Note: A forecast will not be issued on Wednesday, 14 November.
Off-shore flow continues today, and it looks like it'll be around for a few days more. The current off-shore flow pattern has been an unusually dry one. At UCLA, today marked the sixth consecutive day that the relative humidity has fallen to single digit values (typically don't see more than three straight days of such low humidity). As the off-shore flow slowly weakens through the week, humidity levels will gradually rise. However, a sustained return to more normal humidity in the coastal plain isn't expected before Friday (have had a couple days with a brief return to higher humidity but only for a few hours). So, keep the moisturizing lotion handy.
While no significant wind has occurred across most of the L.A. Basin, most Santa Ana wind prone areas have been breezy since last Thursday(at least, periodically). Peak wind gusts in the higher elevations of San Diego County reached 80 mph earlier today. Peak gusts in L.A./Ventura County reached 60 mph. However, most wind gusts in the higher elevations haven't exceeded 40 mph while at lower elevations, peak gusts have generally remained under 30 mph. Occasional surges in the wind (mainly early evening) should continue for a couple of more days, but peak gusts should be noticeably lower than they got early today. (lower with each successive day). A marginal, on-shore flow may begin as early as Thursday, but a full fledged, on-shore flow pattern isn't expected till the weekend.
I've been predicting too high a temperature in the campus forecast in recent days. So, today's preliminary forecast was several degrees lower than what I wrote last week. High pressure aloft is moderately strong, but subsidence warming associated with the high pressure has been weaker than I expected (potentially, it could have warmed into the upper 80s in spots instead of the observed, upper 70s). It may get a tad warmer tomorrow, but for the most part, it's gotten as warm as it can get for the current, wind flow pattern. Overnight low temperatures will remain cooler than normal in wind sheltered areas, but those lows should creep closer to seasonable levels as the week progresses (opposite effect in Santa Ana wind prone areas once the wind dies down).
Since a weak, on-shore flow is predicted this weekend, a shallow marine layer should develop along the coast (possibility for dense fog as early as Friday morning). At this point, no widespread, marine layer, low clouds are expected beyond the coastal plain. Seasonable or slightly lower temperatures should prevail across the Southland this weekend. Early next week, most model solutions show a marginal, surface off-shore flow. However, there should be little or no upper air support for significant wind. Temperature-wise, it might get slightly warmer than normal away from the coast.
A few of the longer range models showed an upper air trough capable of producing showers early next week. Recent model runs show this trough will be too weak to produce showers. However, a number of model solutions continue to show a storm bringing wet weather to the state sometime next week. Potentially, it could be more than one storm producing wet weather (storms would be cold enough for snow at resort level). Depending on which model solution is right, southern California could get widespread, wet weather as early as the 21st (day before Thanksgiving Day) or as late as the 24th. I still have no confidence on which day this wet weather may occur in Los Angeles, let alone if multiple storms reach the Southland. However, it looks likely that cooler than normal weather will occur after early next week and last through the long, holiday weekend (applicable for the entire state).
UCLA Forecasts and analyses are written by James Murakami
– posted: 2018-11-13