| Day | Date | High/Low | Forecast |
| Fri | 30th | 69/61 | Mostly cloudy through the evening. Chance of occasional, light showers, mainly morning. |
| Sat | 31st | 68/63 | Chance of light rain in the morning; Steady rain becoming likely by late day into evening. |
| Sun | 1st November | 69/59 | Chance of early morning showers; Otherwise, becoming partly cloudy during day. Clearing in evening. |
| Mon | 2nd | 74/61 | Some clouds possible but mostly sunny day. Mostly clear evening. |
| Tue | 3rd | 77/61 | Sunny day. Clear evening. |
Synopsis
A large, upper level trough exists along the West Coast today. A disturbance embedded within this trough was responsible for the scattered showers in southern California this morning (waning in coverage, as of this writing). The aforementioned trough center is forecast to reach northern California by early Sunday (currently just west of Washington state). In addition, a separate disturbance several hundred miles southwest of San Diego should make a nearby landfall (San Diego area or farther south). The weather consequences of what I just mentioned should be a continuation of mostly cloudy skies and occasional showers (not necessarily same coverage as earlier today).
While the overall aspects of the weather (i,e, cloud and shower coverage generalized) should verify as forecast, there remains uncertainty about weather details (more so than usual considering the relatively short time frame). It’s not clear to me if numerous showers or steady rain will fall in the L.A. Basin during the day tomorrow. Computer model agreement isn’t great on this point. The most widespread, steady, wet weather is not anticipated till Trick or Treat time (around 5 PM, give or take an hour), but it’s possible that it could be delayed as much as a few hours. Glad I don’t have to make a final call on evening events anymore.
Another issue with the approaching storm is whether any heavy rainfall will occur in southern California. Subtropical moisture is forecast to increase through tomorrow as the disturbance southwest of San Diego nears. How close the disturbance gets upon landfall will have a bearing on where a potential bout of heavy rain falls (currently odds favor San Diego County over L.A. County). There is separately, a chance that main trough center well to our north may provide decent dynamics in the Southland. If so, brief duration, heavy rain is possible late Saturday night (anywhere L.A. County westward).
For this forecast, I’m going with latest model consensus. Storm totals in the L.A. County lowlands (Saturday-Sunday) should range between a quarter to half an inch rain (no snow expected below 8500 feet). If heavy rains materialize, totals may double, especially around favored coastal facing foothills/mountains.
One way or another, clearing skies should develop by late Sunday (possibly morning). Most model forecasts point toward weak off-shore flow developing Monday into Tuesday. Slightly warmer than normal weather west of the mountains is expected by Tuesday (potentially some areas on Monday). A weak trough passing through northern California should promote minor cooling on Wednesday. Another ridge may promote off-shore flow over the subsequent weekend (warmer than normal weather but how much, remains to be seen). If the longer range, model consensus holds up (???), storms may once again reach southern California sometime after 11 November.
Next issued forecast/synopsis should be on Monday, 2 November.