Avalanche Report for Northern Cairngorms

Issued

Avalanche Hazard Forecast

FOR PERIOD 18:00 Mon 02/03/2015 TO 18:00 Tue 03/03/2015

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

Unstable windslab will continue to build on mainly wind sheltered Northerly to Easterly aspects above 900 metres, localised unstable deposits will also be present on North-West and South-Easterly aspects due to cross loading, with steep and convex terrain most affected. Many areas will be wind scoured and bare, especially Westerly aspects. Below 900 metres the snowpack will be generally stable throughout with thin soft deposits in sheltered area. The avalanche hazard will be Considerable

Forcasted Weather Influences

Remaining cold with Freezing levels around 300 metres but rising to 600 metres later in the day. Winds will be strong South-Westerly with precipitation falling as light snow showers throughout the day.

Key Snow Stability Observations

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Observed Avalanche Hazard -

The avalanche hazard is Considerable

Observed Weather Influences

A cold day with strong Westerly winds, occasional heavy snow showers. Severe drifting at times in blizzards.

Observed Snow Stability and Avalanche Hazard

Unstable windslab is present mainly on North-East to Easterly aspects above 900 metres with North and South-Easterly aspects affected due to cross loading, especially on gully flanks and in other wind sheltered locations. All Westerly aspects are generally wind scoured and bare with some firm stable snow in many wind exposed areas. The avalanche hazard is Considerable

Mountain Conditions

Wind scoured and bare on many aspects - deep drifts locally. Whiteout conditions with poor visibility during showers, clear otherwise. Winds 30 -40 mph, progress difficult and tiring, at times.

Comments

Winter continues with a bitterly cold wind- very good climbing conditions with snow-ice in many places.

Weekly Snowpack Summary
  
  • Heavy snowfall and winds at the start of the week presented an unstable snowpack limited mainly to Northerly to Easterly aspects, elsewhere very wind scoured. A thaw midweek provided stabilisation before a new cycle of storms and snowfall arrived on thursday 26th presenting areas of unstable windslab.

    Any subsurface weak layers have been stabilised by the recent warm spell, thaw and refreeze (18th-19th Feb). A new period of wintry weather, snowfall and strong winds will present a dynamic avalanche hazard situation for the next week.

    At the start of the period (6th feb), weak layers remained deep in the snowpack. The recent fine weather and warmer temperatures have slowly penetrated the snowpack and improved stability. Shaded North to North-East aspects remained cold however and surface instabilities have developed here. This may present a buried unstable layer with the forecasted new snow cover from the 13th feb.

    A period with an arctic weather system provided significant snowfall and very cold temperatures. The very cold temperatures resulted in instabilities persisting deep in the recent deposits of drifted snow on mainly East to Southerly aspects. In the last few days slightly warmer air temperatures have slowly started to penetrate the snowpack improving stability, but deep in the snowpack, cold temperatures and instabilities remain for the time being.

    The old snowpack has been through a number of thaw freeze cycles and is now firm and stable. Winds have been mostly strong Westerly. Very cold conditions at present with snow showers. Recently formed accumulations of weakly bonded windslab are affecting steep lee areas.

    Warmer conditions stabilised the snowpack initially in the period. The onset of much colder conditions has presented persistent weak layers at depth, snowfall, strong winds and drifting have presented hard windslab that overlies the weaker layers in many places.

    Warmer conditions stabilised the snowpack initially in the period. The onset of much colder conditions has presented persistent weak layers at depth, snowfall, strong winds and drifting have presented hard windslab that overlies the weaker layers in many places.

    A week of stormy conditions, which included some freeze/thaw cycles. Over the last few days weakly bonded windslab accumulations became more widespread due to very strong winds and snowfall. Currently new accumulations of weakly bonded windslab lie on Northerly to Easterly aspects above 800m.

    A mix of mild and cold temperatures over the last seven days with heavy rain and snowfall. New accumulations of weakly bonded windslab developed; however during the thaw freeze cycles there were periods of instability followed by a re-frozen stable snowpack. Currently new accumulations of weakly bonded windslab continue to develop. The old snowpack remains firm and stable.

    A deep thaw midweek has reduced the snowpack in extent. The snowpack is moist to depth becoming softer but consolidated and generally stable. Colder temperatures in the coming days will eliminate any previous weaknesses that existed (buried surface hoar) and become refrozen and solid. New unstable windslab will progressively develop.

    Continual westerly winds, cold temperatures but very little snowfall has accumulated very localised deposits on mainly E aspects above 900m over the last 10 days. Cold nights have produced surface hoar which is now buried 10 cm or so below surface in some places producing failures in the snowpack with steep convex terrain most affected. Snow cover generally thin in most places.

