Avalanche Report for Torridon
Avalanche Hazard Forecast
FOR PERIOD 18:00 Fri 15/12/2017 TO 18:00 Sat 16/12/2017
Forecast Snow Stability & Avalanche Hazard
Localised instabilities will persist within the snowpack in steep sheltered locations, mainly on Easterly, through South to South-West aspects mostly above 650 metres. Areas most affected will be ridge flanks, scarp slopes, gully exits and steep convexities. Some North-East and West aspects will be affected due to cross loading. Cornices will continue to develop. Exposed ridges and summits will remain scoured. The avalanche hazard will be Considerable.
Forecast Weather Influences
Wintry showers will continue overnight and through the morning and the Northerly wind will gradually moderate through the day, backing South-West. It will remain cloudy throughout. The freezing level will steadily rise to around 600 metres by the end of the period.
Key Snow Stability Observations
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Weaknesses developing in the snowpack due to wind transportation of snow and the formation of windslab.
Windslab development will decrease with easing winds.
Weaknesses within the snowpack that may be present in isolated or widespread locations, and/or a buried layer that has persisted for some time.
Instabilities in the snowpack will persist.
Observed Avalanche Hazard -
Observed Weather Influences
Frequent blustery wintry showers and a fresh to strong Northerly wind with fresh snow lying above 500 metres. The freezing level fluctuated around 600 metres. The cloud base descended to 600 metres during the showers. Some brightness between the showers.
Observed Snow Stability and Avalanche Hazard
Weaknesses exist within the snowpack with localised instabilities in steep sheltered locations mainly on East through South to South-West aspects above 650 metres. Some North-East and West aspects are affected due to cross loading. Areas most affected are ridge flanks, scarp slopes and steep convexities. Some minor cornice growth observed above steep East facing slopes. Exposed ridges and summits are scoured. The avalanche hazard is Considerable.
Deep snow at mid levels - very hard going on foot. Knee deep at 600m! A day of flat light and no definition during the showers. Winds approx 10 - 20 mph fresh, cooling.
Hard going in soft deep snow mainly above 500 metres. High windchill during the blustery showers.
The Weekly Snowpack Summary for Torridon will be updated on Thursday 21st December 2017
The snowpack has remained generally shallow and latterly become very depleted, wet and patchy above 800 metres, although well bonded and stable. High pressure dominated most of the period with mainly cool clear sunny days and some fine cloud inversions. As a consequence, minor weaknesses in the snowpack persisted until the milder conditions arrived, enabling the snowpack to consolidate. Spring conditions prevail.
The avalanche hazard has remained moderate throughout the period. Most snow has existed at higher levels, deposited in cycles of heavy showers and strong to gale force, generally westerly winds. Poorly bonded windslab has persisted mainly on North through East to South-East aspects above 750 metres, but generally in localised steep sheltered areas. Lately, high pressure conditions have dominated, with cold and clear weather maintaining minor weaknesses in the windslab.
Mild conditions have prevailed throughout the period. From having good cover initially, the snowpack has since thawed, becoming patchy and gradually diminished until most hillsides and many summits and summit ridges are bare. Greatest accumulations of snow remain on North to East aspects above 800 metres. Latterly, it has turned more wintry with snow showers and pockets of windslab developing.
There has been a gradual build up of the snowpack over the past week. Due to changing wind directions as weather fronts quickly passed through, most aspects were affected at some point by accumulations of moderately bonded windslab, mostly above 700 metres. Deep drifts and significant cornices were developing by the beginning of the week. Latterly, a strong and showery, but relatively mild Westerly airflow has prevailed and sun induced activity has been noted.
The period started with a very patchy snow pack. Heavy snow showers fell over the weekend and since then it has remained cold. Variable winds and cold temperatures on the relatively shallow snow pack have left underlaying instabilities on most high aspects above 750 metres. There are some extensive areas of wind slab, cross loading and fragile cornices on North - East through to South aspects.
The avalanche hazard remained low throughout the period. The patchy and depleted snowpack continued to thaw at all levels with most remnants of snow on North to East aspects above 750 metres. By midweek, most hillsides and summits were bare. However, by the end of the period, there is a few centimetres of fresh snow on all aspects above 300 metres, most snow falling during 'Storm Doris'.
A very cold and dry Polar Continental airflow dominated most of the period, with mainly sunny and calm conditions and a widespread surface hoar. The cold temperatures and a shallow snowpack maintained localised instabilities which gradually diminished as the snowpack later consolidated. The Easterly wind strengthened with some summit cloud before a mild and wet Westerly airflow became established midweek and a greatly reduced but stable snowpack.
