Upper trough maintains the Mediterranean Sea storm track in late December/early January. North of the storm track, colder east wind from Russia develops. However, dry pattern prevents any snow gain.

Wet weather continues to emerge and intensify across Brazil. The rainfall is making a difference in soil moisture as East Brazil loses their wet signature. Additional heavy to excessive rainfall is on the way!

The DEC-25 U.S. gas population weight HDD is revised colder to 949, the coldest DEC since 2010 and 3rd coldest of this century. Previously, cold JAN-26 forecasts reversed warmer with mid-NOV updates and then colder with the early DEC projection. Operational models are shifting much warmer for JAN-26 therefore a warmer revision is necessary. The JAN-26 HDD forecast warms from 981 to 947 which ranks 13th coldest of 2020-25.

La Nina has recently weakened. Some regeneration is possible for later this month/early January. However, the push toward warming by a recent intense MJO event suggests the weak late 2026 La Nina has peaked, and neutral ENSO generates for Q1/2026. The warming Northeast Pacific generated in-part by the recent intense MJO event requires monitoring. Often, warming of the Northeast Pacific is a precursor to an ENSO phase change toward El Nino. ECMWF and NMME (models) forecast El Nino onset during Q2/2026.