KANSAS CITY, MISSOURI, US — La Niña is weakening and expected to completely dissipate this spring. Some computer forecast models have been suggesting that a quick transition from La Niña to El Niño is possible over several months this spring and summer.

In the past, some of these quick transitions have left the atmosphere a little confused, leading to weather problems in many areas around the world.

The loss of La Niña in this coming Northern Hemisphere summer is likely to induce some areas of dryness in Indonesia, Malaysia, Philippines and mainland areas of Southeast Asia. Portions of India also will experience lighter-than-usual precipitation. 

Most of the lighter-than-usual rain will only raise some concern about dryness and crop production, but it normally takes a full blown El Niño event to induce a serious bout of drought in the tropics. 

The US National Oceanic and Atmospheric Administration (NOAA) has a model that predicts ENSO (El Niño/Southern Oscillation) conditions out several months in time. The latest NOAA ENSO forecast model has suggested El Niño may evolve in June and be influencing the world from July through the end of this calendar year. 

World Weather, Inc. believes the transition from La Niña to El Niño is advertised to be too aggressive, but if the forecast verifies there may be several areas around the world that could experience poor crop weather during the second half of this year.

The withdrawal of La Niña and return of neutral ENSO conditions usually brings on lighter-than-usual rainfall in Indonesia, Malaysia, Philippines, Vietnam, Laos, Thailand, Cambodia and parts of India. The dryness is rarely a serious problem unless a full blown El Niño event evolves. There is potential for El Niño conditions later this year, but World Weather, Inc. believes the transition advertised by NOAA is suggested to occur a little too quickly.

In the past, there have been some interesting dryness issues that have evolved across North America when a prolonged La Niña like that of the past few years is quickly followed by a moderately strong El Niño. Weather in North America during March of those years often is mixed with portions of the Midwest, Delta and southeastern states getting a little more than the usual precipitation while the southern Plains, Atlantic Coast states and far western United States is a little drier biased. 

Comparisons to 1976

US weather in April becomes a little more interesting — or at least that is what has happened in the past. There have only been a few occurrences of rapid transition from La Niña to El Niño after a prolonged La Niña event. 

One of those years was 1976, and last year’s weather was similar to 1975 as well as 1956 and 2000. In 1956, La Niña already was dissipated midway through the fourth quarter of that year, which is quite different from that of this year in which La Niña was weakening, but still present. The multi-year La Niña of 1998, 1999 and 2000 was followed by neutral ENSO conditions in 2001. That suggests that if the NOAA forecast model is correct, the quick transition moving from La Niña to El Niño would be a good match for the year 1976. 

Spring 1976 was favorably mixed with periods of warm and cool weather and periods of rain and dry conditions. March was wetter biased in the northern and western Midwest as well as the Delta and interior southeastern states while the central and southern Plains, Atlantic Coast states and far western United States were reporting lighter-than-usual precipitation. The mix of March and April weather was mostly good for early season fieldwork and the development of winter wheat in many areas outside of hard red winter wheat areas.

Dryness continued in March 1976 in the central and southwestern Plains just as the forecast models are suggesting for the first half of March this year. April 1976 weather, though, turned much wetter in the central and southern Plains and a part of the northern Plains while the lower and eastern Midwest, Delta and southeastern states were drier than usual along with the middle Atlantic Coast states. 

In May 1976, the far western states, northern Plains, Canada’s southern Prairies, Midwest and southwestern Plains were all reporting lighter-than-usual precipitation while the southeastern states and lower Midwest were wetter biased. The quick transition from La Niña to El Niño was suspected to have induced some of the dryness noted in May and that which was perpetuated in June through September across portions of the Midwest.

In contrast to the drier-than-usual bias in the Midwest during the summer of 1976, precipitation was greater than usual in the southern Plains and interior western states during July and August, and some of that wetter bias included the Pacific Northwest and a portion of the southern Canada Prairies. 

This parallel to 1976 and the quick transition from La Niña to El Niño is of some concern, especially since there is other evidence that lighter-than-usual precipitation should occur in the Midwest, Delta and interior southeastern states during a part of the spring and summer season. The 18-year lunar cycle is advertising lighter-than-usual rainfall for many Midwestern locations this spring and then a better mix of precipitation and sunshine during the summer. 

There is also some correlation between excessive precipitation in parts of California during the winter months and a drier bias in the Midwest and northern Plains during the spring followed by a wetter summer from the Pacific Northwest through the northern Plains to the western Midwest.

In addition to all the above, the negative phase of Pacific Decadal Oscillation (PDO), which is prevailing, tends to produce greater ridge building in the central United States during the summer months and that, too, could play into the same trend for a drier finish to the growing season this year after a favorable distribution of rain during the spring.

Overall, there are too many indicators pointing toward a drier-than-usual summer in at least the western Midwest and Great Plains with this latest assessment from rapid transitions from La Niña to El Niño possibly producing one of the stronger correlations of such conditions. 

World Weather, Inc. believes the spring planting season will go well, but summer could trend too dry in some areas. Cold weather is still possible in mid to late April in the eastern half of the Midwest and again possibly in the northern Midwest and eastern Canada’s Prairies in June.