Projecting fire spread with cross slope winds utilizes a vectoring process, where the effect of wind and the effect of slope on Rate of Spread (ROS) may be represented by separate vectors that represent both a magnitude and a direction. The resultant vector represents both a direction and magnitude of maximum spread in that direction
In example A here, wind is crossing more upslope, resulting in an enhanced maximum ROS.
In example B, wind is crossing more downslope, resulting in a reduced maximum ROS.
With winds blowing downslope (±30°), the difference between the spread rates is the resulting ROS using the direction from the larger vector.
If the vectoring process is completed manually, fireline intensity (FLI) and flame length (FL) can be calculated from ROS and Heat Per Unit Area (HPA) using these calculations
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