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.
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 expect a large change from the otherwise 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 at least Sunday.
An upper low over central British Columbia will send several weather disturbances our way from Friday through Sunday. Onshore flow at the surface will 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. Temperatures above treeline for the north and central Cascades look chilly through Sunday. Precipitation amounts should be fairly light over the weekend except for a potential convergence zone Friday afternoon and evening that may locally produce around 0.50 inches of water in the Stevens and Snoqualmie Pass area through Saturday morning. Snow levels will hover in the 4500-5500 ft range through Saturday morning, so be prepared for the possibility for some fresh snow on your tent if camping out above 4500 ft Friday night.
A weak front spinning from the low on Saturday will bring some light rain and snow mainly to the Olympics and north Cascades, again with decreasing cloud cover further south and east.
Sunday looks like to be a transition day with light showers continuing for the north and central Cascades along the west slopes but some moderation in snow levels. The extent of the marine moisture along the west slopes looks shallower in depth, so some sun breaks should be possible Sunday afternoon even on the west side. 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 today, 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. 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 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.