17/451 PM.
A cooler storm system will continue to spread rain across the area through tonight, mainly across Ventura and Los Angeles Counties. Lingering showers may continue into Tuesday. Wednesday will offer a brief respite from the rain with warmer temperatures. Another storms is slated to arrive next Thursday and linger into Friday.
(Mon-Thu), 17/811 PM.
***UPDATE***
Another wet day as a cold front marched through the area. The front is currently over the eastern portion of la county and sill push out by 10 pm. The front dropped between a half inch and inch of rain across the flatter portions of the csts/vlys while the coastal slopes saw 1 to 2 inches. Rainfall rates during the peak of the event was enough to warrant flash flood warnings.
Snow levels started out at 7000 ft this morning but have fallen to 5000 ft and snow has been reported throughout the mtns. Snow levels could fall to as low as 4000 ft by Tuesday morning with some non accumulating snow possible on the Grapevine. A winter weather advisory is out the mtns due to 2 to 5 inches of snowfall gusty winds and dense fog.
Most of the csts/vlys struggled to even get out of the 50s today. The notable exception was the LA cst and San Gabriel Vly where the later arriving rain allowed temps to reach the mid 60s. Most max temps ended up 8 to 12 degrees blo normals today.
While the front will no longer be in the area tonight and Tuesday to cold core of the upper will be. This will bring enough instability to the area for a slight chc of TSTM development.
The forecast was updated for chc of precip, clouds and thunder.
***From Previous Discussion***
Overall, 12Z models in good synoptic agreement through the period. Main issues will be upper low passing across the area, bringing another round of precipitation to the area. The low drop southward across Point Conception tonight/Tuesday before moving east across far Southern California Wednesday and Thursday.
RAIN,
Cold front is currently moving across Ventura county and will move into LA county later this afternoon. In association with the front, light to moderate rainfall can be expected, generating a majority of the widespread measurable rainfall. Behind the front tonight and Tuesday, an unstable and showery pattern will prevail as the upper low drops southward. By Tuesday evening, rainfall totals with this system are expected to range from 0.50-1.00 inches for coastal/valley areas with 1-2 inches for the foothills and mountains. Rainfall rates through Tuesday are expected to generally be under 0.50 inches per hour and will generate nuisance flooding across the area. However, the latest high resolution RRFS and HRRR indicate the potential for rain rates around 1.00 inch per hour along the front this afternoon across Ventura and especially LA counties. If these rates does come to fruition, there could be some significant debris flows across the burn scars, including the Palisades and Eaton Scars.
After a dry day on Wednesday, another system will impact the area on Thursday. At this time, rain looks to begin across the Central Coast Thursday morning, working its way south into LA county by Thursday afternoon/evening. By Thursday evening, rainfall totals will generally range between 0.25 and 0.75 inches.
SNOW,
Based on latest guidance, current snow levels are around 7000 feet, but will drop to around 5000 feet tonight and on Tuesday. The bulk of the rainfall will fall before the snow levels drop. However, there still should be some decent accumulations across the northern Ventura mountains and the eastern San Gabriel Mountains (5-10 inches above 7000 feet and 2-5 inches between 5000 and 7000 feet). So, have issued a WINTER WEATHER ADVISORY for these areas through 1000 PM Tuesday.
As for the Grapevine area, there is a chance of a dusting of snow Tuesday morning as the snow levels lower.
Anyone traveling through the mountains through Tuesday should be ready for winter weather conditions.
THUNDERSTORMS,
Along with the rain and snow, thunderstorms will be a risk for the through Tuesday. As the upper low drops southward today, a cold and unstable air mass will bring a threat of thunderstorms to all areas. On Tuesday, the threat of thunderstorms looks to be confined to LA county as well as interior sections of Ventura and Santa Barbara counties.
Any thunderstorms that develop will be capable of producing frequent lightning and gusty/erratic winds. Additionally, any storms could produce significant rainfall rates, likely exceeding the sub-hourly USGS thresholds, and could generate significant debris flows in and around the recent burn scars.
If you live near a burn scar, be prepared for significant rainfall and potential debris flows. Pay attention to local emergency officials for any actions to take if conditions do deteriorate.
(Fri-Mon), 17/107 PM.
For the extended, models continue to exhibit decent synoptic agreement through the period. Main feature of note will be upper low that will impact the area Friday and Saturday.
On Friday, this upper low will drop southward, southwest of San Nicolas Island and will move eastward into northern Baja Mexico on Saturday and Sunday. With this pattern, the threat of rain will continue for all areas on Friday, but will diminish from north to south through the day with a lingering slight chance of showers on Saturday south of Point Conception. With this system from Thursday through Saturday, rainfall totals are expected to range from 0.25 to 0.75 inches across coastal and valley areas with up to around 1.25 inches across the foothills and mountains. However, given the nature of upper lows, there is the potential for rainfall totals to be a bit higher than currently forecast. Snow levels look to drop to around 5500 feet on Friday/Saturday which could result in several inches of additional snowfall.
On Sunday, the low will move eastward. This will bring some welcome dry conditions to the area.
18/0540z.
At 0445Z at KLAX, there was no marine layer. There was a moist layer extending to 6000 ft.
Moderate confidence in TAFs. There is a 30 percent chc of no MVFR cigs developing overnight at any given site. If cigs do form there is 30 percent chc that there will be IFR cigs.
There is a 10 percent chc of a TSTM at KSMO, KLAX and KLGB after 20Z-02Z.
KLAX, Moderate confidence in TAF. There is a 30 percent chc of no MVFR cigs developing. If cigs do form there is 30 percent chc that they will be BKN008. There is a 10 percent chc of a TSTM 20Z-02Z. There is a 25 percent chc of an 9 kt east wind component 09Z-16Z.
KBUR, Moderate confidence in TAF. There is a 30 percent chc of no MVFR cigs developing. If cigs do form there is 30 percent chc that they will be BKN008. There is a 30 percent chc of bkn040-050 conds 18Z-02Z.
17/822 PM.
For the waters from southwest through northwest of the Channel outside the southern California bight and the nearshore waters along the Central Coast, Small Craft Advisory (SCA) level winds continue through tonight. SCA seas will persist through mid-day Tuesday. Winds and seas will likely fall below SCA levels for Wednesday and Thursday, then there is a moderate to high (30-50 percent) chance of SCA conditions developing on Friday.
Inside the Southern California Bight, SCA level winds will continue through tonight, with a chance to linger into the early morning hours. Conditions will likely remain below SCA levels for Wednesday and Thursday, then there is a moderate- to- high (30-50 percent) chance of SCA conditions developing on Friday.
There is a 10-20 percent chance of thunderstorms across the coastal waters through late Tuesday morning. Any thunderstorms that develop will be capable of producing brief heavy rain, small hail, dangerous cloud to surface lightning, gusty and erratic winds, locally rough seas, and possible waterspouts.
Ca, High Surf Advisory in effect until 10 AM PST Tuesday for zones 340-346. (See LAXCFWLOX). Winter Weather Advisory remains in effect until 10 PM PST Tuesday for zones 377-380. (See LAXWSWLOX). PZ, Small Craft Advisory in effect until 3 AM PST Tuesday for zones 645-650-655. (See LAXMWWLOX). Small Craft Advisory in effect until 3 PM PST Tuesday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 9 PM PST Tuesday for zone 676. (See LAXMWWLOX).
