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RegisterFeb 14th, 2019–Feb 15th, 2019
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New snow falling at warmer temperatures will stress the snowpack on Friday. Use caution around steep slopes at all elevations. Put plenty of space between where you travel and large pieces of terrain where avalanches could start or run to from overhead slopes.
The new snow buried weak and variable old snow surfaces. A widespread natural avalanche cycle occurred Tuesday night into Wednesday. These avalanches failed within new snow and on buried persistent weak layers. Avalanches with the widest propagation occurred on southerly slopes. We continue to receive reports of dangerous avalanche conditions in the northeast Cascades including recent avalanches, collapses, shooting cracks, and unstable results in snowpack tests (observation, observation). Incremental loading is testing buried weak layers of facets found above and below crusts in the upper snowpack. More snowfall and warmer temperatures expected over the next 24 hours will stress the snowpack further.
Most avalanche accidents occur with Considerable Danger. Continue to be aware of your surroundings and check for instabilities. Ask yourself, "Am I in avalanche terrain? Could the snow slide?" Traveling one at a time is good practice, but it does not eliminate the hazard of choosing to enter avalanche terrain. Stick to lower angle, supported terrain, and places well away from large, steep, open slopes.
Since February 8th, the mountains (and low elevation cities) of the Pacific Northwest have experienced cold and very stormy weather. Significant snowfall has added up in all forecast zones. Records from Snoqualmie Pass DOT avalanche workers back to 1973 show that February 11-12th set a record for the most snow recorded in a 24hr period at that location. The table below shows storm totals starting February 8th through the morning of the 13th
5 day totals ending morning of Feb 13th
Water Equivalent (inches)
24hr storm totals
(inches)
Difference in Height of Snow (inches)
Hurricane Ridge
1.97
N/A
+ 30
Mt. Baker
1.94
44
Washington Pass
1.66
NA
+ 16
Stevens Pass
2.71
49
Snoqualmie Pass
3.91
80
Mission Ridge
1.86
38
Crystal
2.91
59
Paradise
4.55
N/A
White Pass
N/A
57 (4400ft)
+ 26 (5800ft)
Mt. Hood Meadows
4.70
43
Heavy precipitation brought many mountain regions to their tipping point. Avalanches ran readily with a peak of snowfall intensity. For Stevens Pass, Snoqualmie Pass, East Central, West South, Mt Hood, and possibly West Central zones we have good confirmation that this cycle happened from the night of February 11th through the 12th. In other zones, snow totals haven’t been significant enough for widespread avalanche cycles, or we lack data (like in the East South zone).
The high rates of precipitation drove avalanches in the storm snow. Notably, a persistent weak layer of facets and surface hoar was buried in most zones on February 8th. Storms produced a widespread and prolonged cycle of avalanches on the February 8th interface, involving a variety of aspects and elevations. Local ski patrols, highway workers, and backcountry travelers reported extensive avalanching with widely propagating crowns and very sensitive conditions. With less stormy weather, observers have just begun to get a sense of the extent of the avalanche activity. Triggering persistent slab avalanches will be a concern for backcountry travelers in zones where the February 8th weak layer is active for at least the near, if not distant future. Stay tuned for more updates.