November 30, 2007

presented by Tim Peterson

Weather

Cold temperatures over the last few days have impacted the early-season, shallow snowpack. Temperatures have not been above freezing at the 5000' level for several days, with occasional periods of clear skies. The storms that came through earlier in the week were brief, quickly leaving the area as fast as they came in. We have seen precipitation in the form of new snow this week, adding nearly 11" over the past couple of days.

Field Observation

A brief tour today during a calm morning and clear skies discovered no signs of instability. The top layers of snow were exceptionally light, particularly below 7200' on eastern aspects. Western slopes showed obvious wind scouring, down to the rocks in some places, with eastern slopes loaded with a deeper snow. Sastrugi formations were slight, predominantly on western slopes showing westerly winds. Ski penetration was regularly 10", with a few localized spots of 3"- 5". Most slopes were displaying small surface hoar formations and faceted crystals.

Snowpack

A shallow snowpack everywhere with some interesting layers. A 20" pit on 30 degree slope at 7100' on a 120 degree aspect showed fist hardness for nearly the entire depth, becoming slightly harder in the last 3". A knife layer has formed at the ground level. Stability tests showed moderate to good strength with moderate structure and low energy. A layer was fracturing at the 9" (from bottom) mark on a layer of buried surface hoar. There was no cohesive slab formed as the top layers remained soft and powdery. A temperature measurement showed a significant gradient in the snowpack of approximately 1.4 degrees C/10cm.

Insight

The shallow snowpack along with the consistent cold temperatures will continue to promote faceting in the snowpack. Expect depth hoar formations to be significant over the next couple of days as long as temperatures remain cold. At the same time, buried surface hoar and faceted crystals will persist; with expected snowfall to increase this weekend, be aware of these layers and their potnetial to be weak.

Constantly make observations as you travel in the backcountry and evaluate all slopes you ride on.

March 12, 2007

presented by Tim Peterson

Weather

Warm temperatures have been consistent all week, having a significant impact on the snowpack. Temps haven't been below freezing at 7800' in the last couple of days, while the freezing level has barely dropped below 8500' in the last 24 hours. Along with light to moderate winds, the warming trend over the past week has brought Spring conditions.

Insight

With highs expected to remain in the 50's and 60's all week, expect some Spring skiing with melt-freeze snow potentially forming. The melting process weakens bonding layers and contributes free-water to the snowpack, creating a layer of lubrication between weakly bonded layers and a hard bed surface. Wet snow avalanches increase in their likelihood during these conditions, especially on Southern aspects. The persistent ice layers that have been present all winter can serve as an ideal bed surface for softer, weakly bonded layers on top. In many areas, this layer is deeply buried (up to 5 feet in some places) and may not impact the weakening layers above. However, as the warm temps continue, free-water may very well be found deep into the snowpack and as deep as these ice layers. Be aware of wet slides on slopes over 30 degrees, especially in the afternoons on Southern aspects all week.

Constantly make observations as you travel in the backcountry and evaluate all slopes you ride on.

With the Spring-like conditions of the snowpack, we will be offering the report once a week until the middle of April.

March 5, 2007 presented by Tim Peterson

Weather

Spring temps have arrived to Central Oregon. Temperatures in the last 36 hours have been above freezing at the 7800' level, with slight winds predominantly out of the South. Warm temperatures should remain through tomorrow, with a wintry mix returning by the end of the week. Colder temps and new snow are expected to arrive by Friday, with a return to winter over the weekend.

Field Observations

A significant slide in the bowl on Broken Top is a strong indicator of the effect of the warm temps on the snow. The wet slide emerges out of the bowl, past the moraine saddle, having started in two different spots. One slide started around 9-O'Clock couloir on the SE aspect, while the other larger slide started across the bowl on the SW aspect. Both slopes exceed 40 degrees and experienced a rapid warming from the sun and air. Surface hoar was observed on the WSW aspect of Tumalo at 7300', on top of a hard crust layer. No ski or boot penetration was observed on this slope, nor was any collapsing or cracking in the snowpack.

Snowpack

A 51" pit dug to a persistent hard layer revealed its weakest layer in the new snow layer, around 7" down. This fracture showed a clean plane, with little speed consistently in the high moderate compression score range. Further analysis revealed rounded grains on top of mixed crystals, all in the 1mm range. The top couple of inches on this WSW aspect was knife hard, and showed remnants of wind scouring. Around the pit, surface hoar was observed on top of this hard crust layer.

Insight

Southern aspects will continue to melt from the current temps and the sun. Warmer temps will assist in stabilizing layers within the snowpack, particularly that one layer around 7" down. Expect the interface of those two layer to continue toward bonding as long as temps remain above freezing for today and tomorrow. In the upper layers where freewater is present, be aware of potential wet slides from skier/rider triggers on slopes greater than 30 degrees. With the potential for colder temperatures later int he week, we may see increasing strength in the snowpack before burying the warm layers with new snow.

