By influencing the position of the jet stream, the persistence of the La Niña phenomenon will have consequences on temperatures and snow cover this winter, particularly in North America. In Europe, the impact of La Niña is not known, but forecasts for this winter all envisage the same worrying scenario.
La Niña appears in phases of one to two years, alternating with its warm counterpart El Niño. These two phenomena are characterized by a temperature anomaly over part of the Pacific Ocean: colder than average water over this specific area is associated with La Niña, while warmer water is associated with El Niño. La Niña has suffered several decreases in intensity since September 2020, before rising again last spring and continuing until September 2022. NOAA climate forecasts indicate that the phenomenon will strengthen over the next next winter for a third consecutive year, a rare but not unprecedented event. Just like El Niño, La Niña strongly influences the weather in any part of the world.
Heavy snow forecast for northern US and Canada
La Niña usually causes the anticyclone to lock over the northern Pacific Ocean, further pushing the jet stream to the north: this gives a very cold winter in Canada and very humid in the northwest of the United States (Washington, Montana, Wyoming), the northeast (New York, Massachusetts, Maine…) as well as the Great Lakes region, and warmer and drier than average over the entire southern half, this is what happened in 2020 and 2021. The site Severe Weather Europe carried out a study of the various long-term weather forecasting models (ECMWF and UKMO): while the ECMWF model predicts significant snowfall in Canada and a deficit in the western United States, the UKMO model reveals more classic forecasts in a La Niña: A very snowy winter starting in December, and even more in January, over the northwestern United States (including the Rockies), the Great Lakes region, the northeast of the country and all of Canada . Forecasts quite similar to what these regions have experienced in the past two years: the snow cover has been very beneficial for the American West in particular, while the southern United States experienced a historically warm and dry winter 2021-2022.
Towards a dry and mild winter in Europe?
The impact of La Niña on the European climate is not known: it may be non-existent, or just unknown by the current state of science. Over the next three months (November, December, January) the snow cover is seen as largely lacking over all of Europe by the two ECMWF and UKMO models, in particular December which promises to be very dry for the moment. Some snowfalls are expected during the month of November, but the following does not look cold enough to allow the arrival of snow, outside the high altitude areas. Remember that long-term forecasts are experimental models to be taken with a grain of salt. But if these forecasts for the winter are confirmed, the lack of snow over a large part of Europe would be very bad news for biodiversity, water resources and the economy of mountain leisure activities.