The Nino34 SSTA cool peak for La Nina was late last October. Since that time La Nina is less intense and choppy. Subsurface water in the equatorial East Pacific is not quite as cool as October.

A vigorous negative phase of the arctic oscillation (-AO) is ahead. In the Dec. 11-25 period, forecast models agree on a -2.2 signature of the AO. The GFS identifies the attendant high-pressure block near the polar region. Interestingly, the polar vortex split which results in 4 northern mid-latitude upper troughs are all located farther north than usual for a full-throttle -AO episode.

In North America nearly the entire continent trended drier during SEP/OCT/NOV most notably across the Southwest U.S., Great Basin and California. Additional drying took place in Alaska and much of Canada. The catalyst to the drier climate is the warm SSTA pattern either side of North America promoting anomalous dry/warm high pressure. The Southeast U.S. wet pattern was fueled by tropical cyclone activity. Central America also reversed much wetter due to late season tropical cyclones.

The midday GFS indicates two important trends/changes. The axis of the heaviest rain shifts east and includes Richmond, VA to Dover, DE and across Rhode Island/southeast Massachusetts to coastal Maine. Many areas receive 3 in. of rain. The snowfall forecast increases. In New England 10-20 in. of snow is forecast with >2 feet in northern New England mountain areas.