Constantly make observations as you travel in the backcountry and evaluate all slopes you ride on.

February 28, 2007 presented by Tim Peterson

Weather

The Central Oregon mountains have seen between 2.5" and 11" above 5500' in the last few days. Cold temps have persisted as well as light to moderate winds predominantly out of the SW. The new snow has been light to moderate in its intensity, and will continue to accumulate over the next several days. Winds and cold temps should remain, inhibiting any consistent processes of stability.

Field Observations

We made only a few observations in the field in the last two days. Snowpits dug at 5200' revealed a very different snowpack than we saw at 6000' over the weekend. This variability is expected and demonstrates the impact elevation can have on the snowpack.

Snowpack

The pit dug at 5200' showed low energy and poor to fair strength on a slope of 35 degrees. Absent from this pit was the hard crust layers witnessed at higher elevations, on predominantly Southern aspects. Shears in the snow were consistently presenting in the new snow layers (the top 18") at low to moderate scores. New and settled snow were observed sitting on top of harder layers of mixed grains (rounds and facets). This layer was observed sitting on top of a thin breakable crust. Below this crust layer, the snowpack appears well consolidated as round grains with strong bonds.

Insight

As in the past few reports, the leeward slopes continue to load with new snow. Be aware of wind slab formations from snow transportation on NW through E aspects, particularly on slopes greater than 30 degrees. With more new snow, the faceted layers above the persistent crust layer may present as a significant source of weakness. In digging your pits, pay attention tho this interface as a potential fracture layer. As well, be aware of the formation of layers within the new snow. As the stress increases from precipitation, expect to see shears in the upper layers of the snowpack that may present moderate energy. Be cautious on all slopes over 35 degrees and any windloaded slope over 30 degrees.

Constantly make observations as you travel in the backcountry and evaluate all slopes you ride on.

February 26, 2007 presented by Tim Peterson

Weather

The Central Oregon mountains have seen up to 16" of new snow in areas above 5700" over the past three days. Continued cold temperatures and cloudy skies have persisted and are expected to remain for much of the week. We haven't seen temperatures rise above 30 degrees higher than 6000' in well over a week. Winds have been light with consistently moderate gusts that have been observed transporting the new snow.

Field Observations

Cornices have been observed on Vista Butte and Tumalo, indicating wind transport of new snow on northern to eastern aspects. The Vista Butte cornice was cut with slight cracking observed, but no significant propagation. Rime formations on trees at the start of tree-line indicate consistent southerly winds. On Vista Butte yesterday, skis were penetrating up to 4 inches, with boot penetration exceeding 16" at times.

Snowpack

The COCC Avalanche Level I course conducted a weekend of stability testing and field observations around Vista Butte. Stability tests consistently indicated moderate strength, low to moderate energy, and poor structure. Rutschblock tests on Saturday indicated increasing instability and were not consistent with compression tests earlier in the day. Sunday's tests indicated similar results, with our focus on the interface between the new snow that began accumulating last week on top of an old crust layer. We witnessed the growth of a slight faceting layer at this interface, which consistently fractured in many of the pits over the weekend. Yesterday afternoon, some students began observing the appearance of layering within the new snow layers, observing low energy shears around the middle of the new snow. Below the old crust, the snow pack appeared strong with low energy and did not present much instability.

Insight

Leeward slopes continue to load from wind transport. As cold temperatures and new snow continue, be aware of wind slab formations on leeward slopes. The interface between the old crust layer and the new snow from the past week may continue to present as a weak layer. With new snow stressing this layer, it will be prudent to test all slopes over 30 degrees with thorough stability tests and field observations. The presence of previous tracks do not necessarily indicate the stability of a slope. Make objective decisions based on the recent weather and personal observations of the snowpack.

Constantly make observations as you travel in the backcountry and evaluate all slopes you ride on.

February 23, 2007

Weather

Light to moderate winds over the past couple of days have assisted in transporting 7"-9" of new snow onto leeward slopes. Winds up to elevations of 8000' have been predominantly SSE to SSW with ample speeds to carry snow over short distances. Cold temperatures have shown to be persistent, with the freezing level barely rising to 5500'.

Field Observations

Winds have have predominantly been SSE to SSW, yet sastrugi formations indicated variable winds at the snow surface around treeeline. The most significant sastrugi was on SW slopes and indicated SW winds. Winds today appeared variable on the SW aspect of Tumalo, blowing snow over, around, and into the test pit. The face of the pit had to be constantly brushed, as snow quickly stuck to the open surface and every conceivable piece of gear and clothing. Snow within the treeline was much less affected by wind. Ski penetration in the trees was consistently 6"-8". In the open, around treeline level, ski penetration varied from 8" to 0" on severely wind scoured slopes on SW aspects. Varaiable pockets of soft wind slabs appeared on the flat terrain, before the summit cone of Tumalo on S to SW aspects.

