Snoqualmie Pass
Issued: 5:20 PM PST Tuesday, May 2, 2017 by Dennis D'Amico
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.
NWAC Spring Forecast Schedule
The NWAC issued daily mountain weather and avalanche forecasts through Saturday, April 15th. Mountain weather and avalanche forecasts will
be issued during the spring transition April 20-22nd and April 27-29th. Weekend outlooks will be issued Thursdays, May 4th, 11th, 18th and 25th.
Special advisories, watches and warnings will be issued throughout the spring for unusual or dangerous avalanche conditions. You can find out
what constitutes a special advisory, watch or warning here.
The Bottom Line: The highest freezing levels/warmest temperatures of the spring are forecast Wednesday and
Thursday. The potential for wet snow avalanches and cornice failure will rise substantially over this period creating
dangerous avalanche conditions. Travel in avalanche terrain is not recommended over the next two days. Snowpack Analysis
Due to the unusually cool and wet spring, our snowpack near and above treeline is in transition from winter to spring conditions in both the Olympics and
Cascades. Normal spring-time consolidation has not happened at higher elevations due to this active and cool pattern.
Forks, WA Average March Freezing Levels
Salem, OR
Spokane, WA
4295 feet
5795 feet
5152 feet
Forks, WA
Average April Freezing Levels
Salem, OR
Spokane, WA
4733 feet
5497 feet
6222 feet
Detailed Avalanche Forecast for Wednesday
Weather: Rain associated with a warm front should come to an end from south to north on Wednesday and be followed by a general clearing trend for Mt. Hood, the
Olympics and the central and south Washington Cascades. Sunshine and isolated mountain showers are expected for these areas Wednesday
afternoon. However, cloud cover, shower activity, and moderate alpine winds will linger through most of Wednesday in the north Cascades.
Wednesday night should be mostly clear. On Thursday, after a sunny start, showers and thunderstorms will develop in the afternoon and generally move from south to north. Some thunderstorms may
locally become strong. Showers and thunderstorms will continue Thursday night. Freezing levels will range from 11,000 to 12,000+ feet from Wednesday through Friday morning, with the warmest mid-mountain (5000 feet) temperatures
expected Thursday afternoon. These will be the highest freezing levels seen since mid-February. Avalanche hazards: The threat of wet snow avalanches and cornice failure will rise substantially Wednesday and Thursday due to the warm weather and create dangerous
avalanche conditions! Travel in avalanche terrain is not recommended over the next two days. The likelihood of loose wet avalanches will increase on steeper slopes on all aspects and elevations over the next two days. Rainfall at higher elevations will
increase the loose wet potential where recent snowfall at higher elevations is available for entrainment. Periods of strong spring sunshine paired with warm
temperatures will quickly break down local melt-freeze surface crusts formed overnight and activate loose wet snow.
Watch for surface wet snow deeper than a few inches, pinwheels and initial small loose wet avalanches that indicate an increasing loose wet avalanche
danger. Loose wet avalanches at lower elevations may be less likely to initiate naturally, but if skier triggered, could entrain older snow layers and become large
in specific areas. Keep this in mind around terrain traps and do not underestimate the power of even small loose wet avalanches. Cornices will weaken during this stretch! Many cornices are still large, and the best advice during this period is to avoid traveling near or below them all
together. Realize that natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Cornice failures above treeline may trigger
lingering wind slab on lee slopes in the alpine. See a blog post regarding cornices here.
Avoid unsupported slopes with overhanging blocks of snow and smooth rock underneath. Glide avalanches are difficult to predict and can release at any time,
not just during the heat of the day.
Mountain Weather Synopsis for Saturday & Sunday
A cold front off the Washington coast is approaching the Olympics Saturday afternoon. Mid and high clouds are filling in over Washington and northern Oregon
Saturday afternoon with light precipitation just reaching the Olympics. The front should bring increasing light precipitation to the Olympics and NW Washington
Cascades later Saturday afternoon. The main frontal passage should move across the Cascade crest before midnight, and pass the Mt Hood area early Sunday
morning. A period of moderate precipitation should accompany the frontal passage with showers following by early Sunday. Only very light amounts of
precipitation are expected along the east slopes of the Cascades. Freezing levels should continue to rise modestly overnight and cool behind the front by early
Sunday. Onshore flow should maintain showers, mainly along the west slope Cascade areas early Sunday and diminish or end during the day Sunday. Upper
level high pressure begins to rebuild along the coast Sunday night to allow for a cool but drying NW flow aloft. 24 Hour Quantitative Precipitation ending at 4 am
Location
Sun
Mon
Hurricane Ridge
.25
lt .10
Mt Baker Ski Area
.50
lt .25
Washington Pass
lt .25
lt .10
Stevens Pass
.25
lt .25
Snoqualmie Pass
.25 - .50
lt .25
Mission Ridge
lt .25
lt .10
Crystal Mt
lt .25
lt .10
Paradise
.25 - .50
lt .25
White Pass
lt .25
lt .10
Mt Hood Meadows
.25
lt .25
Timberline
.25 - .50
lt .25
LT = less than; WE or Water equivalent is the liquid water
equivalent of melted snow in hundredths of inches. As a
rough approximation 1 inch of snow = about .10 inches WE,
or 10 inches of snow = about 1 inch WE.
Snow Level/Freezing Level in feet
Day
Easterly
Northwest Northeast Central
South
Flow in
Olympics Cascades Cascades Cascades Cascades Passes
Saturday Afternoon Night
5500'
5000'
5000'
5500'
6500'
Sunday Morning
3000'
3500'
3500'
3500'
4500'
Sunday Afternoon
3500'
4000'
4000'
4000'
4500'
Sunday Night
4000'
4500'
4500'
4500'
4500'
Cascade Snow / Freezing Levels noted above refer to the north (approximately Mt Baker and
Washington Pass), central (approximately Stevens to White Pass) and south (near Mt Hood).
Freezing Level is when no precipitation is forecast.
* Note that surface snow levels are common near the passes during easterly pass flow and
may result in multiple snow / freezing levels.