Temporal Variations of Cloud Liquid Water during Winter Storms over the Mogollon Rim of Arizona

Abstract

Several winter storms were observed by various instrumentation systems over the Mogollon Rim of Arizona during early 1987. The storms commonly displayed considerable temporal variability in CLW (cloud liquid water) as monitored by a microwave radiometer. The vertically integrated liquid amounts were often inversely correlated with the height of the cloud tops as measured by radar, suggesting that periods with shallow clouds and warm tops may be the most seedable. However, there were important exceptions to this general rule, associated with strong low-level horizontal winds that presumably produced significant uplift and more condensate than nature could convert to snowfall. Three storm episodes were selected for illustration of the short-term variability in CLW. It is shown that shallow clouds with abundant liquid often occurred at the beginning and ending phases of a storm, and sometimes in the middle portion as well. However, the timing and duration of the CLW periods would be very difficult to forecast, and limiting seeding operations to just CLW periods would usually be impractical. Rather, seeding would probably need to be continuous throughout most storm episodes because of inability to respond to short-term variations in available liquid water. It is suspected that the situation is similar for other mountain barriers of the West.