23/1137 AM.
A powerful winter storm will bring heavy rain and strong winds to the area through Christmas Day. Significant flooding issues and strong winds are expected along with the potential for strong thunderstorms. For Friday and Saturday, a cool and showery pattern will persist.
(Tue-Fri), 23/723 PM.
***STRONG ATMOSPHERIC WINTER STORM WITH DANGEROUS FLOODING AND ROCK/MUD SLIDES TONIGHT THROUGH THURSDAY EVENING***
***UPDATE***
The storm has arrived. 00Z mdls show no change in the forecast for this major weather event. 00Z mdls show the rains peaking over Srn SBA county from 11pm to 9am Wednesday, VTA county from 300 am to noon and for LA county 800 am to 400 pm. During this peak period max rainfall rates will be between an inch and an inch and half. Rainfall rates this high are not only capable of created flooding and debris flows in and around burn scars but could well cause flash flooding over non bur scar areas as well. As noted below there will be a break in the action (with some lingering showers). The rain on Christmas day is forecast to begin mid morning across the Central Coast and then overspread the area during the day.
The winds have picked up as forecast and are gusting between 45 and 55 mph across the mtns and 35 to 45 mph across the Central Coast.
The latest guidance from the hydrology department shows many rivers rising to near flood stage tomorrow (Wednesday) between 0800 and 1000 except for the Santa Clara which will peak in the afternoon. All rivers and streams will be watched closely.
***From Previous Discussion***
Overall, 12Z models and their respective ensembles are advertising all systems a "go" for an impactful winter storm through Christmas Day. Still looking at a moderate to strong atmospheric river to roll across the area, bringing heavy rain and strong winds. Here are the details:
RAIN, Light rain will continue to increase across the area this afternoon/evening. For tonight/Wednesday, the first, and most significant, impulse of the AR will move across the area. There will be a relative lull in rainfall late in the day on Wednesday, but a second shot of moderate to heavy rain will move across the area on Christmas Day. For Friday, some lingering showers are expected.
RAIN TOTALS THROUGH FRIDAY: North of Point Conception: 2-4 inches coastal/valley areas and 4-7 inches for foothills/mountains.
South of Point Conception: 4-7 inches coastal/valley areas and 6-14 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. South of Point Conception, rainfall rates are expected to be higher (0.70-1.50 inches per hour), especially on south-facing slopes.
THUNDERSTORMS: Unstable air, associated with the storm, along with strong jet dynamics will bring a chance of of embedded thunderstorms tonight through Thursday evening to all areas. The STORM PREDICTION CENTER placed the area under a marginal risk of severe thunderstorms tonight through Christmas Day. Any thunderstorms that form 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 the 6500-7000 foot range on Christmas Day and down to the 5500-6000 foot range on Friday. So, no winter weather issues are expected through Christmas Eve, but some decent accumulating snowfall will be likely at the resort level beginning on Christmas Day.
WIND: Strong and gusty southeast to south winds are expected today through Christmas Day. Warning level wind gusts, 60-80 MPH, are likely across San Luis Obispo and Santa Barbara counties as well as the Ventura/LA mountains and Antelope Valley. Elsewhere, strong advisory-level winds, gusting 35-55 MPH, are expected. HIGH WIND WARNINGS and WIND ADVISORIES remain in effect.
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). Streams, rivers, and creeks will also see rapid flows, thereby increasing the threat of swift water rescues and there is a possibility of some localized river flooding. 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.
(Sat-Tue), 23/140 PM.
For the extended, 12Z models are in decent synoptic agreement through the period.
On Saturday, upper trough will swing across the area. This will keep the possibility of some light showers across the area through the day. High temperatures will remain 4-8 degrees below normal.
For Sunday through Tuesday, models indicate the trough will cutoff into a low that wobbles well offshore to the southwest. The ECMWF family has the low further offshore, allowing for a ridge to nose in from the northwest. So, the ECMWF solution would be a bit warmer than the GFS solution. With respect to precipitation threat, the current official NBM forecast indicates a slight chance of showers Monday and Tuesday. However, based on the deterministic models looking dry, confidence in the NBM forecast is low.
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.
23/800 PM.
A powerful winter storm will bring widespread, dangerous marine weather to the coastal waters with strong winds, rough short- period seas, heavy rain, and a chance for thunderstorms tonight 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 to dangerous levels will affect the waters tonight. High-end GALE conditions can be expected, 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 tonight through early Thursday, which will bring a threat of erratic gusty winds, heavy downpours, cloud-to-water lightning and a small chance of waterspouts.
23/802 PM.
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 remains 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 through Thursday evening for zones 38-87-88-340>358-362-366>383-548. (See LAXFFALOX). High Surf Advisory in effect until 11 AM PST Saturday for zones 340-346-349-350-354-362-366. (See LAXCFWLOX). Wind Advisory remains in effect until 3 PM PST Thursday for zones 354>358-362-366>368-371>375-548. (See LAXNPWLOX). PZ, Gale Warning in effect until 3 PM PST Wednesday for zones 645-650-655-676. (See LAXMWWLOX). Gale Warning in effect until 3 AM PST Wednesday for zones 670-673. (See LAXMWWLOX).
