With a "possible" El Niño event forecast for next winter it is important to examine the very broad range of past events that make up an "average" El Niño.
Since 1950 there have been a total of 22 El Niños, eight which have been weak, nine in the moderate range and five which have been categorized as strong. [see Oceanic Niño Index (ONI)]. Even within each of these categories there are huge variations. See El Niño and La Niña Winter Historic Precipitation & Temperatures, a catalog of events.
example, 1977-78 and 1978-79 were weak El Niño events but the winter
precipitation patterns and amounts were dramatically different. The first
year, 1976-77, was a drought season in the West (
The bottom line is that first, any climatology is simply an average over a broad range of previous events. And second, a climatological analysis is NOT a forecasting tool.