    Storm force westerly winds and significant snowfall at the start of December produced unstable conditions. Warmer periods with rain to summit levels has diminished the snowpack and a slow consolidation and stabilisation has taken place. The arrival of colder conditions and snow fall thursday evening will present another period of instability.

    Snowpack is diminished in extent but remains in large areas above 800 metres on mainly North to East aspects. Snowpack continues to undergo freeze thaw cycles and remains dense firm and stable throughout.

    The snowpack is gradually diminishing and is generally well bonded and stable in all locations. Glide cracks continue to widen on many steep slopes and remaining cornices prone to spontaneous collapse.

    The snowpack has progressively become more dense and consolidated as the week has progressed and is generally stable throughout the area. Cornices have presented a continual hazard and their stability remains very unpredictable.

    Cold temperatures and new snowfall created an unstable snowpack in isolated locations at high levels at the start of the period. Thaw and re-freeze stabilised the snowpack completely midweek. New snowfall with strong wind has presented poorly bonded windslab on limited aspects mainly above 900m at the end of the week.

    Diminished snowpack with rain to all levels and freezing levels above the summits during last week. Snowpack though has compacted, is dense and generally stable even though soft in places. Cornices have always remained a threat. Cold temperatures have started to re-freeze the snowpack at period end. Fresh windslab beginning to build.

    The snowpack has been thawing at all levels leading to a mostly stable snowpack with some surface instabilities in areas of steep terrain. Earlier in the week weakly bonded windslab consolidated after a thaw. light snowfall followed this with localised weakly bonded accumulations developing above 1000m. This has since thawed and consolidated.

    Freeze then thaw conditions continue to effect the snowpack, calm but snowy conditions at the start of the week presented a weak layer once it became buried, this was still present at the end of the week but rain and thaw conditions followed by a re-freeze has improved this situation. New snowfall and wind presents new windslab hazard.

    Old snowpack has gone through thaw and then freeze cycles and has become generally well bonded and stable. New accumulations of fresh snow present surface instabilities in steep wind sheltered places but these tend to improve with fluctuating temperatures and if calm periods persist.

    Storm cycles followed by more settled weather, leaving instabilities at depth on steep convex terrain. A thaw at all levels followed with wet snow avalanches, now the snowpack is beginning to consolidate again in cooler temperatures.

    Storm cycles continuing, very windy and cold. Periods between storms where snowpack stabilised but more heavy snowfall, with drifting creating new hazard. Some sugar like weak faceted crystals have developed due to cooler temperatures over the last few days.

    Continuing storm cycles with cold and very windy conditions, heavy snow and drifting presenting very unstable snowpack situations. Snowpack beginning to stabilise during calm periods but new storm cycles present new avalanche hazard.

    Strong South-East winds have predominated producing heavy drifting and deep windslab accumulations. Calm but snowy conditions midweek produced a weak layer. This is now covered by windslab to varying depths and presents a persistent weak layer and an unstable snowpack.

    Continual Southerly winds with snow have built significant windslab deposits on all Northerly aspects, very unstable at start of week. Cycles of thaws to summit levels then freezing conditions Improves snowpack stability but new instabilities and weak windslab soon follow. A dynamic and unstable week.

    Thaw then re-freeze cycles have stabilised the snowpack in all areas. Localised, progressively weakening windslab that was present earlier in the weak has therefore been stabilised. New windslab formations are developing on Northerly aspects.

    A week ago, conditions were very unsettled with snowfall and Strong mostly Southerly winds. The snowpack was weakly bonded especially above 900m on NW through N to E aspects. Avalanches Occured on Northerly aspects. This was followed by melt freeze cycles which aided snowpack stabilisation. Now the snowpack is generally well bonded in most locations. Small pockets of windslab lie on N to W aspects above 950m around corrie rims and gully tops.

    Continuing windslab formation with strong winds on mainly North West through North to East aspects above 950 metres mainly. Brief freeze thaw cycles affect windslab with surface crusts and only partially bridge the weaknesses that remain at depth. Corrie rims, gullies and convex terrain affected.

    A week of strong winds and snowfall, with thaw freeze cycles mainly below 900m; however extensive weakly bonded accumulations of windslab have been affecting mostly NW to NE aspects above 850 metres leading to Considerable conditions in these areas and generally moderate below this altitude with localised Considerable in lee areas.

    Old snow has been refrozen. New deposits of wind slab have been deposited on North to North East slopes. Deep drifts of fresh snow interspersed with scoured patches of hard snow. The general cover is still sparse.

    Limited snowpack, patchy and stable

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