I often hear that on the average 10 inches of snow melts into 1 inch of rain. A heavy rain storm can fall at an inch an hour. During this past weekend’s storm on the US East Coast, many places were getting an inch of snow an hour, which is quite a bit. Why are there never snow storms that drop 10 inches of snow in an hour (which is the same amount of water as 1 inch of rain in an hour)?
Because falling snow is fluffy and falls slowly; because snow gets packed down on the bottom when it gets very high; because rainfall is measured by gathering, whereas snowfall is measured by accumulation (where it might conceivably melt away).
I have read a few accounts of up to 6 inches per hour, but most big storms are measured over a 24-hour period, and it tends to even out.
Someone who doesn’t live in California will be along shortly.
I’d think it might be due to the fact that cold air can’t hold as much water vapor as warm air. A 1"-per-hour rainstorm, then, would be much more likely in summer than in winter.
WAG quotient of this answer: 82.3%
Oh, and welcome to the SDMB!
Heavy duty rains come with lots of warm air aloft, causing sleet to mix in, or wetter snow. When snow is dry and fluffy, 1 inch of rain equals 10 of snow, and when extra cold, it could mean more than 10 of snow.
But heavy precip usually is dependent on a fetch of moisture, and often that moisture is with warmer air.
When snowfall and the ‘fetch’ was cranking along the northeast, the snowfall was starting to really crank up, but the fetch from the Atlantic kept temps near 32…meaning moist snow and some sleet. Accumulation rates go down this way.
WAG? Is that some sort of certainty rating?
And thanks for the answers, all.
WAG = Wild Ass Guess. The % is thrown in for a confidence rating . Little humor.
As I understand it, the mechanism for droplet formation in a proper thunderstorm requires that the water repeatedly freeze and re-melt. If it’s too cold to re-melt the forming… um, I need a general term which covers both raindrops and snowflakes… Anyway, if it’s too cold to re-melt the thingies, then you won’t get the massive dumping of precipitation.