SnowFlurry 14 2020/21 | Spring situation: useful information and tools

Weather conditions over the last few weeks

After the heavy rainfall in mid-March, spring arrived in full force and temperatures in the Inn Valley soared to over 20°C in some places. However, it took a few days before a usable snow cover and thus also "firn" could form, as the cold fresh snow needed time to transform. This meant that conditions were initially variable: On the north side, powder was mostly still to be found, but this was to be enjoyed with caution in very steep, north-facing terrain. In these areas, avalanches could occasionally be triggered in deeper layers of old snow and weak layers close to the surface. The drift snow (discussed in the last Gestöber) also took a while to bond with the old snow cover and thus stabilize.

Unfortunately, you only had the pleasure of great firn runs for a few days, as the next cold front rushed in at the beginning of April with more precipitation, even including cosmetic sugaring in the valley. Once again, it was a case of waiting in fine weather until the snow cover and firn formed.

The fresh snow from 6 April fell at temperatures below -10°C in places on a previously warm and, in sunny terrain, damp snow surface, resulting in a huge temperature difference of just a few millimetres. Over the following days, a crust formed at the boundary between the old, wet snow surface and the cold new snow, and a weak layer was subsequently formed as a result of the build-up transformation (hazard pattern 4).

The new snow also insulated the wet, old snow surface, which meant that no more spring snow cover could form and there was therefore temporarily no firn. But there was some powder! Depending on how much fresh snow has fallen, how warm the temperatures and how dry or humid the air was in the days following the snowfall, the snow surface/cover is now soaked faster or slower and converted back into melt forms until the classic spring situation prevails again.

Measuring stations

Measuring stations can be used to retrieve the relevant parameters for us: air temperature, snow surface temperature, relative humidity and dew point, global radiation and wind.

I need to expand a little here to explain what this is all about:

When snow evaporates (liquid to gas) or sublimates (solid to gas), energy is required, which releases heat into the atmosphere and cools the snow surface. Put simply, when water or ice turns to water vapor, energy is exchanged with the atmosphere/air, removing heat from it and cooling it. This happens not only on clear nights, but also during the day when the air is drier, when there is wind that can cool the snow surface through evaporation and even when the air temperature is above the melting point (0°C) if other factors are present. As you can see, the details are quite complex. Many different factors determine how and why a hard cap forms and how strongly it develops, or how quickly and whether it "firns up" at all. Measuring stations therefore only help us if we combine several parameters. One alone does not provide good information about the conditions.

Negative for the formation of a snow cover: favors rapid soaking and a rapid increase in avalanche danger:

• If snow has a temperature of 0°C, it melts. This can be read from the snow surface temperature at some measuring stations. Snow never has more than 0°C. If the station shows higher surface temperatures, there is no more snow (or the station is broken). The snow surface temperature is particularly interesting after fresh snow: if the snow surface temperature is 0°C, the snow surface is wet. Followed by a clear night, you can expect broken snow the next day.

• The higher the air temperature, the more easily snow melts and becomes moist (but this depends on several factors)

• If it is cloudy or overcast at night, this curbs the radiation and thus the cooling of the snow cover. The higher the airhumidity (the closer the dew point is to the airtemperature), the less the snow cover can cool down. It softens faster or does not freeze at all.

• If cloud fields repeatedly pass through during the day, radiation is also restricted and the snow cover softens faster. This is where the global radiation curve provides clues:

  • A high, round and smooth curve shows a cloudless, beautiful day

  • A low, frayed curve shows that clouds have passed through

  • If it is flat/low, it was completely overcast.

• In thaw weather, you can say goodbye to the snow. In the graph, the air temperature and dew point are above 0°C.

Positives for the formation of a hardpack and the containment of moisture penetration of the snowpack: longer travel times, lower diurnal increase in avalanche risk.

• Evaporation and sublimation cool the snowpack - these processes are required for the formation of a hardpack! Takes place during clear nights, dry air, cold temperatures,....

• The colder the air temperature, the lower the moisture penetration

• Dry air favors evaporation and sublimation, slows down the warming of the snowpack and can even prevent "varnishing" altogether. In addition, a snow cover forms faster and better. In extremely dry air, a snow cover can still form at, pi times thumb. + 5°C (air temperature). Example measuring station: Air temperature is at +4°C, dew point at -25°C, the air temperature and dew point lines are far apart. Although it is warm and the sun is shining, the air is extremely dry and the snow surface is cooled throughout the day.

• Wind can also be useful in spring for a change, as it cools the snow cover slightly through evaporation. A wafer-thin layer of ice forms on the snow surface, also known as the firn layer. The wind strength and wind direction can be read off using measuring station graphics.

Avalanche situation report

• Indicates the daily warming.

• Informs about existing weak layers that can be reactivated by moistening.

• Gives information on other danger spots

• And also repeatedly mentions whether or not a snow cover is forming

Weather forecast

• Gives us a forecast of air temperature

• Precipitation

• Clouds

• Whether moist or dry air masses are flowing in

• Partly also mentions whether the following night will be clear or not.

We recommend a mountain weather report, such as that offered by the Alpine Association, which specifically addresses these factors.

Foto-webcam.eu

Here you can browse through the entire night in the archive and check whether it was clear or overcast.

A clear night favors the radiation and a snow cover forms. If it was overcast, it's better to go back to sleep, as the formation of a snow cover is then zero and the risk of avalanches is already high in the morning.

Summer-solid snow

When the snow is summer-solid, many people no longer go ski touring at all. The characteristic, bumpy, undulating snow surface is less than ideal for skiing. In my words: "Waschrumpl skifohrn". On the other hand, there is no more breaking into the snow cover and also no increase in avalanche risk over time.

Finally: In spring, exposure, altitude and slope steepness play a major role in the snow quality and other conditions due to the different levels of sunlight. How quickly it firns up, how long you can be out and about before you collapse and it becomes too dangerous, how long the fresh snow remains powdery until a cap or broken snow forms, the avalanche situation and weak layer formation - all of this can differ depending on the terrain factors.

A look at measuring stations, photo webcams, avalanche reports and terrain maps is always worthwhile and is irreplaceable for good tour planning!

We wish you great firn days and a beautiful summer. See you next season!