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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 18th, 2021 - 7:00AM
Expires
Tue, January 19th, 2021 - 7:00AM
Forecaster
Aleph Johnston-Bloom
High Avalanche Danger
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

The avalanche danger is HIGH today due to heavy snowfall, rain, and strong winds.  Large natural avalanches are likely, and human triggered avalanches are very likely. Travel in avalanche terrain is NOT recommended. With heavy snowfall in the upper elevations and rain to around 1200′(possibly higher), we expect to see a mix of dry slab and wet loose avalanches that could make it down to lower elevation runout zones.

The National Weather Service has issued a High Wind Warning for Portage Valley and Eastern Turnagain Arm.

*Roof Avalanches: Warm temperatures and heavy rain could cause roofs to shed their snow. Pay special attention to children, pets and where you park your car.

Special Announcements

From the Alaska Department of Transportation: There will be intermittent traffic delays today, Monday January 18, 2021, on the Seward Highway for Avalanche Hazard Reduction work at Summit Lake near mileposts 44 to 46. Motorists should expect delays of up to 45 minutes between 10:00 am and 3:00 pm. Updates will be posted on the 511 system. http://511.alaska.gov/

 

 

Mon, January 18th, 2021
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
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. Dangerous avalanche conditions. 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.
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "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. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

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
More info at Avalanche.org

The message is pretty straightforward today. Travel in avalanche terrain is not recommended. Ridgetop winds are already averaging 30-50 mph, gusting 80-100+ mph, with a High Wind Warning in effect until 6 pm tonight. Heavy snow and rain (up to 1200′, possibly higher) are forecast to fall throughout the day (1-3′ snow/1.9 SWE”) today and there is plenty of snow available for transport at upper elevations. Snow and rain have been falling on and off for the past few days. There is light dry snow from Thursday and Friday underneath the heavier snow that fell Saturday and Sunday. All these ingredients are the perfect recipe for storm slabs, wind slabs and cornice falls.  Large avalanches (1-4′ deep) are expected to release naturally, be easily triggered by people and could send debris to valley floors. This means staying well away from larger slopes and runout zones a.k.a on the couch! Below 1000′, where the majority of precipitation is rain and the snowpack is saturated, wet loose avalanches are likely in steep terrain. Today is yet again a day to be patient and give the snowpack time to adjust to the rapid loading.

Satellite imagery of the storm impacting the area this morning, 1.18.21

 

 

 

 

 

Weather
Mon, January 18th, 2021

Yesterday: Skies were mostly cloudy with light snow and rain showers with more precipitation falling in the Girdwood area. Rain/snow line went as high as 2000′. Precipitation picked up in late in the evening bringing 24 hour totals to 0.5-0.8″ SWE and 2-10″ of snow. Winds were easterly 5-15 mph with gusts into 20 and 30s and started to ramp up in the early evening. Overnight winds were easterly 20-40 mph with gusts into the 60s and 70s. Temperatures were in the high 30°Fs and low 40°s at sea level and mid 20°Fs at above 3000′ and cooled slightly overnight.

Today: Cloudy skies with heavy snow and rain throughout the day. Rain/snow line is forecast to be around 1200′ may go as high as 2000′ again today, with 1.9″ SWE during the day and 0.5″ SWE at night (1-4′ of total new snow possible depending on elevation). Precipitation should transition to mostly snow in the the evening and then cut off late tonight. Skies will become partly cloudy early Tuesday morning. Easterly winds will be 25-55 mph gusting into the 80s and 90s easing off in the evening and overnight, becoming light and westerly. Temperatures will be high 30°Fs and low 40°Fs at sea level and mid to high 20°Fs at ridgetops and again cool down a bit overnight.

Tomorrow:  Partly sunny skies with increasing afternoon clouds. Light west winds and temperatures in the mid 20°Fs at ridgetops and mid 30°Fs at sea level. The next storm moves in overnight with snow showers likely into Wednesday and an active weather pattern in the forecast for rest of the week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 2 0.5 128
Summit Lake (1400′) 33 0 0 40
Alyeska Mid (1700′) 33 7 0.7 111

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 NE 27 105
Seattle Ridge (2400′) 27 N/A* N/A* N/A*

*Seattle Ridge anemometer is rimed over.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.