14/153 PM.
An unusually strong storm system will bring widespread rain to the area through Sunday. The period of most concern is tonight through Saturday Night when a large area of heavy rain and isolated but potentially severe thunderstorms will bring a moderate to high risk of significant flash flooding, debris flows, and damaging winds. After a very brief break, another storm will bring light to moderate rain to the area Monday into Tuesday. Yet another storm is possible for Thursday into Friday.
(tdy-Mon), 14/204 PM.
***MODERATE TO HIGH RISK OF DANGEROUS FLASH FLOODING, DEBRIS FLOWS, AND DAMAGING WINDS TONIGHT THROUGH SATURDAY NIGHT***
POTENTIAL IMPACTS: The period of most concern is tonight through Saturday Night. During this time, folks should be prepared for ample traffic incidents, delays, and a few road closures. This includes a few flooded roads, freeway lanes, and on ramps and off ramps. Canyon roads, especially the most vulnerable ones like Topanga Canyon, will likely see mudslide and rockslides. In and near recent burn scars, at least shallow debris flows will occur which would impact roads, with a moderate risk of significant flows blocking or damaging roads and impacting structures. This includes the Palisades, Eaton, and Bridge burn areas which have the highest threat. In creeks and rivers, the flows will be heavy with anyone in or near those channels at risk of being swept away. There will be an area of heaviest rain, but we do not know for sure exactly where that will be. Wherever it sets up, expect all these impacts to be amplified, including a risk for a neighborhood or two experiencing shallow water spilling into businesses and homes. In addition to the water risks, there is a significant threat for severe thunderstorms capable of producing very localized but damaging winds and or a brief tornado.
WHAT YOU CAN DO: Avoid the roads, stay indoors as much as possible, and stay aware of your environment. If you have to drive, allow extra time as traffic will be increased due to slippery roads, low visibility, and localized flooding. If you are near a burn scar, heed the advice of local officials as they know your area best. Reschedule and avoid outdoor activities. If you are outside and hear thunder, see lightning, experience sudden wind shifts, or a sudden increase in rain intensity, head indoors immediately and stay away from windows. Stay out of, and far away from, any streams, rivers, and canyons - especially campers. Avoid parking near tall trees. Be ready for sudden power outages. Boaters, please stay in safe harbor. For everyone, stay tuned to your local news outlet and weather.gov for any updates.
UPDATED DETAILS: The core of the storm system has cutoff from the jet stream, and is now spinning around as it pleases. While there remains some uncertainty in terms of timing and placement of the heaviest rain as a result, all available guidances remain locked in for an increase in rain coverage and intensity tonight through Saturday Night. Peak rain rates during this period of most concern will likely be in the 0.5 to 1.0 inch per hour range over a large portion of our area, with 0.25 to 0.50 inches per hour elsewhere. When considering the rain we have already seen and will continue to see today, which should precondition the ground and lower the bar of what sort of additional heavy rain is needed to trigger flash flooding, the risk for significant and potentially damaging flooding continues to be moderate to high with the expected rain rates. The current Flood Watches look good and there are no immediate plans for changes. In terms of the severe weather threat, we continue to see a number of parameters favoring supercell thunderstorms capable of producing localized damaging winds and or a brief tornado. This include updraft helicity, which the HREF suite of models all point to Los Angeles County having the highest risk with values that are about as high as we have seen for this area. This does not guarantee a tornado, and 99% of the population will NOT see these conditions, but the risk exists for a very localized high impact situation.
There will be a very noticeable break in the steady widespread nature of the rain Saturday Night, but scattered off and on again light to moderate showers will remain over the area through Sunday. The highest chances are over eastern Los Angeles County and northern SLO County Saturday Night, then really anywhere on Sunday. Any additional impacts will be minor.
The break will be brief as the next storm will start to impact the area Sunday Night, first over San Luis Obispo County then pushing south into Los Angeles County on Monday. After a cold front brings light to moderate rain with minor impacts, there is a good chance for the core of the system to move through the area Monday Night and Tuesday keeping showers going and possibly bringing some snow levels down to 5,000 feet. The BIG different between this storm and our current storm is that the Tuesday system will not cut off but will remain plugged into the jet. This means it will move through fairly quickly which means rain amounts and impacts will be on the lower end.
