Summer and El Niño: What You Can Expect

Whether you define the start of summer climatologically (June 1) or by the solstice (June 21), the summer season is now upon us. You may have also heard that we are currently in El Niño conditions. In recent years, it’s been much more common to talk about El Niño as it relates to winter variability. But it can play a role in summertime variability as well.  So, let’s explore some of those possibilities.

One neat tool to play with is on NOAA Earth Systems Research Laboratory’s (ESRL’s) ENSO Climate Risks page. For every season, across the United States, you can see which areas are at an increased (or decreased) risk of temperature or precipitation extremes, during an El Niño or La Niña. The unique aspect of this page is that it doesn’t just show you the averages, but rather if there’s a tilt toward one extreme end of the distribution or the other.

Let’s look at the risk of summer precipitation extremes, for example (map below at left). From the northern Rocky Mountains, and extending east across the northern plains of Kansas, Nebraska, Iowa, and into Illinois, there is an increased chance for an extremely wet summer during El Niño. There is an increased risk for an extremely dry summer in the Virginias and along the North Carolina coast. A risk of wet extremes does not bode well for the middle of the country, still struggling to dry out from a waterlogged spring.

Shifting our focus to temperature (map above at right), we see that much of the Great Lakes region is at an increased risk for an extremely cold summer. Parts of Montana and the Dakotas, the Pacific Northwest coast, and the Florida peninsula are at an increased risk for an extremely warm summer. This is actually (possibly coincidentally) not that different from the temperature anomalies we’ve seen already since the beginning of June – record heat in northern California, and Chicago just can’t seem to shake those cool spring-like temperatures.

These are no guarantees of what will happen this summer. But there are some key takeaways based on our current climate conditions and what these risk maps show. First, areas that have been extremely wet and have an increased risk of wet extremes are very unlikely to develop drought conditions over the summer. This could be good news for many, but maybe bad news for farmers.  Areas that are currently drier and at risk for warm extremes (the Pacific Northwest and northern plains bordering Canada) are more likely to experience that extremely warm summer because of the dryness. Conversely, the wetter regions at risk for cold extremes (particularly in the upper Midwest) are more likely to have a cold summer because of the wet conditions.

Since 1950, El Niño conditions have been observed in the tropical Pacific 15 times, ranging from mostly weak to moderate strength

Does it matter that this is a weak El Niño?

Let’s shift the conversation away from risk of extremes and more to which direction the climate tilts during El Niño events. To do this, we’re going to take temperature and precipitation data from every summer when El Niño conditions were observed in the ocean at that time, and mash them all together to see what they show. Looking at precipitation anomalies (departures from average, map below at left) across all El Niño summers, we see a trend toward wetter than average conditions in the Intermountain Rockies, the upper Midwest, and the Florida-Georgia coastline. A trend toward drier than average (map below at right) conditions shows up over the Appalachians, and in southern Arizona (possibly related to variability with the monsoon). Temperature anomalies show most of the western part of the country with slightly colder than average temperatures during El Niños.

Jun-Jul-Aug Precipitation Anomalies

Jun-Jul-Aug Temperature Anomalies

No two El Niño events are exactly the same, and actually, based on the ocean temperature anomalies in the tropical Pacific, the strength of the El Niño can vary each time. Since 1950, El Niño conditions have been observed in the tropical Pacific 15 times, ranging from mostly weak to moderate strength, with 3 strong events. This current El Niño has been consistently weak since it started. It’s forecasted to stick around until the end of the year, but it’s not forecasted to get much stronger.  So what happens when we look at temperature and precipitation anomalies, but only for the weak events?

It may surprise you to know that this doesn’t necessarily weaken the anomalies from the previous maps. Climatologists and meteorologists who frequently study El Niño patterns and how they drive climate variability have found that there’s not always a perfect one-to-one relationship between the strength of the El Niño and the strength of the climate anomaly.  And we see a bit of that evidence here in these maps.

For the Rockies, the wetter than average signal (map below at left)  is a bit weaker during a weak El Niño. But for southern Arizona and the Appalachians, the drier than average signal is a bit stronger. For Florida, a weak El Niño actually leads to a stronger tendency toward wetter than average. When just considering the weak events and temperature anomalies (map below at right), the colder than average anomaly strengthens over southern California and around Montana and the Dakotas. Which is an interesting observation, considering those northern areas also showed an increased risk for warm extremes on the climate risks maps. This is partly because once we removed the strong events, we removed some of those warmer than average summers that popped up in the record.

WEAK El Niño: Jun-Jul-Aug Precipitation Anomalies

WEAK El Niño: Jun-Jul-Aug Temperature Anomalies

What is the National Weather Service-Climate Prediction Center showing for this summer?

The latest seasonal outlook from the Climate Prediction Center was just released on June 20. The outlook is for the July-August-September time period, but some of the patterns are emerging may look a bit familiar after looking at our El Niño maps. The precipitation outlook (map below at left) shows an increased chance of wetter than average conditions across much of the Intermountain West and into the Midwest. This outlook is fairly consistent with what the composite of all El Niño events showed, although no drier than average chances are shown anywhere in the outlook.

The temperature outlook (map below at right) from CPC shows a good chance for warmer than average conditions in the Pacific Northwest, across the west coast, and all along the east coast as well. While we didn’t see this in our El Niño composite maps, recall the extremes risk maps. Areas showing a risk for warm extremes in the northwest and in Montana/North Dakota also show up in the CPC outlook. People who live in these areas should remain aware of this. An increased chance for colder than average conditions is expected over the plains and Midwest. Given what we’ve talked about, and their very wet conditions over the past couple of months, that forecast makes sense.

Overall, we know that El Niño is not always the ultimate deciding factor into what our weather is going to be like over the next season. The atmosphere is pretty complex, and so many different variables play a partial role in our weather variability. Summer is an even harder time to predict long term, because very local and small-scale factors can make a big difference. But hopefully these maps help shed some light on what may be possible (or not possible) for your region.

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