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The avalanche danger will start off MODERATE and rise to CONSIDERABLE above 1000′ today. Strong winds and heavy snowfall are expected to start midday which will quickly increase the avalanche danger and form wind slabs 1-2′ deep. The likelihood of human triggered and natural avalanches will increase throughout the day as the storm intensifies. Buried weak layers 2-4′ deep could produce larger avalanches at higher elevations. Below 1000′ the avalanche danger will start off LOW and rise to MODERATE.
* Avalanche danger will rise to HIGH overnight tonight with very strong winds and heavy snowfall.
SEWARD / SNUG HARBOR / SUMMIT LAKE: Avalanche danger will rapidly increase across the region with the onset of a large storm midday Saturday. Conservative terrain selection and decision-making is recommended.
* Roof Avalanches: With rain expected below 500′ today roof avalanches will become more likely. Remember to watch where you park and keep an eye out for kids and pets hanging out under roof lines with lots of snow left to slide off.
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Travel Advice | Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. | Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. | Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. | Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. | Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain. |
Likelihood of Avalanches | Natural and human-triggered avalanches unlikely. | Natural avalanches unlikely; human-triggered avalanches possible. | Natural avalanches possible; human-triggered avalanches likely. | Natural avalanches likely; human-triggered avalanches very likely. | Natural and human-triggered avalanches certain. |
Avalanche Size and Distribution | Small avalanches in isolated areas or extreme terrain. | Small avalanches in specific areas; or large avalanches in isolated areas. | Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. | Large avalanches in many areas; or very large avalanches in specific areas. | Very large avalanches in many areas. |
We received report of a wind slab releasing in steep terrain in main bowl on Seattle ridge yesterday. We think this avalanche likely released at the interface of the old snow surface and the Christmas storm snow. After the Christmas storm several large avalanches released on the south and east aspects of Seattle ridge and at lower elevation on the NW ridge of Magnum. Low visibility this week has made detecting recent avalanche activity challenging.
Wind slab avalanche triggered by snowmachiner on a west aspect at 3000′ in main bowl along Seattle Ridge. Photo Hunter McConnel 12.30.22
Signal Word | Size (D scale) | Simple Descriptor |
Small | 1 | Unlikely to bury a person |
Large | 2 | Can bury a person |
Very Large | 3 | Can destroy a house |
Historic | 4 & 5 | Can destroy part or all of a village |
As a large storm approaches today, increasing wind speeds will be the first thing to contribute to increasing avalanche danger. The combination of existing dry snow on the surface plus 6″ of new snow expected today will provide plenty of surface snow available to be transported into fresh wind slabs 1-2′ deep. The likelihood of human triggered and natural avalanche activity will increase throughout the day as more new snow falls and the wind speeds continue to increase. This morning winds are averaging 10-15 mph with gusts to 30 mph and by this evening we expect winds to average 50-75 mph with gusts of 100+ mph possible.
Wind slabs are most likely to be found along upper elevation ridgelines and cross loaded gullies. However, with very strong winds like we are expecting this evening you could find wind slabs in areas that are typically sheltered. To identify areas with fresh wind slabs look for active wind loading, hollow and stiff feeling snow, and shooting cracks on the surface. With conditions deteriorating throughout the day we recommend a conservative mindset and a quick bail out plan if visibility and travel conditions change quicker than expected.
Expected snowfall totals from Saturday at 6am to Sunday at 6am. Heavy snowfall should start between 12 pm and 3 pm on Saturday with winds ramping up prior to that. Graphic courtesy of NWS Anchorage 12.31.22
Signal Word | Size (D scale) | Simple Descriptor |
Small | 1 | Unlikely to bury a person |
Large | 2 | Can bury a person |
Very Large | 3 | Can destroy a house |
Historic | 4 & 5 | Can destroy part or all of a village |
With poor travel conditions and visibility this week we still have a lot of uncertainty about the status of our persistent weak layers at upper elevations. Prior to the Christmas storm, a layer of facets above the Thanksgiving melt freeze crust was causing collapses and concerning test results in portions of the forecast area with a generally thinner snowpack, like in Girdwood Valley and near the Johnson Pass trail. The rain and wet snow up to 2500-3000′ that came along with the Christmas storm has helped to stabilize these weak layers at middle elevations, but we have limited information on how the new load has impacted these persistent weak layers above 3000′. At this point we believe there is still a chance of triggering an avalanche on a persistent weak layer 2-4′ deep that could produce a very large avalanche.