The long awaited snow arrived over the weekend of 3rd to 5th accompanied by strong South-East to South-West winds, with accumulations of moderately well bonded windslab mainly on West through North to East aspects above 700 metres. Other aspects were mainly scoured. From Tuesday onwards, with a generally settled South-East airflow, the snowpack remained shallow and slowly diminished, but weaknesses persisted in isolated pockets of the old windslab.
At the start of the period, it continued dry with a very limited and patchy snowpack, firm and well bonded. Fresh snowfall over the weekend left a general dusting mainly above 700 metres. However, as a mild and moist generally Southerly airflow became established, by midweek, the new snow had thawed, leaving the old and patchy snowpack re-exposed and remaining moist but firm and well bonded.
The avalanche hazard remained low throughout the last week. It was generally mild with insignificant amounts of precipitation and the limited and patchy snowpack quickly became well bonded and stable. By the end of the period, the snowpack was reduced to remnant patches and strips, mainly above 800 metres on East to South aspects. Most hills are bare of snow.
At the beginning of this period we enjoyed good snow cover which in the strong winds drifted on to mainly North - East to South aspects forming localised unstable windslab. After this a milder South - Westerly airflow brought milder temperatures and heavy rain. The past two days have been dry resulting in a now depleted snow pack which is quite patchy and lays mainly on North - East to South aspects above 700 metres. A cooler air mass is approaching which will firm up the generally stable snow.
The period started with warm conditions and a limited slowly melting snowpack. Since Monday there have been strong winds, from between South-West and North-West, and snow showers. This has led to localised deposits of snow mainly in sheltered locations on North-East to South-East aspects.
We had variable conditions at the start of the period with some very strong winds and snow showers over the New Year period. Since then the freezing levels went high to rise above or just around summit levels. Since Sunday it has been cold and dry with a dusting on new snow on the higher summits. The remaining rather patchy snow pack which is mainly on North through East to South aspects is now well bonded and frozen hard.
Initially snow cover was lean. Then wild weather brought some snow cover. Over the Christmas period storm Barbara gave us more wild weather with unstable windslab building on North - East to South - East aspects however no avalanches were recored. Since then Southwesterly winds, high freezing levels and heavy rain have striped much of the snow with only ribbons and banks of well bonded snow remaining on high corrie rims and steep lee aspects on North to South - East aspects above 700 metres.
After an inauspicious start to the forecast season, with a snowless landscape, winter arrived overnight on 19/20th with a light dusting of snow above 450 metres. This heralded a cold showery airflow from the west along with gale force winds. The wintry showers become more frequent and intensified, with an occasional rumble of thunder. By the end of the period, significant accumulations of unstable windslab developed on steep lee slopes.
A diminishing spring snowpack with limited snow cover on Northerly to Easterly aspects above 750 metres. Spells of new snow presenting a wintry scene at the highest levels during the week leading to limited instabilities, otherwise the snowpack has been stable in most areas. Glide Cracks in deeper accumulations on steep East aspects have continued to widen due to snow creep.
A diminishing snowpack with limited snow cover but with new snow presenting a wintry scene during the week. New snow accumulations at the highest levels have presented limited instabilities, otherwise the snowpack has been stable in most areas. New snowfall on the first day of April at high levels will present short term moderate instability.
For the first part of the period high pressure dominated the area and the spring snow pack while diminishing was generally stable. New snow began to arrive mid week above 700 meters on a strong South -Westerly airflow. The cooler weather is to remain for a while with some heavy showers forecast. Windslab instabilities will build above 800 metres with cornices rebuilding around coire rims. Some wet snow instabilities will be present in the diminishing snow pack down to around 600 metres.
High pressure conditions have dominated this period with mild temperatures and dry and mostly sunny from Sunday onwards. The thaw initially affected deep instabilities in the snowpack, combined with collapsing cornices and falling ice. Thereafter, the patchy and diminishing snowpack consolidated and stabilised at all levels. Latterly, surface wet snow instabilities have developed on steep sun exposed slopes.
The snowpack gradually consolidated over the first half of the period, with a widespread surface crust. It was firm and icy on aspects exposed to the prevailing wind, particularly on summits and summit ridges. At the start of the week, new poorly bonded windslab developed on North through North-East to South East aspects and persisted through the week, although it was generally shallow and localised. There is a good snow cover above 500 metres.
High pressure weather conditions at the start of this period produced numerous sun induced single point avalanches on southerly aspects. By contrast, in the shade, -9C was recorded at the snowpack surface, but generally there was a good widespread snow cover. A short thaw followed producing unstable snowpack conditions with noticeable collapsing cornices. A re-freeze and fresh unstable windslab developed on steep North To South-East aspects. Latterly, deep instabilities have persisted.
