Weather forecast goes global


Click image to view animation (requires free Quicktime player).
An AVI version is available. NCAR researchers are testing the ability of a cutting-edge regional weather model to stretch out to global scale. This animation shows precipitable water. The heart of the experiment is NCAR's advanced research version of the Weather Research and Forecasting model (WRF-ARW).

Regional weather forecasting models focus on targeted areas, from a river basin to a continent, at resolutions high enough to depict individual storms and other fine-scale features. But weather doesn't stop at the edge of a model's domain, and the artificial boundaries between regions can create forecasting problems.

This animation illustrates one approach to solving the artificial boundary problem: targeting the entire planet instead of just one region. NCAR researchers are testing the ability of a cutting-edge regional weather model to stretch out to global scale. The heart of the experiment is NCAR's advanced research version of the Weather Research and Forecasting model (WRF-ARW).

The 10-day forecast shown here starts with observed conditions on July 12, 2007, at 12:00 Coordinated Universal Time (UTC), or 8:00 a.m. Eastern Daylight Time. The fine-scale details in emerging fronts and storms are visible as water vapor circulates in the atmosphere. Several tropical depressions on either side of the Pacific grow into full-fledged tropical cyclones (called hurricanes in the eastern Pacific; typhoons or tropical cyclones on the western side). The model captures, for example, the passage of Super Typhoon Man-Yi as it rolls over Japan's southern islands and sweeps north, starting around July 13.

Calculating the evolution of temperature, humidity, pressure, and other key data on a three-dimensional grid requires considerable computing power, a major constraint on model resolution. This experiment used data points about 50 kilometers (30 miles) apart, a resolution typical of the global weather prediction models used by operational forecasters. Test forecasting at 20 km (12 mi) is underway, and the team plans experimental runs at 10 or perhaps 5 km in the near future.

A global version of WRF was first developed to study atmospheres on Mars and other planets by Mark Richardson and colleagues (California Institute of Technology). Researchers in NCAR's Mesoscale and Microscale Meteorology Division extended that version of the WRF-ARW model to forecast weather on Earth. (Image courtesy Earth and Sun Systems Laboratory, NCAR.)