In addition, we have seen some evidence of a weak interface between the old snow surface and the Christmas storm snow which could produce avalanches 1-2′ deep. With the addition of a new snow load and very strong winds today it is possible that these buried weak layers could become reactive again at upper elevations. Sticking to smaller terrain features and lower angle slopes is the best way to avoid buried persistent weak layers. Hopefully after the New Years storm we can get more conclusive information that these layers are no longer a concern, but for now they should stay on our radar.
Yesterday: Broken cloud cover with occasional partly sunny skies and denser clouds towards the coast. Light to calm winds in the 5-10 mph range with gusts up to 20-30 mph overnight. Temperatures cooled slightly overnight but remain close to freezing at sea level and mid to low twenties at upper elevations. No significant new snowfall.
Today: A large storm is approaching today that will bring very strong winds and heavy snowfall. Wind speeds will increase from 10-15 mph with gusts of 20-30 mph this morning to averages of 50-75 mph with gusts up to 100 mph tonight. Winds should increase steadily this morning and be at full force from 6 pm Saturday to 6 am Sunday. Light snowfall is expected in the morning, increasing in intensity sometime around 12 pm to 3 pm. Up to 6″ of snowfall is expected during the daylight hours on Saturday. By Sunday morning we expect 12-18″ of snowfall. Coastal areas near Portage and Placer will likely receive higher snow totals. Snow line is expected to be around 500′ on Saturday.
Tomorrow: The heavy snowfall and strong winds will continue on Sunday. Winds are expected to peak overnight on Saturday and drop off slightly on Sunday with averages of 20-40 mph and gusts of 50+ mph. Another 12-18″ of snow is expected from Sunday morning through Monday morning, with snow line increasing to 1500′ on Sunday. Storm totals from Saturday through Monday are expected to be in the 2-3″ of water range, which is a lot of new load on the snowpack.
PRECIPITATION 24-hour data (6am – 6am)
Temp Avg (F) | Snow (in) | Water (in) | Snow Depth (in) | |
---|---|---|---|---|
Center Ridge (1880′) | 29 | 0 | 0 | 40 |
Summit Lake (1400′) | 21 | 0 | 0 | 27 |
Alyeska Mid (1700′) | – | – | – | – |
Bear Valley – Portage (132′) | 34 | 0 | 0 | – |
* Alyeska Mid stopped reporting at 9am on December 30th
RIDGETOP 24-hour data (6am – 6am)
Temp Avg (F) | Wind Dir | Wind Avg (mph) | Wind Gust (mph) | |
---|---|---|---|---|
Sunburst (3812′) | 22 | ENE | 9 | 28 |
Seattle Ridge (2400′) | 25 | SE | 5 | 18 |
Date | Region | Location | Observer |
---|---|---|---|
10/27/24 | Turnagain | Observation: Tincan | Michael Kerst |
10/21/24 | Turnagain | Observation: Turnagain Pass Road Observation | Trevor Clayton |
10/19/24 | Turnagain | Observation: Tincan – Below Todds Run | Andy Moderow |
10/18/24 | Turnagain | Observation: Taylor Pass | Eli Neuffer |
10/15/24 | Turnagain | Observation: Tincan Common | John Sykes Forecaster |
10/14/24 | Turnagain | Avalanche: Tincan | CNFAC Staff |
05/13/24 | Turnagain | Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South | H Thamm |
05/13/24 | Turnagain | Observation: Turnagain Pass non-motorized side | Amy Holman |
05/12/24 | Turnagain | Observation: Warm up Bowl | Tony Naciuk |
05/07/24 | Turnagain | Observation: Turnagain Pass Wet Slabs | A S |
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