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Here you’ll see the 3 best ways on how snow is measured as precipitation. Most commonly it is done directly by using a ruler if the snow is not too deep, or by using a long rod to poke through deeper snow to the ground.
The National Weather Service does something like this on a daily basis for measuring new snow only. The NWS uses 7AM as a standard reference time to report the 24 hour snowfall. They have a lot of rules to try to keep all the participants doing all the measuring and reporting the exact same way.
We can do whatever works best for our own circumstances and needs.
For a very detailed description of the process the NWS uses to measure snow as precipitation take a look at this page: https://www.weather.gov/gsp/snow
2 concepts in 1 idea
But what’s more interesting and useful is to know not only the depth but the rain content of the snow. This is called the liquid equivalence of snow.
So there are two ideas within the process of measuring snow as precipitation:
- How much snow fell
- How much water is in the snow
I’ll bet that at least once in your life you’ve looked out the window at a foot of new snow in the yard and wondered how much rain that would have been. You may be surprised!
How Snow is Measured as Precipitation
There are 3 main ways to determine the liquid precipitation equivalence of snow.
- Look at the following chart if you know the snow depth and air temperature.
- Measure it by melting snow captured or collected in a graduated container like a rain gauge.
- Weigh the snow if you know the volume of the snow in the container.
#1 Way – First, you need to measure how much snow fell before estimating the water content.
To find the water content of snow on the chart you’ll still need a few things; a ruler graduated in 1/10ths of an inch, a thermometer, and preferably a pre-placed piece of plywood to let you know when your ruler is at the exact bottom of the snow.
Here’s a Chart of the approximate Liquid Water Equivalent of Snow:
|Temperature Range||Inches of Snow to = 1 inch of Precipitation|
|28F to 34F||10 Inches|
|20F to 27F||15 Inches|
|15F to 19F||20 Inches|
|10F to 14F||30 Inches|
|0F to 9F||40 Inches|
|-20F to -1F||50 Inches|
|-40F to -21F||100 Inches|
Isn’t it amazing how fluffy and powdery the snow gets as it gets colder?
If you were to use the often cited rule of thumb that 10 inches of snow equals 1 inch of rain you’d be pretty far off if it was in the mid 20s or colder.
The Pros and Cons of Estimating the Water Content
- Quick & Easy Ballpark Figure
- You Only need a Ruler & an outside thermometer
- No need to melt the snow
- Not Very Accurate
- As with every method, choosing where to measure takes some judgment
- Use a snowboard for better accuracy.
- Use an accurate thermometer close to your snowboard. If don’t have a good thermometer, use a nearby home weather station. I have a page on how to find a local weather station here.
- Choose a different measuring method in deep, wet snow. The first snowfall gets crushed by the heavy newer snow. Weighing the snow should work.
So what’s a snowboard?
Probably the most useful thing you can do in regards to accuracy is to use a snowboard. A snowboard is simply a piece of plywood cut in a 16″ to 24″ square that is placed on the ground before it snows.
If you just stick a ruler in the snow the ground underneath is going to affect your measurement. Grass is springy and holds the snow up a little, gravel holds heat and will melt the first snow, and dirt/ mud is squishy. Use a snowboard.
The snowboard provides a uniform surface and a stable platform that makes measuring the snow a lot more accurate. This is especially true for measuring snowfall on top of existing snow.
Paint the snow board white so it doesn’t absorb any heat.
When you’re done measuring the snow depth, just clean the snowboard off and place it on top of the fallen snow and you’re ready for the next storm.
Be sure to put a stick in the ground next to the snowboard so you can find it!
#2 Way – How to Measure Snow as Precipitation by Melting it
First, let’s look at physically checking the snow for water content. No guesstimating this time.
The idea here is to melt the snow and measure it as you would if it were rain.
You can use an actual rain gauge if it has enough capacity.
As you may have noticed in the chart, it can take a lot of snow to melt to 1″ of rainwater. For instance, at 16 degrees 5 inches of snow would only melt to 1/4 inch of rain.
A Stratus rain gauge might be suitable for you if you don’t get epic snowfalls. The Stratus rain gauge is used as the standard rain/ snow gauge by the CoCoRahs volunteer precipitation network.
