Global warming

[pbrower2a]

It's back -- and it is bad. It's drought in the western United States. Except for the part of Montana bordering North Dakota (and America's winter wheat belt) it looks like what one would expect if the subtropical desert belt moved northward as a consequence of global warming. We have seen many recent years of this, including years in which San Francisco  got less rain than Phoenix usually does. When the winter rains fail, San Francisco has desert-like weather... if more like the Atacama than like the Sonoran desert of southern Arizona and the Mexican state Sonora. 



(National Geographic Magazine).

Quote:The conditions are influenced by many factors, including a La Niña event that began last fall, which scientists know can contribute to dry conditions in the Southwest. In a La Niña event, ocean surface waters in the Eastern tropical Pacific are relatively cool (in an El Niño, this part of the ocean is usually extra warm). That cooling shifts the position of towering high-energy clouds, which tend to form over warm water, further to the west, which in turn affects the shape of planet-spanning weather systems. The effect “is like dropping a pebble into a pond,” says Samantha Stevenson, a climate scientist at the University of California, Santa Barbara; where the pebble is dropped affects where the waves of weather move.


The shape and pattern of the big weather ripples moving away from the Eastern Pacific toward the western U.S. make it more likely that precipitation-rich storm systems curve northward toward the Pacific Northwest and Canada rather than toward the Southwest.

A healthy dose of random chance also feeds into the weather patterns that keep the West dry. But underneath the weather vagaries, human-driven climate change is making those conditions more likely.

https://www.nationalgeographic.com/envir...r-develops

If this is a long-term pattern, then desert and semi-desert zones will expand into the southwestern quadrant of the USA. 

Eric might not want to see cactuses appearing in the South Bay area.