Synopsis: A strong El Niño is expected to gradually weaken through spring 2016, and to transition to ENSO-neutral during late spring or early summer.
A strong El Niño continued during December, with well above-average sea surface temperatures (SSTs) across the central and eastern equatorial Pacific Ocean. All weekly Niño indices decreased slightly from the previous month. The subsurface temperatures in the central and eastern Pacific, while still well above average, weakened due to an upwelling equatorial oceanic Kelvin wave. Significant low-level westerly wind anomalies and upper-level easterly wind anomalies continued over much of the tropical Pacific. During the last week, another westerly wind burst occurred in the east-central Pacific. The traditional and equatorial Southern Oscillation Index (SOI) values remained strongly negative. Also, convection remained strong over the central and east-central tropical Pacific, and suppressed over Indonesia. Collectively, these atmospheric and oceanic anomalies reflect the continuation of a strong El Niño episode.
Most models indicate that a strong El Niño will weaken with a transition to ENSO-neutral during the late spring or early summer. The forecasters are in agreement with the model consensus, though the exact timing of the transition is difficult to predict. A strong El Niño is expected to gradually weaken through spring 2016, and to transition to ENSO-neutral during late spring or early summer.
El Niño has already produced significant global impacts and is expected to affect temperature and precipitation patterns across the United States during the upcoming months. The seasonal outlooks for January - March indicate an increased likelihood of above-median precipitation across the southern tier of the United States, and below-median precipitation over the northern tier of the United States. Above-average temperatures are favored in the West and northern half of the country with below-average temperatures favored in the southern Plains and along the Gulf Coast.
Much of the west and intermountain region should be from slightly warmer to slightly cooler than normal while the Great Plains east and including Wisconsin, Illinois and Missouri and most of Michigan and Indiana should be slightly warmer than normal while the Northeast, Eastern Seaboard, far South and Southwest remain considerably warmer than normal.
Most of the western states will be drier than normal with the upper plain states through Missouri and Indiana and the Gulf state to Northern Florida and Georgia being slightly to moderately wetter than normal along with the Appalachian states. The far northeast from including upstate New York and New Hampshire and Vermont should be drier than normal.
Much of the west and intermountain region should be slightly cooler than normal while the Great Plains east and including Wisconsin, Illinois and Missouri and most of Michigan and Indiana through to Pennsylvania should be moderately colder than normal while the far Northeast, Eastern Seaboard, Appalachia and the far South and Southwest remain warmer than normal.
Parts of central Washington state and Oregon and north Idaho and western Wyoming along with Southern California and the Central Valley and Arizona and western New Mexico should be slightly to moderately wetter than normal. Much of the western plans from Montana through west Texas should be moderately to severely drier than normal. The Mississippi and Ohio valleys should be near normal to slightly wetter than normal. The eastern seaboard all way to Florida should be slightly to moderately drier than normal.