Weather Synopsis – February 29, 2024

James Murakami

Thu29th63/53Possible, partial afternoon clearing; Otherwise, mostly cloudy through the evening.
Fri1st (March)62/54Mostly cloudy through the evening. Slight chance of occasional light rain during the day. Light rain becoming likely by late evening.
Sat2nd59/49Overnight rain tapering to occasional showers during the day. Breezy at times. Partly cloudy evening with a slight chance of showers.
Sun3rd61/47Partly cloudy morning; Mostly sunny afternoon and possibly breezy at times. Mostly clear evening.
Mon4th63/48Some clouds possible but mostly sunny day and possibly breezy at times. Some evening clouds.


The month of February is nearly at an end (for UCLA archives, it’s at 4 PM…Midnight, Greenwich Mean Time). The latest storm officially dropped 0.15 inch rain (not 0.16 as the auto-gauge indicated). The monthly tally is 19.30 inches (Normal is 4.73). So, this month will go down as the second wettest February in campus history (20.51 inches in 1998 is the wettest on record (of February or any other month). The “water year”, which began 1 October last year and ends on 30 September this year, now stands at 25.44 inches. That’s well above the annual normal of 17.73. However, for the moment, it falls far short of the previous water year, which recorded 40.37 inches by its end)

As the numerical models predicted, on-shore flow returned with vigor today. Widespread, marine layer clouds existed west of the mountains (some drizzle/light rain fell in places early today…mainly Inland Empire). It’s also been quite breezy in the interior thanks to the strong, on-shore flow (Lake Palmdale reported a gust to 53 mph this afternoon). This is all occurring ahead of an approaching cold, Gulf of Alaska trough of low pressure. As stated in the previous synopsis, this trough is predicted to be a major storm for much of the Sierras (snowfall totals covering the next few days measured in several feet in places…blizzard conditions at times due to heavy snow and very strong winds). While wet weather will reach southern California, the better storm dynamics are predicted to remain to the north of our region. So, this should be an average or “ordinary”, cold and breezy storm for the Southland.

Some of the models continue to show more widespread drizzle/light rain tomorrow morning (continued deep marine layer and strong on-shore flow). I do indicate a slight chance for occasional, light rain in the campus forecast, but best chances for measurable rainfall should should be up against coastal facing foothills and mountains. More general rain from an approaching cold front should hold off till the evening hours (possibly not till late evening in L.A. County). The passing cold front should produce a period of steady rain in the lowlands in the overnight hours (wee early hours of Saturday). Rain may be briefly moderate or heavy in intensity, but it shouldn’t be widespread in areal coverage nor persistent in duration. If the model consensus is right, numerous showers and isolated thunderstorms are possible for much of the daylight hours on Saturday (originally thought this would be more isolated in nature). Things should settle down by the evening, but I kept some risk for showers Saturday evening. If a number of model solutions are right, that threat could go into early Sunday. I’m still expecting the daylight hours will be dry in lowland areas of L.A. County (wouldn’t rule out a few lingering mountain showers through mid-morning).

Due to the predicted showers following the main cold front, I upped storm totals slightly in the lowlands away from the mountains. Storm totals should be in the one third to three quarters of an inch range (originally 0.25 – 0.50). However, due to the showery nature of the latter half of the storm, totals will probably vary considerably over the lowlands. Snow levels should fall to 5000 feet by early Saturday morning. It may fall a little lower by Saturday night. Snowfall totals could approach a foot around the 6000 foot elevation, but accumulation in the 4 – 8 inch range should be more common. Any snow below 5000 feet should be less than a couple inches (bulk of storm should be gone by then).

This storm may bring the last good shot of polar air into the state. Southland overnight lows should fall into the mid/upper 40s west of the mountains early Monday…isolated readings into the mid/upper 30s possible in some valley locales though only briefly. Daytime temperatures should recover early next week, but temperatures should remain below normal next week.

The model consensus keeps the “storm gate” open to the state next week. However, the North Pacific jet stream shows signs of “getting tired”. As is typical with the approach of spring, the strength of the jet stream is predicted to weaken some (relative to mid-winter). There are a couple of “waves” predicted to affect the state. The one slated for Tuesday looks benign (i.e. no wet weather threat). Depending on which model solution is right, we may have a couple days of wet weather on Wednesday/Thursday of next week (not continuously). It may be a minor to average strength storm (too early to tell with any confidence). There are model trends toward the “storm gate” closing after the subsequent weekend.

Next issued forecast/synopsis should be on Tuesday, 5 March.