22/159 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.
(tdy-Thu), 22/131 PM.
***MAJOR WINTER STORM WITH SIGNIFICANT HYDROLOGIC IMPACTS***
Overall, 12Z models in good synoptic agreement through the period as a moderate to potentially strong atmospheric river event will impact the area Tuesday through Christmas Day. Details have not changed dramatically from previous shift, so will just give expected highlights below.
RAIN, Light rain will begin across all areas during the day on Tuesday. The first, and more significant, impulse of the AR will move across the area late Tuesday night and Wednesday. After a relatively "lull" Wednesday night, a second impulse will move across the area on Christmas Day.
RAIN TOTALS THROUGH CHRISTMAS DAY: North of Point Conception: 2-4 inches coastal/valley areas and 4-7inches for foothills/mountains.
South of Point Conception: 3-6 inches coastal/valley areas and 5-11 inches foothills/mountains.
RAIN RATES: Peak rainfall rates north of Point Conception are expected to be in the 0.40-1.00 inch/hour range while south of Point Conception 0.60-1.25 inch/hour rates are expected.
THUNDERSTORMS: Unstable air, associated with the storm, will bring a chance of thunderstorms Tuesday night and Wednesday to all areas. Per STORM PREDICTION CENTER, the area will be under a marginal risk of severe thunderstorms. So, brief intense rain, small hail, gusty outflow winds will be significant hazards. Additionally, there will be a chance of weak, short-lived, tornadoes or waterspouts.
SNOW: Snow levels will remain above the 7500-8000 foot range through Christmas Eve, but will drop to around 7000 feet on Christmas Day. So, no winter weather issues are expected through Christmas Eve, but some decent accumulating snowfall will be likely at the resort level on Christmas Day.
WIND: Strong and gusty southeast to south winds are expected Tuesday through Christmas Day. Widespread gusts of 35-55 MPH are highly likely across all areas. However, there is the potential for warning level gusts up to 80 MPH across Santa Barbara and San Luis Obispo counties as well as the mountains and deserts of Ventura and LA counties. Therefore, HIGH WIND WATCHES remain in effect for the areas with warning-level wind potential. At the very least, future shifts will need to issue numerous wind advisories.
IMPACTS: Widespread urban flooding will be likely along with mud and debris flows (with the threat not just confined to burn areas). The combination of increasingly saturated soil and the strong winds will bring the potential for downed trees and power lines.
ONCE AGAIN, THIS WILL BE A VERY IMPACTFUL HOLIDAY STORM. ANYONE TRAVELING ON CHRISTMAS EVE OR CHRISTMAS DAY WILL NEED TO EXERCISE EXTREME CAUTION. MAKE SURE TO TAKE THE PROPER PROTECTIVE ACTIONS BEFORE THE STORM HITS.
(Fri-Mon), 22/131 PM.
For Friday and Saturday, models indicate and upper low will drop across the area. This will keep things unsettled with shower activity likely to continue across the area. Additional rainfall totals of 0.25-1.00 inches will be possible. things will be winding down, but will still remain unsettled. There will continue to be shower activity across the area with additional rainfall totals of 0.25 to 1.00 inches through Saturday.
For Sunday and Monday, models have the upper low meander southwest of the area. This will set up a weak offshore flow pattern across the area. So, there will be some locally gusty canyon winds. However, at this time, no widespread advisory-level wind are expected. Depending on where the upper low sets up, there could be some wrap around showers across the area late Sunday and Monday. Confidence in the shower scenario is low, but it will need to be monitored.
22/1856z.
At 1813Z at KLAX, the marine layer was 800 ft deep. The top of the inversion was near 2000 feet with a temperature of 19 C.
High confidence in VFR TAFs for desert airfields (KPMD & KWJF).
Low confidence for remaining TAFs. Timing of CIG/VSBY restrictions could be off by +/- 3 hours, and off by up to 2 categories at any point. -DZ could be possible where CIGs are present.
Rapidly deteriorating conds likely Tuesday afternoon to evening as significant winter storm enters the region.
KLAX, Low confidence in TAF. Good confidence that any east wind component remains below 7 kts through 08Z. 20% chc reaching 7 kts through 12Z Tuesday, then 40% 12Z-15Z Tuesday, and increasing to greater than 60% thereafter through end of forecast period.
Rapidly deteriorating conditions are likely late Tuesday afternoon or evening with south cross winds potentially gusting 15-25 kt, MVFR/IFR cigs/vsbys with -RA/dz at times.
KBUR, Moderate confidence in TAF. Generally expecting VFR conditions through 03Z Tue. LIFR to IFR CIGs possible from 06Z to 12Z Tue then lifting to IFR to MVFR thereafter.
22/255 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 tonight. Patchy dense fog will be possible through Tuesday morning.
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. SCA level southerly winds will develop by Tuesday afternoon with a likely (80-90 percent) chance of widespread Gale Force Winds through at least Tuesday night with a 50-70 percent chance of STORM FORCE winds 45-55 kt for the waters north of Point Sal. 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.
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.
Ca, High Wind Watch in effect from Tuesday afternoon through Thursday afternoon for zones 38-340>353-376>383. (See LAXNPWLOX). Flood Watch now in effect from Tuesday 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 Tuesday to 11 AM PST Saturday for zones 340-346-349-350. (See LAXCFWLOX). High Surf Advisory in effect from 11 PM Tuesday to 11 AM PST Saturday for zones 354-362-366. (See LAXCFWLOX). PZ, Small Craft Advisory in effect from 4 AM to 1 PM PST Tuesday for zones 645-670-673. (See LAXMWWLOX). Small Craft Advisory in effect from 8 AM to 1 PM PST Tuesday for zones 650-655-676. (See LAXMWWLOX). Gale Watch in effect from Tuesday afternoon through late Tuesday night for zones 650-655-676. (See LAXMWWLOX).
