Danger Pattern 4 (cold on warm) possibly important at high altitudes. Complex situation regionally.

 In a nutshell...

Rounding out the recent Blog, we want to draw your attention to the potential development of a weak layer due to cold on warm (dp.4).  All signs currently point to a layer at very high altitudes on sunny slopes (bordering on a layer which last week was the moist-to-wet snowpack surface, then got blanketed by fresh snow) having become a weak layer. That weak layer could cause accidents during the coming days!

Cold on warm (dp.4)

There are currently only a few instances which corroborate this assumption. Nevertheless, they are sufficient to focus our attention on the process by which potential weak layers are formed and inform our readers about that development.

Where do we foresee dp.4?

Cold on warm can be significant wherever the wet snowpack surface was blanketed by thick snow masses (the “slab”) last Friday (24.03.2023). This includes the North Tirol and northern East Tirol regions which recently had major snowfall (see recent Blog). At the moment that means at very high altitudes, at least above 2500m, but applies also to very steep sunny slopes in high alpine regions (above 3000m).

Red line symbolizes potential start of dp.4. At that moment, snowpack was moist-to-wet even at very high altitudes. Arrows in magenta symbolize snowfall since last week. Blue arrow symbolizes temperature drop. All in all, strong indicators for dp.4 (cold on warm) being generated.

Visible at red arrow: the snowpack at Speicherteich measurement station at 2900m (in flat terrain) was at very least moist. Snowpack surface temperature (black line) was 0°, thawing point (blue line) was 0°.

A complex situation regionally

The situation is complex because an expansively metamorphosed weak layer currently developing in some places covers another weak layer which is located somewhat below it. That other weak layer (it lies beneath a thin melt-freeze crust) takes the form of faceted crystals and was generated during the long period with almost no precipitation between the beginning of February and the beginning of March. It occurred increasingly on steep NE/E/SE-facing slopes at about 2500m and upwards

 Faceted weak layer beneath a melt-freeze crust (09.03.2023 profile), blanketed by more fresh snow in the interim. It’s quite possible that dp.4 has since developed at this location or is in the process of doing so....

The faceted layer depicted in upper graph formed during the specified period of very little precipitation.

Be aware of heightened risk at altitudes and aspects we referred to. 

 

We are grateful for all reports from backcountry terrain!

Due to a lack of reports and a dearth of comprehensive snowpack analysis, we are currently highly grateful for all clear professional reports! A quick glance inside the snowpack including a rapid stability test gives us valuable information which we will pass on to all winter sports enthusiasts, lawine@tirol.gv.at

April weather – Snowdrift problem at high altitude – Wet snow at intermediate altitude

 In a nutshell...

Today (Thursday, 30.03.2023) the recently fallen snow was moistened up to high altitudes by the warm April weather. Thereby, a pronounced “slab” was formed. An avalanche is likely to trigger wherever there are weak layers inside the snowpack. Most of the slab-avalanche prone locations currently occur on very steep NE/E facing slopes above 2600m; more often on SE-facing slopes in high alpine regions (above 3000m). General caution is also urged in very steep terrain in all aspects at very high altitudes behind abrupt drops in the terrain: that is where fresh snowdrift accumulations are easy to trigger. 

April weather

Today, 30.03, there was rainfall up to 2300m in North Tirol and northern East Tirol. Thunderstorms were also registered. And the sun returned repeatedly. You guessed it: a genuine April day, when the snowpack was hit by lots of warmth. The recently fallen snow was moistened at least superficially up to very high altitudes.

During last week, only tiny windows of good weather. Today, 30.03, very warm again. Snowpack superficially moist up to very high altitudes. Now the temperature is dropping again.

A day with lots of diffuse radiation furthers warmth inside the snowpack.

Geosphere Austria warned of thunderstorms today, 30.03. They arrived as forecast, often containing graupel at very high altitudes.

The pinnacle of air temperatures has been reached for the moment. Now temperatures are going to drop steadily. The wet-snow problem will recede.

Recent avalanches

Today, 30.03, several avalanches were reported. In some places the fresh fallen snow triggered in the form of numerous wet loose-snow avalanches. Sometimes they were only small slides. In ridgeline terrain at very high altitudes, slab avalanches were reported.

