Heavy precipitation, warming, and wind will overload the snowpack and likely cause a widespread natural avalanche cycle. Avoid all avalanche terrain on Monday.
Avalanches may involve new snow, or could even break several feet deep involving all the storm and wind loaded snow from the weekend. Fresh storm slabs will be widespread throughout the terrain, and touchy to human-triggers, especially in wind loaded areas. Avoid travel on slopes steeper than 30 degrees, and steer clear of avalanche path runout zones.
The warming trend on Monday looks to bring wet heavy snow and rain near and below treeline. The light dry snow from the weekend will likely become wet and weak. If you encounter rain on snow, rollerballs, or pinwheels, expect wet avalanches to follow. These avalanches could entrain quite a bit of snow as the run downslope, or even trigger slab avalanches. Avoid any steep slopes where you find wet unconsolidated snow surfaces or witness rain on snow.
More snow will fall at cool temperatures overnight Sunday before snow levels rise (4000ft), precipitation rates increase, and gusty southwest winds arrive Monday. Large natural avalanches are likely. Avalanches could even run full track to valley bottom. Conditions will become very dangerous by late afternoon. Travel in or below avalanche terrain is not recommended.
Happy New Year!
The pacific northwest rung in the new year with a winter storm cycle that brought changing conditions to our region. This storm exhibited three characteristics: warm, wet, and windy. Let’s take a look at the end of 2019, the beginning of 2020, and where we can go from here.
Wrapping up 2019
The last few days of December were generally quiet and cold. The snowpack seemed to enjoy this break in the weather. Lingering unstable snow from the pre-Christmas storms gained strength, persistent weak layers appeared to stabilize, and avalanche hazard decreased in all forecast zones. All in all 2019 ended quiet and uneventful… until the New Year’s Eve weather party showed up …
Quiet weather led to lower avalanche danger during the last week of 2019. Hogsback, White Pass, WA. Photo: Andy Harrington
Blowing into 2020
A warm, wet, and windy weather system blew into the northwest for New Year’s Eve and New Year’s Day. This brought rapidly changing conditions and increasing avalanche hazard to all areas.
Warm: Unfortunately this system brought with it warm air. Freezing levels measured near the coast reached 9000’ on the afternoon of the 31st. Many weather stations recorded above freezing temperatures during the onset of precipitation.
Wet: While this system wasn’t as wet as the atmospheric river prior to Christmas, it still produced impressive water numbers in many areas. The bulk of the precipitation seemed to be focused on the Passes and Volcanoes, and water spilled over the crest to places like Washington Pass and Leavenworth. Sadly, when combined with the warm temperatures, this translated to rain well into the near treeline band (or higher) for most areas. The main exception appeared to be in the northeastern cascades, where locations like Washington Pass remained all snow.
HurRidge
MtBaker
WaPass
Stevens
Leavenworth
SnoqPass
MtRainier
MtHood
Precipitation (in)
1.84
3.39
1.42
4.56
1.06
6.19
5.39
5.41
Snow (in)
-
15
-
12
0
3
10
8
Table 1: Precipitation and storm totals from selected weather stations during the New Year’s Eve Storm. “-” 24hr storm snow not measured.
Windy: While the warm and wet were impressive, it’s the winds that may set this storm apart. Most weather stations recorded very strong and extreme winds during the storm. Alpental exceeded 100mph just after midnight to ring in the new year. Any dry snow at high elevations was redistributed by the wind and snow surfaces were transformed.
Table 2: Wind speeds from New Year’s Eve from selected wind sites. Note the sustained period of winds between 40-60mph.
Eventually, temperatures cooled, the rain turned back to snow, and winds calmed. Many locations picked up additional snow as the storm wound down, but 2020 was already off and rolling with its first major storm.
New Year’s Resolutions
The active weather pattern that started the new year appears to continue. The snowpack and avalanche conditions will continue to change. So, what can your New Year Avalanche Resolutions be?
Read the forecast. This is a great way to monitor conditions even if you aren’t heading into the mountains.
Get out in the snow! Enjoy the wonderful mountains in your backyard.
Submit an observation. Tell the avalanche center what you saw while out in the snow by submitting an observation and sending in a photo.
Thanks for all of your support in 2019 and here’s to 2020!
-Dallas
