Every so often, a dome of upper-level high pressure sits in place for a few days, sometimes as long as several weeks. A major block can produce seemingly endless stretches of blazing heat or bitter cold. By the time it dissipates, it may leave behind a whole stack of broken weather records and an array of disastrous consequences.

The inadvertent cloud-seeding effect occurs up to about 6 percent of the time at major airports.

Prior to massive flooding early in 2011, long-term drought plagued the Australian state of Queensland . As part of a broad research program on cloud seeding, NCAR researchers have been steadily crunching data from a 2008–09 field project that looked into how to make the clouds drop more rain on the region.

A new study led by NCAR’s Wei Yu and CU-Boulder’s Weiqing Han looks at the effects of the Madden-Julian Oscillation (MJO), the largest source of intraseasonal (within one season) variability in the tropics, causing wet and dry periods to alternate.