Rain vs snow accumulation volume?

Submitted by krenzar18 t3_11r8m56 in askscience

I noticed on my weather app that rain over time follows a smooth curve, but when it’s expected to become snow, the amount jumps to nearly 5 times the amount of rain per hour. Is this a glitch? Or is there an actual difference in rain vs snow volume during the same storm

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CrustalTrudger t1_jc7lxoo wrote

It's real. Snow is significantly less dense than liquid water, so for an identical mass of liquid water, the volume of equivalent snow mass will be much greater than the volume of water. The density, and thus the difference between the amount of snow and the equivalent amount of water (i.e., the snow water equivalent or SWE), is a function of temperature, e.g., this discussion. Generally, as temperature decreases, snow volume for the same SWE goes up, for example the graph on that page highlights that 1 inch (~2.5 cm) of rain can equal ~100 inches (~250 cm) of snow when the temperature is -40 to -21 F (-40 to -29 C) but would only equal ~10 inches (~25 cm) at 28 to 34 F (-2 to 1 C). Importantly, none of these are accounting for compaction of snow after it falls, where the density of snow can increase significantly with increasing accumulation.

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zakabog t1_jc7mkzm wrote

Rain is liquid water, it'll be more dense than the solid snow. Collect a container of snow and compare it to the weight of the same container of water. Or just melt the snow and see how little water there is in a large volume of snow.

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Dunbaratu t1_jc7se9d wrote

Imagine someone who's really bad at playing Tetris. They don't even try to make the blocks fit together well and they make lots of big empty holes in their pile of blocks as the blocks get stuck on each other in the least compact way possible. That makes their pile get high very quickly.

That's what a pile of snow is like. Raindrops are excellent at playing Tetris because liquids will change shape as needed to fill the lowest possible level of the container. Snowflakes on the other hand won't. Their very spread-out shapes, fully of spiky bits at the ends, cannot tessellate.

Snow depth is made mostly of the air gaps in between the flakes that get hung up on each other's spikes.

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JMYDoc t1_jc8xzyg wrote

Yes. The amount of water in an inch of rain generates up to six inches of snow. The amount depends on a variety of factors which affects the snowflake size and shape and thus “compactness.” The light fluffy snow has the most accumulation.

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