18/722 PM.
A significant cool down is expected across southwest California through the middle part of the week. Widespread rain is likely Tuesday night through Thursday with a slight chance of thunderstorms.
(Sun-Wed), 18/809 PM.
***UPDATE***
The cooling trend kicked off today for most of the area due to morning offshore flow weakening compared to the previous days, and the onshore trends increased. A few areas saw a tiny bit of warming compared to yesterday due to some lingering offshore wind across the interior SLO and I-5 Corridor. Otherwise, most areas dropped as much as 8 degrees compared to yesterday. Overall, highs were in the high 70s to high 80s, with a few locations just barely making it into the low 90s.
Current Satellite imagery is not showing much for marine layer clouds so far tonight, just some patchy clouds along the Central Coast and a few along the Santa Barbara/Ventura County Border (though those look to be short lived). The forecast has clouds overspreading the Central Coast, but could easily see it remaining patchy and only a few locations getting overnight low clouds and fog (such as Lompoc, Santa Maria, etc). With continued 500 mb heights decreasing and increasing onshore trends, expect temperatures to continue to drop, with highs in the mid 70s to high 80s tomorrow.
Forecast looks to be in shape and no major updates were needed this evening.
***From Previous Discussion***
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.
(Thu-Sun), 18/213 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.
19/0055z.
At 0020Z at KLAX, there was a marine inversion with a top near 1400 ft with a temp of 24 deg C.
High confidence in VFR TAFs for most airfields. Lower confidence for TAFs at KPRB, Central Coast and LA Coastal sites due to uncertainties with the timing and extent of low clouds tonight into Mon morning. Timing of onset and dissipation of any low CIGs could be off +/- 1-2 hours. KPRB has a 10% chance of LIFR/IFR conds, timing and flight category for Central Coast sites has lower confidence, with 30% chance of LIFR for KSBP and 20% chance of VLIFR at KSMX. For the LA Coast, 40% chance of VFR conds thru the period.
KLAX, Moderate confidence in the 00Z TAF. However, there is a 20 percent chance of MVFR conds 10Z-16Z Mon. Any east wind component is expected to be 6 kt or less thru the period.
KBUR, High confidence in VFR 00Z TAF.
18/814 PM.
For the outer waters, moderate to high confidence in the current forecast. Small Craft Advisory (SCA) winds are affecting the northern two zones (PZZ670-673) and are expected to spread southward over PZZ676 later tonight. For the northernmost area, the gusty winds will only last through late tonight, but further south the SCA conds will persist through late Monday night. There is also a 40% chance of SCA winds again for the two southern zones Thursday through Friday night.
For the inner waters N of Point Sal, generally high 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.
For the inner waters S of Point Conception, high confidence in the current forecast. Conds are expected to largely remain below SCA levels except for a 40% chance of SCA level wind gusts 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. 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.
18/816 PM.
The combination of a west to northwest swell and a 3-ft 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 until 3 AM PDT Monday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Tuesday for zone 673. (See LAXMWWLOX). Small Craft Advisory in effect from 3 AM Monday to 3 AM PDT Tuesday for zone 676. (See LAXMWWLOX).
