Carol Sue McGuire, age 12, of Peoria, Ill., for her question:

How do they measure snowfall?

You can put an open topped can outdoors and measure how many inches of snow falls into it during the night. But this is not a very reliable way to measure the snowfall. Snowflakes flutter and tend to blow around and pile up against a solid object. Nevertheless, the weatherman may use a rain gauge, which is a refined open topped can, to measure a nights snowfall. He uses several rain gauges placed in various positions. This gives him a picture of the average fall of snow over a sizeable areas

The weatherman needs to know two things about the day's snowfall the number of inches which blanketed the earth and how many inches of water this would equal. He can measure the inches of snow by pushing a metal tube straight through the fluffy white blanket. He slips a board underneath the tube at ground level and lifts. He does this in several places, because snow tends to drift in this patch and avoid that patch. An average of these measurements gives him an average picture of the snowfall,

Now to translate this into rainfall. The weatherman cannot assume that so many inches of snow equals one inch of rainfall, because snow comes in different qualities. Light snow, fluffy as feathers, contains only a little water. Dry snow contains more water. Nor does the weatherman put the snow onto the stove to melt it into liquid water. Some would evaporate and give a false picture of the amount of water in the snow. He carefully measures some warm water and adds it to the snow. When the snow is all melted, he subtracts the water he added and measures the remainder.

Measuring snow in terms of rainfall is very important in the overall weather picture. For, come springy this snow will melt and stream down to the dams, the rivers and the reservoirs.

We must know how much water there will be to store, how much to feed the crops. For this reason, the entire winter's snowfall in terms of water must be measured all over the land.

This mammoth job is also done by taking sample measurements here and there. In the ermine coated mountains and plains, troops of weathermen go forth on snow shoes carrying metal tubes. Time after time they pierce the snow and take its measure. Countless samples are needed to estimate the nation wide snowfall that will melt in the spring.

 A sample of snow from the entire winter will be heavy and densely packed. A six foot snow drift which has built up through the winter may equal three feet of rainfall. A six inch carpet of newly fallen snow may equal one inch of rainfall only or one quarter of an inch of rain fall.