20/919 AM.
A storm will bring rain and mountain snow to the area today into Saturday morning, heaviest tonight into Friday morning in Los Angeles County. Gusty east winds are expected Friday in some areas. High pressure will push temperatures back to normal this weekend which will continue through the holiday week.
(tdy-Sat), 20/1006 AM.
***UPDATE***
The rain is arriving a couple hours earlier than expected but otherwise more or less on track. Rain rates with this initial round are expected to be under a quarter inch per hour and in most cases under a tenth of an inch. And for most of SLO and SB Counties this initial batch of rain will be 90% or more of the total for the storm. Elsewhere, and especially in LA County, showers will continue into Friday with the potential for heavy showers and thunderstorms. Hi res models have been consistent showing a strong signal for storms overnight (between 10pm and 6am) tonight in southern LA County with a 30-40% chance of rain rates up to or locally exceeding a half inch per hour. Still not expecting to issue any flood watches at this time but periods of heavy rain are possible tonight in LA County.
***From Previous Discussion***
In general, the storm system remains on track to impact the area today through Friday, maybe into Saturday, with minimal changes to the expected impacts and details.
RAIN IMPACTS: Focused over Los Angeles and Ventura Counties, especially Thursday afternoon and night. With the soils still soggy from the recent rains, the additional rain will bring an enhanced risk for mudslides over vulnerable areas, and rock slides on the canyon roads with additional closures. More traffic than usual with slippery roads and minor flooding. The risk for burn scar debris flows is not zero but very small (5% chance) and tied to an unfortunate thunderstorm forming right over a burn scar. This low risk is especially so considering the minimal impacts from the recent heavy rains. Flood Watches are NOT expected.
SNOW IMPACTS: Focused over Los Angeles and Ventura Counties, where Winter Weather Advisories are in effect. Snow levels will generally be 6000 feet or above for most of the precipitation, but will likely lower to 5000 feet at times. This means some mountain roads and communities will see accumulating snow and icy conditions.
THUNDERSTORM IMPACTS: Thunderstorms and/or enhanced cells will become more likely later this afternoon through most of the day on Friday. Isolated heavy downpours and wind gusts up to 50 mph are possible with any of these storms. Lightning could affect coastal areas and beaches. There is a remote risk for a tornado, mainly over Los Angeles County Thursday night.
WHAT YOU CAN DO: Limit time on the roads and outside. Stay weather aware. If you hear thunder, see lightning, or experience sudden wind shifts, head indoors. If you have to travel in the mountains, bring chains or a 4x4 vehicle. Continue to monitor the latest forecasts.
DETAILS: Our next storm system is headed our way. A long and narrow cold front is currently working through San Fransisco and Monterey and will sweep down the coast today and tonight. Widespread light to moderate rain will affect all four of our counties. By this evening, the center of the low pressure system driving this front will drop south quickly and into the southern California waters by Friday morning. This will also destabilize the atmosphere by tonight and bring a 10-20 percent chance of thunderstorms and heavier rain cells which lingers into Friday. With a fair amount of wind shear, there is a remote risk (less than 2% chance) of a brief tornado, mainly over Los Angeles County. The path of this low will also force some rather gusty east winds on Friday in what one might call a wet Santa Ana. These winds will likely occur over a big area than usual. Expecting impactful delays at LAX airport with a long duration period of east wind operations.
The unusual evolution of this storm will reverse the typical distribution of the rain, with the higher totals and rates to the south compared to the north. The cutoff nature of the system means there will be a larger range of potential outcomes than usual, including timing with an 6-12 hour earlier or later end than currently advertised both on the table. The path of the system and the resulting drying east winds also adds to that range of outcomes, but will enhance the rain and snow for the backside mountains and deserts. With all that stated, the most likely outcomes are as follows. For SLO and Santa Barbara Counties, look for totals of 0.25 to 0.75 inches, with local 0.5 to 1.5 inches in some mountains. Peak rates of 0.10 to 0.25 inches per hour, except for local 0.25 to 0.50 inches per hour in thunderstorms. For LA and Ventura Counties, look for totals of 0.75 to 1.25 inches, with local 1.0 to 2.0 inches in some mountains. Peak rates of 0.2 to 0.4 inches per hour, except for local 0.50 to 0.75 inches per hour in thunderstorms. Snow amounts for elevations above 6,000 feet will be 2 to 6 inches, highest in LA and Ventura Counties. Local 8 inches are possible. Light accumulations down to 5,000 feet. Decided to convert the previous Winter Storm Watch to a Winter Weather Advisory as the snow rates just do not look that heavy. Precipitation over the Tejon Pass/Grapevine should stay as rain through the event, but could be heavier than our previous storms.
Temperatures will be cool today and Friday, but with the east winds some coastal areas will likely see warming on Friday. By Saturday, all areas will see warming as the low should move through and the east winds continue. In fact, we could see highs in the lower 70s.
(Sun-Wed), 20/350 AM.