The slab avalanche on Hinteren Wilden Turm in the Alpeiner moungains triggered at over 3000m, possibly through the impuls of a cornice breaking, perhaps even naturally. (photo 30.03.2023)

Ridgeline slab avalanche near the Ruderhofspitze in central Stubai Alps (photo: 30.03.2023)

Numerous loose-snow avalanches in Gurgler Massif (photo: 30.03.2023)

Knobs forming in the Weisskugel Massif (photo: 30.03.2023)

And again: poor snow quality

In many places the snowpack surface forms a breakable crust due to dropping temperatures. As we all know, melt-freeze crusts reduce the pleasures of skiing. (Two days ago, on 28.03, winter sports enthusiasts who took advantage of the right moment and headed into backcountry very early in the day were rewarded with fantastic powder.) That, too, is part and parcel of springtime: tiny changes effect swift changes in snow quality, as well as in avalanche danger.


What’s on the horizon?

The wet snow problem will recede with each passing day that the temperatures descend. Nevertheless, diffuse radiation will still have a short impact on the wetness of the snowpack, weakening it. Remember that near-surface avalanches can sweep away deeply embedded wet layers particularly at intermediate altitudes. Outside of that, not much change is expected. Be aware that in the regions where recent snowfall was heaviest at high altitudes there is currently higher risk on NE/E/SE-facing slopes. Be on the lookout for freshly generated snowdrift accumulations. And don’t forget to heed the shallow covering of glacier crevices for this juncture of the season. We are entering the phase of highly variable April weather.

Repeated bouts of precipitation, rather windy amid falling temperatures

Details about recent avalanches

 In a nutshell...

Yesterday (28.03) several winter sports enthusiasts were awfully lucky. Shady slopes above about 2300m are currently the most dangerous. In those regions with lots of fresh snow, please exercise immense restraint.


Background of the avalanches

We report on two avalanches: one on Gampberg in the western Verwall Massif, one on Nörderberg in the Glockturm Massif. These were slab avalanches.


Avalanche Gampberg

The slab avalanche triggered on a north-facing slope at 1950m. What was essential for this release was the previous thoroughly wet state of the snowpack, reinforced by rainfall on 24.-25.03. According to reports on-site, it rained quite intensively up to the fracture zone of the avalanche in the early period of precipitation, so the snowpack was utterly wet on 24.03. Thereafter, temperatures descended. Snowfall set in. All in all, 40 cm of fresh snow was registered. We assume that on top of the wet old snowpack a melt-freeze crust had formed. On top of that, wind-impacted fresh snow was deposited. The “slab” consisted of fresh fallen snow and that thin crust. The weak layer was the thoroughly wet old snowpack. The avalanche was remotely triggered by winter sports enthusiasts just above the fracture, in the estimate of latest knowledge. No one was injured.  

Avalanche Gampberg on 28.03.2023

Avalanche Nörderberg

Winter sports enthusiasts were ascending on foot towards Nörderberg in Kaunertal. At an altitude of about 2400m one winter sports enthusiast skied into a very steep NE-facing slope, where a slab avalanche was triggered. Fresh fallen snow was the primary problem. Subsequently the snowpack fractured down to more deeply embedded layers and swept away the entire thoroughly wet snowpack down to the ground. The winter sports enthusiast was swept along by the slab avalanche and was able to activate his airbag. He came to a stop on a step in the terrain atop the surface, uninjured.

Avalanche Nörderberg. Arrow points to entry track. Circle in the upper flat space: landing point after avalanche triggered. (photo: 28.03.2023)

Entry track, avalanche Nörderberg. Initially, a snowdrift accumulation triggered. (photo: 28.03.2023)

Similar observations reached us from the vicinity of Lech. On shady slopes around 2000m, several slab avalanches triggered. We assume the same conditions prevailed that applied to the Gampberg avalanche. 

Avalanches near Lech (photo: 28.03.2023)

Accident prone avalanche situation in major areas of precipitation for a brief spell

 In a nutshell...

