Slight daytime avalanche danger cycle

No sign of April weather

‘Comes in like a lion...’ No sign of that this April. Thus far it is revealing only its very best side: unseasonably warm and dry. The period of extreme dryness will persist, briefly interrupted next week by a weak cold front. Subsequently, high-pressure weather conditions will return, according to current forecasts of ZAMG Weather Service.

Spring makes its entry. Innsbruck (photo: 05.04.2020)

Fine weather, snow depths gradually receding (sublimating more than melting). This stems from the dry air masses around 5 April. Thereafter moisture in the atmosphere has been on the rise. Daytime variations in temperature of the snowpack surface are also flatter, i.e. nocturnal outgoing longwave radiation and re-firming of the snowpack have lessened.

The snowpack: predominantly stable

During clear, star-studded nights, a melt-freeeze crust formed on sunny slopes, capable of bearing loads, which frequently softened up only superficially during the morning depending on altitude. On shady slopes at high altitudes, the snow often remained powdery despite higher temperatures. Where there was wind influence, a corn snow mirror formed on sunny slopes: a shining, thin crusty veil stretched over the surface.

Corn snow mirror on Rosskogel, Stubai Alps (photo: 05.04.2020)

Hardly any avalanches observed

Avalanche activity was very limited. In isolated cases, small slides of gliding snow were observed; on 8 and 9 April on shady slopes between 2500 and 2800 m, small loose-snow avalanche releases, stemming primarily from heightened air moisture, secondarily from higher temperatures. The loosely-packed snow became superficially moist and was weakened somewhat. Thus, avalanche danger was ‘low’ all week, with only minor daytime increases to ‘moderate.’

View of Northern Massif near Innsbruck. A ‘sleepy’ snowpack with isolated glide cracks and small slides in rocky terrain (photo: 05.04.2020)

For comparison, a photo from 9 April. Despite moister air masses (around 3000 m) no new avalanches were observed.

Small loose-snow avalanches on shady slope in Griesskogel Group (photo;: 09.04.2020)

No major change on the horizon

As regards avalanche danger outlook, a continuous moistening of the snowpack on shady slopes seems to be the most important factor, particularly above 2500 m. Due to current weather forecasts, this is not expected in the immediate future.

Otherwise worthy of note

Dryness of the air leads not only to decelerated melting at high altitudes, but also to heightened danger of forest fires.

Swift intervention by the fire department was able to prevent the worst in Halltal. (photo: 08.04.2020 taken in Mils)

A glance at streams and brooks awakes the impression that there isn’t much water flowing. But measurement data shows that water levels are average, typical for this juncture of the season.

Inn River flow at Innsbruck

Water level of the Inn (photo: 09.04.2020)

HAPPY EASTER!

Corona crisis appeal

Due to the current corona crisis, we appeal to the public: no skiing or mountaineering tours, please. Every accident unnecessarily ties up rescue services and health system.

All information and edicts can be seen here:

Information from the State of Tirol on corona crisis

In addition, we permit ourselves to point out that both the Avalanche Bulletin and the Blog of the State of Tirol will continue to be published regularly.

After cold days, spring is on the way

Review: some snowfall in the mountains, cold, half-week of sunshine

Our weather in the last week has been in the grips of a cold NE air current, bringing snowfall in the mountains, frost in the valleys. The ZAMG Weather Service even registered in the eastern regions a new low-temperature record for 1 April.

One interesting aspect was distribution of precipitation. Focal point: southern East Tirol, but also in the northeastern corner of the northern Stubai Alps.

24-hour precipitation in Tirol on 29-30.3.2020 

Corresponding distribution of fresh snow

Precipitation from 29.3 to 31.3, most in the south, seen here at Thurntaler weather station near Sillian. Precipitation in the mountains fell as fluffy powder snow. As the weekend approached, temperataures were below average, but rising.

Wintery scene near Lienz (photo: 30.03.2020)

Despite low temperatures, weather was mostly sunny and dry. But feelings of springtime didn’t awaken until 2 April when temperatures started to rise.

Loose-snow avalanches, isolated slab avalanches on shady slopes

The fresh fallen snow was generally quite fluffy. Due to intensive solar radiation typical at this point of the season, loose-snow avalanches are the expected consequence in extremely steep terrain.

Deposit of a loose-snow avalanche in Defereggental. The photo was taken by a drone. (photo: 31.03.2020)

Apart from loose-snow avalanches there were also isolated slab avalanches on shady slopes above 2000 m. Probable cause: a thin, expansively metamorphosed (faceted) layer deposited atop a melt-freeze crust, then blanketed by the latest round of fresh snow. Wherever wind had an impact, the necessary “slab” was able to form. For a brief spell, the fluffy powder had high potential to generate slab avalanches, as always when it is blanketed by fresher snowfall.

