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.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
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.
071745z, Coast, Low clouds are just about cleared from the entire coastline and should hang just offshore today. More widespread and cohesive low clouds 800-1300ft MSL will move ashore after 02Z and locally inland overnight. There's a 20% chance of reaching KONT by 13Z Friday. Vis reduced 2-4SM for coastal terrain and in valleys, with 4-6SM for coastal areas. Chance of IFR CIGs at KSAN after 06Z around 50%, chance of MVFR > 85%. Clearing will occur between 15-17Z Friday.
Valleys/Mountains/Deserts, Mostly clear and VFR with only FEW clouds around 10,000ft MSL over mountains 18-00Z today. Strong westerly winds with gusts 25-35 kts develop after 23Z through mountain gaps into deserts, continuing into early Friday.
No hazardous marine conditions are expected through Monday.
Ca, Extreme Heat Watch from Sunday morning through Tuesday evening for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
