Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, January 25th, 2019 - 7:00AM
Expires
Sat, January 26th, 2019 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is  HIGH  above 2000′ due to the potential for strong winds to trigger large natural avalanches this morning. As winds decrease and precipitation tappers off this morning triggering a large avalanche in Turnagain Pass will be likely and remote triggered avalanches are possible. In Girdwood and Portage Valley where more snow has fallen in the upper elevations storm slabs could be very large and run greater distances. The avalanche danger is  CONSIDERABLE  below 2000′ where dry snow transitions to wet snow and an avalanche from above will be unsurvivable.

GIRDWOOD:  Numerous ROOF AVALANCHES occurred yesterday and until temperatures dip below freezing this hazard will be important to avoid. Pay attention to children and pets and where you park your car.  

PORTAGE and PLACER VALLEY:    Heavier rain and snowfall rates have occurred and large avalanches above treeline may send debris to sea level and over summer hiking trails such as Byron Glacier Trail.

SUMMIT LAKE / JOHNSON PASS:    A poor snowpack structure exists in this area, which is very different than Turnagain Pass. New snow/rain has added additional stress to the snowpack and triggering an avalanche deeper in the pack is possible. Whumpfing, shooting cracks and recent avalanches are all clues to avoid avalanche terrain.  

Fri, January 25th, 2019
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. Small avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become large enough to bury, injure, or kill people, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Over the last 3 days we’ve seen three significant storms impact our forecast zone bringing heavy rain and snow and hurricane force winds. The third storm is upon us and expected to pass over by late morning. Strong Easterly ridgetop winds averaging 50-70mph with gusts in the 100’s mph will decrease to 15-20mph by early afternoon. An estimated 10-15” of new snow has fallen in the alpine in Turnagain Pass overnight and a few more inches possible this morning. Girdwood has seen double them amount of snow than Turnagain Pass and triple in Portage Valley. See storm totals below.

Large natural avalanches are expected this morning until winds and precipitation decrease. In the afternoon as the weather mellows out human triggered avalanches will be likely in avalanche terrain and will be large enough to bury or kill a person. These storm slabs are expected to be large and could easily connect an entire slope. Storm snow this week has fallen on very weak snow surfaces (widespread buried surface hoar)  and any slope that hasn’t already naturally avalanched will be extremely suspect. Very few natural avalanches were seen yesterday in Turnagain, and don’t forget this poor structure is prevalent across our forecast zone.

Another factor to keep in mind is that precipitation totals across the region have varied significantly over the last three days. The heart of our forecast zone in Turnagain Pass has seen less snow than Girdwood Valley, but observations yesterday did confirm slab depths in the alpine were over a foot. Today we estimate closer to 2’ with the additional 0.7” SWE and strong winds overnight. If you do venture into Turnagain Pass as the weather improves today careful snowpack and terrain evaluation coupled with conservative decision-making are essential. Unlike the last few weeks our current snowpack structure is primed for remotely triggered avalanches. Avoiding runout zones of smaller features is very important.

 Storm totals Tues 6am – Fri 6am: Snow Water Equivalent (SWE) and estimated storm totals

  • Turnagain Pass – SNOTEL (1800’): 1.2” SWE, 12”–25” new snow above 2500’
  • Girdwood – Alyeska Midway (1700’): 2.7” SWE, 3-5’ new snow above 2500’
  • Portage – Bear Valley Tunnel (100’): 7.0” SWE, 7-10’+ above 2500’

 

Avalanche Problem 2
  • Wet Loose
    Wet Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. Small avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become large enough to bury, injure, or kill people, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Storm slabs in the alpine may release naturally while winds are strong this morning and likely trigger wet loose snow in the mid to lower elevations. Seattle Ridge and Sunburst are good example of where this occurred yesterday in Turnagain Pass. In Portage and Girdwood where precipitation amounts have been higher the last few days, storm slab are expected to be large and run father distances in steep channeled terrain. Avoiding all runout zones is recommended today.

Wet debris at the bottom of a North chute on Sunburst occurred yesterday 1/24/19.

Additional Concern
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

South of Turnagain – Johnson Pass/Summit Lake zone: poor snowpack structure exists in these areas.  Multiple mid-pack weak layers of facets and buried surface hoar have been found as well as a facet/crust combination in the bottom of the snowpack. New snow overnight (0.5” SWE), strong winds over the last three days and warming temperatures have added additional stress to the snowpack. A recent natural avalanche that in the alpine that entrained wet snow in the mid elevations was observed yesterday. Rain/snow line was around 2000’. Overnight an additional 5” of new snow may have fallen in the upper elevations and this may also be adding additional stress to older layers in this zone. The possibility of triggering a slab deeper in the snowpack is the primary concern in this area, but finding a newly formed storm slab could be consequential in a terrain trap or step down to an older layer. Look for signs of instability, avoid wind-loaded terrain and evaluate new snow as you travel.

Weather
Fri, January 25th, 2019

Yesterday: A storm front with strong winds passed over our region and ended mid-morning. Easterly ridgetop winds averaging in the 50-60’s mph decreased by 11am to 10-20mph by the afternoon. Rain diminished in the morning and skies were overcast with a broken period late afternoon in Turnagain Pass. Temperatures remained above freezing to ~2000′. Another storm moved into our region late yesterday evening, bringing another round of heavy precipitation, strong Easterly winds, and rain in the lower elevations. Temperatures were slightly cooler and rain/snowline was around 1500′. Precipitation amounts varied significantly around our region. Turnagain Pass SNOTEL picked up 0.7 € SWE in the last 24-hours, but Turnagain DOT RWIS at 1000′ recorded .94 € of rain. The 24-hour precip totals in Girdwood at Alyeska Midway were similar to the Turnagain DOT RWIS, but the Portage Bear Valley RWIS recorded 3.12 € of rain.  

Today: The third storm front this week will pass over our region this morning, and a slight cooling trend is expected. Rain may transition to a few inches of wet snow at 1000′ near the tail end of the storm. This may also cause freezing rain along the Seward Hwy North of Girdwood. Around 0.25 € SWE (2-4 € of snow) is possible by late morning before precipitation tapers off. Strong Easterly winds will also decrease rapidly this morning to moderate by the afternoon. Overcast skies are expected, but a sucker hole or two is not out of the question.

Tomorrow: Partly cloudy skies in the morning may become mostly cloudy by late afternoon. Moderate Southeast ridgetop winds 15-20mph are expected. Freezing level is expected to be near sea level. Scattered showers are possible, but little to no precipitation is expected.  

 *Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  35 10   0.7   63  
Summit Lake (1400′) 36   1-2″ wet snow   0.5    20
Alyeska Mid (1700′) 34   5   1.02   45  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   ENE   37   119  
Seattle Ridge (2400′) 30   *N/A   *N/A      *N/A  
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Riding Areas
Updated Mon, May 06th, 2019
Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Closed as of 4.3.19
Placer River
Closed
Closed as of 3.20.19 due to lack of snow.
Skookum Drainage
Closed
Placer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass
Closed
Closed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile
Closed
Closed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Closed as of 3.22.19 due to lack of snow
Primrose Trail
Closed
Closed as of 4.3.19 due to lack of snow
Resurrection Pass Trail
Closed
Closed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor
Closed
Close as of 5.1.2019
South Fork Snow River Corridor
Closed
Closed as of 3.20.19 due to lack of snow.
Summit Lake
Closed

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