SAN DIEGO (AP) -- A cigarette tossed carelessly along Interstate 5 on a hot, blustery fall day could spell devastation for the wealthy suburb of Mount Soledad.
In 15 minutes, a small blaze could explode into a fast-moving wildfire that threatens scores of homes as twisting, narrow canyon roads slow firefighters and more blazes spring up downwind.
That grim forecast is just one of many generated by powerful computer simulation programs for suburban and backcountry areas of San Diego County since last October's catastrophic wildfires in Southern California.
The blazes killed 24 people while scorching 750,000 acres and destroying more than 3,670 homes and businesses. With drought conditions unchanged, fire officials fear this could be another brutal fire season.
To prepare, fire officials have spent much of the past year traipsing around subdivisions and wooded areas, gathering information on terrain and brush to plug into the computer simulations.
The resulting forecasts can predict the path, size and speed of flames as they chew through communities and forests.
``It's like having a battle plan,'' said Bill Clayton, a division chief with the California Department of Forestry and Fire Protection. ``We're getting ready to attack the enemy.''
The modeling programs _ some powered by everyday personal computing systems, others by supercomputers _ have proven vital in fighting major fires throughout the country.
Last year, as the 150,000-acre Old fire roared through the San Bernardino Mountains, crews cut new fire lines after a simulation showed flames eventually hitting the populated areas of Yucaipa and Big Bear Lake. Rains doused the blaze before that could happen.
Last August, computer forecasts helped persuade Montana officials to redeploy firefighters and equipment after learning that blazes burning near Glacier National Park could leap across a major reservoir.
``Any fire you can think of, they have used (computer software) to model the conditions,'' said Colin Hardy, a researcher at the Forest Service Fire Sciences Laboratory in Missoula, Mont.
The study of fire behavior has been around for decades but surged after World War II, when massive blazes were unleashed by the U.S. military to level German and Japanese cities.
``There was concern that the next war might be a fire war,'' said Steve Pyne, a historian and author of ``Fire in America.'' ``So what you see is the Forest Service has a convergence of interests with the military.''
The federal government opened several labs around the country to study the dynamics of fire. Breakthroughs in mathematical formulas regarding fires led to one of the first computer modeling programs in 1974 _ a crude system of computer punch cards developed at the lab in Montana.
Now, the most powerful programs let analysts ``burn'' virtual blazes across colorful three-dimensional maps. The accuracy of the forecasts depends heavily on measurements of temperatures, wind and terrain _ factors that are themselves complex and difficult to predict.
Rich Wagoner of the National Center for Atmospheric Research in Boulder, Colo., has called computer simulations ``an extremely valuable tool for lessons learned that can be applied to future fires'' but cautioned against considering them as operational models.
Simulations can still bog down on the details that really determine a fire's behavior, such as whether a mountain slope is cool and facing north or warm and facing south. Or, whether the 60 mph winds are gusty or constant. Or finer details, such as the dimensions of leaves and needles on specific plants.
There is also the speed issue. The most detailed simulations are run on supercomputers that operate at trillions of calculations per second, but they still can't keep pace with wildfires.
``It takes several days to run a model to get an hour or two of forecast,'' Wagoner said.
To improve forecasts, researchers have embarked on a five-year, $40 million effort to map vegetation and fire fuels around the country through field investigation and satellite imaging.
The work is intended to help authorities compile computer grids _ known as geographical information systems overlays _ to detail an area's vegetation in high-resolution, 30-square-meter blocks.
Researchers are also working to create a national database of weather measurements to aid the modeling of fires under continuous, real-time conditions, said Larry Van Bussum, national fire weather operations coordinator for National Weather Service.
In San Diego County, the forecast generated by Clayton for Mount Soledad predicts that a fire could reach a speed of 6.7 mph while charring up to 500 acres. Flames could climb 51 feet into the air, creating a 77 percent chance of nearby blazes being sparked by drifting embers.
Until recently, many areas of the county had no formal forecasts because new subdivisions sprouted faster than firefighters could put plans together, officials said.
Now, priority has been given to doing forecasts for the backcountry and suburbs along its borders, but completing maps for the remaining hundreds of thousands of acres could take another year.
On a recent afternoon, Clayton scouted a subdivision north of Escondido, where more than 450 single-story homes were tucked between a road off Interstate 15 and a hillside thick with chamise and buckwheat _ ideal kindling.
He said learning the lay of the land was critical.
``You don't have all day to think this out when fires start,'' he said. ``That's why you do all these mental and computer exercises and developing of plans beforehand.''