El Niño is here. Barely.
The National Oceanic and Atmospheric Administration Climate Prediction Center's Emily Becker said atmospheric and oceanic conditions just barely allowed forecasters to declare an El Niño advisory this week after months of "almost" conditions were recorded.
In a NOAA blog Thursday, Becker said the conditions recorded are "extremely weak El Niño conditions," though a Climate Prediction Center consensus forecast calls for an approximately 50-60% chance that El Niño conditions will continue through the spring.
A NOAA map pairing of historical March-May El Niño precipitation patterns shows how El Niño has affected U.S. precipitation during the 10 years of the modern instrument record during which El Niño was present in the spring: 1953, 1957, 1958, 1966, 1969, 1983, 1987, 1992, 1998, and 2010.
According to NOAA, the map on the left shows March-April-May precipitation during those 10 years compared to the long-term average, with browns indicating drier–than-average springs, and greens and blues indicating wetter-than-average springs.
The map on the right shows how often that wet or dry precipitation pattern occurred. "Cool" colors indicate the particular wet or dry signal occurred less than 50% of the time, while "warm" colors indicate frequencies above 50%, meaning five or more years out of 10.
NOAA said maps show that spring precipitation in some parts of the U.S. has a reliable connection to El Niño; In the mountainous regions of the Pacific Northwest, for example, a moderate dry signal (dark browns) occurred between 60-70% (orange) and 80-90% (red) of the El Niño springs on record.
The Great Lakes region and the Ohio Valley also saw moderately dry springs from 60-70% to 80-90% of the time, NOAA said.
A strong wet signal (dark green and blues) shows up in coastal Northern California, northeast Texas, central Florida, and the Northeast coast from Massachusetts to New Jersey.
The reliability of that signal varies considerably from one place to another, however. The most reliable wet spring signal appears in central Florida, where it occurred in up to nine years out of 10 (red areas), NOAA said.
In most of California and Texas, on the other hand, El Niño brought wet springs less than 50% of the time (light blue and cyan).
As far as using the past to infer what a given region might expect from the current El Niño, NOAA said the maps show the precipitation patterns during all El Niños of the modern record, regardless of how strong or weak they are.
"The current El Niño is weak, and it’s generally the case that the weaker the El Niño, the more likely it is that other weather variability will drown out its influence," NOAA said.