In the extended range, interesting is the drop-off in skill from 0.25 to 0.45 in the 16-20-day period to 0.15 to 0.25 in the 25-30-day period. In fact, the 25-30-day forecast skill of the popular ECM “weeklies” was matched by the 10-year climatology. Not commonly used for extended range forecasts, GFS ENS ranked first for the extended range outlooks for the past 30 days.

Globally, 2025 projects as the third warmest on record (DEC-25 data not yet available as of this writing). As of December 1st, the U.S. has observed the fifth warmest year in the 131-year period of record. A significant contributor to the warmer climate is the influence of increasing ocean temperature, most notable in the middle latitudes accelerated by the presence of marine heatwaves (MHW).

Last week, the Nino SSTA regions warmed too near, or warmer than the La Nina threshold. Implied is the short duration late 2025 La Nina episode is past peak intensity. Upper ocean heat is steadily diminishing in the equatorial East Pacific, a definite sign that La Nina is losing cool fuel to sustain intensity into the New Year.

Climate drivers in the 11-15-day extended-range forecast indicate the Madden Julian oscillation (MJO) is weak therefore tropical forcing is weak. The stratosphere is shifting much colder following the NOV/DEC warm event as indicated by the 40-day CFS V2 projection. The core of the colder stratosphere is in the same location as the NOV/DEC warming event, across northwestern North America.