West Slopes South - South of I-90 to Columbia River
NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.
Outlook updated Friday afternoon due to possible snow in the Northwest Cascades - mainly the Mt Baker area.
Avalanche Forecasts have ended for the 2015 - 2016 season. Weekend Outlooks will be issued Thursdays April 28th and May 5th, 12th, 19th, and 26th. Special advisories, watches, and warnings will be issued throughout the spring for unusual or dangerous avalanche conditions. This is the last regularly scheduled Outlook for Spring 2016.
Recent Weather, Snowpack and Avalanche Observations
Last weekend (May 21st - May 22nd) was cool and wet with many NWAC stations recording 1 to 2 inches of water over a three day period ending Monday morning and snow levels oscillating around 6000 feet. The Timberline snowdepth sensor briefly increased over last weekend and the above treeline elevation band picked up some new snow. During the week generally light showers produced only light precipitation amounts while snow levels slowly moderated.
Fresh reports have been few and far between given the weather this past week, but besides new snow mainly confined to the higher peaks and volcanoes we would not have expected much change from the recent stable and previously identified springtime avalanche hazards.
Weekend Weather Outlook
Too bad we can't slide the forecast for the middle of next week (warm and sunny) up a few days. Unfortunately, the majority of the holiday weekend looks cool and damp through Sunday especially along the crest and along the west slopes.
An upper low over central British Columbia will send weather disturbances our way each day from Friday through Sunday. Temperatures look chilly Friday through Sunday. Snow levels are in the 5-6000 foot range on Friday and should be in the 6-7000 foot range in the north and 7-8000 foot range in the south on Saturday and Sunday. The main precipitation should be in the Mt Baker area on Saturday where several inches of snow is possible above the snow level. Some further snow may be seen there on Sunday. Minor amounts of new snow if any should be seen elsewhere along the crest and along the west slopes above the snow level Friday to Sunday.
In general for Friday to Sunday onshore flow at the surface will also help enhance marine moisture and cloudiness along the Olympics and west slopes of the Cascades. Generally less cloudy and slightly warmer conditions are expected along the east slopes of the Cascades further away from the Cascade crest and also down toward Mt. Hood, further away from the upper low center.
Memorial Day has the potential for a fine end to the weekend. Current forecast models show a upper level ridge building offshore and a drying and warming trend. It's tough to say for sure several days out, but hedge your bets on better weather at the end versus the beginning of the weekend.
You can check out our automatically updating and sorting precipitation table to see who has picked up the most precipitation before heading out the door. Also, we were able to repair the radio link connecting to the top of Chinook Pass and Sunrise on Thursday, so the weather station data is back online.
Weekend Snowpack and Avalanche Outlook
The primary avalanche concern through the weekend will be for shallow loose wet snow avalanches in any areas that accumulate more than a few inches of new snow. This is most likely above the snow level in the Mt Baker area. New snow can get active quickly this time of year, especially if there are sun breaks or solar effects. Watch for new wet snow deeper than a few inches and be aware of terrain traps (such as above cliff bands) where a small loose wet avalanche could have serious consequences.
Glide avalanches are still possible so avoid areas below rock faces and cliffs still holding snow.
It seems a stretch at this time of year, but if you are high enough and there is enough new snow, watch for new wind slab or generally shallow storm slab. New firm wind transported snow is often a good sign of wind slab. Storm slab becomes likely when more than an inch of snow an hour accumulates for more than a few hours. Graupel layers that accumulate during intense showers can also provide a short-lived bed surface for storm slabs. This all should be most likely in the Mt Baker area.
This Weekend Outlook is for areas in the Olympics and in the Cascades up to the crest level and does not apply to higher elevations on the volcanoes. It will not be updated unless there is a significant change from the expected conditions.