A naturally triggered slab avalanche photographed from the valley. Schustertal, southern East Tirol. (photo: 31.03.2020)

The large snow deposit at center stems from a slab, the small deposits from loose-snow avalanches. Northern Stubai Alps. (photo: 01.04.2020)

Below-average snow depths

Following a period of very little precipitation, the overall snow depths have receded further: below average overall depths at high altitudes; at low and intermediate altitudes, if there is any snow on the ground at all, far below average snow depths.

Depiction of snow depths from our observation station in Kühtai. Magenta: current values. Heavy gray line: average values. Upper and lower limits show maximum and minimum values. At the present moment: below-average snow depths.

Snow depths far below-average at observation station in Boden, Lechtal

Outlook: increasingly springlike conditions, with daytime danger cycle

As often mentioned, nocturnal outgoing longwave radiation in springtime is an important factor in snowpack stability for the morning hours of the following day. Webcam photos supply highly important information.

Star-studded skies over Kals am Grossglockner. The snowpack softened during the previous day,  will have sufficient outgoing radiation during the night. The surface will become encrusted, often capable of bearing loads.

In northern regions, more clouds. Nighttime outgoing longwave radiation is thereby reduced.

According to ZAMG Weather Service forecasts, the coming days will be increasingly springlike with rising temperatures.

Avalanche danger levels will be subject to a (slight) daytime danger cycle. Danger will frequently be low or moderate. Avalanches will be registered seldom to start with. Isolated moist/wet loose-snow and glide-snow avalanches are possible. On shady slopes, naturally triggered avalanches are no longer likely. Artificial triggerings will be relevant only in very few cases, i.e. due to breaking cornices or rockfall.

Resist the temptation

A fitting complement to the current situation: Article in ORF-Tirol:  

Favourable avalanche situation continues

A favourable avalanche situation widespread

The danger-level map of the EUREGIO Avalanche Bulletin for Friday 27.03 shows generally low avalanche danger. The situation was similar to that of last week, and it will remain that way over coming days according to weather forecasts of ZAMG Weather Service. As a result of some fresh snow starting in the evening of Saturday 28.03, fresh small snowdrifts at high altitudes and isolated glide-snow avalanches will be the major dangers.

Bildunterschrift hinzufügen

Review of the last week

The information we have received from outlying terrain continues to be quite limited due to the edict of the governor of Tirol (Verordnung des Landeshauptmannes vom 20. März 2020 nach § 2 Z 2 des COVID-19-Maßnahmengesetzes ). Our evaluation of the situation is based primarily on knowledge we gained of snowpack layering before the curfew came into effect; on data coming in from our weather stations; on reports from various valleys; on simulations generated by avalanche models; and from our own empirical analysis linked to current weather conditions.

Cold and windy, very little precipitation

This verbal snapshot was last week’s weather in a nutshell. Before temperatures started to rise steadily starting on Saturday 21.03, some of Tirol’s first (and fairly impressive) thunderstorms of the year could be witnessed on the evening of 20 March.

Convective cloud build-up especially in northern regions led to frequently violent thunderstorms with short bouts of torrential downpour accompanied by thunder and lightning.

At the time, on 20-21 March, huge amounts of precipitation were registered. Subsequently (on Sunday 22.03 and in the furthermost southern regions on 26.03) there was very little precipitation.

The fluctuations visible in the upper graph show last week’s precipitation. The lower graph shows air temperatures and thawing points. The disparity between air temperature (red) and thawing point (blue) is an indicator of cloud cover vs. sunshine. (If both curves run parallel, there is cloud; if not, the sun is shining.)

Eselrücken weather station just north of the Prägraten station portrayed above. Increase in snow at high altitude is visible. Also highly indicative: strength of winds; and the dryness of the air which on 23.03 moved over the land.

The situation in North Tirol closely resembles that of East Tirol. Highly unusual: the thawing point lies at -60°C - in indicator of extremely dry air.

Up to 10 cm of fresh snow in East Tirol on 26.03. seen in the example above at Lucknerhaus.

Extremely dry air masses in some places

The dry air referred to is a major factor during the run-up to spring as regards danger assessment. The snowpack on 23.03 remained firm all day long, despite intensive solar radiation, and developed corn snow if at all, then only slightly on extremely steep south-facing slopes. The snow didn’t melt, but rather sublimated, that is, slipped into a transitional phase from solid to gaseous form. During this situation the snowpack has immense amounts of energy drawn from it, which in turn slows down or halts the melting process. Add the low temperatures to that, and the melting process was brought more or less to a standstill.

