DISCUSSION
FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

An upper level low pressure system digging south into California from the Pacific Northwest will increase onshore pressure gradient for Monday. The increased onshore flow will deepen the marine layer to 5500-6000 ft and will produce areas of light showers west of the mountains and on the coastal mountain slopes. For the coastal areas and valleys, rainfall totals will generally be 0.05 to 0.15 inches.
High-res guidance is still suggesting higher amounts on the south facing slopes of the San Bernardino Mountains. The HRRR has a 50-70% chance of total rainfall accumulations greater than 0.50 inch for portions of the coastal slopes of the San Bernardino mountains, and a 20% chance of greater than 1 inch. Much of the shower activity will occur Monday morning. More isolated shower activity is possible into Monday afternoon along the coastal slopes of the mountains. An embedded shortwave will move across the area Monday night into early Tuesday. That may spark another round of isolated showers Monday night into early Tuesday, most likely in San Diego County.

Southwest to west winds will begin to increase this afternoon and evening for the desert mountain slopes, deserts, and passes. Peak wind gusts for the desert slopes of the mountains and into the deserts will be 35 to 45 mph, with a few local gusts to 50 mph possible through the San Gorgonio Pass. Winds are expected to strengthen for Monday afternoon and evening. The strongest winds are expected through passes and into the deserts. There is a 60 to 70% chance of gusts greater than 55 mph below the San Gorgonio Pass and along I-8 near the Imperial County border. Forecast peak gusts are be 45 to 55 mph, with a few local gusts to 60 mph possible.

Deep boundary layer moisture will still be in place for the middle of the week, but with a weakened/non-existent marine inversion cloud coverage may be patchy. Brief warming will occur Tuesday with a minor cooling on Wednesday as another trough digs south along the California coast. There remains spread amongst the ensembles in exact timing of the trough passage. This introduces some uncertainty in the forecast, particularly surrounding high temperatures on Wednesday and Thursday as well as timing of any precipitation and gusty winds. Current forecast has minor change in temperature from Wednesday to Thursday and best chance of precipitation Wednesday night into early Thursday for areas in and west of the mountains.
The forecast also has the strongest winds Wednesday night into Thursday for desert mountain slopes, deserts, and through passes. As the trough moves east ridging will build in from the west for Friday into the weekend for warmer and fair weather. There is the potential for weak offshore flow sometime next weekend as an upper low/inside slider moves into the Great Basin, but confidence is low. If any offshore flow develops, it would contribute to additional warming west of the mountains.

AVIATION
152000Z
Coasts/Valleys
Hazy conditions continue in the inland valleys due to smoke from the Line and Bridge Fires in the San Bernardino Mountains. Low stratus with varying bases from 2000- 3200ft MSL and tops to 4200-4500ft MSL continues for the coasts and far western valleys, but should continue to see slow clearing this afternoon. There is a 40-60% chance that full clearing does not occur for the San Diego County coasts this afternoon with CIGs continuing through the evening, but intermittent scattering may occur at times. Stratus pushes up to 30 miles inland again this evening between 23-01z with bases likely a few hundred feet higher than this morning. Light rain showers/drizzle will be possible after 03z with very low accumulation expected. Similar to previous nights, FU from the Line Fire may be trapped by the marine later and result in VIS reductions down to 2SM for KSBD with the only other VIS reductions seen where marine clouds intersect higher elevations.
Clearing on Monday looks to be similar to what was observed today.

Mountains/Deserts...Smoke from the Line and Bridge fires will produce localized VIS restrictions near the San Bernardino County Mountains, and the Airport fire will produce similar conditions in the Santa Ana Mountains through Monday. Strong west-northwest winds develop this afternoon/evening, with gusts up to 40kts possible through the mountain passes, continuing into Monday. Light rain will be possibly tonight into Monday for the coastal slopes of the mountains, with little impacts expected. Up to 0.25" will be possible.

MARINE
Expect light precipitation Sunday night through Monday morning, with less than 0.10" expected. Winds will strengthen from the west to northwest in the outer coastal waters Monday and Monday night, with gusts up to 20kts likely. Otherwise, no hazardous marine conditions are expected through Friday.

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



SGX WATCHES/WARNINGS/ADVISORIES
CA...Wind Advisory from 7 PM this evening to 9 PM PDT Monday for Apple and Lucerne Valleys.

Wind Advisory from 11 AM Monday to midnight PDT Monday night for San Diego County Deserts.

Wind Advisory from 7 PM this evening to midnight PDT Monday night for San Gorgonio Pass Near Banning.

PZ...None.