Avalanche Report for Creag Meagaidh
Avalanche Hazard Forecast
FOR PERIOD 18:00 Fri 15/12/2017 TO 18:00 Sat 16/12/2017
Forecast Snow Stability & Avalanche Hazard
Instability will persist in localised deeper accumulations of wind drifted snow on very steep East through South to South-West aspects above 900 metres. Better stability on recently scoured West to North aspects above 800 metres. Snow at most lower altitudes will show early consolidation. The avalanche hazard will be Considerable
Forecast Weather Influences
Any light snow showers will die out overnight leaving a cold, bright day. Moderate North-Westerly winds will ease and become light West-South-Westerly by the end of the afternoon.
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 easing overnight.
Cornices that may present a hazard due to collapse and/or providing an avalanche trigger.
Minor new cornice development. Some old hard and scoured cornices over N and E aspects.
Observed Avalanche Hazard -
Observed Weather Influences
A few light overnight snow showers then dry, cold and overcast. Periods of weak sunshine later in the afternoon. Moderate NNW winds.
Observed Snow Stability and Avalanche Hazard
North-West through North to North-East aspects above 750m have been scoured though there are some patchy deposits of wind-drifted snow in pockets and hollows. Steep, sheltered South-East through South to South-West have more substantial cover including localised accumulations of less well-bonded windslab above 850 metres, snow below 700m is better consolidated. A few selected East aspects above 900m have been affected by cross loading. The avalanche hazard is Considerable.
Deep snow cover at all levels - some exposed ridges scoured Flat light and no definition in morning, brighter later. Winds 20 -30 mph progress difficult at times with stronger gusts
A few older cornices above N and E aspects. Saturday looking like the pick of weekend weatherwise. Quite good snow cover in lower Coire Ardair on Friday.
The Weekly Snowpack Summary for Creag Meagaidh will be updated on Thursday 21st December 2017
After a cool start with snow showers the period became milder with rain at all levels. During Sunday the freezing level dropped with snow showers. Snow showers continued through Monday and Tuesday which saw much more snowfall to low levels and strong generally WSW winds. This deposited unstable windslab on North through East to SE aspects. Wednesday and Thursday were dry with moderate NE then light SE winds;the snowpack started to slowly consolidate.
Mild with thawing conditions throughout. Some avalanche activity recorded mid-period with wet snow avalanches from steeply inclined ledges and benches (see blog from 10th March) of the Post Face and also in the Inner Coire Ardair. Cooling conditions now towards end of the period with fresh snow and some new windslab slab beginning to develop on high mainly North East and Easterly aspects.
The period started with a covering of snow above around 600 metres with deepest deposits on North to East aspects. Easterly winds then redistributed snow to other aspects. The remainder of the period saw significant further snowfall mainly above 800 metres with greatest accumulations on North to East aspects but also some warmer periods which, after an initial reduction in stability, helped to consolidate the snowpack. Some large fragile cornices are present mainly above North to East aspects.
Much depleted, sparse snowpack. Largely coarse-grained and stable but confined to locations above 800m. Heavy snowfall late in the period saw new snow at all levels with instability in deeper deposits on slopes of most aspects above 850m.
Very strong , cold South Easterly winds in the period brought fresh snow above 500m. Instabilities developed and whilst localised and mainly on North West slopes above 900m the instability was variable through North to North East aspects as a weakness developed deeper in the snowpack. A thaw to end the period was accompanied by rain and the cover is now much depleted. Whilst there are now some wet snow instabilities the snowpack has become well bonded and generally stable
The snowpack at the start of the period was very minimal, confined only to coire backwalls. Lowering temps brought snow to all levels with many areas then scoured by very strong South Easterly winds. Areas of marginally stabilised windslab developed on mainly NW through North to North Easterly aspects above 800m. Cold temps are maintaining instabilities on these apects.
Limited and patchy old snowpack. A period of poor stability after snowfall and drifting but sustained thaw afterwards. Firmer but scant snowpack late in the period as temperatures fell. Largest patches on NW through N to E aspects above 750m.
There has been a limited snowpack for the last week with the largest patches on North-East to South-East aspects above 800 metres. It has been mainly dry with inversion conditions leading to a mainly frozen and stable snowpack.
