SACRAMENTO, Calif. — National Weather Service meteorologist Mike Smith sits at a desk most of the year. In wildfire season, however, he takes on a new persona: He wears a fire suit and camps out for days at a time at ground zero of major forest fires.

Smith spent a week and a half recently as the resident meteorologist at the Mill fire in the Mendocino National Forest — the 55th fire where he was the meteorologist on scene.

"I got here the day after it burned 10,000 acres," he said while he was finishing up his work there.

Smith and the weather experts like him are the "incident meteorologists" who inform firefighters of every nuance of the weather: from heat and humidity to changing gusts of wind. They make those calls from their tents and makeshift offices in the camps where fire crews refer to them as an "IMET."

Such on-scene weather experts are essential to building strategies to fight major wildfires. Using an IMET's information, fire chiefs determine the most effective and safe ways to contain raging fires.

"You belong to them," Smith said. "For any incident, any fire, you're the weather support for that particular site."

Julie Hutchinson, a California Department of Forestry and Fire Protection battalion chief, explained the need for detailed information about past, current and future weather. "We can go in and remove vegetation, remove grass, brush, and timber, but the one thing we have zero control over is the weather," she said.

So that the fire crews know what to expect, an IMET briefs them each morning before they head to the fire.

"They're writing the forecast for the shift package that the crew carries in their back pocket," said veteran IMET John Snook. As predictive-services manager for the interagency Northern California Geographic Area Coordination Center, Snook now provides long-term decision-making support regarding wildfires.

During their 15-to-16-hour days, IMETs also provide constant weather guidance and outlooks for the coming days.

By getting out of the office, an IMET "can stand under a fir tree" and take local measurements of temperature, humidity and wind, said Snook. For a firsthand look, an IMET often gets even closer to the fire, doing the same assessments with the firefighters on the line.

Then, back with their laptops, IMETs can run sophisticated weather models with the data, making use of satellites, Internet access, and the same computer programs and models that they use back in the office.

Scott Jones, a Cal Fire battalion chief, was stationed on-site recently at the Robbers fire in Placer County, Calif., to analyze fire behavior and aid with strategy. He relied heavily on his IMET: "I put him right next to me."

The IMETs, though critical to strategy, focus on the safety of firefighters on the fire line, where "change in weather has caused more fatalities than any other thing," said Smith.

So IMETs also teach meteorology courses to firefighters in the offseason. "Like what you would learn at the first quarter at college," said Snook. Firefighters carry meteorological tools and can then interpret signs of weather change, such as cloud cover, on their own.

The courses help firefighters to be "a little weather-savvier," said Kathy Hoxsie, warning coordination meteorologist at the weather service's Sacramento office.

Nationwide, there are only about a hundred meteorologists qualified to be an IMET. It's not a job for everyone.

They're "facing the people who are putting their lives on the line out there, and that's not always something that everyone is comfortable with," said Hoxsie. "They also need to be good at working on their own. They're the only (weather) person out there."

But they seem to love it.

"When you're in the office behind the desk behind the computer ... you're not seeing people getting the forecast," said John Wallmann, another weather-service meteorologist qualified to be an IMET. "When we're out there, we actually see our forecast being used, and we know that we're helping them out, and that feels like a really good benefit."

"You get up in front of the people who you're giving the forecast to, and they're telling you how you did," agreed Smith. "You can see (the fire) growing and changing and how the weather affects it."

"It's a real adrenaline rush," said Snook, who spent almost 20 years as an IMET. "You can really be part of the team to suppress a tough fire."