Mass convergence (and divergence) measured by the Oklahoma Mesonet indicates rising or sinking air near the ground at a particular location based on the change in wind speed over a certain length. If winds speed up at a location, or flow away from each other, mass divergence occurs. The loss of mass near the ground due to divergence requires that air from above sink to fill the void. Therefore, areas of mass divergence are associated with downdrafts. Clear skies or thin cloud layers are often found with downdrafts since it is difficult for clouds to form in areas with sinking air.
Mass convergence is found in areas where winds come together. As winds come together, mass builds up and therefore causes air to rise, creating an updraft. Convergence may occur due to topography or daytime heating, and can be especially strong along fronts and dry lines. Meteorologists look for these areas of strong convergence, or updrafts, for possible storm development if the proper ingredients are present.