Weather Synopsis – January 24, 2025

James Murakami

DayDateHigh/LowForecast
Fri24th72/52Mostly sunny day with some high clouds. Scattered evening high clouds.
Sat25th60/46Partly to mostly cloudy day. Chance of light afternoon showers. Evening showers becoming likely.
Sun26th55/45Periods of showers likely through the evening.
Mon27th55/43Morning showers and a slight chance of a brief thunderstorm. Chance of showers remainder of day. Slight chance of showers in the evening.
Tue28th59/44Partly cloudy day. Becoming mostly clear in the evening.

Synopsis

Off-shore flow continued today, but it was on a rapid decline. While most areas were noticeably cooler this afternoon compared to yesterday, daytime temperatures this weekend will plummet relative to today (much cloudier too). Finally, the wind flow pattern aloft is predicted (by all the computer models) to change to a wet pattern for southern California (much more down here than in northern California…for a change).

Rather than become another in a seemingly endless series of “inside slider” type troughs, an upper air trough passing through British Columbia is expected to travel more along the coast (“outside slider”, as I described earlier in the week…thanks to a ridge of high pressure nosing into the Gulf of Alaska). By early Saturday, a “closed” low pressure circulation should form just off of northern California…around Bay Area around midday). The low pressure center should be off the coast near Point Conception by Sunday late morning. Most of the model runs today show the low pressure center slowly moving east through the Mohave desert though this portion is the forecast is less than clear (varied model solutions…could be closer to San Diego ). The low pressure may move so slowly that its weather influence on the Southland may last through Thursday (current model agreement poor on this point too).

This slow down in the movement of the aforementioned low pressure forced some changes to the forecast I envisioned a few days ago). Widespread precipitation is now all but certain, but the onset of numerous showers in L.A. County (light at first) may not occur till evening (some minor showers near coastal facing foothills/mountains still possible earlier in the day). Much of the precipitation that falls from this storm should be “home grown” (developing locally rather than all traveling down from northern California). Better storm dynamics are now predicted for much of the Southland. There may be periods of steady precipitation Sunday through Monday morning. Although most of the precipitation should be light in intensity, there should be many areas that experience some moderate to even heavy intensity precipitation (infrequent but of short duration). The various models predict limited, atmospheric instability, but isolated thunderstorms cannot be ruled out (Sunday-Monday period). While today’s model consensus greatly diminishes the chance for showers in L.A. County by late Monday afternoon, some model solutions do indicate sufficient instability to host some mountain showers Tuesday, Wednesday, and possibly as late as Thursday (depends on which model solution on the track of the aforementioned low pressure center is right).

Even with mostly light precipitation (limited, available water vapor…no tap into sub-tropical moisture), the relatively long period of wet weather means a wetter storm than I expected a few days ago (first good, widespread soaker west of the mountains this season). Today’s model consensus favors 0.75 – 1.25 inches of rain in the lowlands away from the mountains (potentially twice those numbers around some coastal facing mountains). Snow levels potentially could fall briefly to 2500 feet early Monday, but most model solutions keep the cold core farther to the north. Still, snow down to about 3500 feet should be possible (a dusting). The local resorts could receive 1 – 2 feet of snow, if some model scenarios hold up.

At one time, it looked like off-shore flow would return by the middle of next week. With the expected, slow march of the storm, most models no longer show off-shore flow of consequence. A short period of off-shore flow may still occur in the second half of next week (more northerly than northeasterly). However, most model solutions don’t predict any significant Santa Ana winds. In addition, temperatures next week should remain cooler than normal (just warmer than what’s expected this weekend). There is some chance at seasonable temperatures toward the end of the week, but that’s still uncertain.

Also uncertain is whether any wet weather occurs around the end of the month. Most model solutions show a minor to modest storm for northern California. A few show minor showers reaching the Southland too (rainfall under a tenth inch). There are some model scenarios that feature additional storm threats in the first days of February, but model agreement is rather poor (most show only minor systems though). Well, at least, the models show some chance for wet weather…’tis the rainy season, of course.

Next issued forecast/synopsis may be on Monday, 27 January.