Snowpack

I dug a pit at ~7600', SW aspect on a 33 degree slope on Tumalo. A persistent ice layer remains 12"-20" down on windward slopes. Newer snow remained unconsolidated in most places with a Fist hardness and didn't appear to be strongly bonded to the old ice layer below it. This ice layer did shear out of the test column with STM on a 9cm layer of 0.5mm faceted grains. Compression tests did not produce any significant results in any of the layers. Below the 9cm facet layer is another very persistent ice layer.

Insight

Be aware of leeward slopes (NW to E aspects) , which will be loaded with transported snow. Wind slabs may be present. Assess all slopes you encounter, especially those over 30 degrees. As new snow continues to fall, be aware of the bonding at the interface with the upper most ice layer and the new/settled snow on top of it. Cold temperatures may persist and contribute to perisitent weak layers found in the upper parts of the snowpack.

Constantly make observations as you travel in the backcountry and evaluate all slopes you ride on.

February 21, 2007

presented by Tim Peterson

Precipitation over the last couple of days has left our area with up to 16" of new snow. Significant wind events Sunday through Tuesday has produced significant windloading. Look for slopes from the NW through E aspects to have deeper new snow depths as a result of wind transported snow.

Winds have subsided this morning and the precipitation over the next couple of days is expected to produce trace amounts. Be aware of any continued snow deposition that may continue to add stress to the new layers. Winds should be moderate and continue from the S & SW. Windloading on leeward slopes will continue over the next few days, especially with any new trace amounts of snow.

The new snow layers appear to be bonding well with the old ice layer, that resulted from last weeks rain event. Pay attention the next couple of days to the bonding between these new layers and the older ice layer, as faceting may appear at the interface. As well, the new snow may show signs of forming layers within it, as new precipitation and winds continue.

Below the ice layer, we continue to see the presence of persistent grains around a deeper ice layer, that hasn't demonstrated much weakness in strength or structure.

Be cautious on windloaded slopes greater than 30 degrees. Be sure to assess as best you can the conditions of any slope you consider riding the next couple of days.

Enjoy the backcountry.

February 19, 2007

presented by Tim Peterson.

Moderate to high winds continued over the weekend, along with dropping temperatures, to help solidify the wet snowpack we saw on Friday. New snow began accumulating yesterday morning, loading leeward slopes. Much of the winds around Bachelor/Tumalo/Todd Lake were SE trhough SW, transporting up to 2" of new snow onto mostly NW through NE slopes. A test pit yesterday showed a snowpack with well bonded layers, a result of the freezing water. There was a layer of persistent grains about 2' into the snowpack, around the depth of that ice layer we reported on Friday. Grains at these depths continue to hold some mositure, which is helping to build good bonds between grains. The new snow on the surface easily sloughed off as we skied and scraped against an icy layer.

There were no signs of avalanches in the Todd Lake area, and we did not witness any collapsing or cracking in the snowpack as traveled. In many areas, the snow surface was new snow up to 1" with settled snow up to 3" on leeward slopes. Precipitation was variable over the day. Surface temperatures were 29F, with the air temperature recorded at 28F.

With continued snow accumulation and winds, be aware of deeper new-snow depths on leeward slopes above 5500'. Slopes may form wind slabs above the icy layer that formed from last weeks rain event. Be sure to test stability on all slopes over 30 degrees and look for the bonding of new snow to the older icy layer. Be particularly aware of the persistent layer of faceted grains about 2' in the snowpack. In thinner areas this layer will very likely persist.

Today's snowpack showed LOW energy with GOOD strength and FAIR structure.

February 16, 2007

Here is the latest Snowpack report for February 16, 2007, presented by Tim Peterson.

High winds at all elevations on Thursday transported new snow deposited earlier this week. Look for wind-loaded slopes above 7000' on NW through NE aspects. A persistent light rain has settled over elevations from 4500' and up, saturating the top layers of the snowpack. Water is visible down 14-20", above a persistent ice layer that has only recently begun to show signs of thinning. Still, this ice layer, which is anywhere between 14" and 20" down, provides a smooth surface for the top layers of snow. The rainwater appears to be assisting with bonding of the upper layers. It will be interesting to watch how the interface between the top ice layer and the new/settled snow layers develop. Warm temperatures and continued rain for the next day may continue to add stress to the snowpack. Watch for decreasing stability of the top layers above the ice crust.

Today's snowpack showed LOW energy with GOOD strength and structure down through 48".