18/209 AM.
A significant cool down is expected across southwest California through the middle part of the week. Widespread rain is likely Wednesday and Thursday with a slight chance of thunderstorms.
(tdy-Thu), 18/202 PM.
Decreasing 500 mb heights combined with increasing onshore flow mainly to the east will result in gradual cooling over the next several days. There is lingering pockets of moderate heat risk over the LA Basin, Oxnard Plain, and Santa Barbara area Today (No Heat products needed). Marine layer stratus likely to make a return to the Santa Maria Valley tonight into Monday morning. Fog is possible in the Salinas Valley during the early to mid- morning hours. Mid to high clouds associated with the upcoming storm system will arrive to the Central Coast Tuesday.
Good confidence in widespread rain at times Wednesday & Thursday. Uncertainty in timing and details especially given that guidance tends to handle cut-off lows poorly. The recent trends in ECWMF and GFS have been gradually more offshore and slower timing.
Scenario 1 (70% chance): Cold-core low pressure moves through the region. This scenario would provide better dynamics with increased potential for organized banding of moderate to heavy rainfall with rainfall totals 0.5-1.5 except locally 1.5-3 inches across S-SW facing mountains and foothills. Areas of most concern would be Southern Santa Barbara county through LA county which has the best chance to end up on the higher range of these totals. Convection would be more likely in this scenario providing around a 20% chance of thunderstorms along with some concern for flooding and debris flows - especially near recent burn scars.
Scenario 2 (30% chance): The system slows and peaks in intensity well offshore and weakens considerably as it moves through the area. Both ECWMF and GFS have been trending this way the last several cycles. Rain chances would be more sporadic with 0.25-0.50 and locally up to 1-1.5 inch for some mtn locations. Analogs show this scenario has resulted in reduced impacts - lower (but still present) risk for flooding and thunderstorms.
The final solution could fall in between these two scenarios. Either way the weather will feel chilly in contrast with highs only in the 60s and 70s.
(Fri-Sun), 18/202 PM.
By Friday and Saturday, the upper low will have moved eastward into the Great Basin. This will result in weak-moderate offshore flow mainly from the east. Dry conditions, locally breezy winds, and warming temperatures can be expected.
The Pacific-North American oscillation is expected remain negative likely through the month. This weather pattern would generally favor troughing on the west coast - resulting in better chances for rain and cooler temperatures.
18/1758z.
At 17Z at KLAX, there was a weak inversion with a base at 2600 ft. The top of the inversion was at 3400 ft with a temp of 21 deg C.
High confidence in VFR TAFs for most airfields. Lower confidence for TAFs at KSBP, KSMX and KLGB due to uncertainties with the timing and extent of low clouds and IFR/LIFR/VLIFR conds late tonight into Mon morning. Timing of onset/dissipation/flight cat changes could be off +/- 1-2 hours.
KLAX, Generally hi confidence in VFR TAF. However, there is a 10-20 percent chance of IFR cigs/vsbys 12Z-16Z Mon. Any east wind component is expected to be 6 kt or less thru the period.
KBUR, High confidence in VFR TAF.
18/141 PM.
For the outer waters, generally hi confidence in the current forecast. Small Craft Advisory (SCA) winds are expected to develop later tonight west and south of Point Conception and persist through late Monday night. There is also a 40% chance of these winds again for the same area Thursday through Friday night. In addition, seas will approach SCA levels through Wednesday, peaking up to 9 feet at times through Monday.
For the inner waters N of Point Sal, generally hi confidence in the current forecast. Conds are expected to largely remain below SCA levels except for a 40% chance of SCA level wind gusts at times Thursday night and Friday night. In addition, large seas up to 8 feet can be expected through Monday.
For the inner waters S of Point Conception, generally hi confidence in the current forecast. Conds are expected to largely remain below SCA levels except for a 40% chance of SCA level wind gusts at times for the Santa Barbara Channel Thursday night and Friday night.
A moderate-strength storm system is becoming more likely in the Tuesday night through Thursday timeframe. In addition to reduced visibilities in showers, there is a 10-20 percent chance of thunderstorms Wednesday afternoon and Wednesday night with the possibility of locally gusty and erratic winds and dangerous lightning. It also looks like conditions may become favorable for the formation of waterspouts with this system. Please monitor the latest forecasts and statements over the next couple of days as we draw closer to this event.
18/1241 PM.
The combination of a large west to northwest swell and moderate southerly swell will bring elevated surf of 3 to 6 feet mainly to south and southwest-facing beaches of Ventura and Los Angeles Counties through Tuesday morning.
In addition to the elevated surf, dangerous rip currents can be expected. Minor beach erosion and tidal overflows cannot be ruled out for low-lying beach areas around the times of high tides.
Ca, Beach Hazards Statement in effect through Tuesday morning for zones 354-362-366. (See LAXCFWLOX). PZ, Small Craft Advisory in effect from 3 AM Monday to 3 AM PDT Tuesday for zones 673-676. (See LAXMWWLOX).