Wintry showers in the early part of the period resulted in snow to all levels. A steady thaw thereafter resulted in the disappearance of cover in all but highest coire backwalls and a few sheltered hollows. Accumulations whilst moist to start in the thaw became rapidly well bonded and stable and have now become firmer in the recent high pressure, temperature inversion conditions.
Very little snow to start the period, with any accumulations only at highest elevations. A cold North Westerly airflow then brought storm cycle with snow now lying to all elevations, Winds beginning to ease as showers gradually dying out. Soft slab continues to build in sheltered lee locations.
A depleting snowpack. Mainly old snow patches, larger ones above 700m on North to East aspects. Only a little new snow during the period. A few melt-freeze cycles strengthened the increasingly coarse-grained old snow.
The period started with warm weather and only very limited patches of snow. Snow showers started on Tuesday afternoon and have continued since then. Winds have been strong and from between a Southerly and Westerly direction leading to a substantial build up of windslab mainly on North to East aspects.
Only a little new snow during the week which rounded out quickly after initial surface wet snow instability. Regular re-freeze of older snow above 950m induced a crust or firmer surface to the coarse-grained snowpack. Collapsing cornices were an issue for a time with the onset of a milder spell. Well-established spring snowpack by the end of the period.
Spring conditions. The period characterised by occasional snowfall and drifting at higher altitudes followed by milder temperatures and rainfall. Some initial wet snow instability then a rounding trend in newer snow. Older exposed snowpack is now coarse-grained and moist. Glide cracks widening in some locations. Minor full depth avalanches from some steeper crags.
Variable spring snowpack conditions for most of the week. Persistent but localised instability high on some lee slopes in colder, dry snow. Cornice triggered avalanche activity mid-period.
Spring conditions. Coarse grained snowpack slowly thawing at all elevations. Glide cracks widening in deeper old snow deposits on some East aspects. Minor full depth avalanche activity in the middle of the period.
Milder conditions after prolonged cold with a consolidating trend commencing by the middle of the period. Snowpack stability improved later as the snow went isothermal from top to bottom. Moist wet grains predominate by the end of the week.
Residual weaknesses beneath new and older snow for much of the period, often localised. Storm cycle brought new snow instability on NE to SE aspects but then a consolidating trend in all snow below 800m contour. Cold-induced instability lingering through to the end of the period on NE aspects at higher altitudes. Very large cornices feature over steepest lee slopes.
Buried weak layers due to prolonged low temperatures in the first part of the period. Then a 36hr period with 3 quick evolutions in weather and snowpack conditions: rapid thaw with rain to near summits followed by heavy snowfall and new snow instability, and finally bright, sunny conditions but with residual instability at higher altitudes. Respective avalanche activity due to wet snow instability closely followed new snow instability and cornice collapse.
Heavy snowfall with deep windslab on all NE to SE lee slopes inducing a new snow avalanche cycle in the first part of the period. Then very cold for several days with instability slow to improve in the snowpack in most recent deposits of windslab. Instability in the midpack and near-surface layers. Large cornices. Scoured crust on some S and W aspects.
A generally cold week with one mild/wet day (Tuesday). Strong winds of Friday the 12th caused some redistribution of the snowpack, producing some natural avalanche activity. Varying wind directions over the next few days led to windslab on many aspects, and a complex hazard distribution. Tuesday was very wet, with heavy rain/snow on the summits, and a number of natural avalanche releases. It soon cooled down again, but snow showers deposting fresh windslab created a considerable hazard again.
Two avalanche cycles. Weak new windslab on North and East aspects leading to localised instability and a triggered avalanche. Later, rapid loading on East to South aspects resulted in cornice triggered avalanche activity. Cold temperatures maintaining localised instability. Transition to spring noted; more heat from the sun but with cold interludes giving a widespread melt-freeze crust which is now buried under new snow. Snow consolidated in all locations below 700m.
South-West to West winds throughout the period, very strong at times. Significant accumulations of new snow especially on North through East to South-East aspects. Rain to summit level on Sunday night followed by colder temperatures helped to consolidate the snowpack. Temperature now rising giving a period of increased instability, but then due to freeze again tomorrow. Many slopes and ridges exposed to recent winds are bare.
Significant snow loss during the period with the return of wetter & milder conditions. Fluctuating temperatures consolidated existing weakness within the snowpack. Some cover again returning above 750m. Mountain conditions generally poor to end with fluctuating temperatures and mild storm force Westerlies affecting the area.
