Historic El Niño, La Niña, and Rainfall Animated Loop
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Low Pressure Positions - Wet verses Dry
El Niño/Southern Oscillation (ENSO) events do not have a unique Californian signature. Precipitation patterns are correlated instead with the east-west location of the Aleutian-Alaskan Low. If the low is farther west than normal, as it was in the winter off 1977, a high-pressure cell forms over California, protecting it from winter storms (top).
If the low is farther east than normal, as it was in 1983, storms penetrate into central California and the winter is wet (middle). Brown corresponds to monthly river flow in the lowest quartile and green to a monthly river flow in the highest quartile. Isobar units are millibars. Actual flows for the two years are shown in the graph at bottom.