This week Science Moab is speaking to a scientist whose head is in the clouds: Tony Merriman, the meteorologist for the National Weather Service‘s warning coordination in Flagstaff, Arizona. We cover the science behind weather trends in the Southwest, how storms form, and the relationships he and his team have built with the Navajo nation to discuss weather across languages ââand cultures.
Science Moab: Why do we see so many clouds here when this area has so little moisture and precipitation?
Merriman: There are several main ingredients needed for clouds and thunderstorms to develop. First we need moisture. When it comes to clouds, we speak of moisture in the atmosphere. So it may be dry on the surface, but if we go a few thousand feet into the atmosphere it could have a higher dew point.
Then we need another mechanism called a lift; in the southwest we have orographic upwelling, which pushes air into the atmosphere due to the terrain. So if the air has enough moisture and is forced into the atmosphere through a mountain range or some type of terrain feature, it can condense into clouds. There’s enough moisture in the middle of the atmosphere to create these clouds right now, but you don’t get much, if any, rainfall.
Science Moab: What Will Determine If We Will Get A Monsoon Season?
Merriman: It’s primarily the general weather pattern and location of what we call mean high pressure. For a good monsoon current, the center of this high pressure is over North Texas. This is a really good monsoon flow, but it is always changing. If that high pressure shifted a little further west and concentrated over New Mexico or Arizona, which we saw last year, that monsoon current would actually rise over the west coast of California, not the southwest. Wherever that high pressure center is, it gets hot and dry.
Science Moab: what causes the severity of the thunderstorms we see during monsoons?
Merriman: The so-called wind shear, which has to do with the jet stream, is decisive for the intensity of thunderstorms. The jet stream will be displaced further north in the summer months. So you might actually see stronger storms in the northern plains and east coast. But in the Southwest, due to the moisture we get and the short lifespan of these thunderstorms, they can rain quite a bit in a short amount of time. That leads to flash floods. When it rains on rocks or burn scars after a fire, not much rain is absorbed into the ground. The impact is simply much higher out here because of the rocky terrain, the risk of flash floods, and the low water crossings.
Science Moab: Tell me about your project with the DinÃ© (or politically the Navajo nation) creating cloud maps that incorporated the Navajo language into weather terms.
Merriman: We started a project to create a Navajo weather poster as part of the NOAA Hollings Scholarship Program and worked with the Navajo Nation to get translation and design help. We have worked very closely to ensure we have accurate words for various weather phenomena and also maintain the traditions of the Navajo nation. It was a big project and I was really glad we did it. We look forward to working with the Hopi tribe or the White Mountain Apache tribe to learn more about how their culture sees the weather and uses nature to predict the weather.
An example our main contact with the Navajo Nation uses is how elders look at the elevation of anthills to predict seasonal weather. If the anthills are very high before winter, the ants expect an above-average snowy year. The same applies to the monsoon season: when the anthills are really high, the ants expect an above-average wet monsoon season. The reverse is also true; If it’s a low anthill, don’t expect much rainfall at all.
Science Moab is a not-for-profit organization dedicated to engaging community members and visitors with science in southeast Utah and on the Colorado Plateau. To learn more and to hear the rest of Tony Merriman’s interview, visit www.sciencemoab.org/radio. This interview was edited for the sake of clarity.