08/743 PM.
A warming trend affecting Southwest California will peak Wednesday and Thursday, with many areas 5 to 10 degrees above normal. Temperatures will return to near normal over the weekend.
(Tue-Fri), 08/846 PM.
***UPDATE***
As the upper level low to the north passes east, the gradient will ease off over southern California and high pressure continues building in from the southeast. Expecting this to further compress the marine layer, and limit stratus south of Point Conception. There is potential for patchy dense fog over the waters and near the coasts tonight into Wednesday morning given the shallow, 400 ft marine layer. Onshore LAX-DAG pressure gradients should be weaker, around 2 mb by Wednesday morning further supporting dense fog. However, seeing an even weaker gradient Thursday morning so that will be another promising time to see dense fog near the coasts.
Afternoon clouds moved into the area as some monsoonal moisture, correlating with increasing PWAT values, reached the region. However, this only resulted in some clouds over the Antelope Valley and San Gabriel mountains today. PWAT values above 1" are expected to last through Wednesday before gusty north winds develop Wednesday night, advecting drier air into its place. Thinking there will still be a small chance of showers Wednesday before the north winds arrive.
***From Previous Discussion***
The forecast through Friday remains more or less unchanged. A warming trend began on schedule today with most areas 3-8 degrees warmer than yesterday. Only coastal areas remained unchanged from yesterday due to onshore flow. Additional warming is expected across most areas Wednesday, and interior areas may experience 1-2 degrees of additional warming Thursday before strong onshore flow returns Friday and continues into next week. Highs during the peak of this warming trend tomorrow and Thursday are expected to be in the mid 90s to lower 100s for the valleys, 100-105 for the deserts, and 80s to around 90 in the intermediate areas between the inland coastal zone and the valleys. These temperatures are roughly 5-10 degrees above normal, which combined with still cool overnight lows mostly in the low to mid 60s, doesn't quite qualify for heat hazards. However, people are still strongly encouraged to avoid strenuous activity during the afternoon.
Standard onshore winds will continue during the afternoon and evening in most areas, except for southwest Santa Barbara County where Sundowners will develop this evening and again Wednesday evening, mostly 40 mph or less.
With high pressure overhead the marine layer depth will be dropping to 1000 feet or less through Thursday, confining any stratus to coastal areas and the Santa Ynez Valley. Patchy dense morning fog is possible as well, though Sundowners will likely keep southern Santa Barbara County cloud/fog free.
Several degrees of cooling are expected Friday as the high weakens and onshore flow increases by 2-4mb. Most of the cooling will be across coast and coastal valleys but even interior areas will be 2-4 degrees cooler with increasing afternoon sea breezes. Highs in most areas will be within 3 degrees of normal.
(Sat-Tue), 08/200 PM.
Slightly cooler temperatures are expected Saturday with increasing night and morning low clouds and fog for coast and some coastal valleys. Then very little change most areas into early next week. The one exception will be the far interior areas from the mountains inland where building high pressure again from the east will warm temperatures a few degrees, especially in the Antelope Valley and far interior SLO County. The strong onshore flow in place will also create gusty southwest to west winds in those areas and with low humidities will lead to increasing fire danger.
One other potential issue next week is the possibility for increasing monsoon moisture coming in from the east. Models are still indicating an easterly wave moving in Tue into Wed. However, PW's have been slowly lowering the last few runs so confidence in any precipitation remains quite low.
09/0123z.
At 2125Z, the marine layer was around 300 feet deep at KLAX. The top of the inversion was near 2500 feet with a temperature near 25 degrees Celsius.
High confidence in the current forecast for valley and desert terminals. Moderate confidence in the current forecast for coastal terminals. Arrival could be off by up to two hours. Expecting LIFR to IFR conditions to be more common.
KLAX, There is a 40 percent chance of no low clouds tonight and into Wednesday morning. LIFR to IFR conditions will likely spread in as early as 10Z, or as late as 13Z. Higher confidence exists in IFR conditions at this point. No significant east winds expected.
KBUR, VFR conditions are expected through the period. No wind impacts are expected at this time.
08/749 PM.
South of Point Conception, Small Craft Advisory (SCA) level winds are expected near Point Conception and southward to San Nicolas Island, and over the western Santa Barbara Channel. The winds will continue through at least late tonight. On Wednesday afternoon and evening there is a moderate (40-60 percent chance) of SCA level winds affecting the inner waters, especially the Santa Barbara Channel. Continued SCA winds are likely (60-80 percent chance) for the outer waters southwest through northwest of the Channel Islands through late Thursday night, with a chance they continue into Friday evening.
North of Point Conception, winds will very likely remain below SCA levels through Wednesday morning, then SCA level winds are likely to spread into the northern waters through Wednesday afternoon. SCA winds will likely continue into the evening hours out to 10 NM offshore of the Central Coast, but winds will persist into Friday beyond 10 NM offshore. There is a high-to-likely (50-60 percent) chance of SCA level winds Thursday afternoon and evening out to 10 NM offshore.
Patchy dense fog may affect the coastal waters overnight and in the morning hours, with best chances in the waters off the Central Coast, tonight through Thursday morning.
Ca, NONE. PZ, Small Craft Advisory in effect from noon to 9 PM PDT Wednesday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Wednesday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect from 9 AM Wednesday to 3 AM PDT Friday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Friday for zones 673-676. (See LAXMWWLOX).