This period started with heavy snowfall and a short sharp thaw which resulted in wet slab avalanches and collapsing cornices. Cold conditions returned quickly and heavy snow showers accompanied by gale force Westerly winds produced areas of deep unstable windslab mainly on Easterly aspects. The snow showers continued, sometimes heavy, on a North-Westerly airflow with widespread poorly bonded windslab developing on East to South aspects. Latterly, there is good snow cover on most aspects.
A cold and strong Easterly airflow dominated the first part of this period. Significant snow redistribution onto South-West to North-West aspects produced localised areas of unstable windslab. Over the weekend, the old snowpack became firm and stable with areas of snow ice on exposed slopes. Latterly, strong to gale force South-West winds accompanied by periods of snowfall has produced areas unstable windslab on North to East aspects. Generally good snow cover above 500 metres.
By the end of this period, a good general cover of snow exists on all aspects above 600 metres. After a couple of freeze thaw cycles, by midweek and with a showery North-West airflow, accumulations of moderately well bonded windslab developed on North-East to South aspects above 650 metres. Latterly, areas of unstable windslab have developed on South-West to North-West aspects due to snow redistribution. Areas of firm snow-ice also exists on exposed slopes.
The greatest influence on the weather and snowpack in this period was Storm Henry; unseasonably mild conditions, periods of heavy rain at all levels and storm force winds (generally from Western directions) interspersed with snowfalls. The snowpack has been reduced to stable patchy wet snow, followed by re-freeze and localised unstable windslab accumulations with obvious graupel layers. Latterly, unstable windslab is evident on North, through East to South aspects above 650 metres.
The main theme for the last week was thaw, closely followed by rain and gales. Several freeze thaw cycles over the period did not result in significant deposits of fresh snow. Cosequently, there was a net loss of snow, with a sparse, wet, but stable old snowpack. By the end of the period the mountains were virtually bare of snow. Winter returned with a vengeance on the last day with fresh unstable windslab accumulations on North to East aspects.
Through much of this period the winds have been light, occasionally moderate, generally South-Easterly. It has been cold with light snow showers at most levels. Mainly localised windslab formed above 800m with South-West through West to North aspects most affected. This pattern changed on Wednesday when the freezing level rose to around 800m and on Thursday to around the summits, with associated moistening of the surface of the snowpack.
A ridge of high pressure moved in last weekend heralding a cold, dry, relatively clear period and the extent of previous heavy riming was apparent as the Easterly airflow eased and cleared. Pockets of unstable windslab remained high up on both Easterly and Westerly aspects. Latterly, a cold more showery North West airstream produced further accumulations of unstable windslab on East to South aspects above 800 metres. Little snow below 600 metres.
After a relatively wintry start to the year, very mild weather returned on the 2nd with rain at all levels and a diminishing snowpack. After, a cold and strong Easterly airflow became established delivering patchy light snowfall, but not significantly adding to the snowpack. By the end of the period, light snowfall with South-Westerly winds saw very localised accumulations of fresh windslab develop high up on North to East aspects.
Some exceptionally mild and frequently very wet weather, interspersed with overnight snowfalls (most notable pre Christmas and on December 26th), has resulted in a net loss of snow over the period. The fresh snowfalls generally melted quickly. The limited old snowpack is now refrozen, firm and stable, and on Northerly aspects above 850 metres. The most recent light snowfall lies on most aspects above 800 metres.
24/12/15. The start of the period saw very little snow cover with small patches restricted mainly to Easterly aspects above 850 metres on the Eastern most mountains. Except for a short lived dusting on the 21st, the first snow arrived on the 23rd and continued the next day. Small pockets of windslab developed in localised areas with a North to North East aspect above 800 metres, with a blanket of snow above 300 metres.
The record breaking high temperatures this week have stripped the hills more or less completely of snow.
Warm conditions over the past week has stabilised the snowpack and a slow thaw has resulted in a much diminished snow cover. The snowpack is soft in the surface layers, but compact and dense nearer the ground. Colder conditions (Saturday 11th) will stabilise the snowpack further, but some new windslab will be deposited in localised areas.
The last weekend of March was very mild seeing a huge reduction in snow cover. Quieter weather early in the week saw a well bonded snow pack. Wednesday was a return to winter with heavy snow at all levels on West to North West winds. Thursday was a blue sky day with avalanche activity, an unstable snowpack on Easterly aspects, poorly bonded layers of graupel deep within the new windslab. Temperatures then rose seriously depleting the snow cover at lower levels but stabilising it higher up.
