May is just like April – Weak snowpack at high altitudes

 In a nutshell...

Even if we are already in the month of May, April-weather persists. The variable conditions of recent days have further weakened the snowpack. Rain, high temperatures and repeated bouts of rainfall or fresh snow have weakend it especially on shady slopes above 2300 m. On Saturday, 29.04, there was heightened avalanche activity, including involving persons. On Thursday and Friday, 04-05.05 it is expected to reach early summer temperatures. Avalanche danger is then subject to an intense daytime cycle. Backcountry tours should be brought to a close early in the day.

 

Large-sized avalanche on 29.04 involving persons, below eastern Seespitze in the Stubai Alps, 2950m, north-facing slope.

Review of last week

Recent weather was marked by various rounds of precipitation. On Friday, 28.04 there was precipitation throughout Tirol, including significant amounts of rainfall and fresh snow.

48-hr amounts of precipitation, measured on Friday, 28.04

Over widespread areas there was 30 mm of rain, above 2500m it fell as snow. Particularly in western and the furthermost northeastern regions of Tirol, large amounts of precipitation were registered. The snowfall level initially lay at 2000 m, then ascended to 2500 m.

 

Three bouts of precipitation with varying snowfall levels measured at Pitztal Glacier weather station and compared with reports from our observers.

After the end of the precipitation, it was partly sunny on Saturday, 29.04, and immediately quite mild. The zero-degree level lay at 3000 m. The danger of wet-snow avalanches increased significantly and was, due to the rainfall, warmth and lack of nocturnal outgoing radiation, the main danger during the following days.

On the evening of 01.05, precipitation struck again. On 02.05 there was rainfall at low altitudes all day long. Above 2300 m there was an additional few cm of fresh snow registered. Winds were light to moderate.

Avalanche activity from last weekend (29.04. to 01.05.)

As a result of rainfall and higher daytime temperatures, especially along the Main Alpine Ridge, many wet-snow avalanches released, including large-sized ones. As we said in our last Blog, three ground rules are the prerequisites: high altitude rainfall level and intensity of rainfall; warmth; and the first time dry layers of the snowpack become thoroughly wet. Avalanches can then grow to impressive size for winter sports enthusiasts. Headquarters Tirol received reports of ten avalanches which involved persons.  In three cases, we were able to confirm the involvement of persons. All avalanches ended without grave results.

Typical picture of Saturday, 29.04. Due to a thoroughly wet snowpack, avalanches sweep away a slab nearly to ground level...

...and thereby attain impressively large size.

Also in East Tirol there were avalanches, such as here on Vorderen Plattenkogel.

Large-sized avalanche on Hohe Zahn in the Stubai Alps. Wet-snow avalanches can often take a plummet path which is unpredictable. Deposits of snow can be rather massive.

Outlook for the coming days

On Wednesday night (03-04.05) skies will be predominantly clear, the snowpack surface will have sufficient outgoing longwave radiation, a melt-freeze crust capable of bearing loads will be able to form. Due to the solar radiation which is already quite intensive and the high daytime temperatures, the crust will rapidly soften up and the process of wetness will continue. Especially where the snowpack is not yet isotherm and thoroughly wet, we expect increased avalanche activity, particularly on very steep, shady slopes at 2600-3000 m.

Smart planning and savvy time allotment

As the spring progresses, weather conditions, snowpack and, thus, avalanche risks can vary enormously from place to place. For that reason it is even more important to evaluate the conditions on-site with great precision and be flexible in planning backcountry tours so that you can react to conditions on the spot. 

Over the next few days, your backcountry touring goals need to have exact time allotment. As described above, we expect an intense and a fast-moving daytime danger cycle of avalanche risks.

At high altitudes, the danger zones occur mostly on very steep shady slopes in the near-surface weak layers (persistent weak layer due to cold on warm since the end of March). This affects particularly the altitude band of 2600-3000 m. In high alpine regions, i.e. above 3000 m, isolated sunny slopes are also affected by this phenomenon.

Whoever does not venture up to such altitudes will find quite good conditions on the (now closed) ski pistes.

“What’s up, bro?” Nowadays, backcountry tourers can be looked at somewhat critically.