| Day | Date | High/Low | Forecast |
| Fri | 28th | 74/55 | Variable clouds but generally sunny day. Partly cloudy evening. |
| Sat | 1st March | 65/53 | Variable clouds but generally sunny day. Variable evening clouds. |
| Sun | 2nd | 60/49 | Partly cloudy through the evening with a chance of showers. Possibly breezy at times through the evening. |
| Mon | 3rd | 60/49 | Partly cloudy day with a slight chance of showers. Becoming mostly clear in the evening. |
| Tue | 4th | 63/50 | Partly cloudy with high clouds through the evening. |
Synopsis
Earlier in the week, areas of dense fog and low clouds somehow escaped the effects of an off-shore flow (mainly South Bay area southward). That helped limit the warming trend in those areas (warmer than normal but only slightly). That is, until yesterday. Deep layered, easterly wind flow helped scour away that shallow marine layer. Santa Monica pier warmed 17 degrees yesterday over the. prior day. The jump wasn’t so impressive at UCLA (9 degree rise from the prior day), but it was nonetheless higher than I expected (reached a record for the date 85 degrees).
An approaching, upper level low pressure in the Pacific was expected to promote on-shore flow again. However, through 9 AM, most areas were only modestly cooler than yesterday (comparing 9 AM readings). Shortly after 10 AM (at least, at UCLA), a sea breeze front cooled the coastal plain noticeably (down six degrees in less than ten minutes on campus). Most areas near the coast haven’t exceeded the low 60s since that time (a far cry from yesterday when readings into the low/mid-80s occurred in many areas). With the on-shore flow return and multiple upper air low pressures predicted to pass through the state, a period of cooler than normal weather (several days) can be expected.
The chief weather uncertainty for the next several days is how widespread will wet weather get (secondary issue is the infrequently, tricky problem of timing the wet weather). The aforementioned, upper low pressure (center a couple hundred miles west of San Diego early this afternoon) has produced less clouds than expected (for now). Showers have been limited to near the low pressure center, but some of the computer models predict favorable winds aloft for showers to develop away from the low pressure center (possibly as far north as Ventura County). Most showers are expected to fall south and east of L.A. County tonight through tomorrow morning. Since most showers away from the low pressure center should be minor and only in the overnight hours, I decided to omit any shower threat out of the campus forecast (worst case, sprinkles fall over parts of L.A. County). Even down in San Diego County, where the low pressure center should pass by, maximum rainfall should be less than a quarter inch (exception might be if isolated thunderstorms form). Storm totals under a tenth inch should be common.
A different, Pacific storm is slated to enter the Southland on Sunday. It should be a colder and more dynamic system (more typical of late winter). The models agree on widespread showers west of the mountains, but they can’t agree on when that may occur. Some favor the morning hours while others delay that till the afternoon or even early evening (valid for L.A. County). In actuality, the period of steadiest precipitation should last no more than 2-3 hours (scattered showers after the cold front passes). Because of the uncertainty on when that may occur, I broad brushed the forecast wording with “chance of showers” for the whole day. I expect some rain to fall (under a quarter inch most areas away from the mountains…snow levels 5500-6000 feet for most of the storm but down to 4000 feet early Monday). I just don’t know when.
A few model solutions keep a shower threat going well into Monday afternoon (most end showers by sunrise except lingering a little longer down in San Diego County). In that scenario, one additional “wave” travels down the state coastline during the day. I left a slight risk for showers in the forecast for Monday, but confidence is low. Yet another storm may reach the Southland around the middle of next week. Some models show this one will be the strongest and wettest of the series, but it would still be only an “ordinary” strength storm (for late winter). There are some model solutions that predict a weak system.
At one time, there was supposed to be a storm slated for the end of next week. Well, the model consensus now favors a decent, high pressure promoting weak, off-shore flow (possibly temperatures as warm as it got yesterday). However, many of the longer range models do show a decent storm arriving in southern California around the 11th. A similar storm may follow around mid-March. Whether this actually occurs, that remains to be seen.
Next issued forecast/synopsis may be on Monday, 3 March.