Avalanche Forecast

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 Wednesday night through Friday

A rainband associated with a low tracking northward offshore will bring rain at generally elevated snow levels west of the Cascade Crest. Cold air east of the Cascade Crest will gradually erode from south to north, but may still provide a messy mix of rain, sleet and snow east from the lower Cascade passes eastward in the evening and overnight hours. Mt. Baker continues to be favored by the southerly flow pattern (2" of water overnight), but other areas will start receiving moderate precipitation overnight.

The passage of the rainband is likely to decrease easterly flow enough to change both Stevens and Snoqualmie Passes to rain by Thursday early morning and scour out the and scour out the cold air pool east of the Cascade Crest as the rainband doesn't provide much cooling aloft. Precipitation type has been very difficult to forecast during this event.

A weak warm front will brush the region on Thursday, bringing generally light rain and snow on a southerly flow. 

Thursday night and Friday should see some clearing as most of the weather action stays just offshore to our west with a ridge building over eastern Washington, keeping us dry.