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AgWeatherNet Tests State-of-the-Art Weather Prediction Model for Freeze Events

PROSSER, Wash.—Washington tree fruit growers are often at the mercy of Mother Nature when it comes to weather. Case in point: the severe thunderstorms of July 20 that, in some areas of south central Washington, battered apple crops with golf ball-sized hail, leaving some orchards with losses of 100 percent.

But AgWeatherNet, Washington State University’s automated weather station network, is testing a national, state-of-the-art weather forecasting model as a possible tool for better predicting such weather systems, especially for parts of the state where tree fruit crops are important.

“AgWeatherNet only provides current weather conditions,” said Gerrit Hoogenboom, the network’s director and WSU professor of agrometeorology. “Adding a weather prediction component will allow growers to make more informed decisions with respect to knowing both the conditions that have occurred and the upcoming predicted weather conditions. This can be applied for preparation of extreme weather events such as frosts and freezes, as well as inputs into other models for pest, disease and other management decision aids.”

Hail damage to a Sunnyside, Wash., apple crop on July 20. Better prediction of extreme weather events, such as the severe thunderstorm that resulted in the hail damage, is the subject of a study by AgWeatherNet.

AgWeatherNet releases monthly weather summaries, weekly weather outlooks and warnings based on data received from its 137 automated weather stations located across Washington state. But it doesn’t make predictions of air temperature, dew-point temperature, wind speed and wind direction, Hoogenboom said. Coming up with accurate predictions given south central Washington’s varied terrain has been a challenge.

That’s where the Weather Research and Forecasting (WRF) Model comes in. According to the WRF website, the model is a next-generation mesoscale numerical weather prediction system designed to serve both operational forecasting and atmospheric research needs. “Mesoscale” meteorology means the study of weather systems ranging from a few miles to hundreds of miles wide. WRF can be applied for storm-scale research and prediction, air-quality modeling, wildfire simulation, hurricane and tropical storm prediction, regional climate prediction and more.

“It can provide us with hourly weather predictions at a very high spatial resolution—close to a 2-by-2-mile grid,” Hoogenboom said.

Hoogenboom, postdoc Tes Ghidey, AgWeatherNet meteorologist Nic Loyd and WSU civil and environmental engineering associate professor Heping Liu evaluated WRF’s prediction capabilities for three actual freeze/frost events recorded by AgWeatherNet on Feb. 24-27, April 7 and Oct. 25-27, 2011. The team also provided the model with terrain information, such as elevation and land-use/vegetation coverage.

Results were processed on a high-performance computer purchased with part of the $95,000 in funding from the Washington Tree Fruit Research Commission, which supported the one-year study.

“The model actually performed well for low elevations in eastern Washington and for providing 24- to 48-hour predictions,” Hoogenboom said. “Longer out was more difficult. We are trying to develop a parameter scheme so that it will do better.”

The next step is testing the model for real-time weather predictions by storing its results and comparing them with the actual observations from AgWeatherNet, Hoogenboom said. The researchers have been running the model once a day at night since Aug. 1.

“Our goal is to develop a protocol for implementing the WRF model as a freeze forecasting tool for AgWeatherNet,” he said.

For more about AgWeatherNet, visit the website.