The National Weather Service Forecasts-

TODAY...SNOW SHOWERS. SNOW ACCUMULATION 1 TO 2 INCHES. HIGHS
AROUND 27. LIGHT WINDS BECOMING SOUTHWEST 10 MPH IN THE AFTERNOON.

TONIGHT...SNOW SHOWERS. SNOW ACCUMULATION 1 TO 3 INCHES. LOWS
AROUND 25. SOUTH WIND 10 MPH.

SATURDAY...SNOW SHOWERS LIKELY. SNOW ACCUMULATION AROUND 1 INCH. HIGHS AROUND 31. SOUTHEAST WIND 10 TO 15 MPH.

Over the last 3 weeks weeks we have received 1.4 meters of new snow on the Eaglecrest Mid Mountain UAS Site. During that same time we received about .8 meters on the Mt Roberts Tram Site. The difference is primarily do to elevations and temps. Mt Roberst saw part of this event at above freezing temperatures. The Mount Roberts site measured 210mm of precipitation during this time. So you can see the densities are quite high now.

During this 3 week event temperatures remained near freezing adding to the rapid settlement and good bonding in most of the snowpack.

We had 5 notable wind events during this time with winds over 40knots and gusting over 70...Most every notable event pushed winds out of the SSE.

Spatial Variability is quite high at this time. The depth and layering of the snowpack is quite different from location to location ranging from almost no new snow in places to well over 5' of new snow in others.

Most of this new snow is stable in place. Although there are weak layers in the pack, they do not appear to be avalanching with the presence of humam triggers in most places.

Two days ago into yesterday we received about 3-4\" of new snow that was finished off with winds up to 40knots. This placed tender soft slabs in places that were easily being skier triggered yesterday. This is our primary concern for today.

These slides were mostly small and located in isolated pockets. Summit and ridgeline typically has more wind affect so these are prime areas of concern. Lower in the treeline the dangers are much less.

Recognize that in the backcountry there are still weak layers beneath the one that is being triggered. If a small slide were to release in places there is the possibility for this small slide to tear down deeper into the snowpack then perhaps propagating into a larger avalanche. We have identified weak layers down over 50-65cm so this newly propagated avalanche could be quite large should it occur.

Avalanche danger is MODERATE at this time.

Natural avalanches unlikely, potentially destructive avalanches unlikely to come near or reach developed areas.

Human triggered avalanches possible.

Most of the slopes appear to be safe or showing only small pockets releasing yet be aware that do to spatial variability this will change from location to location.

I would feel good about skiing most of my moderate difficulty lines in the backcountry at this time. If I was thinking about skiing a big mountain open fall line on a unanchored convex slope... I think I would reconsider and stick to safer lines with anchors, safe spots, and escape routes.

This snowpack will continue to stabilize over time and by tomorrow I expect danger levels may drop back down to LOW.

Winds are light over the next few days and precipitation rates are also quite low. Temperatures are to remain cool. This should give the snowpack the time it needs to settle and bond, thus building strength in the snowpack.

Remember- TRANCEIVER SHOVEL> AND A WELL TRAINED PARTNER are the essential tools to safely enjoy the backcountry... Dont leave home without them.

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. 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

For instance, if a skilled avalanche worker digs several snow profiles on a test slope and finds easy compression tests and rutschblock tests, high quality shears, a persistent weak layer with a critical combination grain type, grain size and hardness differences between the slab and the weak layer, plus they find those same conditions in several snow profiles on the same slope, they can safely conclude that the snowpack can both initiate and propagate a fracture. In other words, avoid all similar slopes steep enough to slide.

The tricky part is that these factors change through space and time. Here is an example that we notice in many areas of North America: Typically, during and right after the storm we see widespread soft slab natural avalanche activity on all kinds of slopes, even small slopes with a lot of compressive support and even in relatively thick trees, but the fractures typically don't propagate very far. Since the slab is soft, we can also trigger avalanches easily, and they usually fracture at our feet or snowmobile instead of above us

But as time passes, the slab settles and gains strength. With a persistent weak layer, the slab typically gains strength much more quickly than the weak layer beneath it. Thus, 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.

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.