| Day | Date | High/Low | Forecast |
| Mon | 6th | 73/59 | Low clouds clearing to hazy afternoon sunshine. Chance of evening low clouds. |
| Tue | 7th | 75/59 | Chance of early morning low clouds; Otherwise, mostly sunny day. Chance of evening low clouds. |
| Wed | 8th | 74/59 | Chance of early morning low clouds; Otherwise, mostly sunny day. Chance of evening low clouds. |
| Thu | 9th | 76/61 | Generally partly cloudy with mainly mid/high clouds. Mostly cloudy evening with a slight chance of light showers. |
| Fri | 10th | 76/60 | Partly to mostly cloudy through the evening with a slight chance of light showers, mainly morning. |
Synopsis
An upper level trough axis runs southwest to northeast through the state today. In addition, a weak, upper low circulation lies a few hundred miles west of Point Conception. This pattern has promoted the recent, mild weather in southern California. It has also made forecasting of marine layer clouds accurately a difficult one. On some days, the low cloud field is largely disrupted (no solid blanket of low clouds over most of the coastal waters). On other days such as this morning, low clouds are more widespread. The computer models aren’t forecasting any significant day to day, weather changes, but my low cloud forecast for the next few days is of the low confidence type. To a certain extant, daytime temperatures may vary a couple degrees (up or down) from the forecast numbers.
Uncertainty in the predicted weather details increases in the period Thursday and beyond. Hurricane Priscilla (center about 340 miles south-southeast of the southern tip of Baja California early this afternoon) is expected to move northwest paralleling the Baja coastline for a couple days. All the models show a large, upper level trough forming just west of the U.S. coast by Thursday. While most of the model solutions show Priscilla dying off well before it can reach the U.S., most solutions do show upper level moisture from the tropical cyclone getting advected into the Southwest. Many model solutions also include a portion of southern California under the moist stream of air. Unfortunately for me, the details in where and when the moisture crosses the Southland are rather varied.
Some model solutions show the warm, moist, subtropical air inducing some showers (mainly light in intensity) as early as late Thursday afternoon (San Diego County eastward). The main threat for rain in L.A. County could occur in the predawn hours of Friday. Most solutions favor just nuisance showers (making a dirty car look even dirtier after it stops raining). The more relevant rainfall may stay to the south and east of L.A. County. Isolated thunderstorms are possible, but it potentially may be confined to the southern most mountains and eastern desert region of southern California. With some model solutions keeping L.A. County rainless (only variable mid/high clouds), confidence in the wet weather forecast is very low (at this time). Even among the wetter solutions, timing of the showers vary (could be delayed to late Friday into Saturday).
Whatever actually occurs, improving weather is anticipated on Sunday (aforementioned West Coast trough moves inland). A separate, new trough is expected to set up shop over the state late Monday into Tuesday next week. Some model scenarios include cold air instability showers for the Southland. Other scenarios depict just an “inside slider” trough (marine layer drizzle possible but mostly a wind storm). The cooler than normal weather that should occur this weekend into early next week would be followed by warmer than normal weather later next week (possible, weak off-shore flow). There’s still too much variability in model solutions to take the forecast seriously (for now).
Next issued forecast/synopsis should be on Thursday, 9 October (special issuance due to possible wet weather).