Mt Hood

The bottom line: Easterly winds will transport snow onto unusual aspects Tuesday. Larger wind slabs will build near and above treeline but expect to find wind-affected snow even on open slopes below treeline. If you see signs of wind drifted snow, you can stay safe by avoiding nearby slopes greater than 35 degrees. If new snow piles up quickly, you can also trigger storm slabs on very steep open slopes in wind sheltered terrain.

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 Tuesday night through Thursday

Warm frontal moisture traversing the area from south to north this afternoon will weaken and lift into Canada later this evening with generally light to moderate precipitation transitioning to light and spottier precipitation during the evening hours. Warm air will continue weaseling it's way into the Cascades later tonight and tomorrow, creating the opportunity for freezing rain mainly from Snoqualmie Pass to Mt. Hood as significant offshore easterly flow continues. However, even Mt. Baker could see a period of light mixed precipitation later tonight and early tomorrow. The east slopes of the Cascades will stay insulated for longer during this stretch, squeezing out light but continuous snowfall through Wednesday. 

Precipitation will increase once again tomorrow, first in the Olympics and the Mt. Baker area as the old cold front stalls, and for all locations as the longwave trough kicks the old frontal boundary through tomorrow night. Snow levels will slowly moderate through Wednesday afternoon but it won't be until Wednesday night that snow levels more uniformly mix into the 4500-5000 ft range throughout the Cascades.

Shower activity Wednesday night will wind down Thursday morning. There won't be much of a break from clouds and precipitation as a weak warm front brushes the Olympics and Washington Cascades on Thursday with generally light precipitation.