'Waist deep!', 'Up to my armpits, or 'just to knee deep'. Nothing creates as much discussion as the amount of snow that we ride in. It's quite similar to the discussions surfers have about the wave height. Some people feel like a wave was two meters, others only one meter and a friend of mine who has seen it all said the wave came up to his ankles.
It's a strange discussion, because the amount of fresh snow or the height of a wave is something you can simply measure right? But what do you measure and how you measure it? What seems so simple is pretty complex in real life and often starts a passionate discussion.
Snow cover versus amounts of fresh snow
Some people think that the snow cover grows with 150 cm when 150 cm of fresh snow comes down in three days time. Nope, think again. Once the snow hits the ground the air is pressed out of the snow and it starts to settle. That's the reason why the snow cover doesn't grow with 150 cm, but 'only' with 80 cm for example. If yo measure the thickness of the snow cover after 3 or 5 days you might come to the conclusion that 80 cm of fresh snow came down. But you know now that it was more than 80 cm. Measuring the snow cover every few days does not reflect the amount of fresh snow that has fallen in a given period.
A good example is the following measuring station. 144 cm fallen snow since the measurements of November 19th, but the snow cover itself is less than a meter thick. Because of the settling process the snow cover grew around 70 cm. The other 70 cm literally disappeared as air.
Snow settles because of its mass
A rule of thumb is that 1 mm of water produces 1 cm of snow, but this differs from storm to storm and from location to location. Sometimes 1 mm of water produces only 0.7 cm of snow, but it happened that 1 mm of water produced 3 cm of snow. It all has to do with the amount of air in the snow and in the last example you can probably imagine that there's a lot of air in the snow. This air is (partly) pushed out by the mass of the flakes that fall on top of it again. Snow thus settles because of its mass.
Snow settles because of the wind
The density of a snowflake increases when there's a lot of wind. Snowflakes are pushed together by the wind and sometimes literally pushed into the snow cover. Air is thus forced out of the snowflake and the snow cover gets thinner.
Snow settles because of the temperature
Wet and heavy snow weighs more which puts more pressure on the snow cover. Cold loose snow weighs far less and the snow cover won't 'shrink' as much. Warmer snow also contains less air simply because there is literally more water in the snow.
Measuring more often gives better results
To counter the bias of the settlement of the snow cover, the best thing to do is to measure continuously, but that's an impossible task. That's why you see that many automated measuring stations send their data every 3 to 6 hours. These are pretty reliable numbers, because they give a good impression of the amounts of snow that actually came down in 24 hours. Compare this data with a station that measures only once every 24 hours and the snow cover might have settled 20-40% depending on the temperature and exposition.
Location, location, location
The location is not only key in real estate, but also with meteorologists. A measuring station that is right on the ridge and full in the sunshine has less value than a measuring station which is less affected by wind and temperature.
Measuring the amount of fresh snow that has fallen appears to be not as simple as it seems. For an honest impression you need to frequently monitor a location that matters. Only then you will get an idea how much snow the new storm has brought. And when you put a bit more effort in it, you can find as much snow on similar slopes in the region. Because I like to ride the driest and deepest powder in the safest way possible, you can imagine that I spent quite a lot of time looking at the data spit out by measuring stations.
Because after a dump of 3 meters you rarely ride 3 meters of bottomless powder, but if you search you can ride snow up to your armpits.
Because I daily look at the snow data, I not only ride better powder, I immediately verify my forecast and the forecasting of the weather models so that I can improve my own forecast over and over again. Sometimes it turns out even deeper than the amounts of snow forecasted on the snow maps. But you have to know where to find it.