Operational models indicate an amplified upper trough pattern that could initiate record-cool temperatures in the 11-15-day period across west/central Australia lingering for much of the remainder of November once established (according to ECMWF). The upper trough will cause widespread wetter than normal weather from northwest-to-southeast across Australia in November.

While “atmospheric river” and “bomb cyclone” are new meteorological expressions which were used to describe the potent West Coast storms over-the-weekend there are some climate diagnostics completely unique which helped two 943-947 MB low-pressure systems to form…one just southwest of Alaska last Thursday night and another due west of Washington Sunday morning.

The NCEP CFS V2 (model) upper air forecast offers clues as to what to expect across Brazil and Argentina the next two months. In Brazil, the upper air forecast coupled with warm SSTA in the South Atlantic tropics sustains a wet forecast. However, just to the south of the wet regime a drier than normal climate is favored for northeast Argentina to far Southeast Brazil into early summer where drought concerns evolve.

An exceptionally strong upper trough spawns one of the lowest surface pressures in the North Pacific for a mid-latitude storm forecast for Sunday. Hurricane force gusts with heavy rain strikes the northern California and Coastal Northwest late weekend.

For the first times since 2012, the cool “horse shoe” SSTA pattern stretching from the Gulf of Alaska to just-off the West Coast of North America and southwestward to the south of Hawaii toward the Dateline in the Pacific tropics has emerged. Presence of the cool “horse shoe” SSTA pattern coupled with La Nina normally increases the risk and amplitude of La Nina climate signals which includes heavy precipitation during NOV/DEC/JAN in the Northwest U.S., dryness leading to drought in the Mid-south States and a general warmer-than-normal national pattern.

NOAA/CPC announced yesterday (Oct. 14) that La Nina onset developed in October 2021. The surface/subsurface cool anomalies in the equatorial East Pacific suggest La Nina Modoki. The projected ENSO West-East index (WEI) for October suggests La Nina Modoki. The La Nina episode is forecast to last into early northern hemisphere spring 2022.