textproduct: Los Angeles

SYNOPSIS

21/238 AM.

Temperatures will remain above normal through Sunday in most areas except the coast. A cooling trend will begin Monday as a strong storm approaches with increasing clouds. Rain will begin Tuesday in most areas with periods of heavy rain Tuesday night and Wednesday as well as very strong winds. Showers are expected to continue on Christmas day and through next weekend.

LONG TERM (THU-SUN)

21/111 PM.

For the extended, a wet and unsettled pattern will continue across the area through the weekend. 12Z models agree on the details for Christmas Day, but start to deviate Friday through the weekend.

For Christmas Day, the second surge, associated with the AR, will impact the area. This second surge will bring additional moderate to locally heavy rainfall to the area. At this time, additional rainfall totals for Christmas Day are expected to range between 1 and 3 inches. So, there will continue to be flooding and debris flow issues and the FLOOD WATCH may need to be extended into Christmas Day. Snow levels will begin to drop on Christmas Day, down to around 7000 feet. So, there will likely be a White Christmas at the resort level and Winter Weather products may need to be considered. As for winds, they will shift to more southerly direction and decrease in intensity. However, there will still be a chance of warning-level winds across the mountains and advisory level winds elsewhere.

For Friday, both the GFS and ECWMF continue to indicate wet weather continuing across the area, but the GFS is more significant with rainfall totals than the ECMWF family. Snow levels will drop to the 5500-6000 foot range and winter weather conditions will likely impact more mountain communities.

For Saturday and Sunday, models diverge noticeably. The GFS is much more bullish, keeping some decent shower activity across the area into Sunday. However, the ECMWF is much drier. Forecast currently leans towards the GFS and will keep that going.

IN SUMMARY...TUESDAY THROUGH SATURDAY LOOKS TO BE AN EXTENDED PERIOD OF SIGNIFICANT RAINFALL. BY SATURDAY EVENING, RAINFALL TOTALS WILL RANGE FROM 4-8 INCHES ACROSS COASTAL AND VALLEY AREAS TO 8-12+ INCHES ACROSS THE FOOTHILLS AND MOUNTAINS. PLEASE TAKE THE NECESSARY PROTECTIVE ACTIONS AS FLOODING AND DEBRIS FLOW WILL BE A MAJOR ISSUE THIS UPCOMING WEEK.

AVIATION

21/1752Z.

At 1706Z at KLAX, the marine layer was 500 feet deep. The top of the inversion was near 2500 feet with a temperature of 17 C.

High confidence in VFR TAFs for desert airfields (KPMD & KWJF).

Low to moderate confidence for remaining TAFs. Timing of CIG/VSBY restrictions could be off by +/- 3 hours, and off by 2 categories at any point. KPRB, KSBP, and KSMX may see -DZ at times through the period.

KLAX...Low confidence in TAF. Generally expecting LIFR to MVFR CIG/VSBY restrictions (OVC003-012) through forecast period. Timing of flight cat changes may be off +/- 3 hours and may bounce at times. 30% chance that CIGs clear or remain intermittent in nature from 20Z Sun to 05Z Mon. Good confidence that any east wind component remains below 7 kts.

KBUR...Moderate confidence in TAF. Generally expecting VFR conditions. However, BR or HZ MVFR VSBYs are possible thru period and CIGs could return after 12Z Monday (20% chance).

MARINE

21/1227 PM.

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, SE to south winds and seas will are expected to rapidly increase to dangerous levels as a storm system approaches the coastal waters. There is a 90+ percent chance of SCA level southerly winds developing by Tuesday afternoon with a likely (80-90 percent) chance of widespread Gale Force Winds through at least Tuesday night with a 20-40 percent (highest northern waters) chance of at least brief Storm Force Winds. Large short-period seas are likely to develop Tuesday night and should linger Wednesday into Thursday. There is also a 5-15% chance of thunderstorms Tuesday night through Thursday morning.

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...Flood Watch remains in effect from Tuesday afternoon through Wednesday evening for zones 38-87-88-340>358-366>383-548. (See LAXFFALOX). Flood Watch in effect from Tuesday afternoon through Wednesday evening for zone 362. (See LAXFFALOX). PZ...NONE.