Researchers have developed a fancy graphic presentation that explores the relationship between precipitation and the annual area burned in the Western United States. You should check it out.
They concluded that weather conditions DURING the fire season, humidity and rain, have far more effect on total acres burned than winter snow.
The figures and text (below) here are excerpts from the document.
“Wildfires have been increasing: but why? Is it the effect of increasing temperatures? Declining snowpack? Decreasing precipitation? In their recent paper, “Decreasing fire season precipitation increased recent western US forest wildfire activity,” Zachary Holden and his co-authors explore the relative influence of these factors. They first identified the variables related to temperature, snow, and precipitation that best predicted area burned:
“Temperature: vapor pressure deficit [VPD] (the difference between the maximum amount of water the air can hold and the amount it actually holds)
“Snow: maximum annual snow water equivalent [SWE], and
“Precipitation: wetting rain days [WRD], days with more than 1/10 inch of rain, in the months of May through September.”