Increasing on-shore flow and a large, coastal eddy helped deepen the marine layer overnight. In parts of southern Santa Barbara County, drizzle/light rain fell (even measurable...up to a few hundredths of an inch rain). The low clouds, which were much more widespread than yesterday, cleared away most areas by late morning (still socked in with low clouds parts of Santa Barbara County though). High pressure aloft is forecast to build back into the state over the weekend, which should reduce the on-shore flow (already showing signs of that). So, areal coverage of low clouds should decrease over successive days (mostly near the coast by Sunday or Monday). Those low clouds, however, may not necessarily clear completely each day at some beaches.
I had expected daytime temperatures today would lower a few degrees from yesterday in the coastal plain and a little more so in the coastal valleys. Well,as it turns out, good, vertical air mixing is resulting in temperatures similar to yesterday near the coast (minor to modest cooling though farther inland). Thus, I amended the preliminary, campus temperature forecast back to what I had yesterday. Today's seasonable to slightly cooler than normal weather (latter for more inland areas) should become warmer than normal over the weekend and into next week (departure from normal least by the coast). Based on some computer model forecasts, the surface on-shore flow should be strong enough to temper subsidence warming by high pressure aloft (west of the mountains). Peak temperatures over the next several days may remain slightly lower than it got a few days ago.
A somewhat deeper layer of "monsoon" moisture occurred early today into the Southland low desert (another surge of humid, Gulf of California air). However, deep layered instability is still lacking. Some afternoon cloud build-ups may occur over the southern mountains/eastern desert, but no showers nor thunderstorms should develop this side of the state. Little change is anticipated for the next few days out there. The various models keep any deep layered moisture from tropical storm Ivo well the south and southwest of southern California (storm center about 400 miles west-southwest of the southern tip of Baja California...storm motion roughly parallel to the Baja coastline). Some mid/high clouds might stream into the Southland at some point, but no real increase in muggy weather is expected west of the mountains (other than what the marine layer provides).
Most of the longer range models show only minor day to day changes in the weather next week. Temperatures should be slightly to several degrees above normal (including the coast if the marine layer gets diluted). Any cooling cycle next week shouldn't last more than a couple days (maybe around midweek). There are some model solutions showing a more significant, "monsoon" incursion late next week (continuing into the Labor Day weekend). That could result in afternoon showers and some thunderstorms over the southern mountains/eastern desert. However, deep layered moisture could easily remain to the south and east of the state. There are also some scenarios that include a further warm up at the end of next week (some potential for widespread 90 degree weather inland, coastal plain). As with the "monsoon" scenario, this possible heat spell is of low confidence (for now).
There is fair model consensus for a cooling trend (state wide) by Labor Day. This would continue for a few days. If the predicted, wind flow pattern develops, interior sections would eventually cool well below normal levels (no triple digit heat for a day or two). The inland, coastal plain may see daytime temperatures only in the mid-70s (foretaste of autumn?). Despite fair model agreement, I an not ready to endorse this scenario yet.
UCLA Forecasts and analyses are written by James Murakami
– posted: 2019-08-23