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.
Weather parameters are coming together for a period of strong Santa Ana winds
In fact, if our models are right Southern California will not have any chance of rain before sometime during the week of March 17.
It is unrealistic to think one series of storms is going to have a huge impact on the long-term drought.
The second of two storms has been rapidly intensifying west of California Thursday.
It is because of these dynamics and available moisture that I think some of the south-facing slopes of the foothills and mountains could see higher rainfall than what even I had yesterday.
The first big statewide storm(s) of the entire season will strike California bringing much-needed rain and snow.