Our first week of the new year will feature an uncharacteristic atmospheric pattern that’ll consist of an extended Pacific jet as we see below. Why is it uncharacteristic? Well, we typically see these types of atmospheric rivers, or “Pineapple Express”, in El-Nino’s because of the way the warm sea surface temperatures are structured across the Pacific basin. However, it’s not unprecedented and has happened plenty of times in La-Ninas in the past; there are just complex large-scale processes that manifest around the northern hemisphere that can excite these anomalous patterns.

Above, we see how the Pacific jet is “nosing” its way into Southern CA and generally across the West. This’ll do several things of course, which includes the obvious of providing consistent troughs and storms to allow for heavy rainfall and mountain snow across the Sierra’s, Intermountain West, and the Great Basin, but also provide beneficial rainfall and much needed precipitation! Shown below from the U.S. Drought monitoring site, how in California and an expansive area across the West in at least a level 2, or higher. This is actually very good news!

Heading through the rest of the week, as aforementioned, continuous storminess will occur as a result of the atmospheric river battering the coast. Notice several large-scale storms, especially tomorrow and into Friday sees an impressive system that looks to rapidly strengthen and reach the “bomb cyclone” status.

In terms of rainfall, we’ll see a large area of 4″+, mainly focused across California and high terrain across the Sierra, and into the southern Rockies.

In terms of snowfall, we’ll see easily over 8”, with over a foot especially across the mountains continuing on with an already active start to the season.

By next week, and especially toward mid-month, an expected pattern change will transpire as the jet will look to retract. This has a direct implication on the downstream pattern as now mean troughiness is replaced by ridging, and a break in the activeness commences.