Major pattern change coming; most significant effects in NorCal

Today was a rather odd weather day, with extensive mid and upper-level cloudiness over much of the state. Despite the impressive appearance on satellite, this cloud band in the diffluent east side of the upper low is not producing any precip that is reaching the ground, save for maybe a sprinkle or two near the coast. More clouds and maybe isolated sprinkles will be possible through tomorrow, but for the most part very comfortable and fall-like weather will persist (though it will still be somewhat on the warm side in inland areas). All eyes then turn to the developing longwave shift in the jet stream in the Eastern Pacific…

It does appear that the MJO and the tropical convective forcing associated with it will indeed induce rossby wave dispersion over the far eastern Pacific over the next 1-2 weeks, leading to much wetter weather on the West Coast. If this were mid-winter, we would probably be talking about a significant flood event, but because it is still too early in the season for continuous storms of a necessary magnitude (not to mention  record-breaking antecedent dry conditions), the main concern from these upcoming storms will be urban flooding and debris flows (from clogged storm drains and wildfire burn scars, respectively). There is still the potential for strong winds in NorCal, especially if the most recent 18z GFS is to be believed. The models have trended stronger with these storms today, but most leave far SoCal with little to no rainfall. Although this is possible, I really do think that all parts of the state will see at least some measurable precip over the next 7-10 days. The extended models do not handle explicit forecasts of precipitation magnitude and equator-ward extent  very well when ingesting rapidly changing and relatively anomalous data about tropical forcings, and as a result I think they may be underestimating the tenacity of these systems to bring welcome rainfall to the state. I will have a more specific update later this week on the upcoming change, but I will mention that there does appear to be quite a bit of subtropical moisture that may be picked up and acted on by the very dynamic atmosphere by Thursday and Friday, possibly bring some rain to areas not currently expecting any…