textproduct: Los Angeles

SYNOPSIS

19/452 PM.

Mostly clear skies are expected through Saturday except for overnight to morning low clouds and fog near the coast. It will be cooler each day, but high temperatures will remain above normal. There will be increasing clouds, cooler temperatures and a slight chance of rain over San Luis Obispo county Sunday and Monday. A strong storm will bring many inches of rain to the entire area Tuesday through Wednesday.

LONG TERM (WED-SAT)

20/102 PM.

For the extended, all models indicate systems are still a "go" for a VERY SIGNIFICANT winter storm to impact the area. All residents of Southwestern California should be prepared for a very strong storm.

On Christmas Eve (Wednesday), the AR will exert its greatest punch to the area with moderate to heavy rainfall for all areas. This first wave will move across the area Wednesday morning and afternoon with precipitation tapering off Wednesday evening. On Thursday, a secondary AR punch will impact the area with impressive rainfall amounts (but less than what falls on Wednesday). On Friday, all models agree on a continued shower threat across the area. However on Saturday, models diverge with the GFS indicating another shot of moderate rainfall while the ECMWF just indicates scattered showers. However, will not get bogged down in those differences at the Day 7-8 time frame.

Through Saturday evening, rainfall totals will be very impressive. North of Point Conception, 2-4 inches is expected for coasts/valleys with 4-8 inches across the foothills and mountains. South of Point Conception, amounts will even be more impressive, 4-6 inches for coastal/valley areas and 6-12+ inches for the foothills and mountains. Rainfall rates also will be pretty impressive. Peak hourly rates of 0.50-1.00 inches are likely south of Point Conception and 0.30-0.80 inches north of Point Conception. Given the amount of expected rainfall and the associated rates, significant hydrologic issues can be expected, including widespread urban flooding and the threat of mud and debris flows.

As for snow, given the nature of this system, snow levels will remain rather high through the bulk of the precipitation. Snow levels will remain above the 7000 feet through Christmas Day, but will drop into the 5500-6500 foot range Friday through Saturday. So, resort levels will likely receive some impressive snow totals when all is said and done, but lower elevations will not.

AVIATION

20/1804Z.

Around 17Z, the marine layer depth was near 1500 feet deep at KLAX. The top of the marine inversion was around 4500 feet with a temperature near 19 deg C.

High confidence in the current forecast for desert terminals.

Elsewhere, low to moderate confidence exists in the coastal and valley terminals. Primarily MVFR conds are expected through 19Z at Los Angeles County coastal terminals and LIFR to IFR conds at KBUR, KVNY and KCMA. Conds should improve to VFR at these airfields by 20Z or 21Z. An early return of IFR to MVFR conditions should be expected for the coastal terminals, then moving into valley terminals overnight and lowering. Some airfields could see LIFR conds late tonight into Sun morning as well. The timing of flight cat changes may be off +/- 1 to 2 hours.

KLAX...Low to moderate confidence in the 18Z TAF. MVFR conds are expected through 19Z, then conditions should improve to the VFR before lowering again to MVFR around 03Z. A return of IFR conds is expected around 08Z then improving aft 18Z Sun. The timing of flight cat changes may be off +/- 1 to 2 hours.

KBUR...Low to moderate confidence in the 18Z TAF. LIFR conds are expected through 19Z. VFR conds should develop 19Z and 20Z. IFR conditions should return as soon as 05Z. There is a 50% chance VFR conds will develop around 15Z Sun, but there is also a 50% chance of IFR conds thru 18Z. The timing of flight cat changes may be off +/- 1 to 2 hours.

MARINE

20/1126 AM.

High confidence in the current forecast through Monday night, then moderate confidence thereafter. Confidence lower due to timing and seas. Winds and seas will largely remain below SCA levels through Monday night.

On Tuesday, winds and seas will likely rapidly increase to dangerous levels as a storm system approaches the coastal waters. There is a 70-90 percent chance of SCA level southerly winds developing by Tuesday afternoon with a likely (60-70 percent) chance of widespread Gale Force Winds through Tuesday night. Large short-period seas are likely to develop Tuesday night and should linger Wednesday into Thursday.

Boaters are urged to monitor the latest weather forecasts. If marine weather conditions deteriorate as advertised, boaters should remain in safe harbor during this significant storm. Unprotected south facing harbors may be especially vulnerable to the south swell and winds.

LOX WATCHES/WARNINGS/ADVISORIES

CA...NONE. PZ...NONE.