Avalanche Report for Northern Cairngorms

Issued

Avalanche Hazard Forecast

FOR PERIOD 18:00 Sun 08/05/2016 TO 18:00 Mon 09/05/2016

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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Forecast Snow Stability & Avalanche Hazard

Snow fields remain in all mountain areas above 800m, sometimes extensive above 1000m in the Cairngorms and Ben Nevis areas. These will continue to present a slipping and falling hazard if firm and icy. Cornices threaten many slopes and are unpredictable and prone to collapse in the warm spring conditions also, the potential for full depth avalanches due to snow creep producing Glide cracks in deeper accumulations on steep East facing slopes also presents an unpredictable hazard.

Forecast Weather Influences

Key Snow Stability Observations

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Observed Avalanche Hazard -

Observed Weather Influences

Observed Snow Stability and Avalanche Hazard

Mountain Conditions

Comments

Weekly Snowpack Summary
  
  • Over the past week cold conditions with new snow on all aspects. Some new windslab; however this consolidated quickly. Large unstable cornices overhang many aspects. Most recently mild temperatures with surface instabilities, this will continue through tonight (Sunday 2nd May) before cooler conditions arrive again in the early part of the week. This will help to consolidate the old snowpack.

    Below 900 metres the snowpack continues to thaw and diminish, above this level almost daily snow accumulations have topped up the already good snow cover. Any new deposits, after initial instability during snowfall, have bonded quickly and stabilised. This is due in large part to the 'spring conditions' with increased solar radiation influencing temperatures and fluctuating freezing levels. Surface sloughs on steep slopes as the day warms present a regular hazard.

    Snowfall over the period has improved snow cover. Instabilities have generally been short-lived due to the warm temperatures enabling stabilisation after storm cycles. The snowpack is generally becoming more consolidated at depth but surface instabilities and sloughs due to solar radiation on steep slopes will continue to be a hazard. But the general situation is a stable snowpack.

    A week of snowfall and localised windslab formation on most days at higher levels. Generally though, warmer air temperatures has resulted in rapid stabilisation and diminishing weaknesses after these events. Strong winds with new snow at the end of the period will present another cycle of short term instability.

    A week of good weather, mild conditions and some cold nights have resulted in a stable but diminishing snowpack. Deeper areas of accumulation on mainly Easterly aspects show signs of snow creep with glide cracks evident. Some new localised windslab is now forming but this is fairly shallow in depth.

    Following rain at all levels on the 12th March and subsequent snowpack consolidation, weak layers at depth have diminished to present a moist but mostly stable snowpack. Cycles of overnight refreezing with clear skies and warming in the day provides further improvement. Surface instabilities are now a regular occurrence on sun affected steep slopes.

    At the end of the last week (4th March) a period of snowfall and unsettled weather produced a new blanket of snow cover. Wind and drifting produced a firm windslab which overlay this soft layer presenting a weak snow pack. Cold temperatures have preserved this weakness with any stabilisation being slow. Rising temperatures will present short term instability from the 11th March but thereafter stability should improve.

    At the end of last week ( 27 Feb) diminishing instabilities where still present in deeper but but especially shallower accumulations on East aspects. Freezing levels above the summits moistening the snowpack to depth on Tue 29 Feb and the subsequent refreezing has stabilised this snowpack. A new regime of cold tempereratures with cold Northerly winds will present new windslab instabilities on wind sheltered slopes.

    Weaknesses in the snowpack that produced large avalanches on the 16th Feb have persisted on NE to E aspects for the last week. Cold temperatures have preserved instabilities and have slowed stabilisation. Surface slab is getting firmer and bridges weaknesses in many areas but steepest places and convex terrain remains most affected and suspect.

    Cold temperatures and snowfall over last weekend with light winds presented a blanket of cold snow on monday 16 Feb. Tue presented storm force Southerlies with heavy drifting and rising temps for a while, this produced very large natural avalanches on North aspects which failed on the buried soft layer of monday. Cold temps have stabilised and refrozen snowpack mostly but weaknesses at depth remain Expected new snowfall and strong Southerlies will present further instabilities for the weekend.

    The limited snowpack has improved in extent from wed 10th. Weaknesses in the snowpack on easterly aspects have diminished but new windslab formation on NW-SW aspects due to drifting, cold temperatures and strong East winds are creating new instabilities which will persist in the coming days.

