| Day | Date | High/Low | Forecast |
| Fri | 7th | 61/45 | Mostly sunny day with some afternoon clouds. Mostly clear evening. |
| Sat | 8th | 66/48 | Sunny day. Clear evening. |
| Sun | 9th | 69/50 | Sunny day. Clear evening. |
| Mon | 10th | 67/53 | Mostly sunny day with variable clouds. Becoming mostly cloudy in the evening with a slight chance of showers late evening. |
| Tue | 11th | 61/52 | Mostly cloudy through the evening. Good chance of light rain in the morning; Decreasing chance of rain in the afternoon/evening. |
Synopsis
A storm that brought some precipitation yesterday was centered in Arizona this afternoon. Typically, mostly clear skies would prevail in such a position (for the low pressure center). However, an upper level disturbance was sneaking south on the western side of the aforementioned storm. That helped trigger some afternoon showers and brief-lived thunderstorms in the Inland Empire southward to San Diego County (motion north to south). Curiously, a small area of light showers were detected by radar over Santa Monica Bay (also moving southward). All this should die off by evening when atmospheric instability should wane (disturbance should also be nearing Mexican border).
The aforementioned storm didn’t drop much rain (mostly a tenth inch or less in L.A. County), but it did last longer than I anticipated. The predecessor storm on Wednesday came on the low end of rainfall expectations (averaging around a half inch in the lowland away from the mountains in L.A. County). [FYI–ECMWF model, for a change, underestimated storm totals a couple days in advance of the event]
Dry and warmer weather is expected across southern California this weekend. It actually warmed up today more than I forecast as brisk northerly winds in some areas induced decent subsidence warming (flow associated with the “back” side of the recent storm…not actual off-shore flow in this case). Winds should be generally lighter over the weekend (aforementioned storm should continue to trek eastward). While I expect modest warming (slightly warmer than normal most areas), I’m less sure of modest warming for areas near the coast. No full fledged, off-shore flow is predicted. So, a daily sea breeze should develop near the coast. That in turn, may hinder warming (at least, not getting as warm as the coastal valleys). If the sea breeze stays rather weak, Sunday’s campus forecast may be a little on the low side.
Despite the high pressure forecast for the weekend, at least two, new Pacific storm is slated for next week. The first one is predicted to be a semi-“cut-off” low pressure. Computer model forecasts for this low pressure haven’t been consistent. However, the trend recently has been for the low pressure center to pass to the south of L.A. County. This should lead to only light precipitation for L.A. County (heavier to the south). If the low pressure center winds up too far south of L.A. County (on closest approach), little or no wet weather is possible in L.A. County (one run of the ECMWF favors this). In addition, the timing of the wet weather is somewhat up in the air. The current, model consensus doesn’t bring in showers to L.A. County till the evening hours Monday (maybe after 10 PM). However, there are scenarios delaying the rain till Tuesday morning (after sunrise). Most scenarios end the rain threat by Tuesday night (for the first storm). I used a composite of model forecasts, but confidence in the forecast is low (at this time). Assuming the wetter scenarios are anywhere close to correct, rainfall in the L.A. County lowlands (away from the mountains) shouldn’t exceed a third inch
A stronger, colder, and wetter storm is forecast later next week. Some model solutions show light, marine layer induced showers as early as Wednesday morning. Steady rain in the lowlands isn’t expected till late Wednesday afternoon or evening (a few scenarios delay everything to Thursday, however). If the current model consensus holds up, 0.75 – 1.50 inch storm total in the coastal plain should be common. However, there are some scenarios that forecast just a “ho-hum” storm (half inch maximum in the L.A. County lowlands). So, like the first storm, predictions for timing and amounts remain uncertain (for now).
Longer range model forecasts are more varied for late next week and beyond. The “storm gate” may stay open to the state for several more days (through subsequent weekend), but some scenarios shift the storm track farther north (Southland would be on the southern fringes of wet weather). The model trend has been for a weaker, Pacific jet stream over time, which makes sense considering that spring is nearing (20 March, astronomically speaking). That would gradually lead to weaker storms even in the Gulf of Alaska (compared with earlier this winter).
Next issued forecast/synopsis may be on Monday, 10 March.