| Day | Date | High/Low | Forecast |
| Tue | 20th | 66/53 | Mostly sunny day with scattered high clouds. Chance of evening fog; Otherwise, scattered evening high clouds. |
| Wed | 21st | 68/52 | Chance of early morning fog/low clouds; Otherwise, partly cloudy with mainly high clouds. Partly to mostly cloudy evening. |
| Thu | 22nd | 65/52 | Mostly cloudy through the evening. Chance of light showers during the day; Decreasing chance of showers in the evening. |
| Fri | 23rd | 64/51 | Partly cloudy through the evening. |
| Sat | 24th | 65/49 | Some clouds but mostly sunny day. Mostly clear evening. |
Synopsis
The long streak of off-shore flow (about ten days) has ended in most areas. In fact, a shallow marine layer with fog/low clouds moved into Santa Monica Bay this morning (crept inland somewhat late this afternoon). Several days of near normal, daytime temperatures should occur starting tomorrow (milder overnight low temperatures in the coastal plain as the marine air puts a limit to nighttime cooling, however).
The biggest change in about two weeks is that there will be a good chance of rain in parts of southern California (mainly Thursday, if today’s computer model consensus holds up). An upper level trough of low pressure (several hundred miles west of the state today) will be moving toward the Southland. Model forecasts had varied quite a bit on its course. Some had it moving weakly through the Southland. Others had it traveling inland too far to the south to pose a relevant threat of wet weather. It now appears that the models are more focused on widespread, wet weather affecting L.A. County. Only because there is still a chance that most showers will occur to the east and south of the County that I chose the forecast wording “chance” rather than showers “likely”. While the main threat of showers should be on Thursday, it’s possible for isolated showers as early as tomorrow evening (nothing measurable). I chose not to consider that probable for the campus area.
There are some model solutions keeping a chance of minor showers going well into Friday, but that threat should be mainly down in San Diego County. That also assumes the aforementioned trough (a semi-cut-off low pressure) will move inland more slowly than the current, model consensus. Storm totals for this storm should be under a quarter inch in most areas (possibly well under that most lowland areas away from the mountains). Atmospheric instability should be quite limited, but some convective showers (includes isolated, brief-lived thunderstorms) may be capable of half inch totals. Snow levels should remain above 6500 feet for the bulk of the storm. So, any accumulation at the local resorts should be no more than a few inches.
A return to dry weather in the Southland is expected over the weekend, and it should last through the end of January (short stretch of warmer than normal weather next week, but nowhere near as warm as recent events expected). Some model solutions had shown a decent chance of widespread, wet weather reaching southern California sometime in the last three days of January. While this scenario isn’t totally out of the question, the majority of model solutions now keep subsequent storms up in northern California (average strength systems). There are some model solutions of wet weather coming down here by the 1st of February, but that’s far from certain (for now). Even if this scenario verifies, model solutions show nothing more than an average strength storm (rainfall mostly under a half inch in the lowlands). The actual outcome remains to be seen.
Next issued forecast/synopsis should be on Monday, 26 January.