After briefly higher avalanche activity, danger again low, with daytime danger curve

Ongoingly dry, sunny, warm

Evaluations by the ZAMG Weather Service show that meteorologically speaking this has been one of the warmest and driest in history. “In Innsbruck there has been 27 millimetres of precipitation (72 percent less than average) up till now this spring. It was drier than this only three times since the year 1877, when measurement-taking began: in 1879 (12 millimetres), 1946 (24 millimetres) and 1976 (24 millimetres).”

Current weather goes hand in hand with the dryness: predominantly sunny. Precipitation was registered, if at all, only in single-digit mm, most of it on Sunday, 19 April and Monday, 20 April.

The tiny amounts of precipitation in Tirol, 19 - 20 April.

Inzinger Alm measurement station in the Stubai Alps is now bare of snow. The tiny blue bumps in the upper graph show the precipitation last week.

Effects on the snowpack

The snowpack is becoming moister, even at high altitudes.

Let’s stick to precipitation for a minute: even if it was minor, the air moisture on these precipitation days was quite high, seen in absolute terms. The snowpack “sucked in” the moisture of the air like a sponge and rapidly became moist or wet. That is easy to recognize at the automated weather stations where there is still snow and where snowpack surface temperature, air temperature and air moisture are measured.

What is most significant is the thoroughly wet snowpack, visible through the flat snowpack-surface temperature at about 0°C. An additional important factor is the thawing point, which at times even was above 0°C.

Highly significant is the extent to which the snowpack became thoroughly wet last week, particularly on north-facing slopes at high altitudes, and was thereby weakened.

Snow depths decreasing

The snow diminished further this week, on the one hand through melting, on the other, through sublimation (direct transformation from solid to gaseous form). The former occurred on 18.04 and 21.04 when the air was moist; the latter on 17.04 and 22.04 when the air was very dry.

 The snow didn’t just decrease, in some places it touched a record-breaking minimum over long measurement periods.

For comparison: snow depth on Furkajoch (Bregenzerwald) on 8 March 2020...

and the same spot, today, on 23.04.

A collage of photos from the foto-webcam.eu of this station, showing comparative shots from last winter, is also interesting:

Highly varied rates of snow decrease last winter

Another aspect of snow-decrease (photo: 22.04.2020)

"Summertime corn snow"

The repeated freezing-and-thawing of the snowpack has led to transformation of the snow towards stable summertime corn snow. This is the case at intermediate altitudes in all aspects, insofar as there is still snow at that altitude, and particularly on sunny slopes at somewhat higher altitudes.

Briefly higher avalanche activity on 19.04. and 20.04.

The thoroughly wet snowpack during the days with some rainfall plus cloudy nights subsequently led to higher avalanche activity. Typically, they were nearly all loose-snow and glide-snow avalanches; in very isolated cases, small slab avalanches.

Loose-snow avalanches on Nederkogel, Ötztal, photographed on 20.04 at 4:30 pm

Additional loose-snow avalanches on Nederkogel, Ötztal, photographed on 20.04 at 6:30 pm, just two hours later

Deposits from loose-snow avalanches, Zemmgrund (photo: 22.04.2020)

Similar situation, Kalkkögeln (photo: 21.04.2020)

What’s next?

Following the moist days, the air became much drier, and avalanche danger is again subject to a minor daytime danger curve. As the air masses destabilize and more clouds move in during the next few days, the air will moisten from region to region, the situation deteriorate somewhat.

Danger map for 24.04.2020

Slopes becoming bare – Ongoing daytime avalanche danger cycle will continue

Short review of weather

Fine weather persisted for a month, was briefly interrupted during the night of Easter Monday (13-14.04). A cold front cooled the air masses, brought a few centimeters of fresh snow to far-reaching areas of Tirol above the timberline. On 14.04 the sun swiftly regained the upper hand. What was striking was how dry the penetrating air masses were.

Tirol received a ‘sugar sprinkling’ in the heights.

The slopes are rapidly becoming bare of snow

In accordance with this juncture of the season, weather station measurements register receding snow depths, strikingly so at intermediate-altitude stations.

Successive decrease in snow depths at Lichtenberg weather station in Ausserfern. Easy to spot: the cold front which passed through on 13-14.04.

The diminishing snowpack can also be followed via the web-cams.

10.04.

16.04.2020: a marked increase in grass-covered surfaces, compared to 10.04.2020 

Very few avalanches observed

Continuing the pattern established during the prior weeks, very few avalanche releases were observed: small slides in the wake of the cold front; a slab, NW, 2500m near the Aifner in Tirol’s highlands (triggered by a winter sports enthusiast on a descent down a 40°-gradient slope in a spot where the snow was shallow, in a moment when the surface was frozen and capable of bearing loads, the person was not caught by it). Cornices breaking were reported from Ausserfern.

Isolated future slab avalanches possible esp. on shady slopes above 2500 m

Information on snowpack layering in outlying terrain is hard to come by. However one thing is certain: the snowpack is only slowly becoming thoroughly wet on high-altitude shady slopes (mostly because of very dry air masses). Nevertheless, we assume that the old snowpack on shady slopes is moist up to about 2500 m. As this process continues (and it can progress quickly in this season, regardless of weather - high air moisture, low clouds, warm temperatures, diffuse solar radiation), we expect some slab avalanches above 2500 m on shady slopes. They will probably be in limited spreads of terrain. Potential weak layer unleashing them: the expansively metamorphosed layer of faceted crystals from January

Temperature of snowpack surface is an important indicator of snowpack firmness/wetness at this juncture of the season. At night, melt-freeze crusts are seen to form which, at least on 14-15 April were capable of bearing loads at this station.

Ongoing daytime avalanche danger cycle

Based on the current weather forecasts, little change is expected initially. We will continue to see a greater or lesser avalanche danger cycle each day.

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: