Weather
Written by Emily Becker and published on climate.gov on May 12, 2022
May 2022 ENSO update: piece of cake
La NiƱa continued through April, and forecasters estimate a 61% chance of a La NiƱa three-peat for next fall and early winter. Current El NiƱo/Southern Oscillation (ENSO, the entire El NiƱo and La NiƱa system) conditions, the forecast for the rest of the year, and some potential impacts are all on the dessert menu today.
Mix the butter and sugar together
Weāll start by measuring out the tropical Pacific ocean-atmosphere system. The first ingredient in any ENSO recipe is the sea surface temperature anomaly in the NiƱo-3.4 region of the Pacific. AnĀ anomalyĀ is the difference from the long-term average; in this case, the average is 1991ā2020. When the sea surface temperature anomaly in NiƱo-3.4 meets or exceeds -0.5 Ā°C, weāre inĀ La NiƱa territory. At -1.1 Ā°C, April 2022 was tied with 1950 for the strongest negative April anomaly in theĀ 1950āpresent record. Thatās according to ERSSTv5, ourĀ most reliable long-term sea surface temperature observationĀ dataset.
In the context of repeat La NiƱa events, the April average anomaly was noticeably stronger than any of the other 8 second-year La NiƱas.
The atmosphere also continues to reflect La NiƱa, with plenty of evidence of an enhancedĀ Walker circulation. The normal Walker circulation consists of a loop of rising air over the warm waters of the far western Pacific and Indonesia, west-to-east winds aloft, descending motion over the cooler central/eastern Pacific, and east-to-west winds near the surface (the trade winds). During La NiƱa, the even-warmer west Pacific and even-cooler east Pacific act to strengthen the Walker circulation. In April, both theĀ trade windsĀ andĀ upper-level windsĀ were stronger than average. Along with theĀ April 2022 patternĀ of more rain than average in the western Pacific and less in the central/eastern Pacific, we have ample confirmation that La NiƱa conditions are still going strong.
Beat in the eggs and flour
So whatās in the oven? The odds of La NiƱa drop from 87% for the MayāJuly average to 58% for AugustāOctober, before rebounding very slightly to 61% for the fall and early winter. In the short term, the trade winds are predicted to slow in the coming weeks, which would support a weakening of the cool sea surface temperature anomalies. Most current climate model predictions expect the negative NiƱo-3.4 anomaly will weaken over the summer and strengthen in the fall.
As weāve mentioned a few times here on the ENSO Blog, weāve had La NiƱa for three winters in a row only twice before:1973ā1976 and 1998ā2001. Both of those periods followed very strong El NiƱo events, while the current situation follows a somewhat warm, but officially neutral winter (2019ā2020). ENSO is determined to keep us on our toes, for sure.
One final note about the forecastāweāre still within theĀ spring predictability barrier, when ENSO forecasts are generally less accurate than forecasts made at other times of the year. Weāll start to clear this barrier next month.
Bake at 350 until set
La NiƱa has several important effects on US weather and climate throughout the year. These effects include links toĀ increased severe spring weatherĀ and tornado activity through the U.S. Southeast. So far,Ā 2022Ā has recordedĀ more tornadoes than average. On the other hand, there are a lot of different factors besides La NiƱa at work in creating the conditions for severe weather. For instance,Ā 2021ās La NiƱa springĀ featured aĀ lessĀ active tornado season.
Another reason to care about the ENSO forecast is La NiƱaās influence on theĀ Atlantic hurricane season. La NiƱa conditions decrease the vertical wind shearāthe difference between near-surface and upper-level windsāover the tropical Atlantic. Shear makes it harder for hurricanes to develop, so La NiƱaās reduced shear can contribute to aĀ more active hurricane season. NOAAās official Atlantic hurricane seasonal outlook will be released on May 24th.
Last, but definitely not least, La NiƱaāsĀ northward-shifted jet streamĀ is associated with less rain and snow over large regions of the western and southern US (compare the seasonsĀ here). This can cause andĀ exacerbate drought conditions.
More than half the contiguous US is currently experiencingĀ drought, so I reached out to Brad Pugh, a drought expert at the NOAA Climate Prediction Center, for more information. Brad had this to say about current conditions:
According to theĀ U.S. Drought Monitor, valid on May 3, 53.77% of the continental U.S. is designated with drought (D1-4), with severe to exceptional drought (D2-D4) mostly limited to the West and Great Plains. During the past three months, drought has worsened across much of the Southwest and central to southern Great Plains, which is consistent with La NiƱa during the late winter and spring.
The Drought Monitor is updated weekly on Thursdays; check out the site for lots of fascinating maps.
Brad continued:
The start of the widespread severe to exceptional drought across the Southwest was due to the failed 2020 monsoon. [That would be theĀ North American monsoon, a critical source of rainfall for the southwest. TheĀ 2020 monsoon seasonĀ was the driest and warmest on record for the Southwest.] The persistence and additional expansion of the drought during the past two years is related to the consecutive La Nina winters. La Nina typically favors below-normal precipitation and above-normal temperatures across the southern tier of the U.S.
As far as the forecast goes, Brad added,
theĀ seasonal drought outlookĀ through the end of July calls for drought persistence throughout much of the West, but there could be improvement later in the summer across Arizona as monsoon rainfall increases. The seasonal drought outlook for the summer will be released next Thursday, May 19.
Birthday cake
Whatās with the cake theme? Itās the ENSO Blogās 8thĀ birthday! Hundreds of posts later, we still have a lot to say about ENSO and its extended climate family. Will we be here until the Blog can drive? Only time will tell!
