| Day | Date | High/Low | Forecast |
| Mon | 25th | 68/53 | Cloudy morning with a slight chance of sprinkles; Partly to mostly cloudy afternoon. Mostly cloudy evening. |
| Tue | 26th | 62/54 | Increasing chance of light rain; Rain likely by late afternoon. Occasional light rain likely in the evening. |
| Wed | 27th | 65/53 | Slight chance of light morning showers; Otherwise, partly cloudy day. Partly cloudy evening. |
| Thu | 28th | 70/52 | Partly cloudy with high clouds through the evening. |
| Fri | 29th | 70/54 | Partly cloudy with high clouds through the evening. |
Synopsis
A large, upper level trough continues along the West Coast, but it’s weaker now than it was last week. An atmospheric river (AR) tap also continues from last week, but its axis now crosses through San Luis Obispo County. Precipitation within the AR is considerably less than last week since storm dynamics (associated with the aforementioned, West Coast trough) are weaker (less trigger to convert water vapor to liquid state). In short, while precipitation is significant within the region of the AR (expecting a couple feet of “wet” snow in the southern Sierras), it’s not nearly as active as it was last week (not anticipating any widespread, significant flooding in the lowlands).
There were some lingering light showers over the Inland Empire this afternoon (occurred in parts of L.A. County in the morning hours), but most of the relevant showers remained north of Point Conception (as of this writing). The West Coast trough is forecast to move inland starting tomorrow. That’s when the AR should migrate southward (fading out as it moves down the coast). All the computer models show minor storm dynamics reaching L.A. County (stronger though modest dynamics remaining mostly north of Point Conception). Like this past weekend, light showers may begin in the L.A. Basin late in the morning tomorrow. If the model consensus is right, the best shot at measurable rainfall should be in the late afternoon to mid-evening hours (not necessarily falling continuously). Some lingering showers may persist through mid-morning on Wednesday, but for the most part, L.A. County should be drying out by sunrise (if not sooner). The final gasps of showers (all east of L.A. County) should exit the Southland by late Wednesday afternoon.
The models continue to vary on storm totals, but they’ve mostly trended lower over the last couple of days. Rainfall in L.A. County may range from a few hundredths of an inch to about a third inch (latter around some coastal facing foothills/mountains). It’s not expected to be much different from the past weekend totals (UCLA picked up 0.05 inch). The exception should be north of Point Conception where AR assisted rainfall could be over an inch (already recorded a third to one inch of rain in San Luis Obispo County). Like the last storm, snow levels aren’t expected to fall below 8500 feet (maybe a couple inches highest peaks).
Off-shore flow should begin to develop on Wednesday and continue through the Thanksgiving weekend. The surface off-shore flow may become moderate in strength on Thanksgiving Day (similar strength on Black Friday before weakening thereafter). However, it’s predicted to have little upper air support (partly being relatively shallow in depth). So, wind gusts in Santa Ana wind prone areas should remain under 45 mph (less in lowland locales).
Higher aloft, westerly wind flow should allow for variable high clouds to pass through the Southland. For this forecast, I’ve taken a middle of the road approach in the temperature forecast for the holiday period. It’s possible that with less high clouds than currently predicted, daytime temperatures could rise a few degrees higher than I show in this forecast. High pressure aloft, however, would need to be stronger than predicted for 80 degree readings to occur.
Last week, I mentioned that a predicted, “split flow” in the eastern Pacific would allow a separate, upper level trough to reach southern California sometime over the holiday weekend. That scenario is still be shown by most of the models. However, they’ve trended weaker, and keep the circulation farther to the south than past model runs. It doesn’t preclude showers from happening somewhere in the Southland (late Saturday-Sunday morning being the current consensus), but most of the model solutions don’t favor any relevant showers reaching the Southland (wouldn’t rule out sprinkles, especially south of L.A. County). For now though, I’m sticking with dry weather for the weekend. Dry and warmer than normal weather (weak off-shore flow probable) is currently anticipated next week (all week).
Next issued forecast/synopsis should be on Monday, 2 December (only one issued forecast this week).