textproduct: San Diego

SYNOPSIS

Above average high and low temperatures will continue into Saturday. There is a slight chance of showers and thunderstorms in the mountains and locally into the deserts this afternoon. By Sunday, temperatures will return to below average for this time of year. For Tuesday and Wednesday of next week, increased high cloud cover is likely along with a 20 to 30 percent chance of light precipitation as moisture from Tropical Storm Karina potentially gets pulled northward. This tropical system is forecast to remain well to our south.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

West of the mountains, temperatures at noon were running 3 to 8 degrees warmer than this time yesterday, likely due to the decreased high cloud coverage today. Low temperatures this morning started off in the low to mid 70s for the coast and western valleys, further inland lows were in the upper 70s to low 80s. The warmest conditions overnight were in the low deserts where temperatures overnight only fell to the upper 80s or low 90s.

Lingering mid-level moisture will bring a slight chance of showers and thunderstorms over the mountains this afternoon. Southwesterly flow aloft may push a few of these storms into the low desert. Latest high resolution guidance shows a decrease in coverage compared to earlier runs, with peak rainfall rates expected to be 0.50-0.70 inches per hour where thunderstorms develop.

The upper level ridge will start to get pushed east Saturday as a trough of low pressure moves into the Pacific Northwest. This will allow for a few degrees of cooling for afternoon highs, but overnight lows will remain elevated continuing to limit overnight relief from the heat. Widespread moderate to locally major HeatRisk will prevail for the coast, valleys, and San Diego mountains. Major HeatRisk will be maintained into Saturday for the low deserts. Given the slower cooling, the heat products for the areas mentioned above have been extended into Saturday. The trough will be the main influence over our weather by Sunday, bringing cooler conditions with increased marine layer cloud coverage and an uptick in westerly winds. Both high and low temperatures will finally fall below average.

For next week, troughing remains the prevailing pattern over the west coast. For the middle of the week, there is a potential for increased clouds and light precipitation due to moisture from Tropical Storm Karina. The current NHC track keeps the system far enough south where this will be the main impacts from the storm in addition to an increase in surf. Minor warming is possible late in the week as high pressure tries to expand westward again, though the warmest ensemble solutions only account for about 40% of the ensemble space at this point, with the remaining 60% keeping temperatures closer to midweek values.

AVIATION

281730Z...Coast...Patchy low clouds based 400-700 feet MSL will persist along some beaches. Patchy low clouds to expand in coverage after 06Z tonight into Saturday, yet still not widespread, uniform coverage by 13Z Saturday. Cigs around 500-800 feet MSL and vis 1- 5SM, lowest on mesas, most likely 12-16Z Saturday.

Mountains/Deserts...Cumulus based around 9000 feet MSL over the mountains with isolated CB cloud tops rising to 40000 feet MSL today 20-01Z. There is a 10-15% chance of TSRA/SHRA over the mountains and a 5-10% chance in the deserts. Any TS that develops could produce gusty, erratic winds.

Regionwide...SCT to locally BKN high clouds AOA 150000 feet MSL today, turning mostly clear tonight into Saturday.

MARINE

No hazardous marine conditions are expected through Tuesday.

BEACHES

A 3-foot swell from the south-southwest (200 degrees) at 15-17 seconds moves into the region Saturday-Sunday. This will bring localized elevated surf of 3-5 feet with sets to 6 feet, along with a high rip current risk to southwest-facing beaches, mostly in north San Diego County and Orange County.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Heat Advisory until 8 PM PDT Saturday for Orange County Coastal Areas-San Diego County Coastal Areas.

Extreme Heat Warning until 8 PM PDT Saturday for Coachella Valley-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Deserts-San Diego County Mountains-San Diego County Valleys- San Gorgonio Pass near Banning-Santa Ana Mountains and Foothills.

Heat Advisory until 8 PM PDT this evening for Riverside County Mountains-San Bernardino County Mountains.

Extreme Heat Warning until 8 PM PDT this evening for Apple and Lucerne Valleys.

PZ...None.