December Temperature/Precipitation Outlook

La Nina conditions continue across the equatorial Pacific and are expected to continue throughout the winter. We may not see neutral conditions or maybe and El Nino until late spring-early summer. Upwelling of cool ocean waters continues across the west coast of South America, and strong easterly trade winds continue to advect cool ocean waters westward across the equatorial Pacific. Our current Nino 3.4 index is around -0.825 indicating a moderate La Nina remains in place. The IRI/CPC forecast as mentioned continues to suggest we will remain in a La Nina through the winter.

The current CFS monthly forecast suggests a typical La Nina setup. Warmer and dryer conditions across the southern half of the lower 48 while wetter conditions across the Pacific Northwest and Great Lakes.

The Climate Prediction Centers' (CPC) latest forecast almost looks identical to the CFS suggesting dryer and warmer conditions across the south and wetter weather in the Pacific Northwest and Great Lakes.

Again, this is due to La Nina conditions expected to continue across the equatorial Pacific. Above is a schematic of what a typical winter La Nina pattern looks like across North America and you can see clearly how both the models and the forecast guidance line up due to the teleconnections in our oceans.

The NMME keeps this pattern through the winter as we take a look at their December, January, and February Outlook. As we mentioned above the IRI/CPC forecast suggests that La Nina conditions will likely continue through the winter without seeing neutral or positive conditions until late spring-early summer. Guidance keeps the Pacific Northwest wet and the Great Lakes and the lower half of the lower 48, warm and dry.

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