The Stratus rain/snow gauge is a large cylindrical tube that has a funnel on top to guide the rain into a smaller graduated cylinder that is inside. The inside tube can measure up to 1″ of rain. Any rain more than 1″ spills out into the outer tube which can then be poured into the inner tube 1″ at a time. A total of 11″ of rain can be measured this way.
If you are using the Stratus to measure snow, remove the funnel and the internal graduated cylinder. Place the empty Stratus out where you want to get your snow measurement from, preferably on a snowboard.
This way you get your inches of snow and by melting the snow and pouring it into the graduated cylinder you get your water content.
At 14″ deep and 4″ across, the Stratus rain gauge can be used as “cookie-cutter” in the snow. It would sure help if you had a snowboard in place before you did this. Just push the rain gauge down to the bottom of the snow. You can then slide something under the gauge to hold the snow in as you pick the gauge up. Or you can hold the snow in by picking up the snowboard and gauge together and turn it over.
Another way of measuring the melted snow is using your wireless home weather station rain gauge.
You’ll need to find a container to catch the falling snow in that is EXACTLY the same size opening as the wireless rain gauge. Then you simply slowly pour the water through the rain gauge as if it was falling as rain. Slow is the key.
Just make sure that the capture area of the container is the same as the capture area of the rain gauge. One home weather station that has a 4″ opening is the Davis Vantage Pro 2. On the Davis, the rain gauge is black so the snow should melt a bit quicker. You can read my review of the Davis weather station here.
I have a page on the most popular wireless rain gauges here.
Using the snow that falls into the wireless rain gauge itself to get the snowfall measured doesn’t always well. If some of the snow melts and the refreezes it can disable the gauge. And if you wait for everything to melt you may have a problem with sublimation. Have you ever seen a patch of snow disappear without leaving a puddle or getting anything wet? That’s could be sublimation at work.
Tools You’ll Need
For the best and most consistent results, you should use a snowboard. Hey, this is going to be fun! Nah, the kind of snowboard for measuring snowfall is a 16″ to 24″ square piece of plywood that you paint white.
Your snowboard is white so it absorbs the least amount of heat. You place the snowboard on the ground in an area that is open to the sky and is away from things like your house so nothing can block the snow from any direction. Put a stick in the ground or figure a way to find it again after it snows.
If you find this interesting, take a look at the CoCoRahs website, maybe you’ll consider joining them.
The Pros and Cons of Measuring Melted Snow
- Easy to do
- Good accuracy
- Limited by snow depth
- You need to melt the snow
#3 Way – Measure Precipitation Equivalence of Snow by Weighing it
The weight per volume of water is known with great accuracy. If you know the volume and weight of your container it’s a simple matter to convert the weight of the snow to its water precipitation equivalence. This site has a handy calculator and conversion chart you can use.
To go from weight to inches of water take a look at how the Stratus rain gauge works. In the 4″ tube 7.2 ounces comes out to 1″ of water.
Use a Stratus rain gauge
One product that makes measuring snow a breeze is the official cocorahs rain/ snow gauge by Stratus. When it’s not snowing you also have a very accurate rain gauge.
To use it as a snow gauge you must remove the funnel and inside graduated rain tube.
The gauge is 11″ deep and 4″ across. If your daily snow is more than 11″ deep, you may want to look at this CoCoRahs PDF for directions for making a coring tool.
With the Stratus gauge you can:
- Measure by pouring the melted snow into the graduated rain tube and get a direct measure of the water content.
- Or calculate the water content with the depth of the snow in the tube and the ambient temperature.
- Or weigh the snow. No need to melt the snow. 1″ of water in the 4″ tube weighs 7.2 oz. You can figure any fraction or multiples of the 7.2 oz figure from there. Use an accurate scale! You can use the 4″ tube as a biscuit cutter on your snow board.
- And, of course, you also have a terrific rain gauge.
Why is the snow liquid water equivalent important?
The most obvious use is to know what to expect in terms of snow melt runoff. This helps reservoir managers, farmers, and municipal water officials plan ahead.
As for the rest of us, besides satisfying our curiosity, it may be important to know how much that snow on your roof weighs!
Well, there you go
As you can see, getting an accurate measure of snowfall is not as simple as measuring rainfall is. The problem is in getting a good snow sample being that snow falls and collects very unevenly across the ground. One solution is to take multiple samples and average them.
My page on mounting and siting a weather station can be of help.
Just do the best you can and your judgment will get better with experience.
Most importantly, Have Fun!