A Wind Shift Turns a Fire's Long Flank Into a Wide Head
A fire pushed by a steady wind grows long and narrow, with a small head and two long flanks. When the wind changes direction — as a cold front passes, as a sea breeze arrives in the afternoon, or as a thunderstorm outflow spreads out — the entire flank becomes the new head at once, and the fire's frontal width can increase many times over in minutes without any change in fuels or intensity. Frontal wind shifts are forecastable in direction and approximate timing; sea breezes are near-daily and roughly clocklike on coasts; thunderstorm outflows are the least predictable and can arrive from any direction tens of kilometres from the storm. The confusion this resolves is thinking of a wind shift as changing where a fire goes; it changes how much of the fire is advancing. After this Concept you can predict the change in a fire's shape and active perimeter from a forecast wind shift.
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A fire pushed by a steady wind grows long and narrow, with a small head and two long flanks. When the wind changes direction — as a cold front passes, as a sea breeze arrives in the afternoon, or as a thunderstorm outflow spreads out — the entire flank becomes the new head at once, and the fire's frontal width can increase many times over in minutes without any change in fuels or intensity. Frontal wind shifts are forecastable in direction and approximate timing; sea breezes are near-daily and roughly clocklike on coasts; thunderstorm outflows are the least predictable and can arrive from any direction tens of kilometres from the storm. The confusion this resolves is thinking of a wind shift as changing where a fire goes; it changes how much of the fire is advancing. After this Concept you can predict the change in a fire's shape and active perimeter from a forecast wind shift.
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