11 May 2013

May 11, 2013

Cirrus clouds moved in yesterday morning.

A slow westerly flow.

Fresh activity slightly right of centre, May 9-10, 2013. For the past week there has been wet loose avalanche activity every day especially south of WB Ski Area, mostly cornice failure induced.

At 2240 meters the temperature was +5.5, winds were 20-30 KPH from the SSE. At 1550 meters the temperature was +9.6, no new snow and a base of 150 cm. In the valley it was +9. Observations taken at 07:00 Hrs this AM. Max temp in the valley yesterday was +25.6, at 1550 meters it was +18, and at 2240 meters it was +11.

For the forecast, cloudy skies for today with rain in the mix for later this afternoon. Heavy rain for later tonight into early Sunday morning. The upper level ridge is shifting east allowing a cold front with strong winds and moderate to heavy precipitation into our area. The brunt of the precip will fall early Sunday morning and ease by the afternoon, followed by light to moderate rain Sunday evening. A trailing upper level trough will move onshore Monday. A series of weak fronts will pass over the area next week giving us unsettled conditions. Guesstimates 20-30 mm of rain by Sunday morning, 15-20 mm Sunday, 10-15 mm Monday, 3-8 mm Tuesday, 2-5 mm Wednesday. Freezing levels will be around 3300 meters on Saturday, 2100 meters by Sunday evening, then slowly dropping to 1700 meters by Tuesday. Wednesday the FL will climb back up to approximately 2000 meters.

Another take on Sherpa conflict: Cultural Changes

Ice Free Arctic in our Future : Science Daily

More information on Wet Snow Avalanches: Avalanche Glossary

Large wet slides were possible at the beginning of the week, when the snowpack first became truly isothermal. One reason for this is that free water can be introduced to the  snowpack too quickly if rapid warming occurs, especially if refreezing overnight does not occur. Initially this free water can flow along and lubricate buried bed surfaces, leading to wet slab releases.There was also a concern with several recent buried crusts, which degraded as the week progressed.  The effect of free water in the snowpack can be very difficult to predict. Ultimately, the free water and the melt-freeze process will hinder fracture propagation and break down the layering in the snowpack. After isothermal conditions prevail for a while the hazard of wet slab avalanches is usually reduced. With the introduction of heavy rain Saturday Night and into Sunday the hazard will increase and  climax slides will be likely. Will be interesting to see the outcome!!

A fresh cornice drop from the evening of March 9, 2013, Bushrat Cornice.

The snow pack has melted at an accelerated rate in the past week. At 1550 Meters the HS was 184 cm at 08:00 hrs on May 4, 2013; as of today the HS at that elevation as of 08:00 Hrs was 148 cm.

Many mid mountain runs with a south - west exposure have melted quickly.

These two snow samples were taken only 2 meters apart, this one has smaller grains with less free water. Extracted from an area with heather at the bed surface.

This one has larger grains and there was more water evident in the snow. It was extracted from a large rocky area with space amongst the rocks.

Satellite picture May 10 Th later in the afternoon. Some thick clouds are on their way.

The big picture makes it apparent how the low has taken control!!

No comments:

Post a Comment