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Lots Of Snow Doesn't Mean Lots of Moisture

Lots Of Snow Doesn't Mean Lots of Moisture
Conversion factor to rain makes huge difference.

Don't be too quick to assume we've had a wet winter so far. It's probably fair game to say we've had a snowy winter in most parts of Indiana, and in some more than others. It's also been cold enough to keep most of the precipitation that comes down in frozen form of one form or another. Luckily, it's been snow more than it's been ice.

The catch 22 factor is that it takes a lot of snow to convert into one inch of water, says Ken Scheeringa, assistant state climatologist in Indiana. He is based at Purdue University. His job is to track trends over time, and he also attempts to look ahead and see what might happen based upon overall weather-influencing factors, such as the El Nino/La Nina cycle, the one tied to ocean temperatures in the far Pacific, and the effect varying sea surface temperatures have upon atmospheric pressure, and in turn, on weather systems around the world.

La Nina is currently the dominant force in the cycle. It is the cool phase, where ocean waters far off in the Equatorial Pacific Ocean are cooler than normal. At last check, it was at moderate strength, and was large enough to deliver a La Nina winter to the U.S.

One inch of snow typically only equals about one-tenth of an inch of rain. So far precipitation recording purposes, it takes about 10 to 12 inches of snow to equal one, one-inch rain event. If your area has accumulated two feet of snow, then you've probably received about two inches of actual precipitation. Since the temperature has been at freezing or below for much of the winter to date, there has been little opportunity for actual rain to fall. Most rains that have occurred have been relatively light in nature, at least since late November.

To further complicate maters, no two snowfalls may translate into exactly the same amount of liquid precipitation. It can tale up to 15 inches of snow to equal to one inch of rain. The difference depends upon the type of snow that falls.

Scheeringa is in the process of running calculations on actual precipitation received so far this winter, compared to last winter and to the five-year average. Look for that report here in the near future. Until, then, feel free to make a friendly wager with a neighbor on whether or not actual precipitation totals are above or below normal so far this winter.

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