Note: Regular issuances of forecasts may not occur for some time due to current events.
On-shore flow weakened overnight. That along with some northerly wind flow in the western half of southern California reduced low cloud coverage. Where widespread low clouds were prevalent early today (mainly to the east and south of L.A. County), it didn't occur as a solid overcast. Temperature-wise today, it's little changed from yesterday although most locales are slightly cooler than yesterday (odd, considering the weaker, on-shore flow).
On-shore flow is predicted to increase again tomorrow as a storm passes inland well to our north. Areal coverage of low clouds should be greater again (more like yesterday). However, I'm unsure whether widespread overcast will prevail. Low clouds should clear away fairly quickly in the morning but some high clouds from the storm to the north are expected to reach southern California. Temperatures in most areas should be about the same as today (maybe a degree or two lower).
All weather eyes are focused on a second storm right on the heels of the storm that passes through northern California tomorrow (expecting decent snowfall in the Sierras). Sunday should be a mostly cloudy day in the Southland (interior may be no worse than partly cloudy though). Some computer model forecasts show marine layer induced showers in the morning (probably not measurable for most locales south of Point Conception that experience any showers). By late afternoon or evening, the storm should be close enough for widespread wet weather reaching western L.A. County (wet weather progressing from northwest to southeast).
Details of timing for steady precipitation and intensity remain fuzzy. As mentioned yesterday, this storm transforms into a dreaded, "cut-off" low pressure this weekend ("cut-off" low is a weather person's woe). Numerical models often don't handle properly the smaller scale features of the low pressure. They also infrequently mishandle the forward speed at which the low pressure moves. In short, I'm confident about widespread wet weather early next week. I'm fairly confident that most areas west of the mountains will experience a period of moderate/heavy intensity precipitation (snow levels as low as 5000 feet though more likely around 6000 feet on Monday and perhaps the first half of Tuesday). It should be breezy at times during the early period of the storm. Precipitation should become progressively more restricted to around the mountains after Monday. Beyond that, I have little confidence in the forecast details of weather for next week.
As far as when this storm may exit the state, the model consensus has been trending later and later. Originally, some model solutions favored a Tuesday exit. Today's model consensus now favors Thursday evening, but there are some model solutions that show the "cut-off" low pressure center in the state Friday morning (center nearing the Colorado River, however). I think that for the most part, the coastal plain will dry out by Thursday, but potentially there could be some lingering showers in the mountain/desert region as late as early Friday. Dry weather is likely over the subsequent weekend, but model agreement is poor on whether a good warming trend will occur (some favor just seasonable temperature along with marine layer clouds west of the mountains).
UCLA Forecasts and analyses are written by James Murakami
– posted: 2020-04-03