During the winter months, it is not uncommon for winter storms to dump feet of snow or even back-to-back snow storms to pass allowing snow to pile up. This gets especially tricky when it piles up on rooftops, sometimes leading to failure and to buildings collapsing due to the build up of snow.
The normal ratio of liquid to snow is usually 10:1. This means that for every one inch of rainfall equivalent will lead to 10 inches of snow on the ground. This is the usual ratio that most meteorologists use when forecasting snow amounts especially here in the northeast.
When air is exceptionally dry and cold, the ratio increases. Sometimes this can increase to around 15:1. Or for every 1 inch of rain it would equate to 15 inches of snow on the ground. This is the type of snow we got around here during the snowstorm the week before Christmas. This is considered fluffy snow, and carried less weight than normal snow per square foot. This snow is easy to snow blow and shovel and is common in the interior northeast.
Now if there is a lot of moisture in the atmosphere and temperatures are just around the freezing mark, if snow falls fast enough, the ratio shrinks and can sometimes approach 5:1. That is for every 1 inch of rain it comes out to 5 inches of snow. This is most common in the South and Mid Atlantic where the sun angle is stronger, and temperatures are usually warmer and marginal for snow during the winter months. This snow is very heavy and can cause power outages if enough piles up quickly.
When snow falls and piles up on rooftops it’s imperative to note the type of snow that is falling so you can ensure the roof stays stable and does not collapse. The wet snow is the most dangerous and leads to the most damage and power outages. However, if enough normal or fluffy snow piles up, it can lead to the same result.