Yesterday’s system and the extensive associated subtropical moisture plume did, indeed, generate thunderstorm activity over various parts of the state, including SoCal, the Bay Area, and the Central Valley. Rainfall was fairly widespread but rather light–locally more than 0.50 inches in the far north, and generally under 0.25 inches everywhere else. Scattered showers continue this morning as a very moist atmosphere is acted on by weak instability and occasional weak impulses in SW flow aloft. Instability will increase a bit as the day wears on due to daytime heating, and with plenty of moisture to evaporate from the ground across most of the state, some taller showers and even isolated thunderstorms are possible in the afternoon. Halloween night may actually be pretty good weather-wise across the state, though isolated to scattered showers are possible just about anywhere.
All eyes then turn to the rather strong developing storm due west of CA. This storm is presenting itself very nicely on satellite imagery, and convective development is quite prominent on its eastern flank. Also, long-range lightning detection sensors are indicating a lot of electrical activity with this system.This storm will move inland on Saturday into Saturday night, bringing a period of fairly heavy rainfall and a longer period of moderate rainfall prior to frontal passage. The precipitation along the cold front itself may be intense–given current convective activity and models forecasts of strong instability over NorCal on Sat PM–and thunderstorms are certainly possible in the frontal band. Rainfall from this system may still exceed 1-2 inches in the Valley and Bay Area, with 3-5 inches in favored areas. Favored parts of the Central Coast could alsos see an inch or two out of this, but most of SoCal will see less than 0.50 inches and perhaps less than 0.25 inches. Major problems are expected with the burn areas from the Central Coast northward, especially the NorCal burn scars in the foothills. Some strong (advisory-level) winds may occur over the Valley, near the ocean, and over higher terrain. After the cold front, condtions will be showery on Sunday. A few isolated thunderstorms may occur inland, once again. The models now try to bring another small but fairly potent system into NorCal on Monday as it rides a powerful 180 kt jet into the state, and this system may be convectively active, as well. The GF, which until recently was banking on a return to dry weather over the entire state, now keeps the pacific jet at a much lower latitude and brings periodic precip to NorCal at least through the end of its 16-day run. It will be November, after all–maybe we’ll actually get some normal rainfall this year. I will probably be updating the Seasonal Outlook in the next week or so, as there are some new sub-seasonal and extra-seasonal indicators that were not there a few weeks ago.