Lots of fresh snow regionally, strong-to-storm strength winds, low temperatures and anticipated solar radiation are all adding up to an accident-prone avalanche situation. Winter sports enthusiasts can easily trigger slab avalanches in steep terrain in the areas of major precipitation. Tomorrow (28.03 which is expected will weaken the snowpack further, despite low temperatures. We expect increasingly frequent naturally triggered avalanches particularly on sunny slopes, slab avalanches are possible, loose-snow avalanches are expected, glide-snow avalanches are possible on steep grass-covered slopes. You have to be aware that in the areas of great snowfall in open terrain, there is heightened risk.


Since Friday 24.03 there has been heavy snowfall from place to place. Storm-strength winds transported the snow.

Between Friday 24.03 and Saturday 25.03 as well as on Sunday 26.03 to Monday 27.03 there was snowfall registered in far-reaching parts of Tirol. Whereas in the first bout there was mostly 10-20 cm registered, in northern East Tirol as much as 40 cm, the second round of precipitation brought to the western and northern regions, and also along the Main Alpine Ridge at high altitudes in particular, as much as 40-60 cm of fresh snow. The snowfall was accompanied by storm-strength winds. In addition temperatures dropped noticeably.

72-hr precipitation in Tirol: focus 27.03, 6 o’clock pm

At Pitztaler Glacier weather station, visible are the two bouts of precipitation from 25.03 and 27.03. Overall snow depths rose about 50cm. Temperatures dropped significantly. Winds were blowing at strong velocity, most recently from northerly directions.

Tomorrow (28.03) an interlude in precipitation is expected. Winds will taper off. The sun will come out.

Trigger-sensitive snowpack

Reports from our observers confirm that the snowpack is currently quite prone to triggering. Weak layer for freshly generated snowdrift accumulations: the cold powder snow, flaky forms or also graupel. Graupel was deposited in some places. The solar radiation which is anticipated tomorrow (28.03) will reinforce the bonding of snowdrift accumulations. A pronounced slab atop a weak layer (which is briefly prone to triggering) is unfortunately a good combination for slab avalanches triggering in steep terrain.

Graupel was able to form repeatedly during the most recent periods of precipitation. Wherever this was deposited, a weak layer can form.

The fresh fallen snow lies deposited atop a more or less pronounced melt-freeze crust which formed after the drop in temperatures on Saturday, 25.03. Beneath that there is a wet, at very least moist old snowpack on sunny slopes up to at least 2800 m. On shady slopes this is the case up to about 2400m. The wet old snowpack formed a weak layer for the slab in the course of several avalanche releases, consisting of melt-freeze crust and fresh fallen snow. (In the interim, this weak layer is no longer likely to trigger.) BUT: in the case of avalanche releases in the fresh snow, the moist-to-wet old snowpack can also be swept away due to the additional loading of the triggered snow. Avalanches can thereby grow to larger size.

Danger Level “Cold-on-warm”

At the present moment we are faced with the prerequisites of Danger Level “cold on warm”: a wet old snowpack has been blanketed by cold snow. As to how much the already generated thin melt-freeze crust will generate faceted crystals as a later weak layer, is still an unanswered question. We concentrate on this process and are, naturally, grateful for any and all reports (at best via mail to lawine@tirol.gv.at).

What’s next?

Variable, April-like conditions. Since minimal changes in the weather can unleash maximal changes in avalanche danger, the best thing to do is consult the information in the current Avalanche Bulletin.

Mostly unfavorable conditions – Wet-snow avalanches expected – Wintery again starting Monday

In a nutshell...

Last week was marked by the snowpack becoming increasingly wet up to high altitudes. Numerous avalanches triggered, mostly wet loose-snow and glide-snow avalanches. As a result of highly variable weather conditions the avalanche situation in the morning hours is often very unfavourable up to high altitudes for winter sports enthusiasts. Avalanche danger below 2800m is currently considerable (Danger Level 3).

Wet, wetter, wettest

We are in the middle of a classic wet-snow cycle. Snowpack thickness is below-average for this juncture of the season, and all the way up to heightened altitudes it is now wet down to ground level: on west-facing and east-facing slopes as far up as 2800m, on south-facing slopes higher still, on north-facing slopes it fluctuates between 2200m and 2400m.

