Mt Hood

The bottom line: You can trigger a fresh wind slab near and above treeline that might be large and reactive, sitting on a thin crust interface. Increasing winds and snow at gradually lowering snow levels will move the Wind Slab problem to lower elevations relative to Wednesday. Below treeline, reduce exposure to small wet loose avalanches that you can trigger on steeper slopes.

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. Nowhere 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 a substantial increase in 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 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.