WINTER STORM WARNING FROM 3 PM THIS AFTERNOON TO 9 AM AKST
SUNDAY...

TODAY...LOCALLY WINDY. SNOW. SNOW ACCUMULATION 2 TO 4 INCHES.
HIGHS AROUND 25. NORTHEAST WIND 15 TO 25 MPH. WIND GUSTS UP TO 45 MPH.

TONIGHT...LOCALLY WINDY. SNOW...HEAVY AT TIMES. SNOW ACCUMULATION 6 TO 10 INCHES. LOWS 18 TO 26. EAST WIND 20 TO 30 MPH WITH GUSTS TO AROUND 40 MPH IN EXPOSED AREAS MAINLY LATE TONIGHT.

SUNDAY...SNOW DIMINISHING IN THE AFTERNOON. SNOW ACCUMULATION 5 TO 7 INCHES. STORM TOTAL SNOW ACCUMULATION 11 TO 17 INCHES. HIGHS AROUND 30. SOUTHEAST WIND 15 TO 25 MPH DIMINISHING IN THE
AFTERNOON.

The week long cold temps and wind have created a patchwork of scoured and windslabbed zones that will bond poorly with new snow.

While today's accumulations are not expected to be large, the new snow is coming with enough wind to load slopes and easily slide off the old snow surfaces. As we get more snow tonight the potential for medium size slides develops.

The winds are variable with local topography. It can be blowing one direction at the channel and the exact opposite direction in a bowl at 2000 feet. The Thane, Behrends and White Path slide paths are all loading. Caution should also be used along the Flume and Perserverance Trails.

Slides are not expected to be large, but these are still powder avalanches with airblasts that carry blowing snow that can damage trees, people and structures.

In the backcountry areas with windloading will likely be very tender. Be highly conscious of spatial variabiltiy due to shifting localized winds, and a patchwork of underlying old snow surfaces.

Avalanche Danger is CONSIDERABLE today: Natural avalanches possible, potentially destructive avalanches may come near or reach developed areas.

Human triggered avalanches are likely especially in windloaded areas. Unstable slabs are likely on a variety of aspects and slope angles today.

SPATIAL VARIABILITY AT THE SLOPE SCALE

The snowpack varies widely over short distances, and knowledge of these variations is critical for forecasting avalanches. Natural avalanches are believed to release from zones of localized weakness, while triggered avalanches can be released more easily from relatively weaker areas. All of this has implications for slopes that already have existing tracks on them, for the placement of explosives for avalanche mitigation work and the positioning of snow pits to accurately assess the avalanche conditions while traveling in the backcountry.

A project by the National Avalanche Center from 1988 to 1990 utilizing the digital resistograph demonstrated that average snow strength was relatively high in areas of wind drifting and relatively low in areas with a thin snowpack or areas over the top of rock outcrops.

SPATIAL VARIABILITY ON UNIFORM SLOPES

In the late 1990s Chris Landry worked with the National Avalanche Center to investigate variations in snow stability at the slope scale using the Quantified Loaded Column Test he developed. His research involved doing 10 tests in each of five locations on 30 by 30 m planar, wind-protected slopes with a relatively uniform substrates. His results showed that about a third of all of his snowpits could not reliably predict the snow stability of even these small plots. The reasons for these variations are not entirely clear, but are being further investigated.

This means that even when a slope looks uniform, the weak spots or trigger points are not uniform across the slope.

What does all this mean for the backcountry user? That tracks present on a slope, even one that looks uniform, are not a sign of stability. Unless of course you ski EXACTLY in the old tracks!