What interests us most in current snow profiles is the red line: temperature profile. At this location at 2227m on a 22° NE slope the snowpack on 19.03 was already isotherm (snow temperature = 0°).

Temperature profile on north-facing slope at 2500m. There were still reserves of cold on 19.03.2023.

Last week’s typical weather progress: variable. From 19.03 to 20.03 a bit of precipitation (at this station in the form of snowfall). Then at very latest as the thawing point reached 0° there was a massive penetration of moisture into the snowpack. That is the current situation at this location...

Precipitation will set in during the course of the day today, 24.03. Initially as rainfall below 2400m, which means that most shady slopes below 2400m will be thoroughly wet down to the ground. Caution: in rain-impacted regions, naturally triggered avalanche releases can be expected particularly on very steep north-facing slopes. The rainfall level will actually be even higher up for a brief time. According to GSA (Geosphere Austria) the snowfall level will drop to about 1700m swiftly. About 10-15 mm of precipitation is expected, somewhat more along the Main Alpine Ridge.

Fresh snow forecast for tomorrow, 25.03.2023 (forecast made today, 24.03)

 

Cold air masses penetrating from the northwest (which will cause the snowfall level to descend) are visible on this map.

Avalanche activity last week

Avalanche activity increased steadily over the course of last week, as anticipated. As we know, tiny changes in weather lead to enormous changes in avalanche danger. For example, residual clouds / diffuse solar radiation plus warm temperatures can lead to the snowpack rapidly becoming throughly wet over small areas. In short: it was “shower-room weather” where lots of energy got pumped into the snowpack, weakening it greatly.

Limited avalanche activity on 18.03. Typical: wet loose-snow avalanches on extremely steep slopes. Serleskamm

   

“Shower-room weather” furthered the snowpack becoming thoroughly wet. Visible in the photo are several naturally triggered loose-snow avalanches. Alpeiner Berge (photo: 20.03.2023)

Wet loose-snow avalanches in the Silvretta around midday on 19.03.2023  (photo: 20.03.2023)

Similar situation in Kühtai: naturally triggered and artificially triggered loose-snow avalanches.
(photo: 22.03.2023)

Avalanches could intentially be triggered even by one tiny impulse. The snowpack here was thoroughly wet and loose. (photo: 22.03.2023)

Mieming Massif. Avalanche wedge from previously unleashed wet loose-snow avalanches.
(photo: 23.03.2024)

Unique factor of current situation: heavily tracked terrain can be more dangerous

As mentioned above, lots of wet loose-snow avalanches triggered, also attributable to the shallow snowpack. Water quickly made the surface wet, usually consisting of thin, hard layers. The “slab” which is one of the prerequisites for slab avalanches was thereby destroyed. In open terrain which was heavily tracked during the winter (and where ground-level weak layers from early winter persisted) this “slab” is more pronounced and more massive. Thus, when it becomes thoroughly wet, slab avalanches are likelier to trigger. A paradox, that heavily tracked terrain is currently more dangerous than little-tracked terrain.

Dry-snow slab avalanches still possible at very high altitudes

Apart from wet-snow avalanches, there is still potential for dry-snow slab avalanches on very steep east-facing and west-facing slopes above 2800m. In particular, slab avalanches triggering from near-surface layers by large additional loading. The weak layer is usually of faceted crystals beneath a thin melt-freeze crust (formed during a long phase of fine weather in February and early March). On shady slopes above 2500m there are isolated zones where nests of depth hoar can trigger avalanches, particularly in transitions from shallow to deep snow on extremely steep slopes. Surface hoar which got blanketed by fresher snow at the beginning of this month is no longer likely to trigger.

On the horizon...

Following today’s (24.03)  precipitation mentioned above, tomorrow will bring us April weather: diffuse solar radiation in a powerful westerly air current. The fresh fallen snow will trigger frequent small loose-snow avalanches in extremely steep terrain. What is important everywhere: the ongoing wetness of the snowpack amplified by diffuse radiation. Particular caution is urged on shady slopes at 2200 to 2400m, even higher from place to place.  In short: conditions remain unfavorable, both in terms of avalanche danger and in terms of snow quality.

