Avalanche and Weather Outlook
Monday, December 2nd, 2013
Recent Weather and Snowpack:
A strong plume of moisture, accompianed by very strong westerly winds took aim at the Pacific Northwest this past weekend and produced heavy precipitation, mostly in the form of rain for lower and mid elevations from about Saturday evening through Sunday. Beginning Sunday night and extending into Monday, much colder air filtered into the region.
Storm totals were quite impressive at NWAC stations - 2+ inches of water in the north WA Cascades, 3-4+ in. the central WA Cascades, 1-2 in. for the east WA slopes and 5-10 in. in the Mt. Hood area (Timberline recorded just under 9 in. of water in the 24 hrs ending Monday morning!!).
With plummeting snow levels, a few inches of snow fell at pass levels and below. At higher elevations (generally above 5 kft in the north and central Cascades and above 6-7 kft in the south Cascades and Mt. Hood area) and also the Stevens Pass area near a convergence zone, 1 -2 feet of snow fell.
Surface hoar reported from last week should have been destroyed with the warm storm. Limited ski area/DOT reports tell of generally good bonding between the new lower density snow to the still moist and at lower elevations draining older snowpack.
An additional few inches will likely accumulate early tonight as snow showers continue through the evening. Areas near the convergence zone(s), like Snoqualmie Pass, may pick up an additional 5-10 inches of low density snow.
Weather and Avalanche Danger Outlook this Week:
Newly formed wind and storm slab at higher elevations may be sensitive for next day or two. A cooling and drying trend later Monday night through the middle of the week will aid the overall stabilization trend. As moist sections of the older snowpack re-freeze over the next several days, this will promote stabilization in the deeper snowpack. A weak weather system may glance Washington on Thursday night and deliver light to moderate snowfall totals to the Oregon Cascades early Friday.
Proceed with caution if venturing into the back country - post storm reports thus far have been limited.
At low elevations the shallow snow and terrain and vegetation anchors should continue to limit avalanche danger.
When Do Regular Forecasts Start At The NWAC?
Personnel at the NWAC have had a very busy fall preparing a much anticipated new web site as well as installing and repairing the NWAC mountain weather station network. The date to start regular forecasting has not been decided yet but this usually begins when there is significant snow cover to the lower elevations and when most ski areas begin to open (observations from professional avalanche control programs from ski areas and WSDOT are an important aspect to NWAC forecasts). Statements will be updated as warranted until the start of regular forecasting.
D'Amico/Northwest Avalanche Center