A week of cold temperatures and little new drifted snow. Facetting identified above and below a buried crust. Instability confined to locations above 900m. Slab overlying the buried weak layers became stronger and more supportive by the end of the week. Milder saw temperature gradients in the snowpack ease but buried facets still responsive to compression test. Much milder by week’s end with more consolidation noted in overlying slab.
Snowpack characterised by being comparatively thin in many locations. Deeper accumulations on NW through N to E aspects above 900m. Very cold temperatures in the second part of the period induced buried weak layers in thin and deeper snow on all aspects above 900m.
The period started cold with South-Westerly winds, some windslab and a frozen older snowpack. The rest of the week saw strong East to South-Easterly winds with snow showers but no large accumulations. Freezing levels varied between 750 and 1000 metres. The fresh snow consolidated fairly quickly in the moderate temperatures.
Fluctuating temperatures over the period bringing the all too familiar cycle of snow /rain. Several cycles with some full depth avalanche activity noted at usual sites (Sron a Ghoire). Snowpack remains very limited with existing patches well consolidated and stable. New snow accumulations are beginning to develop on sheltered North to East aspects with new snow instabilities and windslab developing in steep gully exits of these aspects. Some new cornices forming around core rims.
Wintry conditions returned for a spell with fresh snow down to all levels for a brief period. Some avalanche activity followed with new snow instabilities and numerous mainly wet snow single point release events widespread in subsequent solar warming. Cornice lines came down above NE though to East aspects , although remnants remain along with old creep lines in convex terrain, some at low elevations below 800m. High pressure stable conditions and a generally re-frozen snowpack now above 800.
A week when the snowpack consolidated steadily after initial snowfall. Collapsing cornices triggered a few wet snow avalanches early in the period. Snow grains became coarser and moist as the steady thaw set in. Full depth glide cracks opened on steep East to South East aspects and these continue to widen in the warm conditions. Cornices remain notably large and weak over many lee slopes.
Highly variable spring weather conditions with heavy snowfall at times. Snowpack on NE to SE lee slopes now deep and characterised by old snow base below a significant amount of new snow. Storm new instability commonplace in the latter part of the period. Minor wet surface snow releases during periods of sunshine. Very large cornices above all lee slopes.
Well stabilise re-frozen snowpack for most of the period with some softening on sunnier aspects. New snowfall towards end of period from a wintry blast brought fresh slab deposits, mainly on North West through North to Easterly aspects - rapidly consolidating in fluctuating temps. Diminished snowpack elsewhere, moist but generally stable below 800m.
Fluctuating freezing levels to around summits resulted in a generally well consolidated snowpack in most locations. Some light snowfall gave rise to localised accumulations of moderately bonded windslab start of period, which persisted for much of the time above 900m on NW through to Easterly aspects. Elsewhere most slopes remained hard re-frozen and stable. The snowpack is now beginning to soften in a slow thaw, stability remains generally good.
Several melt freeze cycles stabilised the old snowpack though full depth glide cracks widened on East aspects. Some new windslab accumulated on high lee slopes with wet surface sluffing after temp rise or rain.
A brief mild period at the start of the week before turning much colder with snow to all levels and frequent heavy snow showers on a strong Westerly wind. Areas of deep unstable windslab developed on mainly North-East through to South-East aspects above 700m with large unstable cornices building above these aspects. At the end of the week a slow gradual thaw started in conjunction with strong to gale force force South-Westerly winds and light rain showers.
Storm cycles throughout the period brought snow to all levels and areas of windslab were widespread on mainly North through to Easterly aspects, with large cornices building over mostly North East and East aspects. A freeze thaw cycle towards the end of the period helped consolidate the snowpack in all locations, although new slab is again beginning to build as further snowfall brings fresh accumulations above 600m.
Isothermal snowpack and cool temperatures in the early part of the period maintained good stability, though full depth glide cracks widened on SE aspects at 750m. Large full depth avalanche early on the 15th on a SE aspect after freezing level rose to 800m. Other glide cracks widened. Some new snow instability on N to NE aspects after snowfall and drifting followed by much milder conditions and wet snow instability induced by rain at all levels. Re-freeze brought some initial consolidation later
Little or no snowfall but cold early in the period sustaining localised instability in mature windslab on many aspects. Deeper deposits on some steep East to South aspects had widening full depth glide cracks and conspicuous buckling of slab as temperatures eased. Full depth avalanche activity on South East and East aspects at around 750m in Coire Ardair and Coire Choile Rais on 11th Feb in milder weather. Size 3 avalanche in Coire Ardair.
