December 2021 upper air 500 MB height anomalies identify the prevailing weather pattern. A West Coast upper trough propels a stormy regime. In the East both the polar and subtropical jet streams arc into a ridge position bringing historic warmth. Note the upper air pattern runs parallel to the regional SSTA regimes in the northeast Pacific and western North Atlantic.

Arctic air in Western Canada to the northern Great Plains means potential for sneaky cold anywhere that has snow cover. The 12Z GFS indicates a pulse of arctic air across New York/New England next TUE/WED!

The Climate Impact Company 4-week gas population weight observed weekly HDD anomalies identifiers the warm December but is trending toward a colder scenario in January.

While much of Brazil has been soaking wet in recent months, the southeast has remained mostly dry. Additionally, long-term rainfall deficits imply deep layer soil moisture dryness. Northeast Argentina is trending very dry and hot to help accelerate drought concerns.