Which atmospheric condition does not help in fire spread?

High humidity is a condition that does not help in fire spread because it indicates that the air contains a significant amount of moisture. When humidity levels are high, the moisture in the air can dampen vegetation and forest floor fuels, making them less prone to ignition and reducing the intensity and spread of fire. In contrast, elevated temperatures, low vegetation moisture, and dry winds contribute to rapid fire spread by increasing the dryness of fuels, enhancing their flammability, and promoting faster combustion. Thus, high humidity serves as a barrier to fire spread, which is why it is the correct answer in this context.