textproduct: San Diego

SYNOPSIS

Easterly Santa Ana winds will strengthen today along and below the coastal slopes of the mountains with gusts to 45 mph and isolated gusts to 55 mph. The winds will continue into Thursday before weakening in the afternoon. A low pressure system off the northern Baja coast will direct mid and high level moisture and clouds into the area from the southeast Thursday into Friday with a slight chance of light showers late Thursday night into Friday. The weekend will be dry and a little warmer. Another low pressure system will approach the California coast next Tuesday and Wednesday, with cooling and increasing chances for precipitation. Confidence is low on the timing and amounts of any precipitation.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

This morning...Skies are clear and temperatures are near what they were at this time yesterday in the mountains and deserts while the coastal areas and inland valleys are as much as 20 degrees warmer than at this time yesterday. Pressure gradients remain offshore, with -13.9 mb SAN-TPH and -6.5 mb SAN-DAG. In the last hour, the wind-prone locations have reported easterly winds gusting as high as 50 mph.

The Rex Block is in place, with an upper level low about 300 miles off the coast of central Baja and an upper high centered over western NV. The resulting easterly flow over SoCal will continue to enhance the offshore winds at the sfc. As a result, the Santa Ana winds will continue to strengthen today into tonight before beginning to weaken on Thursday as the Rex Block breaks down, the offshore pressure gradients weaken and the flow aloft becomes southeasterly.

Temperatures will trend lower for Thu and Fri but will remain about 10-15 degrees above seasonal averages in the coastal areas and inland valleys. High temperatures on Thursday will range from the lower to mid 70s near the coast to the mid 70s to lower 80s for the valleys and inland Orange County. The coast and valleys will cool around 5 to 10 degrees on Friday with Friday high temperatures ranging from the mid to upper 60s near the coast to the upper 60s to mid 70s for the valleys.

The low pressure system off the northern Baja coast will draw mid and higher level subtropical moisture into the area from the southeast on Thursday into Friday. This will result in a slight chance of showers for late Thursday night into Friday. Showers will be mostly confined to the mountains. If any showers develop west of the mtns or lower deserts, precip is unlikely to reach the ground do to a deep and dry sub-cloud layer. Friday will likely be the coolest day, with daily high temps in the 60s and 70s west of the mtns.

Temperatures will trend higher for the weekend, with Sunday high temperatures as much as 8 to 12 degrees above average for the valleys and lower coastal slopes of the mountains. High temperatures on Sunday will range from around 70 near the coast to the 70s to around 80 for the valleys and inland Orange County with the lower deserts in the lower to mid 80s.

For next Mon-Wed...A more amplified low pressure trough will move in from the west bringing more significant cooling, increasing clouds and chances for widespread precipitation, mainly over and west of the mountains. Forecast details remain very uncertain due to the spread among model solutions.

AVIATION

041730Z...Mostly clear skies and VFR conditions will continue into Thursday morning. Gusty northerly to easterly winds in the foothills will gradually increase in speed and coverage today, with surface gusts up to 40-50 knots through and below mountain passes. Moderate up/downdrafts in lee (west of) mountains. Pockets of BLDU sporadically reducing vis 3-5SM in parts of the inland valleys. Localized instances of LLWS may spread westward to the coasts, especially where offshore winds do not surface and may even be slightly onshore near the immediate coast.

MARINE

No hazardous marine conditions are expected through Sunday.

BEACHES

Increasing long-period swell from the west-northwest will bring elevated to high surf of 5-8 feet with locally higher sets late Friday into Saturday. Impacts will be greatest at west facing beaches, especially across southern San Diego County.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Wind Advisory until noon PST Thursday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains-San Diego County Valleys-San Gorgonio Pass near Banning-Santa Ana Mountains and Foothills.

PZ...None.