El Niño is back.
For the first time in four years, El Niño conditions are in place over the eastern tropical Pacific. NOAA declared the start of the long-expected El Niño event Thursday, June 8, with the issuance of an El Niño Advisory.
The natural phenomenon is part of a recurring ocean-and-atmosphere pattern that warms and cools the eastern tropical Pacific through El Niño and La Niña events that last from one to three years. Once El Niño or La Niña emerges, the odds reliably shift toward hotter, colder, wetter, or drier conditions for various parts of the globe.
The return of El Niño follows an unusually prolonged three-year period dominated by La Niña, which intensified the 23-year megadrought across the Southwest. (This winter’s welcome moisture there – which arrived in spite of La Niña’s tendency toward dry conditions over the Southwest – just goes to remind us that the tendencies fostered by El Niño and La Niña are probabilities, not guarantees.)
One vivid sign of the big transition underway: the U.S. Drought Monitor reported that the percentage of the country classified as being in drought (categories D1 to D4) dropped from 63% at the start of November 2022 to 19% by the end of May 2023 (see Figure 3 below). That’s the most rapid such decrease in drought conditions since the monitor was founded in 2000, according to NOAA.
The consensus of the dynamics-based seasonal climate models used to predict El Niño suggests the unfolding event will rank as a strong one, which would make it the most intense event since the record-level El Niño of 2015-16. The statistics-based models, typically older and less sophisticated than the dynamical models, are less bullish, as shown below.
El Niño events that develop in northern spring and summer typically persist through the following winter. The split jet stream fostered by El Niño tends to smooth out wintertime temperature contrasts across the U.S., leaving the northern states milder and drier than average and the southern states cooler and wetter than usual.
El Niño may not deliver the hurricane-suppressing wind shear we’re used to seeing in the Atlantic. Model output from the U.K. Met Office and the European Center for Medium-range Weather Forecasts has trended toward less wind shear in the Atlantic than usual for an El Niño hurricane season. With sea surface temperatures at or near record-warm levels, that could tip the balance toward an active season, as discussed in our roundup of seasonal outlooks on June 1.
As summarized on Friday by Yale Climate Connections contributor Michael Lowry in a Substack post: “Examining other recent episodes of El Niño coinciding with the peak months of hurricane season, Atlantic waters were generally much cooler than they are today. The tropical Atlantic has been running an astounding full degree Celsius or warmer above its long-term average, blistering warmth that in any other year would signal an active hurricane season ahead.”
A warm, dry spring contributed to Canadian wildfires
Conditions were a bit warmer and drier than usual when averaged across the contiguous United States during spring 2023, especially in May, according to the latest monthly climate update from the National Centers for Environmental Information. As always, there are key regional differences within the national averages – and those regional impacts may get reordered dramatically in the next few months, due to the major switch now underway from La Niña to El Niño.
May 2023 was the 11th-warmest and 29th-driest in 129 years of record-keeping for the contiguous U.S., according to NOAA. An extremely large and strong blocking high led to record-warm conditions across most of western and central Canada, depleting snow cover weeks to months ahead of schedule and laying the groundwork for wildfires from Alberta to Nova Scotia and Quebec (as well as the “perfect smoke storm” in the northeast U.S. during June).
The summerlike heat in Canada bled into the northwest U.S. at times, leading to unseasonable highs in such places as Seattle (91°F on May 15). A block of eight states from Washington and Oregon east to Minnesota all had top-10-warmest Mays, and Washington had its warmest May on record.
Meanwhile, northerly flow around the blocking high helped keep most of the nation east of the Mississippi on the notably mild and dry side, especially along the East Coast. South Carolina had its 10th-coolest May on record, and high temperatures in that state were cooler than in any May on record except for 1972. In stark contrast to the relative coolness that extended all the way south to Georgia, very warm waters in the Gulf of Mexico and northwest Atlantic helped give Florida its 26th-warmest May on record.
During meteorological spring (March-May), no states ranked in their top-10 coolest, while Florida and Massachusetts had top-10 warmest springs. Though it wasn’t an especially warm spring by recent standards when averaged nationally, the season still came in 0.56°F (0.31°C) above the 20th-century average.
May was the driest in 12 years across the 48 contiguous states, with a seasonal total of 2.56 inches compared to the 20th-century average of 2.91 inches. It was a top-10-driest May for Delaware, Michigan, Pennsylvania, and Wisconsin, and every state from the Mississippi Valley eastward was near or below average in precipitation for May, except for Maine. The dry spring was especially intense across eastern Nebraska, where less than two inches of precipitation fell – the lowest spring total there since the depths of the Dust Bowl in 1934, according to NOAA.
The one region hitting the hydrological jackpot was the Southwest, including California, where all states except Utah saw above-average moisture in May. That tendency was even more distinct for springtime as a whole – an extension of the wet, cool conditions that prevailed over much of the winter. Some parts of California’s San Joaquin Valley were hard-hit by flooding, but the lack of a rapid drying out and warming up helped temper the flood risk. Thus, the overall impact of the wet winter will be largely beneficial to the drought-plagued region – though it’s still been enormously difficult for many people in vulnerable communities.
Severe weather peaked in early spring across the United States, most tragically with a sequence of tornado outbreaks that took at least 55 lives from March 24 to April 5. The most destructive single tornado was a just-upgraded, top-end EF4 strength twister that killed 19 people in and near Rolling Fork, Mississippi, on March 24.
Jeff Masters contributed to this post. Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.