Hot, dry, windy days are when wildfires explode
Wildfire agencies across western North America publish a daily fire danger rating that summarises how easily a new fire would start and how...
Wildfire agencies across western North America publish a daily fire danger rating that summarises how easily a new fire would start and how aggressively it would spread under current weather. The rating combines temperature, relative humidity, wind speed and recent precipitation — the same conditions that drive the Canadian Fire Weather Index and the US National Fire Danger Rating System. Low and moderate days mean fires can start but tend to stay small. High, very high and extreme days mean any new ignition can grow quickly and resist initial attack. The practical pattern is well established: hot afternoons, single-digit relative humidity, sustained wind and weeks since the last meaningful rain are the conditions under which most large interface fires occur. Pay attention to your regional fire danger rating during heat waves, follow campfire and OHV restrictions, and treat very high or extreme rating days as the wrong time to use any spark-producing tool outdoors. The same conditions also signal that any active fire near your community will move faster than usual — which is when evacuation alerts deserve maximum attention.
Single-digit relative humidity, sustained wind, and weeks without rain are the conditions behind nearly every major interface fire — the daily fire danger rating quietly tells you when those line up.
Source: Alberta Wildfire Status
Last reviewed 2026-05-02.
See live fires, evacuation alerts, air quality, and road closures for Western Canada and 18 western US states on our free live map, then run through the preparedness checklists before fire season.
This is the same wildfire safety library that lives inside our free app. Browse it all in the safety library.