Three days of snowfall and drifting brought new snow instability and some limited avalanche activity on E to SE aspects. Persistently cold temperatures through the rest of the period preserved instability on most aspects but notably on SE to SW aspects. Less cold conditions later encouraged consolidation in all locations except SE and S where deep snow cover maintained the facetting trend. Glide cracks beginning to appear near the end of the period on some selected SE aspects at around 750m.
Some heavy snowfall at start of period followed by fluctuating temps and wet thawing conditions at the start of the week. Additional snowfall followed with further temp fluctuations, strong winds heavy windward scouring on exposed hillsides and another melt /freeze cycle. Heavier snowfall to end the period with some new snow instabilities and small cornice triggered slides. New slab building mainly Easterly aspects.
Early snowfall and drifting with winds from variable directions brought extensive cover of snow with hard and soft slab persisting on NW through N to SE aspects above 750m. Cold temperatures extended over several days and induced some early facetting notably above a buried crust and in soft surface slab. Instability became localised later with better stability in many places.
Snowfall on the 9th and 10th didn’t accumulate except for localised accumulations with a scoured surface prevalent. More snowfall and fluctuating temperatures followed by heavy snowfall at all levels. Very stormy conditions brought widespread storm snow instability on N to SE aspects above 750m. Overall, fairly typical Scottish snowpack with new snow instability but no lingering weak layers.
After a thaw the snowpack froze in all locations. Run of mainly Westerly winds and some snow showers maintained localised accumulations of cold, multi-layered windslab on NE to SE aspects above 750m. Thaw and light rain brought instability and some avalanche activity on NE aspects on 5th Jan. Colder conditions after the thaw re-stabilised the old snowpack at all altitudes. More snowfall and much colder weather on 6th, 7th and 8th induced new snow instability on NE to SE aspects above 800m.
Very little snowfall during the period but some lingering instability on NE to SE aspects above 800m due to persistent cold temperatures. Minor evidence of facetting noted in the snow profile on 29th producing easy shears but localised in extent. Diminishing instability with onset of milder temperatures and later moist conditions. Onset of very heavy rainfall and mild temperatures induced full depth avalanche activity on some very steep SE aspects 31st/1st. Thawing, wet snowpack elsewhere.
New snow avalanche activity on the 20th on NE to SE aspects. Further avalanche activity on 21st after heavy rain and mild temperatures followed by some snowpack consolidation as temperatures fell. More snowfall with graupel induced new instability on N to E aspects which persisted in cold temperatures on Christmas Day.
Storm snow to start the period resulted in soft weaker layers overlaid by hard more dense deposits. Temperature fluctuations followed mid week with a thaw to all level by end of the week. The depleted snowpack is generally now well consolidated. NB Some cornice collapses mid period with new build up on-going.
A week of persistent thaw with occasional snow showers and cooler interludes. Snow pack now much patchier and what remains characterised by coarse-grained, stable structure. Deep glide cracks and crevasse-like features present as well as partially collapsed old cornice lines.
Slow steady thaw conditions and stable for most of the period with freezing levels above summits occasionally lowering just below. Bright sunshine briefly mid-period with some sun on snow localised instabilities, glide cracks continue to develop with remnants of cornices slumping and collapse prone. Slow thaw persisting to end period.
New snowfall at high levels to start the period were followed by very strong winds with heavy drifting and the rapid slab build up of unstable slab from re-distributed snow. Poor stability with avalanches (class 2 & 3 events)followed these accumulations mid period on NE and E aspects around 900m. Warmer temps and strong sunshine followed with localised wet snow instabilities & cornice debris. A re-freeze now has resulted in much better stability - a few instabilities above 900m from new showers.
More frontal activity coming in from the Atlantic with rain, very strong winds and mild temperatures; colder, wintry towards the end of the week. Snowpack generally moist and stabilising but diminished in thaw. Snow line now 750 to 800m. Most large cornices now down but some remain. Full depth glide cracks in several never seen before locations: all continue to widen. Colder temps encouraging MF crust to form with new windslab developing on N to E aspects above 850m.