During cold days and star-studded nights, water froze and often didn’t thaw during the daytime. Ötztal. (photo: 25.03.2020)

“Penitent snow”
Aside from the positive effect which the dry air had by slowing down the wetness of the snowpack, there was also another interesting phenomenon which could be observed. Through the sublimation process, an unusual snow formation is generated with points rising from the surface, fondly known as “penitent snow” in folk culture. This form is frequently found over widespread areas in the Andes in South America.

Penitent snow in St. Sigmund in Sellraintal (photo: 24.03.2020)

Close-up of the penitent snow (photo: 24.03.2020)

Small snowdrifts at high altitudes

There were very few avalanche prone locations in the mountains last week. At high altitudes and in high alpine regions some snowdrifts were generated which, in the context of the overall situation, had no significance.

An aerial view reveals the snowdrifts generated in the respective aspects. View from Adlersruhe towards Grossglockner. (photo: 22.03.2020)

Isolated glide-snow avalanches

Of note is a minor, highly isolated danger from potential glide-snow avalanches.

Glide-snow avalanche in the Gurgl Group. At upper left, a glide crack and the upturned snowpack are visible, i.e. a further glide-snow avalanche announcing itself. (photo: 22.03.2020) 

Outlook

As outlined above, conditions will be similar to last week’s. Potential minor problem zones stem from fresh snowdrifts at high altitudes and isolated glide-snow avalanches. In isolated cases the latter could be important to highly exposed sectors of roads.

The blog will continue to be published regularly

...so that residents can better evaluate potential dangers to infrastructure and settlements. Please undertake no mountain or skiing tours! (FAQ Quarantäneverordnung) Every accident unnecessarily robs the time and energy of rescue services and health system.

Springtime conditions go on...for a bit

Last week was marked by classic springtime conditions, including a slight daytime avalanche danger cycle. In the morning mostly low, in the afternoons mostly moderate danger.

Brief cloudy phases only on 13.03 and 14.03, regionally on 18.03 during the night. Otherwise brilliant sunshine and very dry air masses. Also highly indicative: daily cycle of snowpack surface temperatures.

Conditions improve on Friday afternoon, 13.03. Northern Stubai Alps

Star-studded nighttime skies and dry air stabilize the snowpack which softened superficially the day before

 Avalanche activity is limited. The main danger stems from isolated glide-snow avalanches on steep grass-covered slopes.

Glide-snow avalanches caught by foto-webcam.eu

Glide-snow avalanche and glide cracks in northern Stubai Alps (photo: 15.03.2020)

Caution: cornices continue to break...

...such as here in Boden, Ausserfern (photo: 18.03.2020)

Decisive: continuing moistness/wetness of the snowpack

The assessment of avalanche dangers is currently based on only a few snow profiles. What matters most: snow temperature.

Isotherm snowpack, SE aspect at 2020 m, 26°, on 14.03.2020, northern Stubai Alps

Temperature reserves, NE aspect at 2540 m, 36°, Gurgl Group on 15.03.2020 

Also currently indicative: frequent sequences of melt-freeze crusts on sunny slopes. Inside the snowpack, frozen meltwater canals are often evident.

Parallel to this, a simulation program called SNOWPACK also provides deeper understanding. With it we can better evaluate the extent of snowpack moistness/wetness and loss of snowpack firmness.

This graph shows the simulated water seepage into a fictitious 38° south-facing slopes near the Nachtweide weather station in the Ischgl ski area during the current season. Through a combination of parameters provided by the weather station and the SNOWPACK simulator, it is possible to calculate how much water seeps how deep into the snowpack. Initial wetness is often dependent on heightened wet-snow and glide-snow avalanches. However, below 2200 m and on sunny slopes below 2800 m, the snowpack has been subjected to rainfall and warmth rather frequently this season, thus, the deeper water seepage of the last few days has very little influence on the wet snowpack stability. On shady slopes and at higher altitudes it is a different matter. There, we expect the first simulation of deeply embedded, faceted layers to lead to heightened activity of wet slab avalanches. But that will still take awhile.

This running graph shows the stability of the wet snowpack, calculated with the SNOWPACK simulator. Red signatures denote an unstable, wet snowpack. Blue signatures show how deep the snowpack freezes overnight, giving an indication of how thick the melt-freeze crust is.

The quintessence: a marked wet-snow avalanche cycle is not currently expected, particularly due to the repeated times throughout the winter when the snowpack became thoroughly wet. 

As of 21 March, a cold front: temperatures will drop, temporarily end springtime conditions

On Saturday (21.03) a weak cold front will bring a small amount of fresh snow. Temperatures will remain down. Wet-snow avalanches are thus unlikely for a time. In accordance with the juncture of the season, caution will then be necessary towards diffuse light conditions and loose-snow avalanches. In addition, isolated glide-snow avalanches continue to be possible.