Above: precipitation last 90 days, percent departure from normal. Click to see larger version.
There are three main factors that influence the behavior of a wildland fire: weather, fuel, and topography. Thankfully topography does not change from year to year in any significant manner. If it did, the job of wildland firefighters would be incredibly more difficult. Weather and fuels (vegetation) do change, not only from year to year from but from day to day — even hour to hour as the fine fuels absorb moisture out of the air. The weather is infinitely variable and has a huge effect on fires and fuels. This turns many firefighters into amateur meteorologists in an effort to master their craft and keep themselves and their colleagues safe.
Often at this time of the year as preparations are under way for the western wildfire season we look back at the winter weather.
There is little doubt that precipitation and temperature over the last 90 days will have an effect on summer fires. Many media outlets find it hard to resist the temptation on a slow news day to exaggerate how, for example, a dry winter might lead to disastrous wildfires. But the fact is summer weather has a greater effect on the number of acres burned than the conditions six months before. Hot, dry, and windy conditions in the summer are usually associated with a busy fire season.
Precipitation
As you can see in the map above, large sections of the forested areas in the northwest had above normal precipitation over the last 90 days. There are regions in Montana, Washington, and Oregon that had 150 to 200 percent of average. However, much of the southwest, southern California, and areas within the states of Colorado, Utah, Nevada, and Wyoming were below normal.
Heavy rain this winter in northern California, 110 to 150 percent of normal, has been adding a lot of water to the reservoirs that have been in pretty bad shape for the last couple of years. The two largest reservoirs in the state, Lake Shasta and Lake Oroville, have both refilled to levels above the historical average and are 81 and 73 percent full. Most of the lakes farther south have some serious catching up to do.
Snow Cover
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