    Limited snow cover once more. Last week saw new snow accumulations without wind, additional snowfall and windslab overlay this weak layer on NE,E aspects, however these weaknesses have slowly diminished. Additionally, Storm Henry with hurricane force winds has stripped and scoured many locations leaving a largely stable snowpack and good climbing conditions. A new cold system with snow arriving at the weekend will present a new stability situation for the coming days.

    Thaw conditions over the past week has significantly reduced and stabilised the old snowpack. More recently new snow was lying on all aspects before being redistributed on the strong Westerly winds. New poorly bonded windslab formed on North through East to South-East aspects above 900 metres. A brief mild spell with rain on Thursday night with cold temperatures, storm force Westerly winds and snowfall into Friday

    Instabilities present in the snowpack at depth on West to Northerly aspects above 900 metres have slowly improved over the last week. However instabilities have persisted in isolated locations in steep places due to cold temperatures and the development of loose grains within the pack. Current rising temperatures (thursday 21 and friday 22) and rain at all levels has produced a cycle of significant instability with avalanche activity, this should diminish in the next days

    Very cold temperatures with snow fall. Snow is lying above 500 metres on all aspects. The snowpack has been, and currently is very cold and dry with instabilities affecting most aspects in areas of steep terrain. Firmer surface layers overlie softer weak layers beneath. Facetted grains are developing within the snowpack. Stronger winds today have begun to erode Westerly aspects. Large unstable cornices overhang Westerly and Northerly aspects

    Continual Easterly winds with progressive amounts of new snow has produced deep areas of windslab, unstable during the storm cycles in the surface layers but a generally stabilising trend within the snowpack. Steepest locations continue with poorly bonded layers. Colder temperatures with new windslab deposits are presenting unstable accumulations once more today (Thursday 7th)

    Limited thin snow cover generally over the last few days. From today, friday the 1st Jan, although very localised, poorly bonded windslab is beginning to build and will increase in depth and extent over the next days.

    So far, cycles of cold weather with snow followed by rain at all levels has depleted the snow pack considerably. Localised build up of windslab in steep places continues to form unstable areas of new snow this is gradually increasing in extent.

    Over the past week there have been periods of snowfall leading to snowpack instabilities. Between each cycle the snowpack began to consolidated quickly. Currently a soft layer lies beneath todays storm snow, this combined has increased the weakness within the snowpack. Mild temperatures and rain are expected within the next 24 hours. A period of instability is expected to develop before the snowpack begins to consolidate again.

    Warmer temperatures with sunshine continued through the week which helped to gradually stabilise the snowpack. New snow and cold temperatures have arrived with weakly bonded windslab developing on North to East aspects. The old snowpack is now re-frozen and firm

    At the start of the period weak layers were present in the snowpack, freezing levels above the summits and rain moistening the snowpack to depth and a subsequent refreeze provided stabilisation by 30 March. New snowfall and strong winds has produced deep unstable windslab in wind sheltered places. Warmer temperatures will help stabilisation but it will take time to effect the current deeper accumulations.

    From the start of the period (fri 20th) the snowpack underwent a number of freeze thaw cycles and became generally well bonded and stable, some limited snowfall presented localised accumulations. New snowfall, without wind overnight on Tue 24th gave a blanket cover of snow. This layer of soft snow with poorly bonded grains has created a weak foundation which is currently covered with deepening windslab accumulations, this will continue to build in the coming days.

    At the start of the period the saturated snow refroze and stabilised. Some new snowfall over the weekend period arrived but amounts were small, presenting limited windslab of moderate instability above 1000 metres. Warmer temperatures and then refreezing have developed a stable snowpack.

    The saturated snowpack at the start of the period (7th March) refroze and stabilised at the start of the week. A series of storms with very strong winds followed, depositing new unstable windslab onto mainly NW through N to E aspects above 900m. Currently, instabilities remain in the snowpack at higher levels but todays rainfall and a re-freeze (Fri 13th) should help stabilise the snowpack.

    Cold temperatures with snow showers on mainly Westerly winds over the past week. Accumulations of unstable windslab became more widespread on North-East to South-East aspects above 900 metres. Currently the snowpack is thawing at all levels; instabilities are present on these aspects mostly in steep convex terrain. Cornice collapse also a hazard.

    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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