A La Niña event in November/December has been predicted lasting several months with a greater than 50 percent chance. Below is a description of what that means in North America – basically cooler temperatures and snowier winters.
North America
La Niña causes mostly the opposite effects of El Niño with above-average precipitation across the northern Midwest, the northern Rockies, northern California and the Pacific Northwest’s southern and eastern regions. Meanwhile, precipitation in the southwestern and southeastern states will be below average. This also allows for the development of many stronger-than-average hurricanes in the Atlantic and fewer in the Pacific.
The synoptic condition for Tehuantepecer winds is associated with a high-pressure system forming in the Sierra Madre mountains of Mexico in the wake of an advancing cold front, which causes winds to accelerate through the Isthmus of Tehuantepec.
Tehuantepecers primarily occur during the cold-season months for the region in the wake of cold fronts, between October and February, with a summer maximum in July caused by the westward extension of the Azores-Bermuda high pressure system.
Wind magnitude is weaker during La Niña years than in El Niño years, due to the less frequent cold frontal incursions, with its effects lasting from a few hours to six days.
In Canada, La Niña will generally cause a cooler and snowier winter, such as the near record-breaking amounts of snow recorded in the La Niña winter of 2007-08 in Eastern Canada.