| Day | Date | High/Low | Forecast |
| Fri | 25th | 62/54 | Partial afternoon clearing. Mostly cloudy evening. |
| Sat | 26th | 60/52 | Rain likely, mainly in the morning; Possibly breezy at times in the afternoon. Partly cloudy evening. |
| Sun | 27th | 63/53 | Partly cloudy morning; Mostly sunny afternoon. Mostly clear evening. |
| Mon | 28th | 68/55 | Some morning clouds possible; Otherwise, mostly sunny day. Clear evening. |
| Tue | 29th | 69/57 | Sunny day. Chance of late evening low clouds. |
Synopsis
A large, upper level trough lies just to the west of the state today. Abundant clouds cover much of the state, and some showers have occurred in parts of northern California so far (nothing widespread nor heavy in intensity). The center of the cold storm (for late April) is forecast to come over or near the northern sections of southern California (maybe Santa Barbara County at closest approach tomorrow morning). The trough axis is expected to be east of L.A. County late tomorrow night or early Sunday.
At the beginning of the week, it looked like some cold air instability showers would be possible by Saturday in southern California. At that time, nothing widespread nor relevant precipitation was forecast by the numerical models. That changed quickly as the various models predicted sufficient dynamics and available, water vapor for widespread precipitation reaching L.A. County. The model consensus favors some marine layer induced drizzle/light rain in L.A. County by early tomorrow morning (daylight hours), but a period of steady, light to moderate rain is now expected some time late morning to early afternoon (up to a couple hours duration in any given location). Snow levels should fall to 5000 feet or slightly lower (briefly). Scattered showers should follow late in the afternoon, but those should be mostly around or over the mountains. Lingering showers may persist into Sunday morning, but that should be to the east and south of L.A. County. Dry weather in the Southland should return by Sunday evening.
Storm totals in L.A. County should range between 0.10 to 0.40 inch away from the mountains (least in southeast coastal plain). Some of the coastal facing foothills/mountains potentially could receive up to two-thirds inch rain. Snow accumulation down to 5000 feet may reach an inch to two, but much of it may have a hard time sticking. The storm is predicted to weaken quickly tomorrow since the center of the storm is forecast to retreat northeastward during the morning (storm dynamics this far south diminishing as the day progresses). So, storm totals to the east and south of L.A. County should also be on the lower end. Isolated thunderstorm potential is very low but not zero (percent).
Tomorrow should be the coolest of the next several days (some areas west of the mountains might struggle to reach 60 degrees). Although it should be mostly sunny in most areas on Sunday, only modest warming is expected that day. A little better warming is predicted for Monday, but a lingering, weak, upper level trough is forecast near or over the Southland. How much warming will depend on whether any northerly winds develop (doesn’t have the be strong). At best, temperatures may return to seasonable levels in spots (better chance of that on Tuesday).
Most of the longer range models don’t predict any well developed, upper level high pressure affecting the Southland next week. In fact, by the second half of next week, an upper level trough may develop (albeit a weak one). This should favor on-shore flow with attendant, coastal low clouds (reaching the coastal plain, at the least). Temperatures should lower some during the latter half of next week (temperatures somewhat similar to earlier this week). There are some model solutions showing a trough at the end of next week that is capable of “May Gray” weather (includes spotty, early morning mist), but that’s far from certain, for now.
Next issued forecast/synopsis may follow on Monday, 28 April.