The ability to accurately determine and report the weather at WAIS Divide is very important for the safety of incoming airplanes. Weather conditions are evaluated and called in to McMurdo via satellite phone every hour when flights are scheduled.
There is a small weather station at WAIS Divide that measures such things as wind speed, temperature and barometric pressure. However, other aspects of the weather and visibility are determined by less “high tech” methods. Visibility is determined by looking at objects with known distances. At WAIS, three flags are set at distances of 1, 2 and 3 miles in two different directions. The visibility is determined by how many of these flags can be seen and how clear they are. Other aspects of the weather report include estimating the fraction of the sky covered with clouds and the types of “obscurations” such as blowing snow or mist which are affecting visibility. We also report on how well the horizon can be seen. When snow is blowing or if there are heavy clouds or fog, one often cannot tell where the snow ends and the sky begins. We also report on the surface definition. When it is very cloudy (no bright sunlight) a condition is created that is referred to as flat light. With flat light, there are very few shadows and one cannot see details in the snowy surface. Since everything is white, it is easy to simply trip over a snowdrift or walk into a big mound of snow without seeing it! This creates difficult conditions for pilots who sometimes rely on shadows to determine how close they are to the surface.
My favorite part of collecting the weather data was determining the height of the clouds (the ceiling). A laser is typically used to measure the height of the clouds. However, when the cloud height is close to the limits of what is safe for a plane trying to land (clouds at least 300 feet above the surface) a weather balloon is often used to confirm the cloud height. A big bright balloon is filled with an exact amount of helium and carefully tied closed. Getting a timer ready, the balloon is released and watched carefully until it disappears behind the clouds. Using the weight of the balloon and the helium it contains, and the amount of time it takes for the balloon to disappear, we can calculate the height of the clouds.
While we make our own weather reports of current local conditions, our weather forecasts are actually made by a remote forecasting station in Charleston, South Carolina.
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