The weather plays a significant role in how a wildfire grows, how fast it spreads, and how dangerous it can become for firefighters, but few tools exist to help fire managers anticipate days when weather conditions will have the greatest potential to make wildfire erratic or especially dangerous. The USDA Forest Service is expanding the options with the Hot-Dry-Windy Index (HDW), a new fire-weather prediction tool based on the key atmospheric variables that affect wildland fire: temperature, moisture, and wind.