20/830 PM.
Fair skies and dry weather will continue through Thursday and most areas will see some warming as well. Rain chances will develop along the Central Coast Friday evening then across Los Angeles and Ventura Counties Saturday. Another round of rain is expected later Sunday into Monday and possibly around Thanksgiving.
(Wed-Sat), 20/829 PM.
***UPDATE***
Quiet conditions are expected tonight into Thursday for most of the area, preceding an extended period of mainly light rain. The main issue for the overnight period is cold temperatures, with a Frost Advisory now in effect for the Ojai and Agoura Valleys from late tonight into Friday morning. Other areas will also see cold overnight temperatures, including the Antelope Valley and other interior valleys. Winds will be mainly light across the area tonight, aiding in efficient cooling. In addition, the air mass is very dry, with humidities likely to drop into the single digits, which also helps with cooling of the air mass.
Daytime highs Thursday will be similar to a few degrees warmer than today, with upper 60s to upper 70s away from the coast, and 60s for coastal areas. Mainly light winds are expected with mostly sunny skies across the area.
***From Previous Discussion***
An impressively large and strong cyclone continues to spin just west of Vancouver Island. The center has moved very little the last 24 hours, and is expected to spin around offshore of the Pacific Northwest through early next week. While there remains quite a large spread in the number of outcomes with this weak atmospheric river, with the upper low staying mostly well north of the area, the most likely scenario is a generally beneficial rain for the area with only about a 5-10 percent chance of rains heavy enough to generate any significant flooding.
For this weekend there appears to be two distinct frontal boundaries coming through, separated by around 24-36 hours. Based on the 12z ensembles, the first one will arrive later Friday along the Central Coast, and Saturday for areas to the south. This will be the weaker of the two with most of the rain falling in a 3-6 hour period. For SLO and northern Santa Barbara Counties there will be minor southwest upslope component that will help generate slightly higher rain rates, with rain amounts expected to be around a half inch, except up to around and inch in the northwest coastal mountains. Rain rates generally a tenth of an inch or less except around a quarter inch in upslope areas. For southern areas amounts expected to be a quarter inch or less. Snow levels will be over 8000 feet so no snow issues expected.
(Sun-Wed), 20/220 PM.
The second phase of this storm is expected later Sunday into Monday. While the ensembles are actually indicating slightly lower precipitable waters with this one, most of the ensembles show the upper low moving farther south which should bring more energy this way. Confidence remains on the lower side but most of the ensembles show more rain with this second wave of precip, but still mostly beneficial rain with around a 10 percent of any significant flooding. The most likely outcome is an inch or less LA/Ventura Counties and 1-2" SLO/SB Counties. Once again snow levels will be over 8000 feet.
Even lower confidence after Monday next week as the models are really struggling with the upper level pattern. Roughly 50% percent of the ensembles show another system coming through Thursday or Friday, and a few of those are quite heavy.
20/2357z.
At 23Z at KLAX, the marine layer was 600 ft deep. The top of the inversion was at 1100 ft with a temperature of 18 C.
Overall, high confidence in VFR flight conds at most sites thru the period with no sig wind issues. There is a 10% chance of brief MVFR conds for KSBP and KSMX after 15z. There is a 30% to 40% chance of MVFR conds from 10 to 18z for KLGB.
KLAX, High confidence in 00Z TAF. No significant east wind component expected.
KBUR, High confidence in 00Z TAF.
20/825 PM.
For the Outer Waters, buoy observations confirm that Small Craft Advisory (SCA) level seas are currently impacting PZZ670 and PZZ673. These conds are expected to persist through Thursday evening. There is a 30-40% chance of SCA level seas for western portions of the southernmost zone (PZZ676) during the aforementioned period, but any high seas most likely will not be widespread enough to warrant a SCA. Winds are expected to remain sub advisory through the weekend, with the exception for the northwest portion of the northern Outer Waters this afternoon thru Friday.
For the Inner Waters N of Pt. Sal, there is a 70-80% chance of SCA level seas developing this evening/night and lasting into Thursday, especially in far western portions of PZZ645. However, winds will remain below SCA levels through the weekend.
For the Inner Waters south of Point Conception, sub advisory level conditions are expected through the weekend. Wind gusts up to 20 kt are possible across the San Pedro Channel Thursday afternoon through evening, but relatively benign conditions can be expected elsewhere.
Rain showers are likely in the coastal waters, beginning in the northern waters Friday morning, progressing south to include all areas by Saturday morning. Periodic showers are likely through the weekend.
Ca, High Surf Advisory in effect until 10 AM PST Thursday for zones 340-346. (See LAXCFWLOX). Frost Advisory in effect from 2 AM to 8 AM PST Thursday for zones 357-371. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 10 AM PST Thursday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 9 PM PST Thursday for zones 670-673. (See LAXMWWLOX).
