| Day | Date | High/Low | Forecast |
| Thu | 13th | 72/60 | Updated…Mostly cloudy through the evening. Chance of occasional light showers. |
| Fri | 14th | 64/59 | Amended…Intermittent rain likely through the evening. Possibly heavy at times. |
| Sat | 15th | 61/56 | Amended…Rain,heavy at times. Rain tapering to a chance of showers by late evening. |
| Sun | 16th | 61/56 | Chance of some showers, mainly in the morning; Otherwise, partly cloudy through the evening. |
| Mon | 17th | 60/52 | Amended…Good chance of rain developing and possibly breezy at times. Decreasing clouds in the evening but still possibly breezy at times. |
Synopsis
Early in the week, most computer model forecasts showed that significant rain would be likely by today (Thursday). Well, that time table got pushed back. Granted, some scattered showers have occurred this afternoon in L.A. County (reason for my tardy, updated forecast valid for today), but they are insignificant compared with what should occur in the next couple of days (more so Saturday, if today’s model consensus holds true).
All the models are unanimous in predicting a good soaking rain for most of southern California (parts of the desert region should see only modest amounts). As is often the case though, model disagreement continues on the finer details of where, when, and how much. In L.A. County, this evening’s activity should be minor (heavier showers mostly Santa Barbara County northward). Some briefly heavy intensity showers may fall over parts of the L.A. Basin tomorrow, but that’s far from certain. Chances for steadier, more widespread heavy rain should increase by late tomorrow evening. Much of Saturday is expected to be a wet one. Areas of intense rainfall may occur, especially around coastal facing foothills/mountains. The chance of rain should diminish for most areas on Sunday, but some lingering showers may persist into the afternoon to the east and south of L.A. County.
I have greatly increased predicted storm totals from my earlier expectations. The models show a slow eastward progression of the storm, ample water vapor (tap into an atmospheric river), and sufficient storm dynamics while passing through the region. Totals through Sunday should range between 2.5 to 3.5 inches for the lowlands away from the mountains in L.A. County (potentially double or slightly higher for favored coastal facing mountain slopes). Snowfall from this storm isn’t expected to fall below 7500 feet for most of the event. Even when the core of this storm passes overhead (late Saturday/Sunday), snow levels should fall much below 6500 feet. At best, a couple inches of “wet” snow may accumulate at that lower elevation (foot possible, however, on highest peaks).
Since this storm is a semi-“cut-off” low pressure, surprises may yet to unfold. Small errors in predicted winds and vertical moisture distributions may result in noticeably different, weather outcomes for some locales (eg. heavy rain coverage might stay mostly west of L.A. County). What I described above for L.A. County weather is a composite expectation. The adage of “a Cut-off low is a weather person’s woe” is still applicable (AI or old fashioned forecasts).
There is another storm predicted for Monday, but most models predict this one will be more “ordinary” (cold, quick mover). Precipitation in L.A. County could begin by mid-morning or be delayed to the afternoon hours. A brief period of heavy rain is possible, but it should pale in comparison to what’s on tap this weekend. Storm totals in the lowlands should be under a half inch (possibly much less, if some model solutions are right). Yet another storm is possible sometime in the Thursday-Friday period next week. A small majority of model solutions favor a wetter, colder storm (closer to one inch rain in the lowlands), but that one could turn out to be an “inside slider” (more wind than wet weather), if some model solutions verify. Model forecasts vary greatly for the week of Thanksgiving (no surprise looking that far into the future), but most favor at least cooler than normal weather.
Next issued forecast should be on Monday, 17 November.