Long-range rain connections
Rainfall in California is unexpectedly linked to sea surface temperatures near New Zealand.
This long-distance link, known as a teleconnection, begins when heating or cooling of the sea surface temperature in the south-western Pacific Ocean causes changes in atmospheric circulation between the equator and a latitude about 30 degrees south. This circulation affects the weather east of the Philippines, which in turn causes the jet stream to become weaker or stronger in the northern hemisphere, and the jet stream directly influences the amount of rain coming off the Pacific onto California between November and March.
So the rainstorm shown above, sweeping across Arizona, owes its genesis in some part on the warmth of the water around New Zealand.
This connection appears to be growing stronger in recent decades, and may be a useful tool for predicting rainfall as traditional indicators such as El Nino variations become less reliable.