| Day | Date | High/Low | Forecast |
| Mon | 28th | 67/55 | Partly to mostly cloudy remainder of morning. Mostly sunny afternoon and possibly breezy. Partly cloudy early evening; Otherwise, mostly clear and possibly breezy at times. |
| Tue | 29th | 68/53 | Sunny day; Possibly breezy at times early. Mostly clear evening. |
| Wed | 30th | 67/54 | Some morning clouds possible; Otherwise, mostly sunny day. Mostly clear evening. |
| Thu | 31st | 66/54 | Some morning clouds possible; Otherwise, mostly sunny day. Chance of late evening low clouds. |
| Fri | 1st November | 65/53 | Chance of morning low clouds; Otherwise, mostly sunny day. Partly to mostly cloudy evening. |
Synopsis
As the computer models had predicted, a large, upper level trough from the Gulf of Alaska lies along the West Coast today (helped end the recent, warm weather in southern California). There aren’t any organized bands of clouds associated with this trough, but it did whip up a deep marine layer overnight (locally). I had thought vertical air motions would clear away clouds (at least partially) by the afternoon hours. However, as of this writing, clouds were hanging tough across most of the L.A. County, coastal plain (mostly sunny in other areas though). Whether its related or not, the afternoon sea breeze (L.A. County coastal plain) hasn’t picked up as much as some other areas.
The various models continue to forecast some cold air instability showers for north facing mountains (mainly Tehachapis) and some of the coastal facing mountains in San Diego County (valid time later tonight through early tomorrow). None of the showers should be heavy in intensity (rainfall up to a third inch in San Diego County but under a tenth being more common). Snow levels may fall briefly to about 5000 feet early tomorrow, but only a dusting of snow is probable.
Besides the threat of minor showers, breezy weather should continue for some areas (mostly Santa Ana wind prone areas as sea breeze should diminish after sunset). So far, peak gusts west of the mountains have stayed under 30 mph (for most part), but some mountain locales may experience peak gusts over 60 mph for a time tonight. Peak lowland gusts could approach 45 mph (usual Santa Ana wind prone areas). Upper air support for the higher winds should wane by late tomorrow morning. A marginal, off-shore flow is forecast through Wednesday morning, but upper air support for widespread, significant wind should be lacking by midweek (relevant winds mainly higher elevations only…still less than 40 mph).
Although high pressure aloft builds into the region after today, it will be fairly weak. So, subsidence warming from the off-shore flow shouldn’t promote significant warming. Peak readings may reach the mid/upper 70s in places (tomorrow/Wednesday), but readings in the upper 60s to low 70s should be more common. If ocean breezes blow earlier in the day than expected, areas near the coast may not warm much beyond today’s readings.
Weak on-shore flow should return for Thursday (more so Friday due to approaching weak trough). There could be a return of marine layer clouds , but there shouldn’t be any widespread blanket of low clouds (Thu-Fri). Halloween evening should be seasonably cool for Trick-or-Treaters.
Confidence in the weekend forecast is rather low at this time. Cooler than normal weather is probable due to another, predicted trough. Some model solutions have shown an “inside slider” passing through (mainly a wind storm though patchy, marine layer drizzle not out of the question). Some solutions favor more of an “outside slider” (one taking an over ocean trajectory…widespread, wet weather in the Southland…a few solutions even showing a good soaking storm with low snow levels). There are also some in between solutions (showery weather but not necessarily all areas). Adding to the confusion (for me), the usually reliable ECMWF model switched from “inside slider” to “outside slider”(i.e. dry to wet). The GFS model flipped the other way (wet to dry). It may wind up being wet for a portion of this weekend (wet scenarios favor sometime Saturday afternoon through early Sunday), but I’m unsure (for now).
It’s far from certain, but for now, most of next week is expected to be mostly sunny and modestly warmer. Of course, there are a few solutions showing additional wet weather around the middle of next week. All may hinge on what the weather ends up being this weekend.
Next issued forecast/synopsis should be on Friday, 1 November.