| Day | Date | High/Low | Forecast |
| Thu | 7th | 71/57 | Sunny day. Chance of late evening low clouds. |
| Fri | 8th | 72/57 | Good chance of early morning low clouds; Otherwise, mostly sunny day. Chance of late evening low clouds. |
| Sat | 9th | 74/58 | Chance of early morning low clouds; Otherwise, mostly sunny day with some high clouds. Some evening high clouds. |
| Sun | 10th | 77/58 | Chance of some early morning low clouds; Otherwise, mostly sunny day with scattered high clouds. Scattered evening high clouds. |
| Mon | 11th | 79/59 | Mostly sunny day with scattered high clouds. Some evening high clouds. |
Synopsis
As the numerical models predicted, high pressure aloft has built into the state. It is expected to cover the state through early next week. Subsidence warming from the high pressure will become significant over the weekend (peak warmth over most of southern California expected to be on Monday). Since no full fledged, surface off-shore flow is predicted (much less common by this time of year), there is some question about how warm areas near the coast will get in the coming days.
All the models predict a stronger, surface on-shore flow for tomorrow. A well developed coastal eddy is also predicted. Thus, despite predicted warming aloft, marine layer clouds should slip into the coastal plain tonight through tomorrow morning (already along the coast in spots of L.A. County). Low clouds should clear away most areas by midday, but as with many marine layer situations, subtle wind shifts could result in persistent low clouds in some areas (i.e. no complete clearing). Daytime temperatures in some areas west of the mountains may be the same or even a tad lower than it got today.
Weakening on-shore flow over the weekend should lead to general warming in the Southland (more noticeable for well inland areas). Coastal valleys may experience widespread 90 degree by Mother’s Day (a little warmer on Monday). Potentially, some desert locales may see triple digit heat. The inland coastal plain should warm well into the 80s through Monday. For this forecast, I stayed conservative in the warming trend for the campus area. The models maintain a shallow marine layer through early next week (possibly diluted by Monday though). A defined marine layer (even a shallow one) could easily limit warming at this time of year (warm air aloft just gliding over the marine layer without mixing down to the ground). The models recently have over predicted warming trends.
The longer range models develop a weak, upper trough over Baja California early next week. In summer, “monsoon” moisture incursions can take place with weak troughs. No relevant incursion is predicted (northern Mexico still on the dry side). However, if sub-tropical air is imported into the Southland, temperatures may remain much warmer than normal after Monday (at least for a day or two). At some point, a different Pacific trough is predicted to move over the state. So, a general cooling trend is likely by the second half of next week (temperatures falling back to near seasonable levels). Whether any “May Gray” weather takes over at some point next week remains to be seen (distinct possibility over the subsequent weekend, however).
Next issued forecast/synopsis should be on Monday, 11 May.