Valley temperatures have remained at or above freezing for the last 4 days with rain on snow occurring at low elevations. A slow down in precipitation is expected today, although temperatures will remain at or above freezing up to 2000′. As rain and warm temps continue to saturate the upper snowpack and push deeper into the snow the likelihood and size of wet loose avalanche activity will be on the rise. Human triggered wet loose avalanches are likely in terrain steeper than 35°, where the surface snow is wet and ski penetration is greater than 6 inches due to unfrozen snow. The size of wet loose activity will directly correlate with the vertical relief of the slope involved and the depth of unfrozen snow.
Avoid being exposed to or traveling on slopes steeper than 35° where the surface of the snow is wet or ski penetration is greater than 6 inches due to unfrozen snow. Wet loose activity may be able to step down to deeper layers in the snowpack creating more destructive avalanches (see problem 4).
Precipitation has been increasing in intensity over the last 4 days. 8-16 inches of new snow since the 25th is likely to exist above ~4000′. Lower amounts exist at mid elevations due to temps at or above freezing preventing more than a few inches of moist snow from accumulating. At low elevations rain is falling with temperatures remaining above freezing.
Temperatures have been steadily increasing along with snowfall intensity since the 25th. This is creating upside down storm slabs (denser snow at the surface) that will be reactive to human triggers up to 2 feet in depth on terrain steeper than 32° above 4000′. Pay attention to new snow amounts and watch for signs of instability such as shooting cracks, collapsing or recent avalanche activity.
Storm slabs will be more sensitive where they overlie a layer surface hoar that was buried on 4/22(see problem 3). This layer is very specific, and exists at upper elevations on protected north aspects. This layer is less likely to exist in areas that are in close proximity to wind channeled terrain.
Moderate to heavy precipitation occurred yesterday with snow lines rising to 2000′. This will translate to top heavy storm slabs up high putting pressure on the 4/22 buried surface hoar layer in specific locations, and rain down low increasing the likelihood for wet loose activity.
Triggering a persistent slab avalanche up to 2 feet in depth is likely today in specific locations at upper elevations. Storm totals are unclear but are likely in the 8-16 inch range above 5000′. This new snow has built an upside down storm slab atop a layer of buried surface hoar that exists at high elevations on protected north aspects. The sensitivity of this layer will likely vary greatly from one location to another. Sensitivity will be affected by depth of new snow and the presence, or lack of buried surface hoar. Slope by slope assesment is encouraged if traveling in steep and/or consequential terrain of mid-upper elevations. It is recommended to avoid slopes steeper than 32° where buried surface hoar is identified with a cohesive slab above.
Surface hoar found on 4/21 prior to being buried on a north aspect at 5500′ just north of Hippie Ridge. This is a potentially dangerous weak layer at upper elevations as incremental snowfall increases stress on a layer that is notoriously weak in shear and can persist for long periods.
The likelihood of deep slab avalanche activity occurring, is slowly increasing as the overnight freezing line climbs in elevation. As our snowpack makes the transition from a winter pack to a spring one, deep slab avalanches become increasingly possible. The most likely trigger to this avalanche problem would include significant wet loose activity or cornice fall. It is highly recommended to avoid traveling on or exposing yourself to cornices, and steep solar aspects where the surface is saturated. As the season progresses and temperatures continue to rise, so does the possibility for deep slab avalanches to occur.
Weak snow exists at the base of our snowpack. On 4/15 our area saw the first deep slab activity occur since late February. This occurred on Meteorite (see avalanche activity section) and was a cornice fall that triggered a series of step down avalanches that eventually stepped down to the ground. This is a clear indication that large triggers can have an affect on depth hoar. Increasing temperatures are expected to produce more significant activity later in the season while our snowpack is undergoing a transition from a winter snowpack to a spring one.
This problem is very difficult to assess due its depth and the fact that signs of instability will likely not be present. You can stack the odds in your favor by avoiding steep terrain that is undergoing rapid changes such as strong solar and avoiding exposure to large triggers such as cornices.
