textproduct: San Diego

SYNOPSIS

Above average temperatures will prevail through the remainder of the forecast period. Warmest conditions will be Sunday through Tuesday with areas of moderate HeatRisk expected in the valleys and major HeatRisk in the low deserts. The marine layer and weak onshore flow will keep coastal areas cooler. A gradual cooling trend expected for next Tuesday through Thursday although conditions will remain above average. Dry conditions will prevail through the forecast period.

..Updated aviation discussion for 06Z TAFs

Highs today are expected to be a few degrees warmer than yesterday along the coast and 7 to 13 degrees warmer than yesterday for inland locations. This warming will push temperatures to above average. Above average temperatures will continue through next Thursday. Weak onshore flow will be maintained, which will help moderate temperatures along the coast and portions of the western valleys. Additionally, areas of at least patchy low clouds and fog are expected to be present along the coast potentially into portions of the western valleys at times through the forecast period.

An upper level ridge of high pressure will expand over California and strengthen early next week. This will bring temperatures 15 to 20 degrees above average for the far inland valleys, mountains, and deserts on Monday, which continues to be forecast as the hottest day of the week. Current forecast has moderate to major HeatRisk in the low desert, with minor to moderate in the valleys and High Desert Sunday through Tuesday. Ensemble guidance from the ECMWF and GEFS continue to align with solutions from NBM guidance, even though the deterministic NBM is still skewed towards the maximum values of the EC and GEFS guidance, especially for Monday. The geographical proximity of the deserts to the center of the high pressure increases confidence in the temperature forecast for that area. There still remains some uncertainty on how warm it will get west of the mountains as prevailing onshore flow will spread cooler coastal air inland with the afternoon sea breeze. The spread between the 10th and 90th percentile of the NBM guidance in the Inland Empire for Monday is about 8 degrees which would be a difference of highs in the low 90s (10th percentile solution) or reaching 100 (90th percentile solution) at the hottest locations.

By Tuesday, most of the ensemble guidance indicates the ridge aloft will weaken, which will bring a few degrees of cooling to areas west of the mountains. For the deserts, there is less confidence in a substantial cooling on Tuesday. NBM spread in 10th and 90th percentile in temperatures is 8 to 10 degrees which is a difference between highs in the upper 90s/low 100s (10th percentile) and 105 degrees or warmer (90th percentile). The upper level pattern becomes more uncertain for next Wednesday and Thursday, with some solutions maintaining weak ridging and others showing weak troughing. Current forecast has gradual cooling from Tuesday through next Thursday. Dry conditions will prevail through the forecast period.

AVIATION

080430Z...Coast/Valleys...Low clouds based 1000-1400 ft MSL will move to about 20 miles inland overnight. There is a 40% chance for cigs to reach KONT 13-16Z. Cigs and vis could lower slightly overnight to 800-1300 ft MSL and 4-6 SM respectively. Clouds clear offshore 15-1730Z Friday morning but will linger along beaches and just offshore through the afternoon, then return after Sat 02Z at 700-1200 ft MSL.

Mountains/Deserts...Mostly clear with VFR through the period. Breezy westerly winds with gusts 25-35 kts through mountain gaps into deserts will gradually weaken early Friday morning, then briefly re- strenghten late Friday afternoon through the early evening.

MARINE

No hazardous marine conditions are expected through Monday.

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.