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East Slopes Central - Lake Chelan to South of I-90

Issued: 8:42 PM PST Friday, December 29, 2017
by Garth Ferber

The recent snow and conditions observed Friday warrant patience and caution on Saturday. Don't step out into aggressive terrain before new or recent snow layers have had a chance to stabilize.

Danger Scalei
  • No Rating— (Info Avail)
  • Low — 1
  • Moderate — 2
  • Considerable — 3
  • High — 4
  • Extreme — 5

Avalanche Problems for Saturday

Storm Slabi

  • Avalanche Problemi
  • Aspect/Elevationi
  • Likelihoodi
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Wind Slabi

  • Avalanche Problemi
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Forecast for Saturday:

A change to strong WSW winds at higher elevations and cooling should be seen along the east slopes of the Washington Cascades Friday night following the front. This area should get about 2-8 inches of new snow with a cooling trend by Saturday morning. Some areas especially at lower elevations will initially warm as cooler air gets replaced by milder air from the west.

The recent snow and conditions observed Friday warrant patience and caution on Saturday. Don't step out into aggressive terrain before new or recent snow layers have had a chance to stabilize.

New storm slab from Friday night or lingering storm slab should continue to be the most widespread avalanche problem Saturday. Ratchet back your plans if you see signs of storm slab such as touchy hand shears or results on test slopes.

With recent varied or WSW winds and stronger WSW winds Friday night new wind slab will be likely.  Avoid lee slopes with these aspects especially if you see signs of firmer wind transported snow.

There remains significant deep, soft snow out there from the past week. Unconsolidated snow, particularly around small trees, can present a non-avalanche, snow immersion hazard. Keep visual and verbal communication with your travel partners when traveling in treed terrain.

Keep the 12/15 crust/PWL interface in the back of your mind as we progress through this storm cycle and determine whether loading awakens any pockets of deeper instabilities. 

Also despite all this new snow, early season hazards still exist at some lower elevation locales and especially around creek beds that are not filled in.

Avalanche Summary:

We are at the tail end of a couple of days of very active changeable complex weather. On Thursday strong westerly flow aloft carried a very moist occluded front across the NW. On Friday a moderately deepening low pressure system is crossing the Cape Flattery area and a strong cold front will cross the Northwest Friday evening. This means a variety of upper snowpack conditions could be found by late Friday on the Cascade East slopes.

By Friday morning NWAC and NRCS station along the Cascade east slopes had about 3-8 inches of new snow that fell with an overall slight warming trend. Winds on Friday have been generally moderate to strong WSW at higher elevations.

Regular though usually light snow also accumulated along the east slopes of the Washington Cascades with cold temperatures as very weak weather disturbances crossed the NW in about the past week. 

About 1.5 to 3 feet of recent snow sits atop the 12/15 crust/persistent weak layer interface in the Washington Pass area and in the central-east Cascades near the Cascade crest. Comments from professional guides in the Washington Pass area are included below that help reduce uncertainty surrounding the 12/15 crust/persistent weak layer interface. 

Snowdepth decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there is not enough snow to present an avalanche danger. 

Observations

North

The NCMG were in the Washington Pass area on Friday and observed moderate snow, warming and very touchy storm slab of 15-25 cm. Several naturals were seen to size 1.5 and several other crowns were seen in steep unsupported terrain. Poor bonds were found in upper snow layers via numerous hand shears and on test slopes.

A summary of previous professional guide reports regarding persistent weak layers for the Northeast zone including Washington Pass:

  • In the above treeline zone, small faceted grains are rounding and gaining strength, down 70 cm and below the storm snow that accumulated starting 12/15. They have not been reactive in snowpack tests.
  • The upper snowpack on solar aspects near treeline are bonding well to a strong solar crust buried on 12/15. However, they cannot rule out buried surface hoar in some sheltered larch glades around 6000 feet.
  • Below treeline, surface hoar that was buried on the 12/15 crust is down 70 cm in flat meadows and creek valleys, but has yet to be found in avalanche terrain.

Central

No recent observations

South

No recent observations

No Corresponding Mountain Weather Forecast Available

USE AT YOUR OWN RISK

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.

Message from Garth Ferber: today Friday December 29th I worked my last shift as an avalanche forecaster at the Northwest Avalanche Center. I started my career here in 1993 and am fortunate to have been able to work here with Mark Moore, Kenny Kramer, Dennis D'Amico and now Robert Hahn. I also have been fortunate to have been able to work with many great people in the NWAC partner groups over the years. You may not have heard the last of me, I may help part time with the NWAC weather stations in the future we will see. Cheers, Garth