| Day | Date | High/Low | Forecast |
| Thu | 19th | 89/61 | Postcast high temperature…Sunny day. Clear evening. |
| Fri | 20th | 84/60 | Sunny day. Some evening high clouds possible. |
| Sat | 21st | 80/58 | Chance of some early morning fog/low clouds; Otherwise, mostly sunny day with scattered high clouds. Scattered evening high clouds. |
| Sun | 22nd | 78/57 | Chance of early morning low clouds; Otherwise, mostly sunny day with variable high clouds. Mostly clear evening. |
| Mon | 23rd | 79/58 | Chance of some early morning low clouds/fog; Otherwise, mostly sunny day. Mostly clear evening. |
Synopsis
Strong (for March) high pressure aloft was centered around the eastern state border (Colorado River) early today. All the computer models show a slow weakening and slight southward displacement by the weekend. In the lower atmosphere, a very weak, marginal on-shore flow has developed. That, along with a coastal eddy formation early today, allowed some fog/low clouds to form over the southern, inner, coastal waters (hugging some beaches in San Diego area briefly). Model forecasts favor more widespread fog/low clouds tomorrow morning (possible dense fog at some beaches). There is some chance that the marine layer will get deep enough by Sunday for early morning low clouds in the coastal plain (not necessarily as a solid overcast, however).
Astronomical spring begins at 7:46 AM tomorrow. However, the strong high pressure aloft will continue to support summer like weather for some time. I expected some minor cooling today for areas near the coast due to a weak on-shore gradient toward the low desert. Ocean breezes, however, were slow to develop. Thus, at least at UCLA, it got warmer than I anticipated (peaked at 89 degrees, as of this writing). I left my preliminary forecast unchanged since subtle shifts in the surface, wind flow pattern could favor an earlier sea breeze (relative to today). An increase in surface dew points (a measure of water vapor content) may also be indicative of a shallow marine layer formation (enough to induce a minor cooling trend).
Even if the minor to modest cooling trend develops in the coming days, it may not last long. Most models show high pressure aloft rebounding somewhat early next week (peaking midweek). It’s not forecast to get anywhere as strong as the current high pressure, and no off-shore flow is currently predicted. However, temperatures near the coast (campus included) may warm back to the low 80s (more inland coastal plain could approach 90 degrees). One uncertainty about this forecast is whether a marine layer will be present next week. Most models dilute whatever marine layer forms by this weekend. If a shallow but defined marine layer persists, warming near the coast would be minor (campus temperatures stay well under 80 degrees). I mention this since marine layer become more common place in spring.
At one time a number of model solutions showed some wet weather in northern California in the last week of March. Recent model runs have downplayed that scenario. It’s not a zero percent chance, but any wet weather up north would be a minor event. A few model solutions also show a minor rain threat around the 30th in southern California, but it is a minority model solution. Even if it comes true, wet weather would be mostly over/around the higher mountains (minor precipitation amounts…under a tenth inch). There have been only three recorded Marches at UCLA with no monthly rainfall (1959, 1972, 1997). Perhaps, this year will be added to the list.
Next issued forecast/synopsis should be on Monday, 23 March.