WASHINGTON (7News) — On April 13, the Climate Prediction Center issued an El Niño watch in its April ENSO Outlook. But what exactly does this mean for the D.C. region?
First, ENSO stands for El Niño-Southern Oscillation, which is a climate pattern driven by differences in sea surface temperatures and rainfall in the equatorial Pacific Ocean. The warm phase of this oscillation is defined as "El Niño" and the cool phase is "La Niña." These phases switch every 2 to 7 years. Now, we're coming out of a 3-year La Niña phase and straight into an El Niño phase.
The watch was issued by the Climate Prediction Center because, a lot like a tornado watch or severe thunderstorm watch issued by the National Weather Service, conditions are coming together for El Niño conditions to begin by the second half of this year. The watch is the first category of alert when El Niños are in the forecast, and they're issued based on the following criteria:
Average sea surface temperatures in the Niño-3.4 region of the equatorial Pacific Ocean were at least 0.5C (0.9F) warmer than average in the preceding month, and the anomaly has persisted or is expected to persist for five consecutive, overlapping three-month periods. The atmosphere over the tropical Pacific exhibits one or more of the changes commonly associated with El Niño. This includes weaker-than-usual easterly trade winds, reduced cloudiness, rainfall over Indonesia and a corresponding increase in the average surface pressure. Or, it could include increased cloudiness and rainfall in the central or eastern part of the basin, and a corresponding drop in the average surface pressure.
This is the criteria, but what does it mean here at home? Well, there's still time for things to change. However, according to the Climate Prediction Center, in their El Niño Watch, there's a 62% chance of El Niño occurring this year. Beyond that, it's difficult to determine (this far in advance) any specific weather forecast.
But what we can do is look to the past and see how El Niños have affected the D.C. region back then.
Historically, El Niños can have catastrophic effects on other parts of the world. But the D.C. region has been spared some of the weather extremes that plagued other areas, when looking back at the past five El Niño events.
Looking at the most recent El Niño events, temperatures didn't veer too far away from average. The biggest disparity was in the 2002–2003 Moderate El Niño where the average temperature was about 1.5 from the average.
There were larger departures from average when it came to rainfall during the same most recent events. A rough correlation would be to interpret that the weaker the El Niño, the more rainfall we picked up.
This information generally aligns with the Climate Prediction Center's El Niño forecast. The gray color painted over the D.C. region indicates that, generally, average precipitation and temperatures are to be expected. Keep in mind, El Niño are climate patterns that affect long-term weather. Individual weather events will vary.