Saturday, February 09, 2008

Mammoth Snowfall in the Cascades

The past few weeks have seen truly enormous amounts of snowfall up and down the left coast mountains - the Sierras in California and the Cascades from British Columbia south into North California. Locally in the Mount Hood area more snow - 7 feet (2.14 m) - fell in a week than falls in some entire winters. Santiam Pass south of here is closed due to avalanches and general conditions at the section with mountain-high steep slopes on both sides. Authorities asked people stay off the mountain roads of Mount Hood last weekend, but few listened with the prospect of all that powder and the potential for good skiing and snowboarding. In California both railroads and freeways have been shut down, trapping many in the mountains. The main east-west highway I-90 in the Cascades east of Seattle has closed repeatedly due to avalanche danger and deep snow. It is closed now but may reopen late today. In the mountain town of Leavenworth on the east side of the Cascades, a large home was flattened by an avalanche a few days ago, right in town! The Stevens Pass road to the town is closed due to avalanche danger. White Pass is also closed due to multiple avalanches burying the road and whiteout high wind conditions.

The snow is so deep and soft that snowmobiles have been lost and their owners stuck far into the backcountry needing rescue.

Reports give a current snow depth of 240 inches at Hurricane Ridge in Olympic National Park. Thats 20 feet (6.1 meters)! At Paradise in Mount Rainier National Park the depth is 210 inches (5.3 meters). Mount Hood east of Portland has 200 inches (over 5 meters) at high-elevation Timberline Lodge, dropping to 160 (still over 4 meters) at Ski Bowl 2000 feet (610 meters) lower. On Mount Hood these are very deep figures, especially at the lower elevations.

The Mount Saint Helens VolcanoCam is currently melting out of a snowdrift which completely buried it in recent days. This large-image webcam provides a view of the only actively erupting volcano in the 48 states. It's been steadily growing the now large lava dome since 2004.

After a less-precipitation today forecasts call for alternating rain and snow until just snow mid-week. This is sure to produce natural avalanches and makes likely traveler-triggered slides, making backcountry travel dangerous.

The network TV weathermen like scare stories to boost ratings, so several are available making it sound like a huge flood is in the offing due to all that snow. There are a few problems with the theory despite the deep snowpack. Required for a big flood is a several day 'pineapple express' rain event with very warm tropical downpours that melt snow to the tops of the mountains. That is not in the picture for the moment. And its getting late for a hard freeze down to the lowest elevations, required to give the frozen soils needed to shed the rains if they arrive.

If we get the necessary combination of factors - a hard freeze to the valley floor, heavy snowfall with some at low elevations, and a rapid warming with tropically warmed rain, then our rare huge floods will occur. They average about a 25 years spread, varying from 17 to 32, with the last one in February 1996. They are invariably labeled '100 years floods'. At our place on the river, these big ones are about 25 feet (8 meters) above summer levels.

My guess is a moderate snowmelt flood come mid-April, such as happened in our last high snowfall year, 2002. During that flood this mallard couple rather tamely allowed this photo taken on our lower lawn, despite the attentions of our cat lurking nearby. Another post on an earlier flood has a photo of cat and bird as close as they ever came.

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