When the relative humidity is lower than around 20 percent, it can be a bit dangerous because fires are more intense due to the dryness. Image of a tree burning as a result of a spot fire. When the relative humidity is over 50 percent, fires may not be able to burn the area completely or may not get to a high enough temperature to achieve the desired result because of the moisture in the air. 3.When a cold front moves through an area, there is usually a temperature drop and a drop in the relative humidity. The lower humidity occurs because of the movement of a warm moist air mass to a cooler drier air mass.
Relative humidity is a factor of prescribed burns that is dependant on all of the other factors.
This is why it is not a good idea to try and predict fire behavior of a burn solely on relative humidity. Burns can be done at any level, but the recommended level promises better burns. Temperature also plays a big part in how well a prescribed burn goes. Image of a fire that has gotten out of hand. The temperature of an area can come into play when conducting burns.