While temperatures might cool a little on Sunday as the east winds turn off and return to a more normal onshore pattern, temperatures will remain around normal through next week (including Thanksgiving). The marine layer with low clouds and fog should also make a return, but might be limited by Wednesday as north winds start to form. A rain-free period through at least Black Friday looks almost certain. There are growing signals however for another storm sometime in the Saturday through Tuesday time range (Nov 29-Dec 2).
20/1801z.
At 1739Z at KLAX, there was a deep moist layer to 5500 feet, with an inversion to 8000 feet and a temperature of 1 degree Celsius.
A storm system will bring widespread rain on Thursday with at least MVFR categories and possible localized IFR conditions during the heaviest rain, with the highest chance of that over LA and Ventura Counties 20-03Z. LLWS 5-15 knots likely at most airports. 10-20% chance of thunderstorms 20/23Z-21/18Z, highest for Ventura County and Los Angeles County. Moderate confidence in timing (+/- 3 hours).
KLAX, Moderate confidence in TAF. -SHRA followed by consistent rain will continue into late tonight. IFR cigs and vsbys possible with any heavy rain, best chances between 00Z-08Z. MVFR and VFR cigs are most likely outside of heaviest rain. 20% chance of TSTM 00Z-16Z. Any TSTM will likely produce very gusty and erratic winds. Winds will remain east-southeast through the period. There is a 30% chance for east winds to reach 15-20 kts as soon as 04Z, strongest winds 07Z-end of period.
KBUR, Moderate confidence in TAF. -SHRA followed by consistent rain will continue into late tonight. IFR cigs and vsbys possible with any heavy rain, best chances between 23Z-07Z. MVFR and VFR cigs are most likely outside of heaviest rain. 10% chance of TSTM 23Z-12Z. Any TSTM will likely produce very gusty and erratic winds. Gusty SE winds will e common
20/820 AM.
A storm system will move south along the California Coast, bringing gusty winds, a large west- northwest swell, rain, and potential thunderstorms Thursday into the weekend. The highest rain and thunderstorm chances exists from Thursday afternoon through Friday afternoon. Any thunderstorm can produce erratic wind shifts, heavy rain, lightning, and even waterspouts. Wind directions will vary considerably through the course of the storm. This will result in rough, confused seas. Due to lack of confidence in exact location of storm's core, Gale Force winds are possible virtually anywhere across the coastal waters. However, more likely south and west of Point Conception.
A combination of Small Craft Advisory (SCA) winds and seas will be common across the coastal waters through much of the weekend. Seas will rapidly increase to upwards of 15 feet across the Outer Waters, 10 feet for the nearshore Central Coast Waters, and 5 to 8 feet inside the Southern California Bight through this evening. 10-20 knots southerly winds are expected ahead of cold frontal passage, and NW winds 20-30 knots expected in the wake of the front.
High resolution models indicate that the low will remain far enough north impacting the inner waters south of Point Conception with an extended period of SCA conditions and thunderstorm chances into at least Friday afternoon.
On the heels of the system moving through, a moderate Santa Ana Wind event will develop. Northeast winds 20-30 knots will be common nearshore from Ventura to Malibu Friday morning through Saturday evening. There is a moderate chance these winds reach the Channel Islands across the Santa Barbara Channel. Northeast to southeast winds 10-20 knots with gusts to 25 kt at times are likely nearshore from the Palos Verdes Peninsula south through Orange County. Models have been trending down slightly, so it is unlikely at this point for winds of that magnitude to reach Catalina Island.
Confidence remains low in the forecast for winds, especially south of Point Conception, as the direction and magnitude of winds is highly dependent on the track of the upper level low pressure system. It is best to alter any plans and remain in safe harbor until conditions improve.
20/404 AM.
High Surf Advisories are now in effect from Today through Sunday night along the Central Coast and Ventura County. There is a 30% chance for High Surf Advisories to be issued for the Los Angeles County coasts during that timeframe.
Highly variable winds will create rough surf conditions across all coasts. In addition, there is a chance for thunderstorms Thursday through Friday night at all beaches. Thunderstorms can produce lightning, heavy downpours, gusty- erratic winds, and even waterspouts.
Beach erosion with isolated, minor coastal flooding is possible for west-northwest facing beaches, especially during peak high tide from 8 AM to 1 PM from Friday through Sunday, with highest risk along the Central Coast.
Ca, High Surf Advisory in effect from 3 PM this afternoon to 3 AM PST Monday for zones 340-346. (See LAXCFWLOX). High Surf Advisory in effect from 3 AM Friday to 3 AM PST Monday for zone 354. (See LAXCFWLOX). Winter Weather Advisory now in effect until 10 AM PST Friday for zone 377. (See LAXWSWLOX). Winter Weather Advisory in effect until 4 PM PST Friday for zones 379-380. (See LAXWSWLOX). PZ, Small Craft Advisory in effect until 3 AM PST Friday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM this afternoon to 3 PM PST Friday for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PST Saturday for zones 670-673-676. (See LAXMWWLOX).
