The main X factor in determining U.S. winter temperatures will be whether an El Nino will develop.
During the past couple of weeks, sea-surface temperatures across the eastern Pacific Ocean have shown some signs of warming again. This trend combined with some of the latest long-range climate model projections yield to at least a weak El Nino developing during the next couple of months. If the El Nino develops, it likely will have at least somewhat of an impact on temperatures and precipitation this winter.
As for December, slightly cooler than average temperatures are forecast for parts of the northern Rockies and north-central Plains with a surplus of monthly heating degree-days of between 30 and 60 projected across these regions. Parts of Texas and Louisiana also might see temperatures average a little cooler than normal during December, which depends on the El Nino’s development. Meanwhile, slightly warmer than normal temperatures are expected throughout parts of the Northeast and Mid-Atlantic, as well as across parts of the Pacific Northwest. These regions likely will see monthly heating degree-day total deficits during December and perhaps slightly below average heating costs. Much of the Midwest, Great Lakes, Tennessee Valley and Southeast are forecast to see average temperatures closer to normal.