During the past month, sea-surface temperatures have remained cooler than average by between 0.5 and 2 degrees Celsius across much of the equatorial Pacific Ocean. This indicates that the La Nina, which has redeveloped during the past few months, is holding strong.
The latest climate models indicate that this current La Nina will strengthen during the next couple months and remain through at least winter. As a result of the current La Nina and the possibility of a negative North Atlantic Oscillation, slightly cooler than average temperatures are forecast across parts of the northern Plains, Midwest, Great Lakes and Ohio Valley during December. A surplus of heating degree-days by between 30 and 90 is expected, which likely will result in higher than average heating costs across these regions.
In contrast, temperatures are expected to average slightly warmer than normal across portions of the southern Rockies, southern Plains, and lower Mississippi Valley. Total heating degree-day deficits of between 20 and 50 are predicted throughout these areas. Much of the southeastern and western United States will see December temperatures that will average closer to normal.