/16

Coverage Observation, Skyscraper Peak, South aspect 12/16

Coverage Observation, Sunnyside of Hatch, showing Southeast and East aspects 12/16

Posted in HPAC Forecasts.
Jed Workman

Forecaster: Jed Workman