Starting on Sunday, 26.03, things will turn wintery again. During Sunday morning, snowfall up to 1600m is expected in some regions. On Sunday night (wee hours of 27.03) we can expect storm winds at high altitudes and some snowfall down to low lying areas, according to GSA Weather Service. What follows then can only be assessed after the coming perturbance has left its mark.

Recent avalanches mostly in NE/E/SE aspects above 2500m (persistent weak layer) – Heed daytime danger cycle

 Summing it up

Several avalanches have been triggered by winter sports enthusiasts during the last few days, increasingly on very steep slopes above 2500m in NE/E/SE aspects. The heightened proneness to triggering of weak layers inside the snowpack was the result of pronounced slabs (see last blog) which formed recently. Most avalanches releases were caused by a persistent weak layer (long-enduring, hard-to-recognize weak layer inside the snowpack). In one avalanche accident near the Scheid in the Samnaun Massif, a winter sports enthusiast died today in backcountry terrain. In other avalanches in recent days, persons were also injured.

As always in springtime, small shifts in weather can have huge and swift effects in avalanche danger. Major factors, apart from air temperature and (diffuse) solar radiation, include in particular air moisture. And of eternal importance: whether nocturnal outgoing radiation is impeded by clouds. Therefore, pay close attention in open terrain to the degree of wetness of the snowpack. This leads to loss of firmness and a rapid increase in avalanche danger.

Fatal avalanche accident in Samnaun Massif

Today (17.03.2023) a winter sports enthusiast lost her life in open skiing terrain in the vicinity of the upper Scheid Lift (ski area Serfaus, Fiss, Ladis) in an avalanche. The slab avalanche triggered when she descended in backcountry ski terrain down an extremely steep NE-facing slope. The fracture occurred at 2550m. She was caught by the avalanche and completely buried in snow masses. She had no beamer. Following an extensive search including avalanche dogs, she was finally found lifeless. The problem which caused the avalanche was a persistent weak layer. Tomorrow (18.03.2023) we will carry out a thorough and detailed snowpack/avalanche analysis together with the Alpine Police (snow profiles will be published on Lawis).

Avalanche accident Scheid, 17.03.2023. Arrow points to the entry track, circle is where she was buried. (photo: 17.03.2023)

 Ellipse shows area of avalanche. It is extremely steep terrain. Violet: lifts of the ski area Serfaus, Fiss, Ladis

Entry zone including a part of avalanche fracture (photo: 17.03.2023)

Other reported avalanches of this week

During this week, a number of avalanches were reported to headquarters Tirol. What stands out (please note this in planning tours) is that most occurred on NE/E/SE-facing slopes above 2500 m. Here is the list:

09.03.2023: Pflerscher Pinggl, central Stubai Alps: no one buried

11.03.2023: Hoher Seeblaskogel, Sellrain, Alpeiner B.: no one buried

12.03.2023: Litnisschrofen, Allgäu Alps: no one buried

12.03.2023: Galtenberg, western Kitzbühel Alps: no one buried 

12.03.2023: Breite Scharte, Sellrain, Alpeiner Berge: NO, 2500m (persistent weak layer), 1 person totally buried, injured

12.03.2023: Hoher Burgstall, Sellrain, Alpeiner Berge: NO, 2500m (persistent weak layer), 1 person swept along, not buried

13.03.2023: Murkarspitze, Sellrain, Alpeiner Berge: no one buried 

13.03.2023: Hintere Neder, northern Zillertal Alps: no one buried

13.03.2023: Walfeskar, Sellrain, Alpeiner Berge: SO, 2750m (persistent weak layer), 1 person partly buried, injured

13.03.2023: Zwölferkopf, Samnaun Massif; NW, 2500m: no one buried 

15.03.2023: Alblittköpfe, eastern Verwall Massif: NO 2500m (persistent weak layer), 1 person buried, injured

15.03.2023: Eisgrat, central Stubai Alps: SO, 2860m (snowdrift problem), no one buried

15.03.2023: Hinteres Rendl, western Verwall Massif: no one buried

15.03.2023: Mitterkarspitze, western Verwall Massif: no one buried 

15.03.2023: Grawa, central Stubai Alps: no one buried

16.03.2023: Riefenkopf, Samnaun Massif: NO, 2600m, (persistent weak layer) 2 persons, no injuries

