Friday, January 30, 2009

Snow To Water Ratios

WxWatcher asked a great question about snow water ratios the other day.

The standard that most people learn in a science class is 10 to 1, written was 10:1.

This means every ten inches of snow typically melts to about an inch of water. It is ok to use that standard for classroom purposes, and I think in real life more times than not that comes out to be true for many.

BUT -- location, time of the year, temperature, the source of water and the upper air connection to that source of water -- all these factors play a big role in what the ratio will actually be.

OSNW3, your link to the chart was great. Click here for the chart. I have never seen a chart like that but it certainly gives a guideline.

And as we all know, there are ALWAYS exceptions to every rule when it comes to weather because there are just so many variables to consider.

Ricker, you are right --- temperature plays a large role in the ratio. It also varies by location and the time of the year.

Here in Colorado, the early and late season snows are closer to the 10:1 range, while the mid-winter snows are 15:1 or more. The high mountains can see 20:1 or 25:1, meaning 25" of snow for just 1 inch of water. Now that is what you call powder!!

In March 2003, Colorado had a very wet snow that ended a drought and broke numerous records. In my part of southeast metro Denver, I recorded over 40" of snow but it never piled up more than 28" on the ground because it was so full of water and so heavy, it just kept compacting.

It also had a blue tint to it and the weight of the snow literally "squeezed" the water out of the snow below it. The ratio was something like 6 to 8 inches of snow for every 1 inch of water. Just crazy -- particularly for this part of the country!

One might not be shocked to see that ratio near a coast, but we are 1,000 miles away from the nearest major source of water -- an ocean. That pipeline of moisture slammed into here as if it were coming straight out of a fire hose that stretched all the way to the Gulf of Mexico.

So the larger your ratio, meaning 15, 20 or 25 inches to every inch of water, the colder it likely was during the snow. And the opposite it true --- heavy, wet snowfalls usually come with more mild temps, holding in the lower to mid 30s.


  1. Thanks for the info, Chris.

    Your snow in '03 reminds me of one we had early December 2006. We officially had 16" in Fulton, and I noticed the bluish hue at the base of the snow as well.

  2. Chris, the chart comes in handy as a reference when we have blowing conditions during a snowfall. The chart is distributed to all the Co-Op Observers in WI... as far as I know.

    Thanks for explaining more in depth as it's important for observers to know that snow can be less then the 10:1 ratio. I struggled with that in my early days of reporting.

  3. Here's some suggestions for snow observer comments, from the "100 Inuit Words for Snow"
    Though I think some entries like "snow mixed with the sound of old rock and roll from a portable radio" might be padding to fill in the 100...

  4. Great Chart OSNW3! That's what I like about this Blog, good people and links to great weather resources. The chart may be more than a middle school science class can absorb (no pun intended) but what a tool to help spark their interest.

    If my math is correct Chris, that 2003 storm of 40" snow along the CO front range could have contained up to 5" of water... almost 1/3 of our annual average.

  5. Great post! Also, great chart OSNW3! In fact, great blog!