December 28 Avalanche Advisory
Good morning, this is Dudley Improta with the West Central Montana Avalanche Center’s avalanche advisory for December 28, 2009.
Current Avalanche Danger
There are pockets of CONSIDERABLE avalanche danger above 7000′ on terrain steeper than 35 degrees. Terrain with talus slopes, boulder fields and rock outcroppings are holding the loose snow towards the bottom of the snowpack.
Overall the snow has settled since last week; but we are still seeing weak failures with stability tests around the aforementioned rocky features. The wind has been moving snow onto North, Northeast and East aspects as well. Any wind loading on the rocky areas described will increase the chance for an avalanche.
On other steep slopes above 7000′ and slopes above 6000′ that are steeper than 35 degrees and void of anchors the avalanche danger is MODERATE.
On all remaining terrain above and below 6000′ the avalanche danger is LOW.
We are, once again, describing a situation that varies with elevation, aspect, steepness and the underlying character of the slope. We have a low snowpack and the temperatures have been wildly variable at elevation. On shaded slopes, where it has stayed cold, the temperatures have worked on the snowpack and the weak, loose snow Steve Karkanen has described for the last two weeks remains near the bottom.
Weather and Snowpack Analysis
We have had no appreciable snow since Christmas Day. As I mentioned, the temperatures in the mountains have been variable to say the least. Anyone who has been recreating at elevation has experienced the warm sunny temperatures on Southerly and Westerly slopes and the bitter cold temperatures on Northerly and Easterly slopes. Winds have been moderate at elevation; but strong enough to move snow on the high ridges. There are wind loaded slopes and cornice buildup on ridges above 7000′.
Crystal clear skies above 6000′ have allowed all this warming and cooling. The cold faceted snow at the bottom of the pack remains on shaded protected slopes, particularly around rocky areas. Spaces between the rocks allow the air to move through the snow to create and hold the loose weak crystals. On our tour Christmas Eve we noted all the slopes that had avalanched had Northerly aspects and rock outcrops with steep rollovers.
Saturday we had some pleasant low angle turns through surface hoar. The cold clear nights have created an abundance of surface hoar. The sun on the clear days has destroyed these crystals on Southerly and Westerly slopes. The surface hoar is beautiful now but may create a weak layer on those shaded protected slopes when it snows again (note my optimism).
For the time being, carefully analyze the terrain aspect, elevation and character (rocky features) before committing to any steep slopes
Weather Forecast and Avalanche Outlook
The ridge of high pressure we are experiencing is supposed to break down today as a pacific system moves in. Possibly we will see light snow in the mountains tonight and then better chances for snow by Tuesday. There is snow in the forecast for the week due to Southwest flows.
I would expect the avalanche danger to decease slightly until we experience a significant weather change or snowfall. There is a possibility of significant snow in the mountains by Wednesday. I would remain cautious around the steep, rocky terrain I described in this advisory.
The next avalanche advisory will be posted on New Year’s Day.
If you haven’t visited the Missoula Weather Service’s Snow/Avalanche page at www.wrh.noaa.gov/mso/avalanche/ , I advise you to do so. Although the snow forecast is a bit depressing right now, the newly designed page has some great information.
For Beacon Park information click on the link on our home page.
If you get out and see avalanche activity or want to send us quick snow observations, send us a note at [email protected] or call us at 406-530-9766 (530-9SNO).