| Day | Date | High/Low | Forecast |
| Mon | 14th | 69/58 | Partial afternoon clearing. Mostly cloudy evening. |
| Tue | 15th | 67/58 | Morning low clouds; Partial afternoon clearing. Mostly cloudy evening. |
| Wed | 16th | 66/58 | Possible partial afternoon clearing; Otherwise, mostly cloudy through the evening. Slight chance of early morning drizzle. |
| Thu | 17th | 65/57 | Possible partial afternoon clearing; Otherwise, mostly cloudy through the evening. Slight chance of drizzle early morning and evening. |
| Fri | 18th | 69/54 | Some early morning clouds possible; Otherwise, mostly sunny day and breezy at times. Clear evening and breezy at times. |
Synopsis
Well, predicting the daily, clearing patterns for marine layer clouds isn’t any easier in autumn than it is in summer. Slightly stronger on-shore flow and a coastal eddy helped deepen the marine layer overnight. I thought low clouds wouldn’t clear away completely in many areas, including the campus area. That idea proved wrong (good clearing coastal areas L.A. County southward…some patches hanging tough in parts of Santa Barbara/Ventura Counties though). The better than expected, vertical air mixing, which contributed to the complete clearing, also produced a little more warming near the coast than I anticipated. However, I left the campus forecast alone. Subtle changes predicted by the numerical models might favor the remainder of my forecast (crossing fingers).
I have the least confidence in the drizzle forecast. A deep marine layer and intermittent, coastal eddy could support some drizzle/light rain in spots (happened early today in parts of coastal Santa Barbara County). However, deep marine layers and good on-shore flow don’t always lead to drizzle in the campus area. The models do show a “dry” cold front passing through southern California late Thursday night (reason for drizzle chances that evening). The front may help “squeeze” some showers out of the deep marine layer, but the models favor that happening mainly to the east and south of L.A County (“rain shadow” effect over most of our County). Still, any rainfall is expected to be minor (at most, a few hundredths of an inch away from coastal, mountain slopes).
All the models predict a “closed”, upper level low pressure forming in the Southwest late Friday into Saturday (departing to the east thereafter). Most model solutions show moderately strong, northerly winds developing early Friday (breezy, westerly winds prior to that in the interior). Unless the low pressure winds up much farther to the east than predicted or it turns out to a weak circulation, there should be an period of widespread, mostly northerly winds (Westside included). Peak wind gusts in the higher mountains may reach 60 mph. Some lowland areas may experience peak gusts to 45 mph (based on today’s model consensus). The wind should diminish greatly on Saturday (weakening upper low pressure), but some Santa Ana wind prone areas may remain on the breezy side (less windy than what occurs on Friday, however). By Sunday, all areas should quiet down, wind-wise.
The predicted, wind flow pattern will scour away the low cloud field by mid-day Friday (at the latest). While not a classic, Santa Ana event set-up, the off-shore flow will induce warming on Friday and over the weekend. An influx of polar air associated with the upper low pressure should limit warming on Friday (at most, warming into the mid-70s in spots west of the mountains). Better warming is expected over the weekend, but at this point, highest temperatures aren’t expected to exceed the mid-80s in most locales (probably around 80 inland, coastal plain). The lack of a marine layer should promote temperatures well into the 70s at most beaches. Finally, the off-shore flow should bring about some of the driest air since the spring.
Most of the models show mundane and slightly warmer than normal weather for next week. An upper low pressure is forecast to approach the state late next week. That should promote some cooling toward the end of next week. There is a chance of showers with this predicted low pressure, but at this time, the model consensus keeps wet weather north of the Southland. Even if wet weather comes farther south, this predicted “storm” doesn’t look impressive (for now).
Next issued forecast/synopsis should be on Thursday, 17 October.