textproduct: San Diego

SYNOPSIS

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.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

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.

AVIATION

150600Z...Coast/Valleys...ISO-SCT -SHRA is lingering off the San Diego County coast this evening and will continue to do so into the afternoon, though the showers will gradually drift further offshore. FEW-SCT low clouds based 3-5 kft will also linger near the coasts through into the afternoon. With this, VFR conditions are expected to persist through the forecast period. Showers (and locally lower CIGs/VIS) will spread back towards the coast around 12z Monday.

Mountains/Deserts...Cloud bases 3-6 kft MSL in place across the coastal mountain foothills obscuring higher terrain will gradually decrease in coverage throughout the night. Otherwise, VFR conditions prevail throughout the period.

MARINE

Conditions have improved over the waters this morning, and will remain sub-hazardous until Monday. Scattered light rain showers are lingering off the coasts, and will continue through much of the day today.

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. These conditions will persist into early Wednesday morning with improving conditions by Wednesday afternoon.

Conditions look to deteriorate once again come Thursday afternoon as the next storm system approaches. Steep, high seas of 7-9 ft are expected with wind gusts near 25 kts for Thursday into Friday.

BEACHES

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. As a result, the High Surf Advisory currently in effect has been extended through 4 AM Wednesday. 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 producing surf of 4 to 7 feet with higher sets. Surf could peak around 6 to 10 feet later this evening into tomorrow. A High Surf Advisory is in effect until 10 AM Sunday, with dangerous conditions for both swimming and surfing.

High surf will coincide with high tides peaking 6.2-6.5 feet around noon today to produce minor coastal flooding, particularly along west-facing beaches where surf is highest. A Coastal Flood Advisory is in effect until 4 PM this afternoon. Surf begins to subside 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 into mid-week.

SKYWARN

Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.

SGX WATCHES/WARNINGS/ADVISORIES

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.