Well-below-normal temperatures for the entirety of the forecast period. Additional precipitation and stronger winds expected through Saturday, with hazards for both the marine waters and the beaches prevailing through the weekend. Additional wind and rain/snow possible with another system Monday/Tuesday. A third system late next week may bring similar impacts but with lower confidence.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
This morning's sounding showed a decent amount of CAPE over coastal Southern California, evident with the line of thunderstorms that made its way across the marine waters early this morning, fizzling out once they moved ashore. Generally 0.25-0.50" fell this morning, but some thunderstorms that reached coastal communities were able to provide closer to 0.75" before sunrise. Radar currently has a few piddly showers over parts of the coastal and valley zones, with very little in terms of accumulation. In a lower-CAPE environment, chances of thunderstorms for the remainder of the day are very low, generally 5% or less, but on-and-off showers could continue at times through this evening.
The low responsible for our morning convection has transitioned to an open trough, currently positioned over Southern California according to mid-level water vapor satellite. With a tighter gradient, winds increase this afternoon and evening over the marine waters, mountains, and deserts, with intermittent gusts to 30 mph over the waters and 45 mph for the wind-prone spots in the mountains. Winds will be strongest tonight as the shortwave on the backside of the trough moves through, with winds slowly weakening through Saturday morning. Additional rain/shower activity will accompany this shortwave, although the very low thunderstorm chances point to lighter accumulation through Saturday morning compared to this morning. Expect up to an addition 0.25" through Saturday morning for most spots west of the mountains (and up to 0.50" of additional rainfall for the mountains and foothills). Marine and beaches will see impacts as well through Saturday, please see these sections below.
Any rainfall should quickly come to an end Saturday afternoon, with drier air filtering in behind the trough. Weak upper level ridging will build in late Saturday and early Sunday, with less cloud coverage. Sunday will be a nice break in between systems, as the next trough is poised to move through Monday/Tuesday. Models continue to struggle to resolve the next system, especially timing and strength, with the GFS a bit faster compared to the ECMWF. The timing of this system will dictate marine and beaches impacts with another round of strong winds and high seas. For the inland side, a front associated with the trough will bring gusty winds and additional precipitation, as well as isolated thunderstorm chances. While this next system will be cooler than the previous, trying to nail out snow levels with such mismatch in the global models is difficult, especially with the heavier precipitation likely to be pushing through on Tuesday. For now, snow levels are generally at or above 6000ft during the precipitation window on Tuesday, which could allow for some of the higher elevations and mountain roads to see low snow impacts. Depending on the track and strength, snow levels could range anywhere from 5300-7000ft+. Regardless of how this system shakes out, guidance has been trending drier with each model run, and the latest guidance indicates less than 0.25" for most locations Mon-Tue (0.50" for the mountains). Additionally, temperatures will fall Mon-Tue to around 8-17 degrees below normal.
Further on in the week, another system could bring additional wind and rain to SoCal Thurs/Fri, but there is low confidence in any discernible impacts as global models are displaced with the core of the low by well over 100 miles. It is possible that the low swings too far north for us to benefit from, but NBM persists with around a 50% chance for rainfall on Thursday and 20% for Friday.
Much of this weeks forecast depends greatly on how these lows move across and how far south they make it. As is typical, models are struggling with these shoulder season systems, even in the shorter 3-4 day window. Close eyes will be kept on how the Mon/Tue system develops, with the possibility of some snowfall for the higher terrain.
140030z, Coast/Valleys, This evening, expect layers of clouds: FEW- BKN at 2-3 kft MSL, SCT-OVC at 3-6 kft MSL. SCT SHRA tonight with a line of -RA/RA sweeping through the region from NW to SE from 06-13z Sat. Periods of MVFR vis and cigs during RA. Clouds scatter out in the morning, becoming VFR and SKC by Sat afternoon.
Mountains/Deserts, SCT -SHRA through this evening in mountains with cloud bases 3-6 kft MSL obscuring higher terrain. More steady -RA and vis reductions expected with the passage of the precip band (06- 14z Sat). Gusty W/SW winds this evening and tonight with widespread gusts to 25-35 knots (locally 40-45 kts over typically windy ridges, desert slopes, and through passes). Winds will gradually taper off through Saturday morning.
Southwesterly winds gusting to 25 kts and seas 5 to 9 feet continue through tonight into Saturday morning. A Small Craft Advisory is in effect through Saturday afternoon. Winds and seas diminish late Saturday and Sunday, before increasing again Monday afternoon, with gusts up to 30 kts and seas 8-12 feet through Wednesday morning.
A series of swells (15-17 seconds) from the west-northwest (280-290 degrees) will generate periods of elevated and high surf through next week. The current northwest swell is causing surf 3 to 6 feet with high sets, increasing overnight to a peak of 6 to 10 feet Saturday and Sunday. A High Surf Advisory is in effect for these two days with dangerous conditions for both swimming and surfing. Surf begins to wane Sunday afternoon but will remain elevated for west- facing beaches into Monday morning. Another northwesterly swell will arrive on Monday, extending the threat for high surf and strong rip currents.
Ca, High Surf Advisory until 10 AM PST Sunday for Orange County Coastal Areas-San Diego County Coastal Areas.
Coastal Flood Advisory from 7 AM to 4 PM PST Saturday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, Small Craft Advisory until 4 PM PST Saturday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm- Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.
