textproduct: San Diego

SYNOPSIS

Above average temperatures will continue through next week, although less so after Monday. Warmest conditions will be Sunday and Monday with areas of minor to moderate HeatRisk in portions of the valleys and major HeatRisk in the low deserts. The marine layer and weak onshore flow will keep coastal areas cooler, with some amount of low clouds during the nights and mornings. A gradual cooling trend expected for next Tuesday through Thursday although temperatures will remain above average. Dry conditions will prevail through the forecast period.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

This morning...The marine layer is about 2000 ft deep with low clouds covering the coastal areas and extending as much as 15 miles inland in San Diego County. A weak coastal eddy seems to be developing and pushing low clouds into the Inland Empire from the south. High-resolution models indicate that by sunrise, a significant portion of the IE will be covered by low clouds.

An upper level ridge of high pressure will expand over the western states and strengthen through early next week. This will continue the warming trend which will likely peak on Monday. Numerical model guidance is in good agreement through Monday with respect to the synoptic pattern, although there is some uncertainty with respect to the details of the forecast. Monday is expected to be the warmest day of the forecast period with temperatures 15 to 20 degrees above average for the far inland valleys, mountains, and deserts. This will result in moderate to major HeatRisk in the low desert, with minor to moderate HeatRisk in the valleys and High Desert primarily on Monday. The risk is somewhat less on Sunday and Tuesday. There is more confidence in the temperature forecast for the mountains and deserts while the effects of the marine layer and onshore flow make the temperature forecast less certain west of the mtns as the models have less skill in resolving the marine layer effects.

For Tuesday through the end of next week, model solutions diverge significantly even with respect to the synoptic pattern, however most of the ensemble members as well as the deterministic models show the upper level high pressure ridge weakening and shifting east in response to a trough of low pressure approaching from the northwest. We can reasonably expect a gradual cooling trend for nest Tuesday through Friday, although temperatures will likely remain several degrees above seasonal averages for the mountains and deserts. Falling heights and a deepening marine layer will allow the onshore flow to spread low clouds farther inland during the nights and mornings keeping daytime temperatures near or a little above seasonal averages. Even with a low pressure trough moving in for the second half of next week, we expect conditions to remain dry.

AVIATION

080945Z...Coast/Valleys...Low clouds based 1000-1500 ft MSL are slowly moving into parts of the Inland Empire, otherwise covering the rest of the coastal basin. Generally VFR vis with the exception of elevated interior valleys 0-4SM. Cigs and vis could lower before sunrise for lower valleys and coast to 800-1300 ft MSL and 4-6 SM (from BR/HZ) respectively. Clouds clear offshore 15-1730Z this morning but will linger along beaches and just offshore through the afternoon, then return after Sat 02Z at 700-1200 ft MSL. Bases may oscillate a few hundred feet up and down throughout the evening and night. VIS reductions 0-5SM begin to develop for inland valleys east of I-15 after 05z Sat.

Mountains/Deserts...Mostly clear with VFR through the period. Breezy westerly winds with gusts 25-35 kts through mountain gaps and deserts slopes will weaken slightly this morning, then re-strenghten to 25-40 kts (locally 50 kts) through the gaps, desert slopes and locally in the lower desert valleys late this afternoon through the late evening.

MARINE

No hazardous marine conditions are expected through Monday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Extreme Heat Watch from Sunday morning through Tuesday evening for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.

PZ...None.