textproduct: San Diego

SYNOPSIS

A low pressure system over the western states will continue the cool weather with periods of showers through early Friday. Shower activity will increase again tonight through Thursday evening with the greatest coverage and accumulation over the mountains. Dry and warmer for the weekend into next week, with high temperatures rising to around average over the weekend and 10 to 15 degrees above average for inland areas for the middle of next week.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Evening update... Showers are generally confined to areas around the San Bernardino Mountains, with only isolated very light showers further south. A few lightning strikes have been observed in a heavier shower along the northern slopes of the San Bernardino Mountains south of Lucerne Valley. A spotter even reported large snowflakes falling and sticking to the ground in Lucerne Valley with this thunderstorm.

The broad upper level trough over the southwest US will continue to amplify tonight as a weak short wave drops south on the back side of the trough. Shower activity will increase tonight, especially across San Diego County. With the trough amplifying and colder air aloft moving in, snow levels will fall to around 4000-4500 ft tonight, rising to around 5500 ft Thursday afternoon. The colder air aloft will also lead to increasing instability tomorrow afternoon as daytime heating occurs, with ensemble mean CAPE of around 100-300 J/kg along and west of the mountains, good enough for Southern CA. The NBM has a 15-20% chance of thunderstorms tomorrow afternoon, and even if thunder doesn't occur, there will certainly be enough instability for another round of scattered showers. Showers will generally end by late Thursday evening. While NBM precipitation probabilities are less than 10% on Friday, hi-res guidance is suggesting another round of showers on Friday as the low lingers nearby and we get another burst of afternoon instability, mainly over the mountains.

Through Thursday, additional rainfall accumulations of up to 0.20" for the coasts and valleys, and up to around 0.40" in the mountains, is expected. Given how scattered the showers will be, some areas may receive little or no rain/snow. Additional snow accumulations will be around 1-3 inches with locally higher amounts above 7500 ft. Otherwise continued cool conditions through Friday with high temperatures well below normal. Noticeable warming will begin on Saturday as the upper trough begins to shift east.

Previous discussion... By Sunday, daytime high temperatures rise to above seasonal averages as the upper level low pressure trough moves east and a ridge of high pressure moves over the region from the west. A weak trough of low pressure moves inland to the north but will have minimal impacts for SoCal. A more robust high pressure ridge begins to build over the west on Tuesday and by Wednesday, temperatures will rise to as much as 18 degrees above seasonal averages in the inland valleys.

AVIATION

030300Z...Coast/Valleys/Coastal Mountain Slopes...SCT to occasionally BKN clouds based between 2500-4500 feet MSL, with tops reaching 7000 feet, will continue to fill in throughout the night. Cigs below 3000 feet MSL and -SHRA most likely far inland against the west-facing slopes, mainly in San Diego County. West-northwest winds gusting 15-25 kts near the coast are currently diminishing, and will continue to do so throughout the night. Clouds will lower and become more widespread, more widespread -SHRA return. Cloud bases will locally lower to 2000-3500 feet MSL, lowest in any isolated -SHRA developing through the morning, most likely near mountains and in San Diego County. Bases rise again to mostly above 3000 ft MSL after 13Z Thu. Partial scattering will occur late Thursday morning into the afternoon, but clouds and -SHRA will linger along the coastal slopes and in San Diego County. -SHRA tapering off by 05Z Thu. There will be some CIGs redeveloping after 05Z Thu, mostly for the coastal an inland valleys of San Diego County, with bases around 1500-3000ft MSL.

Desert Mountain Slopes/Deserts...Mostly clear skies tonight. Some bases around 4000-5000ft MSL could provide some isolated -SHRA and possibly even -TSRA over the mountains tomorrow afternoon. Westerly winds are continuing to weaken, with gusts now below 35 kts for most locations. They will further decrease and gradually become calm overnight.

MARINE

Winds and seas are continuing to gradually diminish from the inner coastal to the outer coastal waters this evening through early Thursday. See the Small Craft Advisory for details. Winds and seas will further decrease going into tomorrow and beyond, and no additional hazardous marine conditions are expected through Sunday.

BEACHES

Surf of 3 to 6 feet, with local sets to 7 feet, in San Diego County may still generate dangerous rip currents, and hazardous swimming conditions, through this evening. Surf will gradually subside overnight and into Thursday. The High Surf Advisory is in effect through 10 PM PDT this evening and contains more details, which will likely be allowed to expire, given that conditions are currently improving, and are expected to continue to do so.

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 PM PDT this evening for San Diego County Coastal Areas.

PZ...Small Craft Advisory until 7 AM PDT Thursday for Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.