Meanwhile, some 930 kilometers (1,500 miles) away, relentless rainfall was simultaneously pounding Pakistan and generating intense flooding. The Pakistan Meteorological Department reported nationwide rain totals 70 percent above normal in July and 102 percent above normal in August.
New research conducted by William Lau, an atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., suggests the two seemingly disconnected events were actually closely linked.
Under normal circumstances, the jet stream pushes weather fronts through Eurasia in four or five days, but something unusual happened in July of 2010. A large-scale, stagnant weather pattern — known as an Omega blocking event — slowed the Rossby wave over Russia and prevented the normal progression of weather systems from west to east.
As a result, a large region of high-pressure formed over Russia trapping a hot, dry air mass over the area. As the high lingered, the land surface dried and the normal transfer of moisture from the soil to the atmosphere slowed. Precipitation ceased, vegetation dried out, and the region became a taiga tinderbox.
Meanwhile, the blocking pattern created unusual downstream wind patterns over Pakistan. Areas of low pressure on the leading edge of the Rossby wave formed in response to the high, pulling cold, dry Siberian air into lower latitudes.
This cold air from Siberia clashed with warm, moist air arriving over Pakistan from the Bay of Bengal as part of the monsoon. There's nothing unusual about moisture moving north over India toward the Himalayas. It's a normal part of the monsoon. However, in this case, the unusual wind patterns associated with the blocking high brought upper level air disturbances farther south than typical, which in effect helped shifted the entire monsoon system north and west.
This brought heavy monsoon rains — centered over parts of India — squarely over the northern part of Pakistan, a region ill-prepared to handle large amounts of rain.