16.03.2023: Rostocker Eck, Venediger Massif: no one buried

16.03.2023: Weißseejoch, Glockturm Massif: N, 2500m, no one buried

17.03.2023: Scheid, Samnaun Massif: NO, 2550m (persistent weak layer), 1 person dies

17.03.2023: Riffljoch, Glockturm Massif: no one buried

17.03.2023: Tiefenbachferner, Weisskugel Massif: SO, 3000m (snowdrift problem), no one buried

17.03.2023: Gaiskogel, Kühtai-Geigenkamm: NW, 2580m, no one buried

Here are some photos of selected avalanches:

Avalanche release on Breite Scharte with point of burial marked. A 5-person group was in their ascent. One person was totally buried, could be found with beamer and dug out of 1.5 metres of snow. The person was unconscious, but started to breathe after the rescue. (Avalanche fracture could not be completely explained due to snowfall and wind immediately following the release.) (photo: 15.03.2023)

Avalanche Walfeskar (near the Breite Scharte avalanche). A group of six was in their descent from Zwieselbacher Rosskogel over the Walfeskar towards Pforzheimer Hütte. One person was caught in the avalanche, swept along and injured. (photo: 15.03.2023)

Avalanche Alblittköpfe with entry track and point of burial marked. The buried and injured person was part of a group known as “Dutch Freeride Championship.” They traced several different paths in backcountry at the Kappl ski area. (photo: 15.03.2023)

In the vicinity of Tiefenbach Glacier: recently generated snowdrift accumulations which triggered when a winter sports enthusiast descended. The snowpack surface at 3000m on a SE-facing slope was already moist. (photo: 17.03.2023)

Several slab avalanches triggered naturally last week, particularly in the western part of North Tirol.
Western Verwall Massif (photo: 15.03.2023)  

Repeated bouts of precipitation and fluctuating temperatures enhanced snowpack’s proneness to triggering

Springtime comes knocking - Heed daytime-induced cycle of avalanche danger

To round out our last blog we would like to devote some attention to the anticipated further development of conditions. Tomorrow (Saturday, 18.03) will be a complex weather situation. Air temperature will recede somewhat from today’s (17.03) levels and the air will become more moist. Dust blown up from the Sahara Desert will fill the skies. On steep west-facing slopes it may still occur in the afternoon that water seeps down to deeper layers. Expansively metamorphosed (faceted, often encrusted) weak layers could be weakened still further and the snowpack could become prone to triggering.

Our “Snowpack” model shows that water on a simulated 38° gradient west-facing slope at Falkaunsalpe Station in Kaunertal will seep down to ground-level layers tomorrow (18.03).

At the higher Sonnbergalm Station in the Gurgler Massif, water seepage down to the ground will take somewhat longer, on a simulated 38° gradient slope.

 

Through the impulse of a naturally triggered wet loose-snow avalanche, a slab avalanche was triggered today (17.03) at 11:30 am. East-facing slope, 2750m. Steintalspitze, Kühtai

On Sunday, all signs point to a brief pause in spring, according to current weather forecasts. A minor perturbance will make the zero-degree level descend to 2000m. The sun will presumably be shaded. Next week, mild weather will return and continue.

Temperature development in coming days. Today (17.03) was the warmest.

Spring weather has massive impact on the snowpack and on avalanche danger. A good avalanche forecast is especially challenging for that reason. To master that art, you need to be on-site. (photo: 15.03.2023)

A week full of fluctuations, wildly varied leaps of temperature, repeated bouts of precipitation (snow and rain) including lots of wind in places, is coming to an end.

Don’t forget: last week also offered winter sports enthusiasts some good powder. 

Powder widespread in Tirol, which will become rarer day by day due to diffuse radiation. 
(photo: 15.03.2023, (c) Lukas Ruetz)

 

The upshot

Pay close attention to the moistness of the snowpack. Focus on the devilishly tricky persistent weak layer problem. It starts at 2200m on shady slopes, above 2400m on east-facing and west-facing slopes, especially where snowfall has been heaviest. Caution urged on little-tracked very steep terrain.

Snowpack analysis, the foundation of our work. (photo: 15.03.2023, (c) Lukas Ruetz)