Avalanche Report for Lochaber

Issued

Avalanche Hazard Forecast

FOR PERIOD 18:00 Thu 18/12/2014 TO 18:00 Fri 19/12/2014

Hazard level
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Low
Human triggered avalanches not likely. Generally safe travel conditions.
Moderate
Human triggered avalanches are possible, so good visibility and good route selection is important, especially in steep locations as indicated in the reports. Groups should be managed carefully, keeping good spacing between people to reduce loading on slopes.
Considerable
Natural avalanches may occur - and a single person load is likely to trigger an avalanche on some slopes. Good visibility and route finding in mountain terrain is important, as is experience in avalanche hazard evaluation.
High
Natural avalanches will occur - and a single person load will trigger an avalanche on some slopes. Good visibility and good route-finding in mountain terrain is essential, as is experience in avalanche hazard evaluation.
Very High
Widespread natural avalanches will occur - and a single person load will trigger an avalanche on most slopes. Good visibility and good route-finding in mountain terrain is essential, as is experience in avalanche hazard evaluation.
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The avalanche hazard will be Considerable

Forcasted Snow Stability & Avalanche Hazard

The existing wet snowpack will continue to refreeze and stabilise. Fresh areas of unstable windslab will form in areas sheltered from the Westerly winds. Greatest accumulations will be on steep North and North-East aspects above 800m. Localised areas will also be present on North and South-East aspects. Old snow exposed to the wind will be hard frozen The avalanche hazard will be Considerable

Forcasted Weather Influences

Moderate to Strong Westerly winds over the summits. The freezing level will be around 600m with snow showers throughout the period.

Key Snow Stability Observations

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Observed Avalanche Hazard -

The avalanche hazard is Moderate

Observed Weather Influences

Strong Westerly winds with rain at all levels turning to wet snow above 1000m around lunchtime

Observed Snow Stability and Avalanche Hazard

The snowpack is thawing at all levels. Localised wet snow instabilities are present on some steep North, North-East and East aspects. The avalanche hazard is Moderate

Comments

Weekly Snowpack Summary
  
  • There have been a number of thaw/freeze cycles during the past week: Friday and Saturday saw cold and snowy conditions followed by the freezing level rising above the summits on Saturday night. This was followed by cold and snowy conditions again until a second major thaw early in Wednesday which has continued through out most of Thursday. There were several avalanche events associated with the rising freezing levels

    It has been another week of generally mild conditions. There has been the odd dusting of fresh snow over the summits but overall the snowpack has been thawing at all levels. Stability has been generally good

    This week has seen predominantly Spring conditions. The freezing level has fluctuated between 1000m and well above the summits and there has been no significant precipitation. The snowpack is generally stable and gradually thawing, although there is still a reasonable cover above 650m. Glide cracks are appearing on many steep snow slopes and along cornice edges

    Early in the period there was a return to winter conditions with fresh snow at most levels with strong South-Westerly winds. Monday saw the wind swing round to the South-East with extensive redistribution of fresh snow. Tuesday and Wednesday saw the freezing level rising and the snowpack gradually thawing at all levels. Colder temperatures on Thursday have frozen and stabilised the snowpack. There has been no fresh precipitation since Saturday night.

    The majority of the week has seen rain at all levels and a considerable thaw of the existing snowpack. There have been some spectacular cornice collapses during this period with some long run-outs. Thursday afternoon has seen a return to colder conditions with the wet snowpack starting to stabilise and some fresh windslab development.

    It was a variable week weather wise, with a big thaw and heavy rain on Saturday, before becoming more settled from Monday onwards. There was a small amount of fresh snow on Friday and Sunday, but not much. Some significant full depth avalanches occurred in the Mamores and Grey Coires following Saturdays thaw. On Monday and Tuesday there were some significant cornice collapses, in some cases triggering the slope below on Aonach Mor and Ben Nevis.

