Drought Worsened by a Persistent La Nina

Drought persists from the Prairies of southwestern Canada to the entire western half of the United States. The dry weather in January and February allowed the drought to spread eastward into the western US Corn Belt, which is a bad omen because winter is usually a time for reducing drought rather than expanding it.

La Nina conditions have prevailed since 2020, and their persistence can be attributed largely to the dryness. Some forecasters have recently debated how long the event will last, but World Weather Inc. says it won't matter much once we reach June.

La Nina events in both the Northern and Southern Hemispheres remove moisture from the mid-latitudes. La Nina's mere presence for the past 20 months has allowed the phenomenon to remove significant amounts of moisture from the atmosphere.

The dryness that occurred last summer in Canada and the central United States, affecting crop production, was easily attributed to La Nina, with some assistance from the negative phase of the Pacific Decadal Oscillation (PDO). Dryness in Russia's eastern New Lands and Kazakhstan last summer can also be attributed to La Nia.

Most La Nina events last only eight to fourteen months and younger forecasters began to believe that La Nina was no longer having much of an impact on global weather because it had been so long since an event had lasted this long. The most recent occurrence of prolonged La Nina conditions was in 2010-12, lasting 23 months and resulting in the now-famous 2012 drought in the United States. Prior to that, the previous significant drought in the United States occurred in 1988. However, drought-affected a portion of the North American continent from 2000 to 2004, with Canada and a portion of the central United States being the most affected.

Rain is expected to fall more frequently and heavily from the central US Plains into the upper Midwest over the next few weeks. Over the next few months, it will be the most likely time for rain. If rain frequency and intensity increase sufficiently, drought in the Plains and western Corn Belt could be reduced, allowing for more time for spring planting to take place while soil moisture is favourable. However, if weather patterns are less conducive to significant rain in the coming weeks, warm to hot temperatures and dry weather will begin to diminish the possibility of further drought relief.

Many forecasters predicted that La Nina would dissipate in the spring just a few weeks ago, but this has not happened and is not expected to happen. Statistics indicate that La Nina will persist for a longer period of time, which has been a source of concern for this meteorologist for some time. All indicators indicate that this La Nina will persist throughout the spring, and some forecasters believe it will last into the summer.

World Weather, Inc. believes that whether or not La Nina prevails after June will be unimportant. The reasons for this are numerous. First, if La Nina dissipates in June, there will be a lingering footprint in the atmosphere that will most likely last for a couple of months. Second, this La Nina event has not yet lasted as long as others have in the past.

Most previous extended La Nina events, which occurred after the solar minimum and were accompanied by the negative phase of the Pacific Decadal Oscillation, lasted between 23 and 36 months. With this being the 20th La Nia month in a row since 2020, there is some chance that it will last longer. Third, looking at subsurface ocean temperature anomalies across the Pacific's equatorial region, there is good evidence for a slightly better organized La Nina that may gain some intensity for a while.

With drought already in place across the central and western parts of North America, a high-pressure ridge could form over the US Great Plains during the middle and end of spring. If La Nina persists through the spring, the summer ridge of high pressure will begin to build strength across the region prior to the arrival of summer heat.

The development of high pressure in the central United States earlier than usual will suppress rain events and allow warming to occur, exacerbating the dryness. Once a well-defined high-pressure ridge forms over the US Plains, it will suppress rainfall and block weather systems from the west from entering the region.

Essentially, La Nina conditions that last through spring will leave enough dryness in agricultural areas to allow drought to fester, expand, and intensify, potentially leading to a more severe bout of dryness.

If La Nina disappears after the ridge has become well established in June, there will be insufficient time to change the weather pattern until seasonal cooling arrives in late summer or autumn, resulting in a more persistent ridge of high pressure and greater drought regardless of what happens to La Nina after June.