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Clouds and asphalt

Accounting for clouds in weather forecasting could greatly improve road safety

road stretching to horizon, with blue sky and clouds above

Highway 395, Umatilla County, Oregon. (Gary Halvorson, Oregon State Archives, via Wikimedia Commons.)

August 21, 2012 | A single cloud can have dramatic effects on local weather conditions, but forecasting models do not fully capture individual clouds or cloud types. Now researchers at NCAR are developing tools that could enhance the precision of weather forecasts by taking clouds into account, with results that could help drivers, road crews, and others.

“When you’re looking at storms or high-pressure systems across a large region, the cloud is like a little tiny speck of sand,” says Curtis Walker, a 2012 SOARS protégé at NCAR who is beginning a master’s program in atmospheric science at the University of Nebraska, Lincoln, this fall. “Today’s technology can’t really get a good grip on where an individual cloud might be or its impact on a small, localized area.”

In addition, he notes, many current models are only generated every six hours, but clouds can move within minutes.

Walker, under the direction of his science mentor, Michael Chapman, a scientific project manager at NCAR, applied the Naval Research Laboratory Cloud Classification algorithm, which uses satellite imagery to identify cloud types, pixel by pixel, over an 8-square-kilometer area. He classified cloud types into five categories: cirrus clouds, which are thin and feathery; mid-level, ‘alto’ clouds, which often occur in layers and have a “bubbled” or cellular appearance; stratus clouds, which are low-level clouds that produce fog or rain; cumuliform clouds, which include thunderstorm clouds that often form large, vertical towers; and clear conditions. The system gathers cloud data every 15 minutes.

The researchers then overlaid cloud observations onto radiation measurements to quantify how much solar energy reaches Earth’s surface in the presence of different cloud types and sizes. The results can help forecasters anticipate how much heat from the Sun will reach the ground in the next few hours.

Professional racing organizations have a keen interest in understanding how tires will grip the surface on race days, and municipalities and the aviation industry would also benefit from being able to more precisely predict atmospheric conditions. The ability to take clouds into account will also help the solar energy industry determine how much solar power can be harvested.

Walker, Curtis L., “The Impact of Cloud Type on Surface Radiation and Road Pavement Temperature,” 2012: unpublished poster presentation: PDF