    It has been a mixed week. Initially the freeing level was around 600m with several days of snow showers, mainly overnight. Winds have been predominately from the West or South-West. Wednesday saw the freezing level starting to rise and by Wednesday night there was a significant thaw with heavy rain at all levels. Fairly constant avalanche activity through out the period with some large wet snow avalanches on Wednesday night. Stability improving greatly during Thursday.

    There were snow showers during Friday Saturday before the freezing level rose above the summits on Saturday night and heavy rain fell. This caused numerous substantial avalanches, including some large full depth ones in the Mamores running out to low levels. The freezing level fluctuated over the rest of the time with snow showers. Some avalanche activity was recorded, but they were not particularly large.

    Earlier in the week, the freezing level was around 6-700m and mainly Westerly winds producing an avalanche cycle on Sunday. Tuesday say a brief rise in the freezing level to the summits before cold and dry on Wednesday. Wednesday night saw a significant that with rain at all levels causing a series of wet snow avalanches. This has helped to consolidate the old snowpack however further windslab development on Thursday is producing fresh areas of hazard

    There has been further snowfall and drifting throughout this period. The freezing level was around 850m at first, dropping during the period to 300m. On Tuesday, Wednesday and Thursday snow fell at most levels. It has remained generally windy with the direction varying but mainly between SE and W. Extensive areas of unstable windslab have been present on most aspects; greatest accumulations on W through N and E to SE aspects.

    Snow has fallen most days during the week. It has been quite windy, with the main wind direction being South or South-East. The avalanche hazard has remained considerable or high throughout the week, and avalanches have been recorded particularly on Sunday when some large ones were observed on Ben Nevis.

    On Friday evening the freezing level rose above the summits with rain causing a period of high instability. SInce then the freezing level has been around 5-800m. The old snowpack has been stabilised. Heavy snow showers since Saturday have produced extensive areas of fresh unstable windslab. Strong Southerly winds, backing to the Easterly quadrant in the early part of the week before easing slightly. Extensive areas of moderately to poorly bonded snow on many aspects.

    It has been a slightly milder week dominated by SE to SW winds and snow showers. The freezing level has generally been about 1000 metres, although Tuesday and Thursday were colder. Although further windslab has been building up during the period, this has tended to begin to consolidate relatively quickly in the slightly milder conditions. Although some smaller scale avalanche activity was observed, particularly on Monday, no large avalanches were recorded.

    On Friday and Saturday there were frequent snow showers above 900m with strong winds producing a period in instability. Generally colder for the next few days with some shower activity before a thaw to all levels on Wednesday afternoon and early evening. The thaw was followed by colder conditions which refroze and stabilised the snowpack

    This week started with a storm on Friday, with large natural avalanches releasing on N to E aspects, either during this storm or during the overnight rise in temperature. Thereafter fluctuating freezing level 700-1100m. Further natural avalanches on Monday. After Fridays storm there were snow showers each day, with moderate or strong generally SW winds. Snowpack consolidating but fresh windslab each day mainly on higher N to E to SE aspects.

    Over the past 7 days there has been fresh snowfall every day with significant accumulations, mainly above 900m. Winds have generally been strong and between SE and SW, though also some W. On Sunday and Wednesday nights the freezing level rose briefly to, or near, the summits, before falling again. This helped consolidate the snowpack. Instabilities persist in the snowpack on higher W through N to NE aspects and currently there is fresh unstable windslab mainly on N to E aspects above 900m.

    The theme for the past week has been very strong Southerly or Westerly winds with a significant amount of fresh snow above 600m. On Friday and Monday evening there were some brief warm periods with the freezing level rising above the summits which helped consolidate the snowpack slightly. Currently there are significant fresh unstable snow deposits in many N and E facing corries above 700m.

    After some significant snowfall on Tuesday consolidation took place during Wednesday with the freezing level rising above the summits. Colder again on Thursday with snow to approx. 300m. Strong SW winds have also been a feature with new accumulations forming mainly on sheltered locations only. Old snow remains in many of the deeper gully lines and high corries.

    Limited snowpack. Localised deposits of old, wet, stable snow on some steep N, NE and E aspects above 1000m.

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