TONIGHT...PERIODS OF RAIN. SNOW LEVEL RISING TO 1100 FEET LATE.
EARLY LOWS AROUND 34. SOUTHEAST WIND 20 TO 30 MPH WITH GUSTS UP TO 40 MPH.

TUESDAY...RAIN SHOWERS. SNOW LEVEL 1400 FEET. HIGHS AROUND 40.
SOUTHEAST WIND 10 TO 20 MPH.

As of 10pm (2/20/12) snowfall amounts have remained modest, about 20cm at the Tram and about 15cm on top of Eaglecrest. Temps have warmed but still remain below freezing in the starting zones. Winds have picked up and there is a lot of snow being transported in the alpine zones.

The avalanche danger has been increasing throughout the day, but the amounts of precipitation have been a bit less than expected so far and slide sizes are still going to be on the smaller side.

The forecasted storm is still expected to be warm and wet. More than an inch of expected precipitation tonight, accompanied with warmer temps, and more wind.

This is our classic storm cycle hazard, and natural releases within the new storm snow tonight and/or tomorrow morning are to be expected.

Because the expectation is for the snow line to be about 1100ft, the rain in town SHOULDN'T affect the starting zones, but if the storm is warmer than expected a higher snow line will mean rapidly increasing avalanche danger.

The wind is expected to change direction almost 180 degrees mid storm and that will lead to wind and cross loading on all aspects including White Path, Behrends, and the Thane Rd Paths.

At this time travel on the Thane Road is still considered safe but caution is advised when approaching or under avalanche paths, and pay attention tonight as the hazard level might increase significantly late tonight.

As of 10pm (2/20/12) avalanche danger is CONSIDERABELE. Natural slides possible. Human triggered slides likely. Destructive avalanches are possible and capable of reaching structures and roads in urban areas.

Be increasingly cautious in avalanche areas.

Small natural releases can be expected any time tonight but are less likely to have destructive slides reach developed areas.

In the backcounty be hyper-aware of changing storm conditions and the amount of new snow and wind you find yourself in.

Its a great time to think about alternatives to Perseverance and Flume trails as the new snow accumulates up high. Minimize your exposure and stay safe out there.

PROPAGATION

Propagation is the spread of a crack in a weak layer from an initial fracture location. A fracture can propagate at about the speed of sound, which makes it possible for huge slabs of snow to release from a mountainside instantaneously.

This is what distinguishes an avalanche that takes out a whole mountianside, vs. one that only releases in a small pocket. How far did the avalanche propagate?

The propagation potential of a particular slab and weak layer dictates how large an avalanche may become once triggered, and also determines if it?s possible to trigger avalanches from flatter terrain connected to steeper slopes.

Whether a localized crack propagates or not, or how far the propagation will proceed, depends on several factors including:
? Snow structure
? Stored elastic energy in the snowpack
? Snow stability
? Spatial variability of the weak layer and slab

Avalanche books tell us that most avalanches occur during or immediately following storms, which is true, but especially with persistent weak layers such as surface hoar, avalanche danger to people is sometimes worse after a storm than during a storm--after the slab has had a chance to stiffen up. Most avalanche professionals I know would rather deal with the slab while it's still soft because the hazard is both more obvious and easier to manage.

Over time, we usually see fewer avalanches and they are less sensitive to triggers, but the ones we do see will occur on large, open slopes without anchors, the fractures will occur above us instead of at our feet, and because of the stiffer slab, the fractures will propagate much longer distances.

With very fragile, persistent, weak layers such as surface hoar and faceted snow, it's not unusual for fractures to propagate around corners and over ridges, or to trigger the slopes \"remotely\" or ?sympathetically? meaning from a distance away. This is partly because the stiffer slab transmits energy farther and can store more elastic energy.