La Niña has finally emerged after months of anticipation, but there’s a catch. The climate pattern — which typically has an outsized influence on winter weather in the US — is rather weak and may not stick around for long. But that won’t totally eliminate its effect. And, despite its late arrival, it’s already played a clear role in this winter’s weather. Forecasters closely monitor La Niña and its counterpart El Niño because they influence global weather in a way that’s largely consistent and predictable well in advance – especially when the patterns are strong. … Despite the timing and its weakened state, La Niña’s atmospheric influence has already been apparent this winter. California is the most obvious example. Winter in Northern California is typically wetter during La Niña while the southern half of the state is drier than normal. Those extremes are playing out in a major way: Northern California has had plenty of rain while Southern California is so tinder-dry that thousands of acres ignited this week.

Related article:

• The Associated Press: NOAA says La Nina ocean cooling has finally arrived, but it’s weak and may cause fewer problems