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RegisterFeb 14th, 2019–Feb 15th, 2019
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East to Southeast winds built firm wind slabs on unusual aspects and cross-loaded slopes Thursday. Look for wind stiffened snow in lower angled terrain as clear evidence you can trigger a large wind slab in steeper terrain on similar aspects. Shallow wind slabs may also be found on steep open slopes below treeline.
An amazing amount of snow, 4-5 feet, has fallen in the West Slopes South zone since the weekend, with the storm peaking Monday night and Tuesday. Avalanche activity associated this cycle tapered off through midweek. A fresh round of E-SE winds redistributed the recent low density storm snow, wind scouring windward aspects and cross-loading slopes Thursday.
It's important to note we have had limited field observations over this stretch due to the strong storm conditions. Throughout this cycle, Paradise has been closed for several days due to winter storm conditions. Based on the information we do have, all the recent snow is sitting on a hard crust 2-4 ft down, but unlike in adjacent forecast zones, a weak snow(facet)/crust combo isn't widespread and/or reactive.
Keep the touchy and dangerous avalanche conditions capable of producing very large avalanches found in adjacent zones in the forefront of your mind Friday while we gather more snowpack information heading into the weekend.
We've received a lot of snow over the last few days. The risk of tree well and snow immersion suffocation is real in the trees. Don't travel alone and always keep in contact with your partner. You can learn more about deep snow safety here.
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.