Two thaw cycles have affected the snowpack over the period with associated wet snow avalanches and a number of cornice collapses primarily on North West through North to East facing slopes. Between these cycles regular snow showers mostly above 700m brought new snow instabilities with drifted accumulations. Some deep seated weaknesses persist within accumulations above 900m.
Lots of avalanche activity to start the period with numerous large events from a temperature rise accompanied by rain on snow, all mostly below 800m, in some cases these ran to full depth on North through North East and Easterly aspects and involved significant volumes of wet snow. Cooler temps mid week brought some consolidation. New snow showers continuing to build slab again at highest elevations above 900m on same aspects to end period. Good consolidation at lower elevations
Frequent frontal activity brought snow then warm sector conditions throughout the week. Pattern as follows: initial dry snow instability then transitional wet snow instability followed by a period of consolidation. Avalanche activity has been both dry and wet varieties. Some of the massive and commonplace cornices collapsed in the last wet-warm cycle. Large and deep full depth avalanche on 17th-18th at 750m on a ESE aspect of Sron a Ghoire.
Blizzard conditions to start the period gave rise to lots of snow transport at high levels. This was followed by avalanche activity (temp rise)primarily NE & E aspects - inner Coire Ardair , although due to cross-loading on high, sheltered areas some activity also noted on SE aspects. Mid-week strong, mostly SE winds and regular snow showers maintained areas of poorly stabilised slab above 850/900m,a cooler period delivered snow to all levels mid-week. Strong mostly SE/SW winds throughout. Highs
Fresh snowfall followed by some high avalanche activity at the start of the period with several events in Inner coire Ardair NE through E aspects. Further snowfall through the period maintained areas of poorly stabilised slab which became more widespread in variable winds. A feature throughout has been the high level nature of the instabilities and whilst some run out zones affected terrain down to 700m the hazard remained for the most part high on slopes above 900m.
Snow showers above 800m throughout accompanied by mostly SE winds. Good cover in high plateau areas with pockets of harder windslab around coire rims with new cornice development. Snowpack fairly well consolidated at lower elevations. Snow lie towards end of week with fresh showers and new soft slab NW aspects. Cooler FL around 500m
A showery and predominately SW airflow over the period. Very little snow lying below 800m but above this regular showers have added to areas of windslab mainly lying at very highest elevations above 900m on N through to E aspects. FL levels seldom rising above summits or lowering below 400m. Greatest additions of new snow towards end of period with heavy snow showers on tops - but still only bringing a dusting below 800m. Thaw to summit with rain forecast to end week.
Sequence of snow showers throughout with drifting, then colder temperatures. Significant windslab build up followed by milder temperatures and consolidation. Cool temperatures followed with little snowfall continuing the stabilising trend within the snowpack. Snowpack is currently moist and well stabilised in all locations. Large old cornices above some very steep locations.
Periods of snowfall with windslab development, followed by melt/freeze conditions saw snow avalanche activity before and after thaw. Some of the avalanches cornice triggered. One or two small full depth avalanches during thaw on very steep ground. Snowpack currently moist with a surface crust at higher altitudes and humid windslab confined to locations above 1050m on N to E aspects.
Fluctuating temperatures helping to consolidate existing snowpack. Strong South westerly's throughout bringing snow showers to highest elevations only, with any new snow weaknesses and windlslab accumulations confined primarily to NW to E facing gully tops and exits above 850m and around coire rims. Localised Considerable for much of period.
Strong SW throughout with some frequent snowfalls (some very heavy) Temperatures fluctiating althoufh remaing below summit levels. Weakness in windslab accumulations persisting at highest elevations. Deep drifts at lower levels with breakable crust towards end of week below 750m. Little activity in coires - good cover above 750m. Ice forming in usual watercourses. Some cornices beginning to build above Easterly aspects with avalanche activity mostly cornice / some soft slab triggered on E aspect
Patchy snowpack to start then a stormy week with periods of snowfall and drifting particularly near end of period. New snow instability in thinner windslab noted but this improved with milder temps. Deeper windslab later with notable new snow instability due to rapid build up.
Sparse and patchy snowpack with larger patches only above 850m. Some South to South East facing coire rims hold a little more old snow. Thawing at all levels.