(Tue-Fri), 14/206 PM.
There should be a break in the rain on Wednesday, but yet another storm will be in the window Wednesday through Friday. This one carries much more uncertainty that Monday's storm, as really anything is on the table between no rain and a lot of rain. Cooler than normal conditions will remain.
14/2351z.
At 23Z at KLAX, there was no marine layer.
Overall, low confidence in 00Z TAF package. High confidence in periods of rain for all sites through the period, but low confidence in timing of flight category changes (and the flight categories themselves). CIGs and VSBYs will vary from VFR levels down to IFR through the period.
There is a 20% chance of thunderstorms for TAF sites south of Point Conception thru the fcst period. Any thunderstorms will be capable of producing heavy rain, frequent lightning and gusty/erratic outflow winds.
KLAX, Low confidence in 00Z TAF. High confidence in varying intensities of rainfall through the period. However, low confidence in timing of flight category changes as well as the flight categories themselves. MVFR conditions most likely through this evening with IFR conditions becoming more likely overnight. Through 11Z, there is a 50-60% chance of easterly winds above 8 knots, then a 60-80% chance of easterly winds above 10 knots 11Z-17Z.
KBUR, Low confidence in 00Z TAF. High confidence in varying intensities of rainfall through the period. However, low confidence in timing of flight category changes as well as the flight categories themselves. MVFR conditions most likely through this evening with IFR conditions becoming more likely overnight.
14/1248 PM.
There is a 20-30% chance of thunderstorms across the coastal waters south of Point Conception from late this afternoon through Saturday night. Any thunderstorms that develop will be capable of producing brief heavy rain, dangerous cloud to surface lightning, gusty and erratic winds, locally rough seas and possible waterspouts.
For the Outer Waters, moderate to high confidence in current forecast. Today through Saturday morning, high confidence in Small Craft Advisory (SCA) level seas and a 20% chance of SCA level seas. From Saturday afternoon through Sunday, high confidence in winds and seas remaining below SCA levels. For Monday and Tuesday, high confidence in SCA level seas with a 30-40% chance of SCA level winds. For Wednesday, high confidence in winds and seas remaining below SCA levels.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through Saturday morning, high confidence in SCA level seas. For Saturday afternoon through Sunday, high confidence in winds and seas remaining below SCA levels. For Monday through Tuesday, high confidence in SCA level seas with a 30-40% chance of SCA level winds on Monday. For Tuesday through Wednesday, high confidence in winds and seas remaining below SCA levels.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Moderate confidence in SCA level southeast winds tonight and Saturday morning across PZZ655 with conditions expected to remain below SCA levels elsewhere. For Saturday afternoon through Sunday, high confidence in winds and seas remaining below SCA levels. On Monday, there is a 60-80% chance of SCA level winds across all the southern Inner Waters. For Tuesday through Wednesday, high confidence in winds and seas remaining below SCA levels.
14/1248 PM.
A moderately long period west-northwest swell will bring hazardous surf conditions to portions of Southwest California today through at least Saturday morning. In addition to the west-northwest swell, a storm system will bring gusty southerly winds which will add a southerly wind swell component to the surf. HIGH SURF ADVISORIES remain in effect for the Central Coast and the Ventura county beaches. Please refer to the LAXCFWLOX and LAXSRFLOX for details.
There is a 20-30% chance that HIGH SURF ADVISORIES may be needed for the LA county beaches today and tonight.
Additionally, there is a 20-30% chance of thunderstorms across all the beaches at times from late this afternoon through Saturday night. Any thunderstorms that form will be capable of producing locally strong winds, small hail, dangerous lightning, heavy rainfall, and possibly even a weak/brief tornado.
Ca, Flood Watch now in effect from 1 AM PST Saturday through Saturday evening for zones 87-88-346>358-362-366>383-548>550. (See LAXFFALOX). High Surf Advisory in effect until 3 PM PST Saturday for zones 340-346-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect through Saturday afternoon for zones 349-350. (See LAXCFWLOX). PZ, Small Craft Advisory in effect until 3 PM PST Saturday for zones 645-670-673-676. (See LAXMWWLOX). Small Craft Advisory in effect until 11 AM PST Saturday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect from 3 AM to 3 PM PST Saturday for zone 655. (See LAXMWWLOX).
