Weather queries

摘要

How do you know if it is fog or haze here in the mountains of south-central Pennsylvania? I have a terrible time figuring this out. This is not an easy question to answer, but I'll try to answer it without regard to your geographic location. There is a narrow range of relative humidity, from slightly less than 100% to slightly more, that marks the transition from haze to fog. Within this narrow range, you won't be able to measure the relative humidity with sufficient precision: the instruments for doing so are just too expensive. So backyard humidity measurements will not suffice to tell you whether the reduction in visibility is due to haze or fog. A more promising way to tell the difference is to note the color of what's suspended in the air. If it's white or gray, it's probably fog. If it's a subtle shade of blue or yellow-brown, it's probably haze. The reason for this is an interesting story.