Mt Hood

Gusty winds will easily transport cold, dry snow above 5500 feet maintaining the possibility of triggering an avalanche. Stay safe by traveling on scoured slopes and ridges. Avoid slopes steeper than 35 degrees where you see signs of wind transported snow such as pillowlike drifts, firm or textured snow surfaces and cornice formation.

A firm and supportable rain crust exists underneath recent cold, light snow. Moderate winds have been able to easily transport the dry snow and build wind slabs up to about 1 foot deep, especially above treeline.

On Monday, the free air wind direction has changed and become more northerly. This means that many slopes that are often scoured may be holding snow and slopes that are usually wind-loaded may be scoured. Look for clues about the recent wind transport by observing the direction of new snowdrifts, texture on the snow surface and the current wind direction on the slopes you are traveling. Common wind loading clues, like cornices, won’t tell you about recent changes in wind direction. Keen observation of recent wind transport will be critical for safe travel. When in doubt, choose lower angle terrain.

Note the scalloped features on the shallow drifts of snow. The scalloped ridges point toward the direction that the wind was coming from. These surface clues can be very helpful especially during times of changing wind directions. Photo: Peter Moore (2/1/20)

January 30th, 2020 (The regional synopsis is updated every Thursday @ 6 pm)

Looking Back at January

As we turn the corner from January to February, this is a good time to look back at the last month’s snow, weather, and avalanche conditions. January was notable for continuous storms and elevated, yet quickly resolving avalanche danger. In most parts of the region, the snowpack grew significantly. Snow depths went from far below average at the New Year to near normal by the end of the month. While numbers are still being compiled, January 2020 could rank high for total precipitation amounts in some locations. As we move forward, there are currently few layers of concern in the existing snowpack. 

Snotel weather stations report well above average precipitation amounts for the month of January. Source: www.nrcs.usda.gov

Weather

January was marked by an onslaught of storms with very few breaks in precipitation lasting 24, or even 12 hours. Most notable was the sheer amount of precipitation that these storms delivered. Most NRCS Snotel weather stations are reporting at least 125% of average precipitation amounts for January, with many over 200% of average. Not all of this fell as snow. For the month of January, the Mt. Baker, Snoqualmie Pass, Paradise, and Mt. Hood Meadows weather stations measured an astounding 42”, 33”, 32” and 28” of water (both rain and snow) with 1 day still left in the month. If you do some quick math, those 4 stations average near or above an inch of water a day!  

Snow levels and temperatures were less consistent than the overall stormy weather. On the heels of a warm December, the first week of the New Year followed suit. From about January 8th through the 19th a cold period had its grasp on the region, bringing snow to the lowlands and copious amounts of light, champagne powder to the mountains. The last third of the month saw continued storms. Temperatures moderated and warm air brought occasional rain to middle and even upper elevations. 

A small skier triggered avalanche (D1) within new snow on a NE aspect at 5600ft on Mt. Herman. 01/28/20 Photo: Zack McGill

Snow and Avalanche Danger

After a meager start to the winter, the snowpack grew exponentially in January. In fact, the storms were so intense in the middle of the month that they challenged the accuracy of remote weather stations. Snow blocked precipitation gages and knocked out cellular towers and phone lines used to transmit data. Currently, snow depths from reporting sites are near average.

While the storms often brought rapid spikes in avalanche danger, the hazard was quick to taper off. Throughout the month, there were 12 days when NWAC issued High Danger in one or more zones and 11 days when there was at least some Low Danger in forecasts. It’s notable that there were no days with all Low Danger in any forecast zone. In addition to the snowpack growth, a positive side to the storms was that weak layers had little time to form. In general, any facets or surface hoar that formed were very short-lived weak layers. Most avalanche problems involved new snow, wind or wet snow. There are still some areas of shallow, weak snowpack in typical places like the Wenatchee Mountains and the most eastern extent of the Cascade Mountains. Aside from that, the snowpack layering in most zones is marked by a few lingering storm interfaces in the upper snowpack and intermittent crusts from rain events. If you dig in the snowpack around the region, the most prominent crusts you’ll find formed from rain events roughly around January 1-3rd, 7th, MLK weekend, 23-25th, and the 31st.

Looking Forward

The winter snowpack is now well established for recreating and traveling through the mountains. Much more so than it was a month ago. Looking ahead, there’s a good chance this stormy pattern will continue at least into early February. We’ll keep monitoring how the snowpack continues to change near the surface with each weather event. You can check the daily Avalanche and Mountain Weather forecasts for the most up to date information.