Forecast as of 04/21/2019 at 08:00 and expires on 04/22/2019

Above 4,000ftConsiderable

2,000 to 4,000ftModerate

Below 2,000ftLow

Degrees of Avalanche Danger

Avalanche Problems

Problem Details

Problem 1:  Storm Snow

Distribution: Widespread above 3000', all aspects.  Size: Small- Large. Likelihood: Likely. Sensitivity: Reactive-Touchy 

Description: 12"+ of new snow in the past three days plus steady winds and near freezing temperatures create our storm snow concern.  If triggered, storm snow could easily cause a step down to initiate a persistent slab deeper within the snowpack.

Problem 2: Persistent Slab

Distribution: Primarily above 3000', especially northerly aspects.  Size: Small- Large. Likelihood: Possible (in steeper terrain). Sensitivity: Stubborn 

Description: Notable density differences exist at old storm interfaces, and areas where buried surface hoar, and facets were preserved within the upper snowpack (top meter).  

Problem 3: Falling Cornice

Distribution: Primarily ridges above Treeline. Size: Small- Large. Likelihood: Unlikely - Possible. Sensitivity: Stubborn-  increasing as temperatures and direct solar input increase. 

Description: The advisory area has significant cornice formation in the alpine - keep your distance!  As the temperature increases and/or weight is added (rain/snow or humans), they're much more likely to fail.  Cornice failure can trigger other avalanche concerns.

Additional concern: Glide Avalanches.

There are open cracks from the port to 42-mile between 1000-4000' on multiple aspects; but predominantly on solar aspects. There has been much more glide activity through the main part of the winter than normal and they're now more active as the temperatures rise above freezing .  Glide cracks can release at any time and are not associated with human triggers. The best way to manage this problem is to limit (AKA avoid) travel underneath and beside them.

Avalanche Activity

April 19: several small human triggered loose snow avalanches in steeper terrain above 3000', all aspects
April 12-13: numerous natural small - large wet loose avalanches below 2500',
Numerous natural and human triggered small D1-D1.5 persistent slab and storm slab avalanches reported above 3500' on Northerly aspects

Please share your field observations including signs of stable snow HERE.


The most recent NWS rec Forecast can be found HERE:

The Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
Worthington Glacier.
                   Today        Tonight

Temp at 1000`      46 F         33 F

Temp at 3000`      31 F         32 F

Chance of precip   100%         100%

Precip amount
(above 1000 FT)    0.26 in      0.37 in

Snow amount
(above 1000 FT)    2-5 in       1-2 in

Snow level         1800 ft      2000 ft

Wind 3000` ridges  E 10-30 mph  SE 5-20 mph

Additional Information

SNOWPACK BIG PICTURE:   Above 3500', 12"+ of consolidated snow from the last three days sits atop notable storm layers from the past 2 weeks.  Winds capable of transporting snow have come from all directions, but primarily from the south.  Temperatures near 2500' have been hovering around freezing.  Older layers of snow are adjusting and include: sun and rain crusts, near surfaces facets, and buried surface hoar. Below the top meter of snow, the snowpack has a weak temperature gradient and is actively rounding. Dig and test.  The snowpack below 2500' is steadily becoming isothermic.

Recent snowpack history, from top to bottom:

4/18: Rain event previous to 3"+ new snow with several hours of light to moderate Southerly winds above 2500'.  Freezing level from 4500-2000' during the cycle.

4/8 - 4/12: Three storm cycles produced 20"+ of snow above 2500' and rain below.  The advisory area experienced a brief wind event which distributed snow and added to cornice formation.  

April 6-7:  Light winds, 6"+ snow in the alpine above 3500'

April 4-6: No new notable precipitation.  Mostly calm but occasional gusty winds, and freezing level reaching below 1000'.

March 25-April 2:  Clear skies, calm winds, and freezing level reaching above 4000'.  No additional precipitation. Above freezing up to 5600' during the day, freezing down to ~2500' at night.

March 16-24:  An atmospheric river dominated the forecast with light winds, steady rain in the lower elevations, and accumulating snow in the upper elevations. 4" of rain (SWE)!  Below 3200' the snowpack is diminishing.  4+ feet of new snow is accumulating in the upper elevations.  There was reports of natural and human triggered slab avalanches during this time period and numerous small - large wet loose and wet slab avalanches in steep, low & mid-elevation terrain.

March 7-16: A consistent series of gulf lows produced slow and steady precipitation. 2.4" SWE in Valdez, and 3.1" at Thompson Pass which produced up to 3' of new snow above 3000'. There has been light-moderate south and easterly winds loading north and west faces slightly more than east and south faces. There were no reports of natural slab avalanches during this time period, but numerous small wet loose avalanches in steep, low elevation terrain.

Feb 22-March 7: Calm high pressure with overall warm temps (40F in town on multiple days) and only a few hours of moderate north winds. There have been no signs of the Jan 23rd persistent weak layer in the maritime region. There has been widespread surface facet formation; especially further north/interior.

Feb 20-22: High N-NE winds, rapidly transporting any available snow (70mph gusts). In certain places the wind built new slabs and alternatively stripped all the new snow back to old layers and rain crusts. 

Feb 16-18: Over 2" SWE and 2' of snow with little wind. 

Feb 7-14: Nearly 0" new snow and building north winds (70mph NE gusts on Feb 14 at Thompson Pass.) Widespread surface hoar growth up to 6mm. In windy locations, and close to the pass, most of this surface hoar has been knocked down. A 'drizzle crust' formed near the pass up to 5500' and was observed buried 55cm down on Loveland at 5000' (on Feb 20.)

Feb 3-6: 0.7" SWE and 8" of snow from Valdez to Thompson Pass. 8" of new snow was recorded at 5500' on Catcher's Mitt. Freezing level was sea level throughout this cycle.

Jan 30-Feb 1: Natural avalanche cycle on all aspects above 3000', up to size D3. Most ran on buried surface hoar (Jan 23rd layer).

Jan 28-30: 2" SWE in Valdez, moderate winds, freezing level 1000'.

Jan 23-25: Multiple days of warm and wet with periods of rain up to 2500' which buried the Jan 23rd Surface Hoar layer.

Jan 13-22: Mostly clear, cold, and dry with light to moderate north winds. Widespread Surface Hoar growth (up to 15mm) and Near Surface Faceting.

Jan 12-13: 3-10" of new snow with little wind.

Jan 4-12: VERY cold and dry: moderate winds and wind chill reaching -50F. Pockets of surface hoar and widespread near surface faceting.

Dec 30-Jan 3: The New Year's Eve storm brought nearly 2.5" of SWE to Valdez and almost another 1" (SWE) on the 2-3rd of January. The rain line was 1200' during the Jan 2-3 storm, forming a 1-3" crust locking up all the snow beneath it. These storms accumulated over 3' above 2000' near Thompson Pass. Both of these storms had little wind.

If you get out riding, please send in an observation.

Do a rescue practice with your partners. Always carry a beacon, shovel, and probe, and know how to use them. 

Practice good risk management, which means only expose one person at a time to slopes 30 degrees and steeper, make group communication and unanimous decision making a priority, and choose your terrain wisely: eliminating unnecessary exposure and planning out your safe zones and escape routes.


Consider supporting our friends conducting research!:  CSO

Share your field observations with the community HERE.