03/851 PM.
Cloudy and cool conditions will continue through Tuesday, with increasing chances of mostly light rain. Warming and drying to follow Wednesday through the next weekend, with high temperatures approaching 90 degrees in some areas by Friday.
(Sun-Wed), 03/917 PM.
***UPDATE***
A very deep marine-like layer is bringing cloudy and cool conditions from sea-level to 6,000 feet above. This is the result of an onshore pressure gradient that almost reached 10 millibars (topped out at +9.8) and low pressure aloft approaching the area. With such a strong onshore wind pattern, we knocked on the door of a Wind Advisory for the Antelope Valley and foothills today, but stayed just under. Expect more of the same with those aspects tomorrow.
A 560 decameter (at 500 millibars) low, currently centered 250 miles west of Santa Barbara, will slowly move to the east and into Arizona by late Tuesday. This means that the core of the cold air aloft associated with this low will pass right over the area, which also means that the chances of showers will be on the rise Monday into Tuesday. At this point, the highest chances are over the mountains Monday afternoon and night, especially over the Ventura County Mountains where rain is more likely than not. All the classic convective parameters are fairly benign, but experience shows that anytime a low's core moves over the area, thunderstorms are in play. The previously advertised chances of 5 to 10 percent still look very reasonable. While most showers will be light, the added convective potential means that there will likely be a shower or two or three that will bring brief moderate- to-heavy rain over some undisclosed location. None of the models have rates above 0.50 inches per hour, so the likelihood of one of those heavy showers resulting in significant flooding is really small, but some localized minor road flooding should be planned for. With all of this stated, this low is not being forced by the prevailing jet-stream (aka a cutoff low), so there is some play in the timing, but the other aspects of this system are less sensitive to the exact track and speed of the system.
***From Previous Discussion***
Clouds from a 4000 ft marine layer are struggling to clear this afternoon, keeping temperatures mostly in the upper 50s to mid 60s at noon, 10-25 degrees below yesterday. Probably won't see too much more warming today except in the Antelope Valley where highs will be in the 70s. Still a 5-10% chance for a shower or brief thunderstorm in the mountains due to instability from the upper low.
A slow moving upper low just off the coast will continue to create a deep marine layer at least through Monday and likely into Tuesday unless the inversion gets too weak, which is possible. In any case, temperatures will remain well below normal with highs mostly in the 60s. Brief periods of drizzle or light rain are possible each of the next two days, though more likely across the eastern San Gabriel Mountains and adjacent foothills and the Central Coast. Lowest chances for rain will be from southeastern Santa Barbara County through southwestern LA County where downslope flow off the Transverse range will limit rain from reaching the surface. Any amounts should remain below a quarter inch, with many areas getting little to no rain.
Gusty west to northwest winds are expected following the system Tuesday afternoon and evening, possibly requiring wind advisories in some areas.
A warming trend will begin Wednesday and continue into next weekend.
(Thu-Sun), 03/1252 PM.
Models continue to favor a return to summer-like weather later next week and especially next weekend into the following week. A strong ridge of high pressure start building over the eastern Pacific Friday and move onshore will move over the region over next weekend and likely peak early the following week (May 11-12). Models are also showing a little north to northeast gradient during that time to provide an additional boost in temps. By next Sunday and Monday there is a 40-50% chance of 90 degree temps in Downtown LA and 100 degrees in the warmer valleys.
04/0336z.
At 23Z at KLAX, the marine layer 5600 feet deep with an inversion top at 6500 feet and 9 degrees Celsius.
Onshore flow will persist longer than usual tonight. Moderate confidence in SCT-BKN025-050 common through Monday. There is a 20-30 percent chance of -SHRA and a 5 percent chance of -TSRA on Monday at most places.
KLAX, Current west winds will last longer than usual tonight. Moderate confidence on ceiling timing and categories. There is a 20-30 percent chance of -SHRA that will peak 22-06Z. High confidence in any easterly winds staying below 8 knots.
KBUR, Current south winds will last longer than usual tonight. Moderate confidence on ceiling timing and categories. There is a 20-30 percent chance of -SHRA that will peak 22-06Z.
03/828 PM.
A Small Craft Advisory (SCA) was issued for the nearshore waters inside the SoCal Bight, with gusty W-NW winds expected this evening through late tonight. The stronger winds will be in the central to eastern channel, extending into the northern half of zone PZZ655. Additional SCA west winds are likely (40-60% chance) Tuesday afternoon and evening with a chance (30-40% chance) Wednesday and Thursday nights, mainly in the channel.
For the outer waters, SCA NW winds are likely (40-60% chance) for the waters near Point Conception to the northern Channel Islands, possibly extending south to San Nicolas island. Winds will increase again from the NW Wednesday night (for PZZ676) into Thursday for the remaining outer zones through Thursday night. Stronger winds will be possible Friday into the weekend.
Nearshore along the Central Coast there is a 30% chance for SCA NW winds Tuesday and Wednesday nights, with a 30 to 40% chance of SCA conds Thursday afternoon and night.
Ca, NONE. PZ, NONE.
