Expert: Dave Dombek - 8/31/2004

Question
I was asked recently why it is so humid in Kansas even though Kansas is so far from the ocean. So, my question is, what causes humidity, and why is it higher in some inland areas (like Kansas), and lower in some coastal areas (like California)?

Thanks for your help.

Answer
Paul,
Humidity is simply the amount of water vapor in the air. Water vapor comes from many different sources through evaporation, such as streams, lakes, puddles, trees, all kinds of vegetation, etc. However, the biggest source of humidity in the air is a big body of water like an ocean, a large bay, the Gulf of Mexico, etc. A big determining factor in which areas tend to be most humid is the prevailing wind direction. In Kansas, the flow is at least occasionally southerly, and when that happens, very moist air from the Gulf of Mexico is able to flow northward into the state. Keep in mind that in the summer, water temperatures in the Gulf can reach the low to mid 80s. That means that the dew point of the air (a true measure of how moist the air is), can be quite high...well up in the 70s. That makes the air feel like a tropical rain forest. However, the Pacific Ocean is much cooler. Water temperatures rarely get much above the low 70s off the California coast, and that is generally from LA southward. The rest of the California coast experiences water temperatures no higher than the 60s. So, even though California does experience a westerly flow from off the Pacific Ocean quite often, the potential amount of water vapor that the air there can obtain is ALWAYS lower than the air that comes up from the Gulf, simply because the dew points are never as high. Dew points, again the true measure of humidity, rarely get any higher than the 60s in California. That makes a big difference in how it feels!
I hope this answered your question.

Sincerely,

Dave Dombek
Expert Senior Meteorologist
AccuWeather.com