A rather strong upper-level low for the time of year has been dropping south along the Oregon coast today. By tomorrow, it will come to rest in northwestern California where it will sit and spin into Thursday. The water vapor satellite picture below easily shows this low on the Oregon coast and also shows how that low has really dried of much of California and westernmost Arionza.
The low will cause noticeably cooler-than-normal temperatures in California the next two days, especially at the coast and coastal valleys along with the Central Valley as temperatures run 5 to 10 degrees below normal. The low is also likely to cause scattered showers and thunderstorms in parts of Oregon and Washington.
As the low sits in place into Thursday, it will actually snap up the upper-level disturbance from Fabio in the Eastern Pacific. While Fabio itself will not be a factor, the upper-level feature at the very least will carry mid- and upper-level moisture northeast with it, bringing it into southern California late Wednesday into Thursday morning and anytime Thursday in central California. While mostly clouds are likely, it is not impossible that there could be a shower or thundershower in spots with the upper-level feature.
On this move through, the 500 mb high that retreated east will move back to the west Friday through the weekend. This is likely to turn the flow into the southeast bringing monsoon moisture back to the west, entering California by the weekend. This is likely to renew the thunderstorm threat for at least the mountains and deserts again.
Parts of Southern California are likely to have temperatures near 90 degrees again by Monday and Tuesday.
A prolonged rain-free pattern is setting in.
By this time in 1998 there was twice as much rain that had occurred to date compared to 2015-2016.
Could an unusual El Nino precipitation pattern be as simple as looking at the state of water temperatures?
One thing that I find interesting is that the pattern since fall has not been your typical El Nino storm pattern.
There are signs of a possible stormier pattern beginning the week of Jan. 18.