Avalanche Forecast
Jan 9th, 2019–Jan 11th, 2019
Alpine
3:
Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3:
Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2:
Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2:
Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2:
Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2:
Moderate
The avalanche danger rating below treeline will be moderate
Regions: Snoqualmie Pass.
The bottom line: The wind and its movement of the snow is the main story at Snoqualmie Pass. Recent strong winds formed slabs in a variety of unusual locations including well below ridgelines. Fresh cornices, the snow blown out of the trees, and firm hollow snow under you can all be signs that wind slabs are likely nearby. If you see or feel any of these observations, you can travel safely by avoiding slopes greater than 35 degrees.
Snowpack and Avalanche Discussion
The weather models are struggling to determine the freezing levels and precipitation amounts for Wednesday night and Thursday morning. Small shifts of the freezing level could cause moderate rain in the below treeline band, or keep all snow at the Pass. Since the weather is driving the avalanche danger, we have a high degree of uncertainty for this avalanche forecast. Keep your eyes open. If you see observations that don’t line up with the weather or avalanche forecast, stop and reevaluate. We are confident the avalanche danger will slowly decrease as this weather system exits the region and unstable snow has time to gain strength.
Regional Synopsis
January 7, 2019
This latest round of storms in early January continues to highlight some of this season’s region-wide themes in our snowpack. I’d describe them as Bottom to Top, North to South, and East to West. Let’s take a look at each of these.
Bottom to Top:
In general this winter has been on the warm side in the Cascades. No where is that more evident than in the lack of low elevation snow. Heavy rain events continue to wash-away and thoroughly wet the lower elevation snowpack. In most regions you will see substantial increase is the height of snow from low elevations (3000 ft), to mid elevations (4500 ft), and again at upper elevations (5500/6000 ft). Above the typical rain lines (5000-6000 ft) a deep and cold mid-winter snowpack exists.
North to South:
With few exceptions, this season’s storm tracks have favored the North Cascades. Sunday, Mt Baker’s Heather Meadows weather station passed 100 inches of snow on the ground. A quick look around the state’s weather stations demonstrates just how deep this snowpack is. Most other locations are reporting between 50 and 75 inches. The massive amounts of snow for the northern forecast zones are reflected in several impressive avalanche cycles spread out over the last month.
East to West:
Several stacked persistent weak layers have been buried in the eastern forecast zones. This isn’t unusual, but it is noteworthy. The thickness of the slabs over these weak layers can vary greatly. Closer to the Cascade Crest, the deep snowpack may more closely resemble Stevens or Snoqualmie Passes. Further east, shallower snowpacks, and significant variability are keeping snowpack assessment tricky.
So what now? Well, on January 3 and 4 a high elevation rain event impacted areas from Mt Baker to Mt Hood. In many locations this has created a firm and thickening crust. In these locations, this new crust is limiting the impacts of any deeper weak layers. In locations that didn’t receive as much rain like WA Pass, Mission Ridge, Crystal Mt, and White Pass, how the small amount of rain impacted the mid and lower snowpacks remain to be seen.
One thing is for sure, we’re not even a month into the winter season, there’s a lot more winter to come.
This latest round of storms in early January continues to highlight some of this season’s region-wide themes in our snowpack. I’d describe them as Bottom to Top, North to South, and East to West. Let’s take a look at each of these.
Bottom to Top:
In general this winter has been on the warm side in the Cascades. No where is that more evident than in the lack of low elevation snow. Heavy rain events continue to wash-away and thoroughly wet the lower elevation snowpack. In most regions you will see substantial increase is the height of snow from low elevations (3000 ft), to mid elevations (4500 ft), and again at upper elevations (5500/6000 ft). Above the typical rain lines (5000-6000 ft) a deep and cold mid-winter snowpack exists.
North to South:
With few exceptions, this season’s storm tracks have favored the North Cascades. Sunday, Mt Baker’s Heather Meadows weather station passed 100 inches of snow on the ground. A quick look around the state’s weather stations demonstrates just how deep this snowpack is. Most other locations are reporting between 50 and 75 inches. The massive amounts of snow for the northern forecast zones are reflected in several impressive avalanche cycles spread out over the last month.
East to West:
Several stacked persistent weak layers have been buried in the eastern forecast zones. This isn’t unusual, but it is noteworthy. The thickness of the slabs over these weak layers can vary greatly. Closer to the Cascade Crest, the deep snowpack may more closely resemble Stevens or Snoqualmie Passes. Further east, shallower snowpacks, and significant variability are keeping snowpack assessment tricky.
So what now? Well, on January 3 and 4 a high elevation rain event impacted areas from Mt Baker to Mt Hood. In many locations this has created a firm and thickening crust. In these locations, this new crust is limiting the impacts of any deeper weak layers. In locations that didn’t receive as much rain like WA Pass, Mission Ridge, Crystal Mt, and White Pass, how the small amount of rain impacted the mid and lower snowpacks remain to be seen.
One thing is for sure, we’re not even a month into the winter season, there’s a lot more winter to come.
Weather Forecast
Weather Synopsis for Thursday night through Saturday
The Pacific Northwest will be quite mild at the end of this prolonged period of warm generally southerly flow which has scoured out the cold air pool east of the Cascade Crest. Meanwhile, a ridge is amplifying across the Inter-mountain West, pushing out the last moisture from the moist southerly flow during the early evening hours. The ridge diverts storms to the north and south of our region. It will also re-amplify the pressure gradient across the Cascades, setting up a prolonged pattern of moderate easterly flow. Inversion conditions will also develop, leaving a shallow pool of cold air in the deeper valleys east of the Cascade Crest. This low cloud will likely stream through the lower Cascade passes.
The Freezing level will climb to 7000 ft or higher in many locations west of the Cascade Crest Friday through Saturday. Expect cooler temperature through the pass and on the east slopes with the inversion conditions in place.
Avalanche Problems
Wind Slabs
You will need to use your eyes and sense of touch to locate wind transported snow as you travel. Look for signs like blowing snow, fresh cornices, and the snow blown out of trees. Feel the snow under you as you travel. Does it feel more firm in one location than another? Does it feel hollow? If you see or feel any of these observations, wind slabs may be nearby. Recent winds formed slabs in some unusual locations like well below ridgelines, on the sides of gullies, and in places that are normally scoured. You can stay safe by traveling on ridges, scoured areas, and any slope less than 35 degrees.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 3 - 3
Loose Wet
If the east-flow at Snoqualmie Pass weakens, warm air will cause a change to rain. Rain on dry snow is a perfect setup for loose wet avalanches. They may occur naturally from very steep and rocky features where it is raining. If you experience rain or find wet surface snow you may cause a loose wet avalanches on any slope greater than 35 degrees. Don’t let this avalanche problem fool you. Even small loose avalanches can still be dangerous if they carry you over cliffs or into gullies.
Aspects: All aspects.
Elevations: Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1