As we turn the corner into the second half of the rainfall season, it is becoming increasing apparent that the ongoing El Niño is becoming the poster child for "all El Niños are not alike!". While it is still way too early to know what this will ultimately mean for California's rainfall season, it is noteworthy to look at some of the differences.
While most attention has been focused on the Niño 3.4 region (see map) which has been very similar to the very strong El Niño event of 1997-1998, there have been some significant differences in the adjacent regions. The Niño 4 region to the west alongthe equator has been warmer than 1997-98, while Niño 3 and Niño 1+2 regions have been cooler.
There have also been significant differences in the monthly rainfall patterns compared to previous strong and very strong events. The following sample is for the San Francisco, Los Angeles, the Northern Sierra Nevada (8-station index) and the Central Sierra (5-station index), with monthly totals for November and December and for January through the 26th.
Please insert the usual caveats, that it's still only the midpoint in the rainfall season and we don't know how these differences will impact the remainder of the rainy months. But it is different, so stay tuned.
Jan Null, CCM
Golden gate Weather Services