Drought reprieve for Lower 48

By May 21, drought coverage in the Lower 48 states fell to 12.55%, lowest in more than four years, according to the U.S. Drought Monitor. As recently as October 2023, U.S. drought coverage had been above 40%. The dramatic improvement was directly related to El Niño, an episodic warming of the central and eastern equatorial Pacific Ocean that typically leads to enhanced winter and spring storminess across much of the U.S. However, El Niño is quickly fading and will soon be replaced by La Niña, possibly as early as summer 2024 and certainly by autumn.

With La Niña, a cooling of those same Pacific equatorial waters, U.S. impacts tend to be opposite of those associated with El Niño. Notably, La Niña-related impacts that could begin as early as autumn 2024 may include warm, dry weather across the southern tier of the U.S., as well as cold, stormy weather from the northern Rockies into the Midwest. Of more immediate concern is the Atlantic hurricane season. The National Weather Service recently issued its 2024 tropical outlook, which indicates that as many as 17-25 tropical cyclones and 8-13 hurricanes could form this year in the Atlantic Basin. Enhanced tropical activity should contribute to wetter-than-normal weather during summer and early autumn 2024 along and near the Gulf and Atlantic Coasts, possibly extending as far inland as the Ohio Valley.

Unrelated to the El Niño-to-La Niña transition, National Weather Service forecast guidance suggests that the summer of 2024 could be hot and dry across the Rockies and Great Plains, with possible adverse implications for rangeland, pastures and summer crops. Fortunately, much of the western U.S. enters the 2024 growing season with adequate irrigation supplies, with statewide reservoir storage above average in all states except Washington and New Mexico. However, storage remains significantly below average in larger, multistate watersheds such as the Rio Grande and the Colorado River Valley, with end-of-April storage in the latter basin standing at 60% of the historical average.