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.
(tdy-Thu), 23/747 AM.
***UPDATE***
Latest satellite and surface observations indicate cloudy skies across the area with a mix of low/mid/high level clouds. Southeast winds are starting to establish with gusts currently in the 20-35 MPH range across the area.
Forecast-wise this morning, it's the "calm" before the storm. All systems are a go for a very impactful event for Southwestern California. For today, current forecast looks good with chance of light rain developing across the area while southeasterly winds increase. Current start time for the HIGH WIND WARNINGS and WIND ADVISORIES of noon looks good as winds should increase noticeably this afternoon.
Overall, the details below from the night shift are still on track. So, no significant updates for the immediate short term and likely only minor tweaks to the forecast for tonight through Christmas Day (depending on what the 12Z model suite shows). Again, be ready for a strong winter storms with heavy rain and very strong winds through Christmas Day.
***From Previous Discussion***
***STRONG ATMOSPHERIC WINTER STORM WITH DANGEROUS FLOODING AND ROCK/MUD SLIDES TONIGHT THROUGH THURSDAY EVENING***
The 00Z and 06Z mdls and ensembles are in decent agreement and do not deviate from the current forecast. All hi rez mdls do show some timing and coverage differences, but nothing significant enough to initiate any changes to the forecast.
This morning will be cloudy with a chc of a sprinkle just about anywhere. The chc of rain will increase this afternoon as the AR sets up into a more N to S orientation and approaches the state.
Everything still points for a major storm to affect Srn CA late this evening and through Wednesday. A strong upper level southwesterly jet will interact with a very moist tropical air mass with PWAT values peaking around 1.5 inches and IVT values between 750 and 1000 kg/m-s. The combination of strong jet dynamics, lots of warm air advection, and strong southerly winds will bring prolonged periods of heavy rainfall (Especially across south facing slopes south of Point Conception). Because of this The south facing mtns and foothills as well as the coastal and vly areas below them were designated as a high risk area for DANGEROUS AND WIDESPREAD FLOODING CONCERNS. Some of the latest high resolution model data show rain rates locally reaching 1.50 inches per hour (especially across favored south facing slopes).
RAIN, Light rain will begin across all areas during this afternoon. The first, and more significant, impulse of the AR will move across the area later this evening 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. There is a 20-30 percent chance of isolated rates as high as 1.50 inches per hour across favored south facing slopes (south of Point Conception).
THUNDERSTORMS: Unstable air, associated with the storm, along with strong jet dynamics will bring a chance of of embedded thunderstorms tonight and Wednesday to all areas. The STORM PREDICTION CENTER placed the area under a marginal risk of severe thunderstorms. Any TSTM that forms will bring brief intense rainfall. More importantly, due to the strong upper level winds, any convective element will have a high risk to bring damaging winds. Additionally, there will be a chance of weak, short-lived, tornadoes or waterspouts, especially during the second wave of energy on Thursday when there is colder air aloft and more instability.
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. Warning level gusts of 60 to 80 MPH are likely across SBA/SLO counties as well as the mtns and deserts of VTA/LA counties from noon today through 3pm Christmas Day.
IMPACTS: Widespread and significant urban flooding will be likely along with rock/mudslides and debris flows (with the threat not just confined to burn areas). The high intensity rainfall and prolonged duration of heavy rain will bring the threat of debris flows to the recent burn scars. Streams, rivers, and creeks will also see rapid flows, thereby increasing the threat of swift water rescues. A FLOOD WATCH IS IN EFFECT FOR ALL AREAS OF SOUTHWEST CALIFORNIA DUE TO THESE MAJOR HYDROLOGICAL RISKS. The combination of increasingly saturated soil and the strong winds will bring the potential for widespread downed trees and power lines, especially in areas under a High Wind Warning.
ONCE AGAIN, THIS IS A VERY DANGEROUS 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), 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.
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.
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.
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.
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).