The early part of the week saw stable weather and a stable but diminished snowpack. Greatest cover was on Easterly aspects above 750 metres. Wednesday and Thursday brought significant new snow on strong winds down to 500 metres. Thursday night and Friday saw avalanche activity on Easterly aspects before a rapid thaw accompanied by heavy rain followed on Saturday. The temperatures then dropped as yet more new snow arrived from the west.
A mild and very wet start to the period produced many wet snow avalanches. By Monday the snowpack was much diminished. A period of stormy freeze thaw cycles midweek did not result in a significant amount of new snow accumulation. The snowpack was becoming stable again. High pressure dominated by the end of the week further stabilising the snowpack and giving fine settled weather conditions.
A week of two contrasting halves. The start of the period saw frequent wintry showers down to low levels on generally South-South-West to Westerly winds adding to the snowpack particularly on North-East to East aspects. Wednesday saw a fine and brief interlude before a very wet, very mild and very windy end to the week with rapid snow melt and wet snow avalanches observed before the snowpack became more consolidated. Colder on Sunday.
The start of the period saw the existing snowpack topped up with snow showers interspersed with longer periods of snow on strong to gale force South-West to North-West winds and cold temperatures. The temperature rose dramatically on Wednesday and Wednesday night with rain to all levels but quickly dropped again on Thursday with fresh snow down to 300 metres. By Friday there were significant localised areas of unstable windslab on North to East aspects.
A generally diminishing snowpack throughout the week. There was a freeze/thaw cycle at the beginning of the week with milder temperatures during the day. Wednesday was a very wet, very windy and very mild day and a lot more snow and ice disappeared. Colder conditions with light snow showers down to 750m and strong South-Westerly wind arrived Wednesday night. These have deposited some fresh windslab in very sheltered locations on North-West to East aspects.
The week say several cycles of freeze thaw. The combination of the sun and milder temperatures have significantly depleted the snow cover. There has been no new snow this week. The cover is most extensive on East to South East aspects. Overall the snow is generally well bonded but with localised instabilities on steep terrain on shaded aspects. Falling ice was observed later in the week.
After the extensive snow accumulation from last weekend's storms, mainly on NE to SW aspects, the beginning of the period was more settled, but with a smattering of snow showers adding to the snowpack on all aspects. By Wednesday, high pressure became established bringing milder and cloudy conditions to the NW with little in the way of precipitation. Snow melt at lower levels and with the freezing level hovering around the summits by the end of the period, the snowpack is consolidating.
Sunday 25th January saw a rise in freezing level to above the summits. The mild weather continued through Monday with rapid depletion of the snow cover. Falling temperatures then refroze the snowpack which became stable. Midweek saw significant snow to sea level in light winds. Heavy falls of snow on Northerly winds later in the week and weekend added considerably to the cover. Deep accumulations of poorly bonded snow on many aspects. Natural avalanche activity observed on South aspects.
Cold stable weather during the week. Strong temperature gradient in the snowpack with facets developing. A lot of graupel evident throughout the snowpack. Towards the weekend cycles of freeze thaw. Exposed ridges and aspects exposed to the wind scoured. Greatest snow accumulations on North East to South East sheltered aspects. large build up of ice on most aspects.
The snowpack has been steadily added to over the period, particularly on Easterly aspects. Snow showers from the South West led to a more intense period of snow to all levels on Wednesday accompanied by strong winds. A mild spell followed with rain to summit level. By the end of the period, a cold westerly airflow brought in frequent blustery snow showers, mainly of hail and graupel, which led to unstable conditions higher up.
The freezing level has been above the summits several times as well as to valley level this week. A net loss of snow. Main feature of the week has been Westerly winds gusting in excess of 130 mph. Stormy weather. Ridges and areas exposed to the West scoured. Heavy drifting, much of this settling at lower levels and melting. Precipitation often rain at all levels, a lot of hail and graupel evident in high sheltered locations.
A heavy thaw midweek considerably reduced the extent of the snow and reduced earlier instabilities in the snowpack that were there over the weekend. Patchy wet snow remains that is generally stable and firm underfoot. Colder temperatures over the next days will freeze the existing snow and new unstable windslab will develop.
The middle of February saw more build up of snow above 400 metres. Continued precipitation combined with freeze thaw cycles have led to a depletion of the snowpack at lower levels but an ever increasing build up at higher levels.
The cycles of melt freeze have contributed to a well consolidated snow pack with isolated pockets of poorly bonded windslab high on corrie rims and gully exits.
Generally a thin snow cover, moist and fairly stable snowpack, some localised instabilities high in corries and gully exits on all Northerly aspects. A week of high winds and precipitation, freezing levels around summits.