(WKBN) – Snow is falling from the sky today and with colder air coming down the pipe, snowfall measurements will soon be important. You might be wondering how much liquid water it takes to create an inch of snow. Today, I will tell teach you about liquid-to-snow ratios and their importance when forecasting snowfall totals.

A general rule: 10:1 ratio

Some of you reading this article might have heard that one inch of liquid water equals one inch of snow and that is always the case. This would mean that it would take 0.1 inches of liquid water to make an inch of snow.

This is generally a fair standard, but it is certainly not always the case. The snow-to-liquid ratio depends mainly on the temperature of the atmosphere where the snow forms and then the temperature of the atmosphere from the snow formation to the ground.

If the air temperature is colder, then less liquid water is needed for snowfall accumulation. Below are a few examples of the air temperature and the associated snow-to-liquid ratios:

Air Temp = 34° to 28°F (10:1 ratio)
Liquid of 0.01″ = 0.1″ of Snowfall
Liquid of 0.25″ = 2.5″ of Snowfall
Liquid of 0.50″ = 5.0″ of Snowfall
Liquid of 1.00″ = 10.0″ of Snowfall

Air Temp = 27° to 20°F (15:1 ratio)
Liquid of 0.01″ = 0.2″ of Snowfall
Liquid of 0.25″ = 3.8″ of Snowfall
Liquid of 0.50″ = 7.5″ of Snowfall
Liquid of 1.00″ = 15.0″ of Snowfall

Air Temp = 19° to 15°F (20:1 ratio)
Liquid of 0.01″ = 0.2″ of Snowfall
Liquid of 0.25″ = 5.0″ of Snowfall
Liquid of 0.50″ = 10.0″ of Snowfall
Liquid of 1.00″ = 20.0″ of Snowfall

Air Temp = 14° to 10°F (30:1 ratio)
Liquid of 0.01″ = 0.3″ of Snowfall
Liquid of 0.25″ = 7.5″ of Snowfall
Liquid of 0.50″ = 15.0″ of Snowfall
Liquid of 1.00″ = 30.0″ of

Air Temp = 9° to 0°F (40:1 ratio)
Liquid of 0.01″ = 0.5″ of Snowfall
Liquid of 0.25″ = 10.0″ of Snowfall
Liquid of 0.50″ = 20.0″ of Snowfall
Liquid of 1.00″ = 40.0″ of Snowfall

Air Temp = -1° to -20°F (50:1 ratio)
Liquid of 0.01″ = 0.5″ of Snowfall
Liquid of 0.25″ = 12.5″ of Snowfall
Liquid of 0.50″ = 25.0″ of Snowfall
Liquid of 1.00″ = 50.0″ of Snowfall

The snow-to-liquid ratio is not a constant

During the duration of a snowfall event, the snow-to-liquid ratio rarely stays constant. In fact, the snow-to-liquid (SLR) ratio can change rapidly spatially and temporally. In the past, meteorologists have used constant snowfall ratios to evaluate forecast snowfall totals. This can sometimes lead to an overestimation of underestimation of snowfall measurements.

Therefore, a method was developed in 2004 by Evan Kuchera to account for changes in atmospheric temperature during snowfall events. The method is called the “Kuchera method” and the method is explained below:

Step 1: Find the warmest temperature in the lowest half of the atmosphere

Step 2: If that temperature is > 271.16 K (28.4°F) then SLR = 12.0 + 2.0*(271.16-MaxT)

OR

Step 3: If that temperature is < 271.16 Kelvin (28.4°F) then SLR = 12.0 + (271.16-MaxT)

Here are a couple of examples below:

Example 1:
Max temperature = 26°F (269.82 Kelvin)
Snow-to-liquid ratio = 12.0 + (271.16 K-269.82 K) = 13.28:1
This means that if there was one inch of liquid then you could expect around 13″ of snow,

Example 2:
Max temperature = 32°F (273.15 Kevlin)
Snow-to-liquid ratio = 12.0 +2.0*(271.16 K – 273.15 K) = 8.02:1
This means that if there was one inch of liquid then you could expect around 8″ of snow.

Average snow-to-liquid ratios for the Valley

The National Weather Service compiled an extensive database of snow-to-liquid ratios over the entire country throughout the years. The results of this study are shown below:

Snow-to-Liquid ratio climatology by National Weather Service Forecast zone.

The color bar on the left side of the image shows values of snow-to-liquid ratio. The map is fairly self-explanatory. In locations where the weather is colder (Rocky Mountains, Great Lakes, Upper Great Plains), the snow-to-liquid ratios are higher. Where the temperature is warmer (the southeast) the snow-to-liquid ratio is lower.

In the Valley, the average snow-to-liquid ratio is around 13-14:1. However, this can be lower or higher based on the snowfall event.