Sea-surface temperatures are cooler than average from the west-central Pacific to the eastern Pacific. This indicates that the much-anticipated La Nina has firmly developed in the Equatorial Pacific Ocean. The latest long-range climate models suggest that this La Nina phase will persist through the upcoming winter and possibly into next spring. With that being said, slightly above normal temperatures are forecast across portions of the Intermountain West, Desert Southwest, and southern Rockies during the month of December.
Parts of New England may also see temperatures average slightly warmer than normal in December. These regions of the country are projected to see monthly heating degree day deficits of between 20 and 60 as well as lower energy costs with respect to heating. In contrast, parts of the Pacific Northwest, northern Rockies, and northern Plains are expected to see temperatures average slightly below normal in December. These areas will likely see a bit of a surplus of monthly heating degree days of between 20 and 50. It should be noted that the area of slightly below normal temperatures could possibly extend down to parts of the central Plains and Midwest, especially for the second half of December. On a whole, temperatures are predicted to average closer to normal from the southern Plains over the Southeast.