textproduct: Los Angeles

SYNOPSIS

23/820 AM.

A powerful winter storm will bring heavy rain and strong winds to the area through Christmas Day. Significant flooding issues are likely along with the potential for strong thunderstorms. For Friday and Saturday, a cool and showery pattern will persist.

LONG TERM (FRI-MON)

23/1226 AM.

A second colder trof/upper low drops into the area on Friday moves through the area on Saturday. Rain will be likely across the areas on Friday as the max lift of the trof moves into the area. Snow will be much more of a concern with snow levels between 4500 and 5000 ft. rain will turn to showers and diminish on Saturday as the storm moves out of the area. The best estimate for rainfall friday (midnight to midnight) is about a half inch for coasts and a half inch to an inch in the mtns and foothills. Saturday's rain will be a quarter inch or less.

Very little mdl agreement for the Sunday / Monday time frame as the GFS is forecasting an upper low with 560 hgts and the EC a ridge with 579 hgts over the area. A majority of the ensembles favor the EC solution and the official forecast is dry with a warming trend - though not as robust as the operational EC would have.

AVIATION

23/1819Z.

At 1641Z at KLAX, the marine layer was 2200 ft deep. The top of the inversion was near 3700 feet with a temperature of 14 C.

Overall, moderate confidence in 18Z TAF Package.

CIGs should rise a bit through at least 21Z Tue. Expecting MVFR conditions with IFR conditions during heavy rainfall. Cannot rule out brief periods of LIFR.

Chance of -SHRA through around 05Z Wed then rain will begin to overspread the area from the east. S-SE winds will strengthen during this time. Timing of wind shifts may be off by +/- 2 hrs and wind speeds could be off by 10-15 kts at any given time.

These strong winds combined with moderate to heavy rainfall will result in poor flight conditions including on ascent/descent. LLWS and turbulence is possible to likely anywhere, but especially over and near mountainous terrain and with any thunderstorms that develop due to erratic winds. Specifically, frontal turbulence will be an issue.

KLAX...Moderate confidence in TAF. Good confidence that CIGs will raise a bit more through about 21Z Tue. Rain will likely develop around the terminal by 06Z. Expecting E-SE winds to continue increasing thereafter. Strong east winds are likely through Wednesday. Frontal Turbulence is expected. There is a low chance that winds briefly switch to the west sometime from 18Z to 00Z Wednesday, but high confidence that even if it occurs will switch back to the east.

KBUR...Moderate confidence in TAF. Good confidence that CIGs will raise a bit more through about 21Z Tue. Rain and stronger winds are expected to develop around 10Z Wed. Frontal Turbulence is expected.

MARINE

23/743 AM.

A strong winter storm will bring widespread, dangerous marine weather to the coastal waters with exceptionally strong winds, rough short- period seas, heavy rain, and a chance for thunderstorms this afternoon through Thursday.

Vessels, especially small vessels are strongly advised to remain in safe harbor for the duration of the storm, as these conditions can sink boats. South- facing harbors will also be especially vulnerable to the south swell and strong winds.

Details: South to southeast winds and seas will rapidly increase to dangerous levels this afternoon to evening as a storm system approaches the coastal waters. SCA level southerly and seas will further strengthen to GALE to STORM FORCE conditions this afternoon to evening, likely strongest north of Point Conception. These strong winds are expected to impact the nearshore waters, especially for unsheltered south- facing coastlines and areas north of Point Conception.

Large southerly short- period seas will develop tonight and should linger Wednesday into Thursday, leading to elevated, choppy seas at south-facing harbor entrances. There is also a 15-30% chance of thunderstorms late today through early Thursday, which will bring a threat of erratic gusty winds, heavy downpours, waterspouts, and cloud-to-water lightning.

BEACHES

23/745 AM.

A short to moderate period southerly wind swell will produce choppy, large, dangerous surf and rip currents through Thursday. A longer period NW swell will take over Friday, and surf will continue to be significant into the weekend. It is best to remain out of the water during this time. See High Surf Advisory (CFWLOX) for details.

While peak tides are not very high, minor to locally moderate coastal flooding may occur for south facing shores through Thursday.

LOX WATCHES/WARNINGS/ADVISORIES

CA...High Wind Warning in effect until 3 PM PST Thursday for zones 38-87-88-340>353-369-370-376>383-549-550. (See LAXNPWLOX). Flood Watch remains in effect from 4 PM PST this afternoon through Thursday evening for zones 38-87-88-340>358-362-366>383-548. (See LAXFFALOX). High Surf Advisory in effect from 9 PM this evening to 11 AM PST Saturday for zones 340-346-349-350. (See LAXCFWLOX). Wind Advisory in effect until 3 PM PST Thursday for zones 354>358-362-366>368-371>375-548. (See LAXNPWLOX). High Surf Advisory in effect from 11 PM this evening to 11 AM PST Saturday for zones 354-362-366. (See LAXCFWLOX). PZ...Small Craft Advisory in effect until 1 PM PST this afternoon for zones 645-650-655-670-673-676. (See LAXMWWLOX). Gale Warning in effect until 1 PM PST Wednesday for zones 650-655-676. (See LAXMWWLOX).