A few dedicated weather crazies recently ventured into a spring Rocky Mountain snowstorm. Every half hour throughout the night they captured a snowflake on pieces of black velvet. They peered through a hand-held magnifier that enlarged the snowflake 30 times. They recorded the time, temperature, humidity, and wind speed.
Nearby, in the National Center for Atmospheric Research at Boulder, Colo., a tape was rolling to record the image of falling snow that appeared on a Doppler radar screen.Later this summer, after the last storm has passed through the Rockies, John McGinley and his volunteers will run their winter's observations through a computer and compare what appeared on radar with the types of snowflakes that fell in different areas.
McGinley hopes to correlate the radar picture with a particular type of snowflake. Yes, there are different types of snowflakes. McGinley is concerned with two: dendrites and graupels.
Dendrites, the classic six-sided snowflake, are light, but make lots of snow.
"Typically, one inch of water equals 20 inches of dendrite snow," says McGinley, Forecast Research Group chief of the Program for Regional Observing and Forecasting Services in Boulder.
Graupels are colder snowflakes that have been rimed by super-cooled, but still liquid, water droplets as the flakes tumble through the clouds. The droplets hit the snowflakes and freeze onto the surface. Those snowflakes come out looking like little Apollo capsules, says McGinley. The dense graupels aren't as fluffy as dendrites. One inch of water makes seven inches of graupel snow, says McGinley.
There are also column snowflakes, which look like little unshaped pencil stubs, and plates, which are little flat hexagons, but McGinley isn't concerned with those. It's the graupels and dendrites that he wants to be able to identify with the Doppler radar.
Highway departments, airports, school districts, and utility companies have a vested interest in knowing how deep the snow will be, and what type it will be so they can better prepare for plowing and repairs.
Doppler radar was invented in the late 1960s. It enhances regular radar, which detects only the presence of raindrops, by peering into severe warm-weather storms to determine which way and how fast the drops of rain are moving. Forecasters can easily detect tornadoes and storm cells with Doppler technology.
"It allows you to see the circulation and airflow in a thunderstorm so you can diagnose it a lot better," says McGinley.
McGinley's project is to devise rules for Doppler radar use during the winter. Because rain returns a much stronger signal on the Doppler radar screen than does snow, scientists didn't think that the technology would be useful for winter weather. But McGinley has already discovered something interesting about snowstorms using the Doppler radar. He found bands of heavier snowfall within a snowstorm, when the popular theory was that there wasn't much variation.
If he can identify different types of snowflakes within the bands with the Doppler radar, then he may be able to determine where the heaviest snow accumulations will occur.
"Highway department crews will be able to direct their snow plows to where the snow is heaviest," McGinley says. If his research pays off, the results will also influence the design of the Doppler radar system scheduled to be put in place across the United States in the early 1990s to be fine-tuned to pick up snowflakes.
"Of course, all of this is hypothetical now," says McGinley. "We're just doing basic research. We may get nothing useful."
But he won't feel guilty, he says, if nothing useful comes from this project. Very little money has been spent on it. The major work has been done by 40 or 50 dedicated volunteers who don't mind being rousted out of bed at 3 a.m. to catch snowflakes.