National Weather Service United States Department of Commerce

Cold Temperatures for the Eastern U.S.; Lake Effect Snow in the Great Lakes; Heavy Rain in the Pacific Northwest

Cold temperatures will continue across much of the eastern U.S. into today. Heavy lake effect snow continues into today east of Lakes Erie and Ontario. Two Pacific cold fronts will cross the Pacific Northwest early this week followed by another atmospheric river. Heavy rain and gusty winds are expected through midweek, with the potential for renewed urban and river flooding. Read More >

A Discussion on Water Vapor (Moisture)

QUESTION 1:

In the winter, if the air temperature was 40 F and the dewpoint was also 40, what would the relative humidity be? Now, in the spring, if the air temperature was 70 and the dewpoint was 70, what would the relative humidity be? In which situation would if feel more humid? What does this tell you about relative humidity?

ANSWER 1:

If the air temperature and dewpoint temperature were both 40, the relative humidity would be 100 percent. Likewise, if the air and dewpoint temperature were both 70, the relative humidity would again be 100 percent. Despite the relative humidity being the same in both cases, it certainly would feel more humid if the air and dewpoint temperatures were both 70 degrees. This shows how the relative humidity tells you little about the actual moisture content of the air (much more moisture is contained in the air for the summer case), and how the same relative humidity value can occur in completely different situations having very different "feels" to our bodies.

Back to Discussion on Water Vapor