Unseasonable warmth across the American West and overall dry conditions across the South is causing drought to expand throughout many parts of the United States.
According to the U.S. Drought Monitor, most of the southern half of the United States is presently experiencing abnormally dry or drought conditions. Meanwhile, an intense drought that has remained in place over the Dakotas and Montana for multiple months continues to persist.
A strengthening La Nina in the Equatorial Pacific is helping to generate a drought tendency for the Southern U.S. However, various climate change related features including above normal temperatures and a persistent high pressure ridge in the West are lending intensity to the rising drought regime.
(U.S. 30 day average shows much warmer than normal conditions for the lower 48 with extreme warmth prevalent over the American West. Image source: Global and Regional Climate Anomalies.)
Over the past 30 days, temperatures for the U.S. as a whole have been 1.52 C above average (see image above). Much of this excess heat has been concentrated over the West, with mountain and Pacific regions seeing between 4 and 5 C above average temperatures.
Present drought is nowhere near as intense as it has been during recent years. Especially in California which during 2017 has experienced a bit of a respite. However, with La Nina gaining traction in the Pacific, with global temperatures now in a range between 1.1 and 1.2 C above 1880s averages, and with persistent ridging again taking hold over the U.S. West, the risk of a return to intense drought — especially for the Southwest — is increasing.