Avalanche Forecast
Jan 6th, 2019–Jan 7th, 2019
Alpine
3:
Considerable
The avalanche danger rating in the alpine will be considerable
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
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: Mt Hood.
The bottom line: You can trigger a large wind slab due to continued transport of fresh snowfall with moderate, gusty winds. Wind slab hazard will increase as you ascend. Before crossing steeper slopes at lower elevation, check for a layer of snow near the surface that wants to release as a cohesive unit.
Snowpack and Avalanche Discussion
Mt. Hood Pro Patrol reported that a freezing fog layer formed Saturday produced a breakable crust into the above-treeline terrain, which mitigated avalanche hazard on Sunday. The wind event Saturday night had blown snow out of start zones.
Recent professional reports indicate the bottom 50†of the snowpack to comprised of well-bonded dense snow and crust layers. The most recent crust was buried January 4th and should extend to the top of the near treeline terrain. New snow of varying depth sits on top of the crust.
Regional Synopsis
January 6, 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 Monday night through Wednesday
5 pm Update: Corrected precipitation type in Weather Forecast for Tuesday.
A transitory upper level ridge will quickly pass through the region tonight, opening the door for mid and high level clouds to spread up from the south. A mature low pressure system well offshore will spin light warm frontal moisture over the area on Tuesday also from south to north during the daylight hours, with the highest snowfall amounts likely in the Mt. Hood area and to a lesser degree the Crystal Mt./Paradise area.
Offshore easterly flow will ramp up quickly overnight through Tuesday and E-SE winds should increase quickly near and west of the Cascade crest from Snoqualmie Pass and southward. The easterly flow will also mute the warming trend during the day for all areas. The associated weak cold front should move through Tuesday night, producing generally light precipitation.
A trailing longwave trough will begin to quick the whole mess through late Wednesday afternoon and Wednesday night. With each round of precipitation in southerly flow, the cold air trapped in and around the Cascades including Mt. Hood will erode with gradually rising snow levels and increased chances for mixed precipitation.
Avalanche Problems
Wind Slabs
Wind slabs were not particularly reactive on Sunday due to shallow new snowfall and the thin ice layer formed on Saturday. However, winds continue to transport lower-density fresh snow. Wind slabs should be growing and more reactive than Sunday near and above treeline.
The problem can be avoided by sticking to wind-sheltered locations or choosing wind-scoured aspects and ridgelines.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2
Storm Slabs
A subtle snow density change in the shallow snow that accumulated Sunday will create a layer for storm slabs to run on. Very shallow 1-2” storm layers were reactive on Sunday at Mt. Hood Meadows. If the depth of the new snow is greater than 8”, use small slope tests and hand shears to look for a layer that wants to release as a cohesive slab. If present, avoid unsupported slopes and slopes steeper than 35 degrees.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1