The Pacific decadal oscillation cool phase strengthened in November. Meanwhile the warm phase of the Atlantic Multi-decadal oscillation ended last month. The -PDO pattern is not expected to last long becoming neutral in 2021 while the AMO pattern should rewarm for the 2021 North Atlantic tropical cyclone season.

The SSTA pattern is very warm. Easterly component of wind will increase the amount of moisture flowing into the developing storm. Heavy rain causing a flood risk is likely in east/northeast Virginia to southeast Maryland while well inland where temperatures stay cold over-achieving snowfalls will occur.

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.