Avalanche Forecast
Issued: Mar 30th, 2018 11:40AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet.
NWAC,
Northwest Avalanche Center
Warmer temperatures and sun are making it easier to trigger wet avalanches on steep, rocky, and sun exposed slopes. If you see recent roller balls, Loose Wet avalanches, or experience wet surface snow deeper than your ankle, move to shaded and drier slopes. Avoid areas where you could be pushed off cliffs or through rocks by a wet avalanche.
Summary
Detailed Forecast
Warm temperatures and sun on Saturday will make it easier to trigger wet avalanches, especially in areas where they haven't recently run. Loose Wet avalanches may occur at higher elevations or on more shaded aspects (facing west, north, and east). While Loose Wet avalanches are often smaller and easier to predict, they can be dangerous in high consequence terrain. Avoid extreme terrain or areas where getting caught in a wet avalanche would be especially dangerous. This includes steep slopes above rocks and cliffs, tight gullies, or trees.
Minimal freeze Friday night raises concern for other warming and wet snow related avalanches. Watch out for snow-covered rock slabs at mid to lower elevations and slopes with exposed cracks where Glide avalanches could occur. Avoid any known locations (especially near Snoqualmie Pass and the Mt Baker backcountry) that are notorious for producing Glide avalanches. Cornices have built in the past week. They typically fall during warming periods like what we will experience on Saturday. Whether your walking on a ridge or traveling on slopes, give cornices plenty of room. Wet Slabs are very difficult to predict and can be very large and destructive. Avoid avalanche terrain, if you find slopes with unsupportive, wet snow or where a known weak layer is getting wet.
Snowpack Discussion
Warm air temperatures, light rain, and sun over the last several days created moist to wet surface snow in many locations. Generally, two or more feet of melt-form snow exists at the snow surface. Wet surface snow resulted in a loose wet avalanche cycle in the Snoqualmie Pass area. This likely occurred in other locations as well.
At higher elevations drier soft snow can still be found. The elevation where this transition occurs can vary even with in a zone. Typically drier snow can be found above 6500 feet in the southern areas an near 5000 feet in the northern areas. Moderate winds formed wind slabs as recent as Wednesday near and above treeline. Wind Slab avalanches are now hard to trigger.
Several avalanches 3/24-3/27 in the Crystal and Stevens areas failed on a layer of weak older snow buried on 3/22. Observations this week demonstrate this layer has been gaining strength. In some locations you may find a layer of small sugary facets above a firm melt-freeze crust. This layer has generally been reported 12-20” (30-50cm) below the snow surface and may be most prevalent above 5,500ft.
The much older 2/13 facets layer just above the 2/8 melt-freeze layer can still be found 4-6 feet (120-200cm) deep in the snowpack. While neither of these layers are listed in our current avalanche problem set, they may reawaken if they become wet.
Observations
North
On Wednesday Mt Baker Ski Patrol reported 8-12 inches (20-30cm) of soft snow over a recent melt-freeze crust. This snow was very rapidly effected by small sun breaks and thinning in the clouds. Winds earlier in the weak formed new wind slabs at higher elevations.
Central
On Thursday NWAC professional observer Jeremy Allyn traveled in the Snoqualmie Pass area. Jeremy reported numerous wet avalanche below and near treeline that over the last few days. He found moist to wet surface snow up to 4600 feet.
South
On Wednesday. NWAC professional observer Ian Nicholson traveled in the Crystal backcountry. Ian found a 1" (2-3cm) surface crust on all aspects in the morning. This crust quickly broke down on sun exposed slopes as clouds thinned mid-day. Ian did observe the 3/22 interface and found that it was still reactive in some snowpack tests. This layer was 12-18" (30-45cm) below the snow surface.
Problems
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 31st, 2018 11:40AM
