That's 56lbs. That's going to get real heavy real quick. Especially for an area where shovelling would take a while. Which is when you'd want something like this.
Ice and snow are both less dense than liquid water. Depending what type of snow and whether or not it's had a chance to thaw and refreeze, snow might even weigh less than 5lbs/ft^3 -- an order of magnitude less than your napkin math. I'd venture a guestimate that most snow people are shoveling sits somewhere around 15-20lb/ft^3, which is for snow that's settled for about a day, with wind, in below freezing temps.[0]
That having been said, you are not wrong. When we're talking about tarp-sized areas, any significant snowfall (i.e. anything not more quickly/easily cleared with a quick broom sweep) will get really heavy really quickly.
The rule of thumb I used when I lived in the frozen wastes was that 10cm of snow is about 1cm of rain in terms of water. Qualitatively I know it is much lighter than 56lb/ft^3, because you can easily pick up that much snow even if it is compacted. Otherwise snowmen would be very hard to create.
Good to know. I have very little experience with snow itself.
I figured it would be lighter due to all the things people said, but had no rule of thumb to go on. And I try to go by the principle of being wrong in the best way possible. And since I wasn't aware of the density difference, I figured it would be safest to ignore it. Because people kind of forget how fast water gets heavy.
The weight of the snow depends entirely on the temperature gradients in the air, from cloud to ground. People in the mountains seem to have consistently light, powdery snow, while people in the plains seem to have consistently heavy, wet snow. But sometimes it is the opposite!
Each gallon of water weighs 8lbs.
1 cubic foot is about 7 gallons.
That's 56lbs. That's going to get real heavy real quick. Especially for an area where shovelling would take a while. Which is when you'd want something like this.