The weather forecasts Michael Purves prepares in winter focus on the temperatures and conditions Yukoners can expect near their communities. In the summer, he might be more concerned with conditions on a remote mountainside or in a wilderness river valley.

Purves is a meteorologist with Environment Canada's Yukon Weather Centre in Whitehorse. In summer he specializes in preparing forecasts for the people who monitor and fight forest fires.

"It's much more detailed work," he says. "I have to generate about 400 numbers every day."

Forest fire weather predictions are based on conditions at one o'clock in the afternoon, which is close to the hottest and most fire-prone part of the day. Each day, Purves provides the predicted temperature, humidity, wind direction, and wind speed for the current day and for three days in the future for about a dozen different locations.

"We start in May and end in September, but the exact dates depend on the weather."

The forest fire protection people use the four-day predictions to generate their preparedness reports, says Purves. Advance warning of dangerous conditions allows them to move crews and equipment closer to vulnerable areas.

As well as the four-day forecasts, Purves puts together detailed forecasts of conditions for the current day, the current evening, and the next day. The information in these forecasts includes temperatures, humidity, precipitation, cloud cover, temperature and humidity maximums, and wind speed and direction.

Purves also tries to predict lightning strikes, one of the more common causes of forest fires in the north.

The systems used to predict lightning in southern Canada don't work well in the north, he says, so several years ago Environment Canada conducted a major study to find a better way. The result was a complex computer model that forecasts the probability of lightning across the forecast region for the next three days. The model allows forecasters to zero in to within about a hundred kilometres of where lightning is likely to strike.

"In the north, we now have the best models for forecasting lightning in the country," says Purves. "Alaska and other places are now borrowing our model."

Once a forest fire starts, a different kind of weather forecasting becomes important.

"If it's a big fire, we do a special forecast for the fire," Purves says. "For those forecasts, we provide temperature and humidity predictions every four hours, as well as winds, cloud cover, precipitation, and a general synopsis."

These "spot forecasts" allow the firefighters to plan their activities and to be prepared for changing conditions like a shift in wind direction.

"Those are very difficult to do because it's usually out in the middle of nowhere," says Purves. The standard information that goes into forecasting, pulled from satellites, weather balloons and monitoring stations, isn't enough for predicting conditions on the side of a remote mountain, he says. The forecaster has to have a good knowledge of the terrain as well.

Environment Canada's Atmospheric Environment Branch is looking at other ways it can help in the management of forest fires, besides weather prediction, Purves says.

"We use our weather satellites to look for forest fires," Purves says. The department is still experimenting with different ways of using the satellite information to pinpoint forest fires, but the results are encouraging.

"We think we can pick them up as small as 20 hectares. We found one in northern British Columbia this spring that was that small."

For more information about weather forecasting and forest fires, contact the Yukon Weather Centre, Environment Canada, in Whitehorse.