textproduct: Los Angeles

SYNOPSIS

12/201 AM.

Dry conditions with a warming trend are expected today through Saturday. A strong storm system will affect the region starting on Sunday and Monday, bringing the potential for heavy precipitation with flooding and mountain snow, thunderstorms, strong winds, as well as marine and beach hazards. These conditions could last through much of next week.

LONG TERM (SUN-WED)

12/327 AM.

At least three distinct storm systems are expected to move through southwest California next week, the first one arriving sometime Sunday, likely later in the day or possibly even holding off until early Monday for LA/Ventura Counties. Timing for this and the following storms will be refined as we get closer to arrival. In the meantime, the first system appears to be the strongest in terms of overall rainfall amounts and rain rates. Similar to the last storm, it's moving at a fast clip, but it's a larger storm so it will take longer to move through than the last one. It also has some diffluence aloft and that will create stronger updrafts and heavier rain as well as possible convective activity. PW's are averaging around 1" on Monday with some of the ensembles indicating closer to 1.2" which would be over the 95th percentile. Most coast/valley areas should see at least 1-2" of rain Monday and twice that in the mountains. This will generate the usual assortment of hydrologic hazards like ponding of water on roads and minor mudslides in the canyons. There is about a 20% chance that this first storm will generate amounts that are in the 1.50-3.00" and 3-6" range if the higher end ensembles pan out.

Snow levels with this first system look like they should remain above 6000 feet for most of the storm's duration, but that could still result in significant snow accumulations over the higher mountains.

At least a couple more systems will come through the area Tuesday and Wednesday with decreasing PW's but also much colder air and lowering snow levels. 500mb temps drop to -32 over the Central Coast Wednesday morning which will create an increasingly convective environment with scattered thunderstorms possible and also snow levels down to 3000 feet or possibly even slightly lower. Rain amounts in this scenario would be much more variable, but the potential for rain rates to exceed debris flow thresholds would be much higher due to the increasing convective threat.

Interests across the local area are encouraged to monitor the latest information from the National Weather Service in Los Angeles/Oxnard, California, as forecast details become refined over the coming days.

AVIATION

12/1111Z.

Around 0745Z, there was no marine layer depth at KLAX. There was a surface-based inversion up to around 600 feet with a temperature near 14 degrees Celsius.

Low to moderate confidence in the current forecast. There is a moderate chance of sub-VFR conditions at all terminals through 16Z with equal chances of IFR to MVFR conditions in stratus or LIFR to IFR conditions in ground fog. Otherwise, VFR conditions are expected. There is a low to moderate chance of LIFR to IFR conditions at coastal terminals after 03Z Friday.

KLAX...There is a 30 percent chance of VLIFR to LIFR conditions in ground fog through 16Z, otherwise VFR conditions are expected through 08Z Friday. There is a 30 percent chance of LIFR to IFR conditions after 08Z Friday. Any easterly winds will remain less than 7 knots.

KBUR...There is a 30 percent chance of VLIFR to LIFR conditions in ground fog through 16Z, otherwise VFR conditions are expected. No wind impacts are expected at this time.

MARINE

12/315 AM.

Moderate confidence in the current forecast. Lower confidence in the forecast for seas versus winds.

A series of storm systems will move over the coastal waters early next week, bringing hazardous winds and seas along with rain and a low chance of thunderstorms. Confidence is growing in dangerous marine conditions across the coastal waters, thus it is encouraged to think about altering plans during this timeframe.

For the waters southwest through northwest of the Channel Islands and beyond 10 NM offshore of the Central Coast, winds and seas should remain below Small Craft Advisory (SCA) levels through this afternoon, then SCA level northwest to north winds will increase rapidly through this evening. There will be a likely to imminent (60-80 percent) chance of SCA winds by this evening, continuing into Friday afternoon and evening. There is a moderate (30 percent) chance of a lull in the winds on Friday morning. Winds will diminish through Friday night and into Saturday. There is an increasing chance of SCA level winds between Saturday night and Sunday night with widespread SCA conditions (winds and seas) likely (60-80 percent chance) by Sunday, and an imminent (80-100 percent) chance by Sunday night. There is a moderate to high (30-50 percent) chance of GALES between Sunday night and Tuesday.

For the nearshore waters along the Central Coast, winds and seas will remain below SCA levels through Friday morning, but there is a low to moderate (20-30 percent) chance of SCA level northeast winds from late tonight through early Friday morning. Then, there is a high to likely (50-60 percent) chance of SCA level northerly winds developing between Friday morning and Friday evening. Winds will diminish through Friday night and into Saturday. There is an increasing chance of SCA level winds between Saturday night and Sunday night with widespread SCA conditions (winds and seas) likely (60-80 percent chance) by Sunday, and an imminent (80-100 percent) chance by Sunday night. There is a moderate to high (30-50 percent) chance of GALES between Sunday night and Tuesday.

Inside the southern California bight, winds and seas will remain below SCA levels through this afternoon, then there is a high to likely (50-70 percent) chance of SCA level winds, particularly affecting the western two-thirds of the Channel west of Anacapa Island, in the vicinity of Point Dume, and south into the San Pedro Channel. Winds will diminish tonight and early Friday, then there is a moderate to high (30-50 percent) chance of SCA level winds developing again for Friday afternoon and evening. Winds should diminish through Friday night and into Sunday, then there is an increasing chance of SCA level winds between Sunday afternoon and Sunday night with widespread SCA conditions (winds and seas) likely (60-80 percent chance) by Sunday night, and an imminent (80-100 percent) chance by Monday night. There is a low to moderate (20-40 percent) chance of GALES between late Sunday night and Tuesday.

BEACHES

12/312 AM.

After a lull, surf and swell will build again at area beaches through Friday night. There is a high to likely (50-70 percent) chance of a high surf advisory being needed, especially west and northwest facing shores, from Friday afternoon through Saturday.

A period of very large waves continues to be advertised by the latest swell model guidance early next week. There is a high to likely (50-70 percent) chance of widespread high surf between Monday and Thursday as a combination of southwesterly and west- northwesterly swells arrive along the California coastline. Sets above 10 feet will be possible across all beaches, but there is a higher chances for west to northwest facing shores. There is a 20-30 percent chance of damaging sets developing between Tuesday night and Wednesday night, highest for northwest-facing shores along the Central Coast.

Elevated high tides as the new moon cycle approaches will coincide with the arrival of the higher surf and swell with storm system early next week. This will bring an elevated chance of coastal flooding, or at the very least, minor tidal overflows during times of the highest high tides each evening. A coastal flood advisory may be needed should swell guidance indicate similar surf and swell and locally wind-driven swell affect the beaches and coastline.

LOX WATCHES/WARNINGS/ADVISORIES

CA...High Surf Advisory in effect from 9 AM Friday to 2 AM PST Saturday for zones 340-346. (See LAXCFWLOX). PZ...Small Craft Advisory in effect from 9 AM to 9 PM PST Friday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM this afternoon to midnight PST tonight for zones 650-655. (See LAXMWWLOX). Small Craft Advisory in effect from 9 PM this evening to 9 AM PST Saturday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM this afternoon to 9 AM PST Saturday for zones 673-676. (See LAXMWWLOX).