Weather patterns can have a big impact on snowfall totals. Subtle influences in the atmosphere can allow for the same amount of moisture to lead to different amounts of snow.
The temperature and moisture content of the atmosphere play a large role in the types of snow flakes that form. Different types of flakes stack differently and make snow more efficiently. With more efficient snow-making, the same amount of moisture leads to more snow falling.
When snow falls, observers collect the snow in their rain gauge. Once the snow melts, they come up with a measurement of the amount of liquid that it took to create their total snow. This is compared to the snowfall measurement that they take.
For example, a 5″ snowfall with 0.5″ of liquid would have a 10:1 snow to liquid ratio. This is what is used as a general guideline, but it is possible to have smaller and larger ratios. A ratio of 5:1 would mean the snow is heavy and wet, while a ratio of 20:1 or 30:1 would mean the snow is very light and fluffy.
If we carry the example through, 0.5″ of liquid with a 5:1 snow to liquid ratio would yield 2.5″ of snow. Likewise, 0.5″ of liquid with a 20:1 snow to liquid ratio would yield 10″ of snow.
Moisture is the constant in the above examples. As with all weather, it is usually more dynamic than that, causing some bursts of snow to over-perform and others to under-perform.
It is possible to have differences in snowfall ratios within the same system, depending on the location of colder air and moisture. We often see higher snowfall ratios in the mountains during upslope snow events. For more questions on upslope snow, see our Weather 101 segment on upslope snow showers.