Large natural avalanche on Meteorite triggered by cornice fall on 4/15.
Below is a summary of observed Avalanche activity from the last 7 days. Avalanches that were noted earlier in the season can be viewed by clicking the link below.
If you trigger or observe an avalanche consider leaving a public observation.
Valdez Avalanche Activity
4/28- D2.5 Natural wet slide in snow slide gulch. Timing is uncertain but likely happened between the 27th and morning of the 28th. Debris terminated ~200′ above the river.
4/17- Large natural avalanche reported on the upper Tasnuna just east of “The Wall”. Cornice fall was likely the initial trigger with other sympathetic avalanches occurring as well as full depth step downs. SS-Nc-R2.5-D3
– Skier triggered avalanche reported in the Tasnuna valley “The Hammer” SS-ASu-D2-I down 40 cms on 4/7 buried surface hoar/ NE aspect ~5500′. 5th Skier on slope was caught and partially buried in a crevasse/ skier did not sustain any major injuries.
4/15- A cornice fall produced a series of step down avalanches on Meteorite which resulted in failure at the ground. This intiatied as a cornice fall at 6500′ that triggered an avalanche most likely at the 3/9 interface which then stepped down to a persistent slab around 6100′ NE and stepped down to the ground at 5600′ NE.
SS/HS-NC-D3-O/G 6200′ NE, step down to ground ~5600′ NE
Check out our updated weather tab! A collection of local weather stations are available for viewing with graphs and tabular data included.
NWS Watches, warnings and advisories
NWS Point forecast for Thompson Pass
Date Sunday 04/30/23 Monday 05/01/23
Time (LT) 04 10 16 22 04 10 16 22 04
Cloud Cover OV OV BK OV OV OV OV OV BK
Cloud Cover (%) 90 70 60 95 100 100 100 90 65
Temperature 32 34 36 31 30 33 34 31 27
Max/Min Temp 37 30 35 26
Wind Dir S SW SW SE SE SE S S SW
Wind (mph) 3 4 6 9 17 18 16 11 8
Wind Gust (mph) 36
Precip Prob (%) 70 20 10 50 80 90 90 80 50
Precip Type S S S S S S S S S
12 Hour QPF 0.05 0.11 0.23 0.23
12 Hour Snow 0.2 0.7 1.4 1.7
Snow Level (kft) 2.0 1.7 1.6 0.9 1.1 1.5 1.6 0.6 0.4
Click on link below for Thompson Pass weather history graph:
*HN24W- 24 hour Snow water equivalent in inches
*SWE– Snow water equivalent
**46 mile seasonal snowfall total begins December 1st.
Click on the link below for a running summary of the seasons weather history.
Valdez Weather History
The avalanche hazard is Considerable at all elevations. Human triggered avalanches are likely up to 2 feet in depth. Natural avalanches are possible. A prolonged period of incremental precipitation along with rising temperatures since the 25th has increased the likelihood of multiple avalanche problems. The likelihood and size of wet loose avalanches that could occur today is on the increase due to temperatures at low elevations remaining at or above freezing the last 4 days. At upper elevations new snow has formed upside down storm slabs and added stress to a weak layer in the upper snowpack increasing the likelihood of human triggered storm/ persistent avalanches. Avoid avalanche terrain that has become isothermal at low elevations and observe the depth and sensitivity of new snow at mid-upper elevations. Thanks to everyone that used and/or contributed to the avalanche forecast this season! This is the last public avalanche forecast of the season, although does not mark the end of avalanche season in the mountains. Avalanche hazard continues to exist in the Valdez- Thompson Pass region. Current conditions moving forward will likely differ form todays forecast.
Posted by Gareth Brown 04/30 6:00 am.
For a description of current avalanche problems, weather information, season history and more click the (+ full forecast) button. Avalanche forecasts will be issued Wednesday-Sunday through April 30th.
If you have pictures of recent natural or human triggered avalanches or notice signs of instability such as shooting cracks or collapsing, leave an observation to help improve forecast accuracy.
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