Leading into the 15+ day period negative phase arctic oscillation continues and negative North Atlantic oscillation strengthens. Coupled with snow cover, the East U.S. cold continues and eventually re-widens. Cross polar arctic air flow fuels another cold blast week-4 ahead for the Central U.S. Additionally, cold week-4 forecasts by AI were correct (from early January) for the current pattern. Finally, strong -AO in January has historical precedent to continue in February.

The latest 15-day ERCOT daily temperature average outlook indicates a double dip of cold weather ahead centered on Houston. The evolving double dip cold rival other cold outbreaks for Texas this decade. The 12Z GFS enhances the cold air mass over snow cover in the 6-10-day period where record cold is likely.

The U.S. HDD outlook in today’s week-4 outlook is colder than normal utilizing a consensus between AI 4CastNet V2 ECM ENS, AI 4CastNet V2 GFS ENS, and AI Graph Cast ECM ENS. The CFS V2/ECM consensus is warmer. Of interest is the record strength 295 HDD forecast for the last week of January from overnight compared to week-4 forecasts made earlier this month. AI was much colder than the CFS V2/ECM consensus.

The equatorial subsurface warmed during the past few weeks although losing some intensity as mid-January approaches. Also losing intensity is remnant cool waters in the subsurface off the northwest coast of South America.