Continued moderate snowfall have been steadily building storm slabs since 11/25. Our thin “weak” snowpack will slowly adjust to this added weight. Natural and human triggered storm slab avalanches will be likely on 11/30, at mid and upper elevations. Expect this hazard to increase as the next storm enters our area bringinging heavy precipitation and rising temperatures.
On 11/29 a full depth avalanche was observed at ~4000′ on a North aspect of Billy Mitchell. See avalanche activity section for more details. Clouds have prevented further avalanche observations. This indicates basal facets at the ground that are being overcome by increasing storm loads. The distribution of basal facets in our area is unknown at this time. This is a very dangerous problem since it will include the entire snowpack and it is very difficult to predict and manage. This hazard is increasing with additional snowfall and rising temperatures forecasted.
Winds have been blowing from multiple directions since the last round of storms began 11/25. With abundant dry snow available for transport, and changing wind direction expect wind slabs to have formed on a variety of aspects. Avoid slopes that are actively, or have recently been loaded by wind. Signs of recently loaded slopes include: new snow that gets rapidly deeper over a short distance, like over a ridge or pass. Pillowed snow surfaces, shooting cracks and freshly formed cornices.
Many Cornices are in their infancy stages of forming at this point in the season. While traveling on or below cornices is always dangerous and never recommended. They can be especially dangerous early season when they may be made primarily of freshly drifted snow that almost surely can’t support the weight of a person or snowmachine.
11/15: Natural avalanche observed in Loveland Basin on a South aspect, down the ridge from Tones Temple. This slide was triggered by recent NE wind loading and failed at the ground. SS-N-R1-D2-G
11/16: Natural avalanche observed on Billy Mitchell “Cry babys shoulder”. Released from~3500′ with a crown length of ~200 meters, North aspect. This slide was triggered by recent NE wind cross loading the slope. SS-N-R2-D2-U
11/29: Natural avalanche observed on Billy Mitchell Cry babys shoulder, similar elevation as 11/16 slide but originated a couple hundred meters further west. Released from ~4000′ with a crown length of ~ 200 meters, North aspect, ~ 37°, failed at the ground. HS-N-R2-D2.5-G
11/30- A large low pressure system with jet stream support will begin to affect our area the afternoon of 11/30. The precipitation associated with this storm will start out as snow and change over to rain sometime late Monday or early Tuesday for low lying areas. Between 2-3 inches of snow water equivalent is expected (SWE) in the next 48 hours. Models are indicating that the freezing line may move up to 4000′ by late Tuesday/ early Wednesday.
The Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
This forecast is for use in snow safety activities and emergency
Temp at 1000` 31 F 31 F
Temp at 3000` 25 F 23-29 F
Chance of precip 90% 100%
(above 1000 FT) 0.11 in 0.88 in
(above 1000 FT) 1 in 1-9 in
Snow level 500 ft 600 ft
Wind 3000` ridges E 5-20 mph E 15-45 mph
Remarks...Warming temperatures, rising snow levels, rain, snow
and heavy precipitation expected tonight. Snow levels rising to
1,600 feet Tuesday, then rising higher Tuesday night.
Thompson Pass weather history 20/21. Click on links below the images to see full size view
TP NOV as of 11/18
The avalanche hazard is Considerable at all elevations. A series of winter storms beginning 11/25 has deposited more than 3 feet of snow on Thompson Pass. This snow has been deposited on a thin/weak snowpack that needs time to adjust. A brief break in precipitation late Sunday/ early Monday will not be sufficient time for the snowpack to heal. Human triggered avalanches are likely and natural avalanches are possible. Conservative terrain choices will be critical if traveling in the mountains today. Avoid avalanche paths and terrain traps today. Hazard will be increasing with continued heavy snowfall through Wednesday.
For more information click the (+full forecast) button below.
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