We're facing another brown Christmas. As much as Minnesotans hate snow, or at least shoveling it and driving in it, the prospect of a brown Christmas is universally depressing. So what would it take to guarantee a white Christmas in 2015? With a little research and a lot of assumptions, I've crunched the numbers and come up with an answer. It requires snow-making guns, lots of them.

A white Christmas is defined as 1 inch or more of snow on the ground. A rule of thumb is that an inch of snow requires 2,715 gallons of water per acre. (Actual amounts vary based on whether the snow is heavy and wet or light and powdery. I will be making lots of these assumptions.)

There are 640 acres per square mile. The Twin Cities metro area has 6,324 square miles, or 4,072,960 acres. To cover the entire metro area with 1 inch of snow, we would have to convert more than 11 billion gallons of water into snow.

That's a lot of water. Assuming that the average resident uses about 80 gallons of water per day, 1 inch of snow requires as much water as we collectively use in 36 days. We may have to drain a few lakes and dry up the Mississippi River to guarantee a white Christmas in 2015, but let's keep going to see where this leads.

Assuming that we have the water, the next step is to line up the snow guns. The best guns on the market can convert about 200 gallons of water per minute into snow, assuming we can pump 200 gallons per minute to the gun (an average garden hose puts out 3 to 5 gallons per minute). We also need air temperatures between 10 and 20 degrees Fahrenheit and humidity in the 5- to 20-percent range. For the sake of simplicity, let's assume those conditions are available around the clock during our 2015 White Christmas Project.

We'll need to order those snow guns soon. The supply is limited. A large snow gun manufacturer like SMI in Midland, Mich., or Techno Alpin in Italy makes about 2,000 guns per year. If we purchased their entire year's production, we would get 4,000 high-volume snow guns in time for the 2015 White Christmas Project.

If we spread them around the Twin Cities area, hook them up to high-volume water supplies and start creating snow when the temperature is ideal, we will be able to convert 800,000 gallons of water per minute into snow. It would take us more than nine days to lay down an inch of snow.

We would all have to stop taking showers and flushing the toilet during that time in order to supply water to the snow machines.

This assumes ideal snow-making conditions, no machine malfunctions, no breaks to move the snow machines, no water-main failures and no power outages.

Or we could wait for Mother Nature to do it for us. She could pull it off in an hour or two.

Doug Shidell is a publisher and writer in Minneapolis.