A series of low pressure systems will keep temperatures near or below normal throughout the next 7 days. The first of these will impact southern California primarily on Monday and Tuesday. It will bring another round of precipitation and gusty onshore winds, along with a slight chance of thunderstorms over the coastal waters and beach hazards. Another system late in the week will likely bring similar impacts but may have stronger onshore winds.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
This morning, Satellite imagery shows low clouds extending from the coastal waters to the low deserts. A weak wave undercutting the dynamic ridge currently over SoCal is likely producing a low- level circulation which is bringing low clouds from the south into the Borrego Desert and the Coachella valley. Radar shows a cluster of weak echoes nearly stationary over the coastal waters. These are light showers. High-resolution short-range models show these echoes (light showers) remaining nearly stationary until Monday when a low pressure system moves in from the northwest.
Ahead of this system a transient (dynamic) ridge will bring fair weather and slight warming for today, although scattered low clouds will persist. Daytime highs today will be mostly about 5 degrees higher than yesterday.
The first low pressure system will bring another round of widespread and organized precipitation. Ahead of the main band of rain and showers, light precipitation could begin as early as Monday morning. The main band of precipitation will move through SoCal from northwest to southeast Monday night/Tuesday Morning, moving off to the east by late Tuesday afternoon. As the upper level trough axis approaches, enhanced instability and dynamic forcing could produce some isolated thunderstorms late Monday/early Tuesday. Snow levels will likely remain above 7,000 ft through Tue morning before dropping to around 6,500 ft Tuesday afternoon. By then, most of the precip will have moved east. This system will not have access to large amounts of precipitable moisture. As a result, current rainfall estimates range from 0.10-0.25 inch in the coastal areas and valleys to between 0.25 and 0.40 inch on the coastal mtn slopes. Most of the snowfall will remain above 7,000 ft and accumulations are unlikely to exceed about 1 inch. Onshore flow begins to strengthen on Monday then peaks late Tuesday morning, with southwest to west winds gusting 35-40 mph in the mtns and adjacent desert slopes. This will not be a particularly cold system and daytime high temperatures on Tue will be similar to what they were yesterday, remaining in the 60s west of the mtns, the 50s in the high desert and the 70s in the lower desert. Temperatures in the mtns will range from the 40s in San Diego County to the 20s in the higher elevations of the San Bernardino and San Jacinto Mtns.
Another brief period of fair and (slightly) warmer weather on Wed under a weak transient ridge sandwiched between low pressure systems. Daytime high temps will likely still be 5-10 degrees below normal in the inland valleys and as much as 10-15 degrees below normal in the mtns.
Although the timing and track of the next system are still somewhat uncertain, it does seem likely that we will get more unsettled weather for Thursday into Saturday. Colder conditions with widespread precipitation is likely for late Thursday and Friday. This system does seem to have tighter pressure gradients so is likely to produce stronger westerly winds than the preceding event. Winds will likely peak Thu night/Fri morning. The system will move east on Sat with precip tapering off Saturday morning.
151800z, Coast/Valleys, VFR conditions through this evening with FEW-SCT low clouds based 3-6 kft. SCT-BKN high clouds move into the region late this evening followed by an increase in low to mid level clouds based 3-7 kft for the coastal basin overnight. ISO-SCT -SHRA over coastal waters may begin to push ashore as early as 14z Mon. -SHRA chances increase for San Diego/Orange Counties through the late morning into the early afternoon. Best chances for -SHRA will be in San Diego County. Intermittent MVFR cigs/vis may occur with any passing -SHRA for coastal TAF sites.
Mountains/Deserts, VFR conditions through early Monday morning with SCT-BKN high clouds moving into the region late this evening. Mid-level clouds begin to obscure higher terrain once again starting 12-18z Monday ahead of the next low-pressure system.
Isolated light showers will continue over coastal waters through early Monday. Shower activity increases again on Monday ahead of a low pressure system with a slight chance (10%) of a thunderstorm or two Monday afternoon and evening.
Winds and seas ramp back up Monday afternoon with 25-30 knot gusts expected in addition to steep, high seas of 8-11 feet with an average period of 8 seconds. Wind gusts will be strongest near San Clemente Island, where near-gale conditions are possible. With this, a Small Craft Advisory has been issued for both the near-shore and outer waters zones due to the hazardous conditions expected from the gusty winds and high seas. This Small Craft Advisory in effect from 4 PM Monday until 4 AM Wednesday. Winds and seas will slowly diminish Wednesday morning.
Conditions look to deteriorate once again Thursday as the next storm system approaches. Steep, high seas of 7-9 ft are expected with wind gusts peaking near 25-30 knots for Thursday into Friday morning.
A series of a mixture of long-period (3-5 feet at 15-17 seconds) and short period (6-8 feet at 7-8 seconds) swells, both from the west- northwest (280-290 degrees), will generate periods of elevated and high surf through much of this week. The current swell that produced waves up to 10-12 feet yesterday will gradually weaken today and into early Monday, but surf will remain elevated at 3-6 feet, with sets to 7-8 feet for west-facing beaches.
The next surge of northwesterly swells arrives Monday afternoon, ramping surf back up to 6 to 8 feet, with sets to 10 feet along west- facing beaches. This will extend the threat for high surf and strong rip currents into mid-week. A High Surf Advisory remains in effect through 4 AM Wednesday.
Ca, High Surf Advisory until 4 AM PST Wednesday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, Small Craft Advisory from 4 PM Monday to 4 AM PST Wednesday 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.
