Never a shortage of dramatic weather events as 2025 comes to a close. A lingering negative phase of the Antarctic oscillation (-AAO) causes a mid-latitude trough east of Argentina that extends northwestward to soak Brazil into the New Year. Meanwhile, excessive rainfall across Northern Australia will continue. The arctic air source region across Western Canada during December is likely to dissipate in early January due to a cold stratosphere.

Excessive rainfall causes widespread flooding in North/West Queensland this week. Residual effects extend southward to South Australia. Heavy rain continues on the Northwest Coast. Heavy rains are likely to continue next week in the East.

Many weather hazards continue this holiday weekend. Ongoing flooding is widespread in California as the “atmospheric river” storm track begins to wind down. Heavy mountain snow continues for Northern California and Sierra Nevada Mountain Ranges. Snow advisories extend inland to the Rocky Mountains. Dense fog in the Midwest and Northern Gulf States, typical of unseasonably mild air. An ice storm rages in Western Pennsylvania and Winter Storm Warning for the northern Mid-Atlantic region today for heavy snow.

The negative phase North Atlantic oscillation forecast continues and inevitably drives colder changes in the East U.S. Helping to increase East U.S. cold risk is a southern and sustained shift of snow cover across the Northeast States.