Why This Isn't Really the First El Niño Storm of the Season
Many headlines in recent days have been touting the current and upcoming rain as the first El Niño storm(s) of the year. In reality, every weather system we have seen in California, and elsewhere, have been influenced by El Niño; going back to its strengthening in the eastern tropical Pacific last fall. And every storm will continue to have to some "El Niño DNA" in them, well into spring.
The pattern that we saw in December, with a series of colder storms from the Gulf of Alaska, were not as characteristic of El Niño, but they were certainly related as distant cousins.
The current pattern, with a series of storms moving almost directly west to east (i.e., zonal flow) across the Pacific in the middle latitudes, is what is more commonly thought of as a "typical" El Niño pattern.
This pattern is more closely related to the impact of El Niño on the jetstream pattern in the Pacific; and to extend the familial metaphor are more like brothers and sisters. This is very reminiscent to what we saw in January through March of 1998. It should be noted that during those months in 1998 that while there were lots of rainy days, most of the daily amounts were in the moderate category and not heavy rain days.
Jan Null, CCM
Golden Gate Weather Services