textproduct: San Diego

SYNOPSIS

Bands of showers with a slight chance of embedded thunderstorms will slowly move southeastward across the area through this evening. Drying will develop over the weekend and continue into early next week, with periods of weak to moderate strength gusty Santa Ana winds for Sunday through Tuesday. Slight warming will accompany the offshore flow for Monday and Tuesday. A low pressure system from the southwest could bring a return of precipitation for Wednesday through Friday.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Extensive troughing over the west coast of the US, with embedded shortwave troughs, will continue to bring precipitation to SoCal through tonight. Bands of showers with a slight chance of embedded thunderstorms, associated with a frontal boundary, will slowly move southeastward across the area today through this evening. The convective elements within the band are moving to the northeast at about 30 mph with the steering flow aloft. This pattern of flow will result in orographic enhancement of rainfall amounts on the coastal mountain slopes - especially the San Bernardino Mountains. Showers could linger in San Diego County overnight after the passage of the frontal boundary when the winds become northwesterly and low level convergence downstream of offshore islands produces convection in the cold air behind the front.

As the low pressure trough moves inland and a high pressure ridge builds over the PAC Northwest, a drying trend develops for the weekend into early next week. For Sunday through Tuesday, weak to moderate offshore flow develops. Northeast Santa Ana winds gusting to 35-45 mph in and below the mtn passes and canyons are expected for Sunday and Monday.

By Monday, a closed upper low develops to our southwest while the high pressure ridge builds to our north. This will likely bring a warming trend for Sunday- Wednesday. Tuesday will likely be the warmest day with temperatures in the 70s (as much as 5-6 degrees above averages) west of the mtns.

For the middle to the end of next week...A low pressure system from the Gulf of Alaska will approach the west coast, displacing the high pressure ridge and drawing the closed low to our southwest northeastward into the mean flow over SoCal. There are significant differences among numerical model solutions with respect to how this pattern will evolve but an increasing number of ensemble members are indicating the possibility of precipitation for SoCal between next Wednesday and Friday. At this time, precipitation amounts are highly uncertain.

See the HYDROLOGY discussion for precipitation details.

Mountains/Deserts

Widespread mid level clouds based 4000-6000 ft MSL along with RA in the mtns will slowly exit the region 06-09Z Sat. SCT -SHRA in the low deserts may intermittently lower cigs/vis to MVFR in the low deserts 03-09Z. Clouds will linger along coastal slopes through 18Z. Southwesterly winds turning westerly 06-09Z and gusting 25-35 knots and downwind of desert slopes through 18Z. Locally higher gusts through mountain passes. Mod up/downdrafts downwind of the mountains.

MARINE

South to southwest winds gusting to 20 kts will turn northwest this evening and gradually decrease late tonight into Saturday. Otherwise, no hazardous marine weather expected through Wednesday.

BEACHES

Westerly swell (250-270 degrees) will lead to surf heights increasing to 5 to 8 feet through early Saturday. Highest surf is expected for west-facing beaches. A High Surf Advisory remains in effect until late Saturday morning.

HYDROLOGY

Additional rainfall through tonight for Orange and southwestern San Bernardino Counties is expected to range from 0.50 to 0.75 inch near the coast to 1 to 2 inches in the San Bernardino County mountains, locally up to 3 inches on the coastal slopes of the eastern San Gabriel Mountains. Amounts will decrease from north to south with around 0.25-0.35 inch expected over far southern San Diego County.

By Saturday morning, high-resolution models indicate a 50-70 percent probability of exceeding 2 inches of rain in the San Bernardino Mountains and about a 20 percent chance in the Santa Ana Mountains.

The snow level is now above 7500 feet, but will fall to around 4500 feet by late tonight. Snowfall in the San Bernardino County mountains of 1 to 3 inches is possible down to around 7000 feet with snowfall of 8 to 12 inches above 8000 feet.

Preliminary precipitation estimates for next Wed through Fri: 0.25"-0.50" in the low deserts, 0.40"-0.75" inch in the high deserts, 1.25"-1.60" in the coastal areas and valleys to 2-3 inches on the coastal mtn slopes.

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 11 AM PST Saturday for Orange County Coastal Areas-San Diego County Coastal Areas.

PZ...None.