31/737 PM.
Numerous showers will prevail tonight into Sunday morning. Some showers may be heavy at times. Warmer and drier conditions can be expected next week.
(Sat-Tue), 31/733 PM.
***UPDATE***
Forecast continues on track this evening as an upper level trof over the E Pac is forecast to move into the CA coast overnight, bringing numerous showers to SW CA. The area will be under the favored right rear quadrant of a strong 160 kt jet this evening which, combined with some divergence aloft, will enhance dynamic lift and help to produce convective showers with locally heavy rain. These convective showers have already developed early this evening along portions of the SLO/SBA Counties as well as the VTU County coast. The HRRR was forecasting enhanced convective showers for various parts of the region closer to the coast overnight as well. Altho this model may be over-forecasting the intensity of these showers, it may have the right idea about the prevalence of heavier showers given the current activity and the favored upper level dynamics. At any rate, numerous showers with locally heavy rain continues to be in the offing with this weather system tonight, with lingering showers expected into Sun morning. Current forecast is in good shape and no updates are expected this evening.
***From Previous Discussion***
Overall, latest models remain in decent synoptic agreement through the short term period. At upper levels, a low will impact the area through Sunday (bringing widespread shower activity) then a ridge will build over the area on Monday before getting "flattened" on Tuesday. At the surface, weak onshore flow will prevail through Sunday with weak offshore flow developing on Monday and Tuesday.
Forecast-wise for the short term, main issue remains rain chances for the area. Based on latest guidance, no major changes to previous forecast thinking. Scattered showers will continue through this afternoon, before more substantial rain moves into the area tonight/Sunday morning. As has been the case over the last several days, models indicate heaviest rainfall will remain south of the LA county. So, for our area, most locales can expect between 0.25 and 0.75 inch rain totals through Sunday afternoon. However, based on high resolution models (HRRR, RRFS, etc.), there may be some locally moderate to heavy showers through Sunday morning. Local totals between 1 and 2 inches will be possible with any heavy shower activity. As for any thunderstorm threat, the chances look to be in the 5-10% range for our area. So, that potential will need to be monitored through tonight. As for rainfall rates, hourly rates of 0.10 to 0.33 will be common, but isolated rates of 0.50+ inches/hour will be possible with any heavier showers.
After the system moves east and shower activity ends Sunday evening, the upper level ridge and weak offshore flow will bring dry and warmer conditions to the area on Monday. At this time, upper level support looks minimal, so any offshore winds on Monday are expected to remain below advisory levels. On Tuesday, the ridge will flatten, but weak offshore flow will still prevail. So, there may be a degree or two of warming on Tuesday.
(Wed-Sat), 31/1250 PM.
For the extended period, models continue to exhibit broad synoptic agreement through the period. Cyclonic flow aloft will prevail over the area Wednesday/Thursday then an upper level ridge builds in from the west on Friday/Saturday. At the surface, weak diurnal flow will likely prevail although the ECMWF indicates a bit of weak offshore flow in the Thursday-Saturday time frame.
Overall, the above synoptic pattern will result in benign weather for Southwestern California. Dry conditions will prevail through the period. High temperatures will remain relatively persistent on Wednesday/Thursday with some warming expected on Friday and Saturday. There may be some gusty offshore winds through the period, but nothing that looks to be near advisory levels.
31/2337z.
At 23Z at KLAX, there was no inversion or marine layer.
Overall, moderate confidence in 00Z TAF Package. -RA with MVFR-VR ceilings and visibility expected. Isolated and brief IFR conditions possible tonight, especially from KSBA through KLGB. Improvement likely 12-18Z. Wind gusts of 20-30 knots likely at most coastal sites starting around 21Z.
KLAX, Moderate confidence in TAF. -RA with MVFR ceilings will likely become more common by 06Z, with possible brief IFR RA under any heavier cells. Improvement likely by 01/15-18Z. 30% chance of east wind component developing and reaching 8 kts from 01/10-16Z. West winds 20-30 knots likely starting around 21Z Sunday.
KBUR, Moderate confidence in TAF. -RA with MVFR ceilings will likely become more common by 06Z, with occasional IFR RA under any heavier cells. Improvement likely by 15-18Z.
31/707 PM.
Moderate confidence in winds and seas staying well below Small Craft Advisory (SCA) through this evening, except for a low chance of brief gusty downdraft winds with any heavier showers. There is a very low chance of a waterspout forming in a stronger cell.
High confidence in post-frontal SCA-level W-NW winds and choppy seas forming later tonight from the Central Coast to San Nicolas Island, then spreading to most coastal waters on Sunday, including the entire Santa Barbara Channel and the Santa Monica Bay. The winds turn to the NE on Monday and will likely stay below SCA- levels. There is a chance for another round of post-frontal winds on Tuesday and Wednesday, but likely a step below in strength compared to Sunday.
Ca, NONE. PZ, Small Craft Advisory in effect from 11 AM to 9 PM PDT Sunday for zones 645-650-655-670. (See LAXMWWLOX). Small Craft Advisory in effect from 2 AM Sunday to 3 AM PDT Monday for zones 673-676. (See LAXMWWLOX).
