America's Divided Weather Extremes Explained
The eastern United States drowned in June while the West parched and burned. Blame the jet stream for this duality of drought and drench.
A fast-moving, narrow current of air, known as the jet stream, flows from east to west across the United States. This June a kink developed in the flow, according to the National Oceanic and Atmospheric Administration.
An area of high atmospheric pressure, called a ridge, formed over the West from Mexico to Montana. This ridge forced the jet steam to re-route to the north around the region. The jet stream took with it the much needed rain. A heat wave further dried out the drought-desiccated region. The deadly Yarnell wildfire in Arizona occurred under these hot, dry conditions. The rain that would have quenched the West’s thirst instead fell on Montana and southern Alberta, causing flooding in Calgary.
At the same time, a low pressure area, known as a trough, formed east of the Mississippi River allowing heavy rains to soak that half of the nation. Tropical Storm Andrea followed the trough northward and deluged the East Coast. Some parts of Maryland, Delaware, New Jersey, and North Carolina received more than 400 percent of normal rainfall.
Precipitation map of U.S. in June (NOAA Climate.gov team)
Fire ladders draped with American flags honor the 19 fallen firefighters that died fighting the Yarnell Fire in June. (InciWeb)